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Chemical Gamma-Resonance Spectroscopy.

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yet known. It is interesting to note, however, that some
molecules of this type do have structures that are closer
to the tetrahedral shape than is predicted by consideration of the repulsions between five electron-pairs. In
the molecules
the angle between the axial ligands is greater than 180
instead of less than 180 as predicted (see Table 6). It
seems that the lone pair is not exerting its full stereochemical effect.
These seem to be the only cases where the simple rules
discussed in this article d o not predict the correct structures. It is perhaps not unreasonable to claim that these
rules give a better understanding of the structures of
simple molecules than any other theory. For example,
no other theory can successfully account for the changes in bond lengths and bond angles in the molecules
PF5, CH3PF4, and (CH3)2PF3.
Because of the similar energies of different structures,
predictions are less certain for high coordination numbers, but this must also be the case for alternative theories. It is to be hoped that in the future, the ideas presented here can be given a sounder theoretical basis and
that they can be incorporated into a still more comprehensive and more successful theory of molecular
structure.
Received: March 31st, 1966; revised: July 24th. 1967
[A 597 IE]
German version: Angew. Chem. 79,884 (1967)
Chemical Gamma-Resonance Spectroscopy I - + ]
BY V. I. GOLDANSKII[*I
Two of the most important contributions that nuclear physics has made to modern science
and technology have been in the fields of nuclear energy and isotope labeling.
In recent years nuclear physics has stimulated the appearance and extremely rapid
development of yet another new and equally important scientific discipline, namely
gamma-resonance spectroscopy. This new branch of’spectroscopy, which is based on the
Mossbauer efect l1-31 is playing an increasingly important role in physics, chemistry,
biology, geology, and in the elucidation of various technical problems. - This paper
deals briefly with the basic physics of the Mossbauer efect and the characteristics of
Mossbauer (gamma-resonance) spectra, and then considers various applications of this
new type of spectroscopy. Particular attention is paid to the fundamentals and development of chemical gamma-resonance spectroscopy 14-91 as a technique for the resolution
of problems in various fields of chemistry and biokgyand to the range of problems
tackled in recent years in our laboratory of nuclear and radiation chemistry at the Institute
of Chemical Physics of the Academy of Sciences of the USSR. A number of reviews
and monographs dealing with the application of the Mossbauer efect in chemistry have
already been written [4-121. The folIowing work is based mainly on experimental results
obtained by research workers in the Soviet Union.
I. The Mossbauer Effect
Let us first consider the Mossbauer effect, the phenomenon of recoil-less resonance absorption and emission of gamma-quanta, which was discovered by Rudolf
Mossbauer in Germany in 1958 and for which he was
awarded the Nobel prize in physics in 1961.
[*] Prof. Dr. V. I. Goldanskii
Institute of Chemical Physics
Vorobjevskoje Shaussee 2-B
MOSCOW,
B-334 (USSR)
I**] This review reproduces in part and with some alterations
the report delivered at the Annual meeting of the Academy of
Sciences of the USSR on February 8, 1966.
[ l ] R. L. Mossbauer, Z. Physik 151, 124 (1958).
[2] R. L. Mossbauer, Naturwissenschaften 45, 538 (1958).
[ 3 ] R. L. Mossbauer, Z. Naturforsch. 14a, 211 (1959).
[4] V. I. Goldanskii: The Mossbauer Effect and its Applications
in Chemistry. Consultants Bureau, New York 1964; Atomic
Energy Rev. I, No. 4, 3 (1964).
830
T h e phenomenon of resonance is known in mechanics,
acoustics, optics, a n d radio engineering. When tuning o u r
radio t o t h e transmitting station we adjust t h e frequency of
t h e receiver’s oscillatory circuit to the s a m e frequency a s
that of the transmitters oscillatory circuir. Sometimes even
considerable revolving of the tuning knob leaves t h e audibility
.
.
151 E. Fluck, W. Kerler, and W. Neuwirth, Angew. Chem. 75,461
(1963); Angew. Chem. internat. Edit. 2,277 (1963).
[6] E. Ffuck, Advances inorg. Chem. Radiochem. 6, 433 (1964).
Fortschr. chem. Forsch. 5 , 395 (1966).
[7] R. Herber, J. chem. Educat. 42, 180 (1965).
[8] R . Herber, Annu. Rev. physic. Chem. 17, 261 (1966).
[9] G . K. Wertheim: Mossbauer Effect. Principles and Applications. Academic Press, New York-London 1964; Science
(Washington) 144, 253 (1964).
[lo] J. Duncan and R . Golding, Quart. Rev. (chem. SOC.,London)
19, 36 (1965).
1111 N. N. Greenwood, Chem. in Britain 3, 56 (1967).
[12] Applications of the Mossbauer Effect in Chemistry and
Solid-state Physics (Report of a Panel Discussion, Vienna;
April 16-30, 1965). Int. Atomic Energy Agency, Vienna 1966.
Angew. Chem. internai. Edit./ Vol. 6 (1967) / N o . I0
almost unaltered, and at other times even the slightest touch
may abruptly disturb reception. In the latter instance the
resonance is sharper or, in other words, more sensitive to
any interference.
Quantum systems, i. e. molecules, atoms, and atomic
nuclei, represent resonant radiation receivers and
transmitters. The radiation frequencies w of such systems are determined by the energy difference Er between the excited and the ground state:
either to destroy or reproduce resonant conditions. (If
this degree of accuracy (10-12) were to apply in the
measurement of the radius of the entire solar system
then figures would be obtained which would be accurate to within the height of a two-storey building.) It
can be appreciated that the prospects of observing
gamma-resonance seemed very attractive; however,
because of the extreme selectivity of this resonance,
combined with the great energy of gamma-quanta, the
discovery of gamma-resonance was delayed for a number of years.
where w 6.6 x 1 0 - 1 6 sec-eV is Planck's constant (see
Fig. 1). Another important characteristic of resonance
is its width I?, which is related to the average lifetime
of the excited state 7:
A gamma-quantum (or an optical quantum) departing
from a nucleus (or an atom) imparts to that nucleus
(or atom) a momentum in the opposite direction. The
energy of the recoil is given by
R = Er2/2mc2,
The ratio r/Ercharacterizes the resonance sharpness; the lower its value, the better the selectivity of the
resonance system.
Fig. 1. Illustration of the resonance phenomenon.
Left: Probability of resonance excitation W ( E ) depending o n deviation
of the transmitted energy E from resonance value Er. I? is the natural
resonance width.
Right: Emission and absorption resonance lines displaced by the recoil
energy R = Er/Zmcz towards energies lower than or higher than Er.
Two characteristic cases of resonance - atomic (yellow
D-line of sodium) and nuclear (transition from an excited 23.8 keV state of 119Sn to the ground state) - are
given for comparison in Table 1.
Table 1 . Main criteria of characteristic atomic and nuclear resonance
transitions.
Parameter
Transition energy Er (eV)
Lifetime of excited state T (sec)
Natural resonance width r (eV)
Resonance sharpness I'lE,
Recoil energy R (eV)
Ratio of recoil energy to transition
energy RIE,
Ratio of recoil energy to resonance
width Rlr
2.1
1 . 5 10-8
~
4.4x 10-8
2.1x10-8
10-10
23 800
2.7~
10-8
2.4~
10-8
10-12
2 . 5 10-3
~
= 4 . 8 10-11
~
= 10-7
%
2 . 3 10-3
~
= 105
It is obvious that the resonance width I? of the atom
and that of the atomic nucleus are approximately
equal, whereas the energy of transition in the nucleus
is higher than that in the atom by four powers of magnitude; therefore, the selectivity of nuclear resonance
is thousands of times higher than that of atomic resonance. A change in the energy of an emitted or absorbed gamma-quantum by only one trillionth suffices
Angew. Chem. intenrut. Edit. 1 Vol. 6 (1967)
No. 10
where m is the mass of the source of radiation and c is
the velocity of light. In the case of an atom, the recoil
energy is much less than the resonance width (R
I?),
and consequently recoil does not interfere with observation of the resonance phenomena. The situation is
quite different in the case of nuclei; the recoil energy is
hundreds of million times greater, and the emission
line is displaced far away (by 2 R)from the position of
the absorption line (Er + R) towards lower energies
(Er - R). The position of the absorption line is accounted for by additional kinetic recoil energy R imparted to the absorbing nucleus excited by energy Er.
Resonance appears to be possible only at the expense
of partial superposition of two lines separated by recoil; moreover the shapes of these lines are distorted
owing to thermal motion of the nuclei and the resulting
Doppler shift of the gamma-quantum frequency.
<
Recoil-less nuclear gamma-resonance (NGR) was discovered under conditions where the emitting and absorbing nuclei (191Ir in Miissbauer's first experiment)
were in a crystal lattice, bound by chemical bonds to
billions of nuclei of the same sort. The recoil on emission or absorption of a gamma-quantum is insufficient
to break these bonds and therefore the recoil energy is
dissipated in excitation of the quanta of atom vibrations in the lattice, i.e. of phonons. The case may be,
especially at low temperatures, that n o phonon excitation is effected, the transition energy is then divided between a quantum and the whole lattice and the denominator of the expression for recoil energy will represent not the mass of an individual nucleus but the
mass of the lattice. As in the case of firing an infinitely
heavy gun, the recoil energy tends to zero, i.e. it becomes much less than the resonance width (R
I?)
and does not interfere with observation of the latter.
An intense resonance line, maintaining its position
and width, appears on the background of shifted and
broadened absorption and emission spectra whose
peaks are separated by 2 R from one another by recoil
(see Fig. 2).
It is of interest to note that Massbauev explained his
experimental results on the basis of a theory proposed
by Lamb for the explanation of the appearance of a
similar line in experiments on neutron scattering. This
<
831
Absorber
y-Counter
Fig. 2. Illustration of the Mossbauer effect
Left: The spectra of gamma-quanta emission and absorption. A resonance line of natural width is observed against a background of
displaced and broadened spectra (scale of 1:ZOO in case of 191Ir at
88 OK). Formulae f o r the Mossbauer effect probability f' in the Debye
approximation (Q = Debye temperature):
Top center and right: decay diagrams for "9Sn and 57Co + 57Fe. Halflives, transition energies, and natural abundances f o r tin and iron are
shown. Bottom center and right: schematic representation of a gammaresonance experiment (i.e. dependence of the gamma-quantum counting
rate on the velocity of the absorber (or source) and the approximate
shape of such a spectrum.
Y
-
r = (lo-'* :
L --
10-13) c
Er
-
(10-2
:
10-3) cm/sec
theory had been developed some 20 years before the
discovery of recoil-less nuclear gamma-resonance. It is
rather unfortunate that, due to excessive specialization,
both by those conducting experiments with gammaquanta and by those concerned with interactions of
neutrons in solids, the discovery of the Mossbauer
effect should be delayed for such a long time.
From the discussion so far it is clear that the nuclearresonance line of natural width represents a kind of
high-precision measuring instrument. How is the Mossbauer effect observed and quantitatively studied?
First of all, a transmitter and a receiver are needed;
their parts are played, respectively, by the excited emitting nucleus and the stable nucleus of the same isotope,
i. e. a resonance absorber for gamma-quanta. Figure 2
shows decay schemes for two nuclei most commonly
utilized in gamma-resonance spectroscopy, namely
119Sn and 57Fe (formed in the radiation source from
the 57Co parent nucleus by K-electron capture). Secondly, a control of the gamma-quantum energy is necessary. The frequency and the tone of a sound signal
are known to change with displacement of the sound
source; such changes are due to the Doppler effect.
The same effect was utilized by M6ssbauev to change
the gamma-quanta energy in GR spectroscopy, where,
due to extremely sharp resonance, a low velocity movement of the absorber relative to the source is sufficient.
This velocity V = c/Er is estimated according to the
value of FIEr, 1.e. on the properties of the nucleus
selected for study, in fractions of mmjsec (119Sn, 57Fe)
and occasionally in fractions of micron/sec (67Zn).
r.
832
Study of the dependence of the counting rate on the
velocity of the absorber placed between the source
(emitter) and the counter, is the most important experimental step in gamma-resonance spectroscopy. The
approximate shape of this function, called the gammaresonance or Mossbauer spectrum (GR spectrum), is
given in Fig. 2. The peak or the resonance line corresponds to minimum counting, i . e . to maximum adsorption, when the absorber is moving at some certain
velocity. Thus the essence of obtaining gamma-resonance spectra consists in compensation of all external
factors affecting the resonance transition energy by appropriate displacement of the absorber or the quanta
source, and thereby making a quantitative investigation of these factors.
Miissbnuer's discovery provided research workers with a
tool for the precise measurement of gamma-quanta energy.
However, the potentiality of this new tool was not immediately appreciated. At first the new phenomenon seemed
to be confined to the relatively limited scope of clucidating
problems of nuclear physics. The development of GR
spectroscopy, and its application in solid-state physics,
chemistry, biology, geology, and engineering was the result
of work carried out by many scientists of various countries.
11. Parameters of Gamma-Resonance Spectra
The motion of atoms within molecules and in crystal
lattices, as well as the interaction of the charge and the
electric and magnetic moments of the nucleus with surrounding electron shells all affect the gamma-quantum
energy; consequently, each of these effects can be investigated by means of gamma-resonance spectroscopy.
A schematic list of Mossbauer spectrum parameters
and of information contained therein is presented in
Fig. 3.
Let us begin with the probability of the Mossbauer
effectf' displayed in the resonance peak area (Fig. 3a).
Thef' value defines the range of thermal atomicvibrations within molecules and lattices, i.e. their mean
square amplitude 2.A detailed theory connecting the
f' value and its temperature dependence with the vibrational frequency spectrum of a composite crystal latAngew. Chem. internat. Edit. J Yol. 6 (1967) 1 No. I0
+ +
crystal axes (2 .Z 2).Indeed,such a n anisotropy in single
crystals was soon established 116-181.
It should be noted here that the width of a resonance line
also gives 2 certain amount of information abour the diffusion of atoms[!9-20]. If the emitter and the absorber of our
first example are chemically identical and their temperatures
are the same, then maximum absorption occurs with the
absorber at rest: V = 0. If the absorber temperature To is
now changed t o 71,the absorption maximum will shift by a
certain value ST as shown in Fig. 3b.This temperature shift [211
defines the average kinetic energy of the atomic vibrations in
the lattice, and hence their mean squarc velocity
w.
A parameter of paramount importance is the isomeric
(chemical) shift of the resonance line (Fig. 3c) due to
the difference of chemical state of atoms of the emitter
and the absorber. This shift, which is caused by
changes in the electrostatic interaction energy of electric charges of the nucleus and the electron shells, was
first observed by Kistner and Sunyar [221 during experiments with various compounds of iron.
a
&
Fig. 3 Parameters of gamma-resonance spectra and information
supplied by them (E = source, A = absorber):
-
a) Source
absorber, the peak area is proportional t o 1’ (7) exp
[-r2/(i./2~)2] where r 2 is the mean square of the atomic displacement;
absorber, the temperature shift of the line 6~
b) Source
gives the value of mean square velocity
motion;
c) Source
8 - q
Y2
=
“’
2 E r 2
of the atom in vibrational
+ absorber, the isomeric (chemical) shift of the line
{l$(o)
! 2
A - lo@)
1 g)
supplies information on density (square
of wave function) of s electrons at the nucleus;
d) Source
*
absorber, quadrupole splitting A
electric field gradient o n the nucleus 9
=
a2V
-.
-
Q9 gives the value of the
;
312
e) Source
absorber, the asymmetry quadrupole splitting supplies
information about the anisotropy of atomic motion in molecules and
lattices: x2
y2 zz or on electron paramagnetic relaxation;
+
*
+
+
f) Source
absorber, magnetic splitting(1/2++1/2; 3/2++3/2, & 1/2):
AM
u / I H (where I is the spin. p the nuclear magnetic moment)
characterizes a n effective local magnetic field H on the nucleus.
tice and impurity atoms was developed by Yu. M .
Kagan [13,14J.
An important part of this theory deals with the role of the
so-called optical branches of vibrational spectra in the
probability of recoil-less gamma-resonance. The optical
branches possess comparatively high energies (and consequently small amplitudes) and characterize, in the long-wave
approximation, the motion of atoms relative t o their nearest
neighbors in contrast to simultaneous displacements of
many atoms in acoustic vibration branches. The existence
of optical branches is essential because they provide for the
possibility of observing gamma-resonance spectra in systems
containing light atoms (this is of particular importance for
chemistry), as well as at rather high temperatures. The
theory predicted also the possibility of anisotropy of the
Mossbauer effect in single crystals 1151, which is associated
with different amplitudes o f atomic vibrations along different
[13] Yu. M . Kagan and V. A . Maslov,
659, 1296 (1961).
i.eksper. teoret. Fiz. 41,
[14] Yu. M . Kagan and Ya. A . losilevskii,
42, 259 (1962); 44, 284 (1963).
i.eksper. teoret. Fiz.
[15] Yu. M. Kagan, Doklady Akad. Nauk SSSR 140, 794
(1961).
Angew. Chem. internat. Edit. / Vol. 6 (1967) / N o . I0
Isorneric shift is determined by z product of two magnitudes,
one of nucleai origin (relative change of the nuclear charge
radius due to nuclear excitation) and the other of extranuclear origin. It is the latter, i.e. the difference in squares o f
electron wave functions (in other words of electron densities)
in the region of absorbing and emitting nuclei that is of
special interest for chemists since it defines the structures of
s-electron shells and the participation of s electrons in chemical bonds.
Interaction between the nuclear electric quadrupole
moment (in the ground and/or excited states) with a
non-uniform electric field results in quadrupole splitting of gamma-resonance spectrum lines (Fig. 3 d) proportional to the product of the quadrupole moment Q
and the electric field gradient q. Of these two values the
first is nuclear; the second is a molecular value, which
defines the properties of p- and d-electron shells. The
possibility of describing separately the contribution
from s, p, and d electrons to chemical bonds by means
of correlating isomeric shifts and quadrupole splitting
is an essential advantage of chemical gamma-resonance spectroscopy allowing, for instance, distinction
to be made between the role of changes in ionicity and
in the extent of hybridization of chemical bonds [22al.
Quadrupole splitting frequently turns o u t to be asymmetrical even for absolutely isotropic polycrystalline
substances (as shown in Fig. 3e)[2Zbl. Such an integral
asymmetry of two peaks with respect to their area was
[!6] N.A. Alekseevskii, Fam Sui Clrien, V. G. sapiro. and V. S.
Spinel’, Z . eksper. teoret. Fiz. 43, 790 (1962).
[17] P . Craig, N.Erickson, D . Nagle, and R. Taylor: Proc. ofthe
Second Mossbauer Effect Conference. Saclay 1961. Wiley,
New York 1962, S . 280.
[181 H . Pollirk, M . de Coster, and S. Amelinckx: Proc. of the
Second Mossbauer Effect Conference. Saclay, 1961. Wiley, New
York 1962, p. 112.
1191 M . I . Podgoretzkii and A . V . Stepanov, 2. eksper. teoret.
Fiz. 40,561 (1961).
[20] M . A. Krivoglaz, Z . eksper. teoret. Fiz. 40, 1812 (1961).
[21] B. D. Josephson, Physic. Rev. Letters 4 , 337 (1960).
1221 0. G. Kistner and A . W. S n y a r , Physic. Rev. Letters 4, 412
(1960).
[22a] V. I . Goldanskii, E . F. Makarov, and R . A . Strrkan, J. chem.
Physics, in press.
[22b] The asymmetric quadrupole splitting observed in the
Mossbauer spectra of polycrystalline substances is termed the
Goldanskii effect.
833
observed for the first time in spectra of organotin compounds and thoroughly investigated and interpreted at
the Institute of Chemical Physics in Moscow [23-251.
This asymmetry is a result of the Mossbauer effect
anisotropy in respective crystallites (2
=k 3 =# 2)and
its observation opens up possibilities for investigating
structural features of single crystals by experimenting
with polycrystalline material (in a sense similar to plotting of X-ray debyegrams). Recently, the above mentioned cause of asymmetry of the quadrupole splitting
was quantitatively studied and confirmed for single
crystals and polycrystals of siderite (FeC03) [25aJ.
It is also worth mentioning that investigation of the “anisotropic’’ asymmetry of quadrupole splitting and its explanation has done away with confusing trivial hypotheses on the
overlapping of spectra of various hypothetical admixtures
or structural isomers.
A further variant of asymmetric quadrupole splitting is connected with interaction between the electric field and the magnetic field occurring at nuclei
under the influence of unpaired electrons of the atomic
shells 1261. This “paramagnetic” asymmetry is more intense the longer the time of paramagnetic relaxation,
i. e. the slower the electron spin flipping. Therefore, unlike the “anisotropic” asymmetry of quadrupole splitting, the “paramagnetic” asymmetry weakens as the
temperature increases.
The ordered or very slowly relaxing unpaired electrons
of external shells cause polarization of the internal electrons thus cancelling full compensation of the magnetic effect of anti-parallel spins of two s electrons of
the shell closest to the nucleus. As a result, enormous
magnetic fields are set up inside the atom; these can be
determined from magnetic (Zeeman) splitting of gamma-resonance spectrum lines (Fig. 3 f).
nucleus or a random system, occupies a prominent
place in papers on gamma resonance. As a result of
this suppression, the lifetime of an excited nucleus in
an ordered lattice may turn out to be longer than that
in the free state, i.e. the width of the excited level will
be less than the natural resonance width. Conversely,
shorter lifetimes and more rapid disintegrations are
also possible [2*cl. The problems of coherent effects in
emission and propagation of gamma-quanta, the wavelength of which is many thousand times less than that
of visible light, are naturally of exceptional interest.
There is little doubt that any future achievement in
solving these problems will be closely connected with
the Mossbauer effect.
A striking variety of experimental methods are currently in use in research on the structure of matter:
optical spectroscopy, electron spin resonance, nuclear
magnetic resonance, and quadrupole resonance, X-ray
structural analysis, electron and neutron diffraction,
and neutron scattering. Of course, none of these methods may be considered as a panacea for solution of all
problems connected with crystalline or molecular
structure. The nuclear gamma-resonance method
presents no exception in this respect; despite its potentialities, a given problem can be solved only when it
is used in conjunction with other methods.
The greatest limitation of gamma-resonance spectroscopy is that the Mossbauer effect can be observed only
for a substance in the solid phase and not for all chemical elements (see Fig. 4). Because of the general increase in energies of the lower levels with decreasing
nuclear mass, the recoil energy for light-element nuclei is so great that the Mossbauer effect becomes
A number of theoretical papers (cf., for example, l7-71)
are concerned with problems of the magnetic splitting
of nuclear gamma-resonance lines, which can range
from a single line to a well-resolved hyperfine structure. The spectrum is temperature dependent, the
width of individual peaks being related to the time of
paramagnetic relaxation and, of course, to the transition from paramagnetic to ferromagnetic or antiferromagnetic states.
The theory of coherent phenomena [28,29J, for example,
of suppression of gamma-resonance absorption in an
ordered nuclear setup, as compared to an individual
[23] V. I. Goldanskii, G. M. Gorodinskii, S. V. Karjagin, L. A.
Koryrko, E.F. Makarov, I.P. SurdaZev,and V. V. Chrapov, Doklady
Akad. Nauk SSSR 147,127 (1962).
[24] V. I. Goldanskii,E. F. Makarov, and V. V. Chrapov, 2. eksper.
teoret. Fiz. 44,752 (1963).
1251 S. V. Karjagin, Doklady Akad. Nauk SSSR 148, 1102
(1963).
[25a] I. A . Vinogradov, V. I. Goldanskii, E. F. Makarov, and I. P.
Suzdalev, 2. eksper. teoret. Fiz., in press.
1261 M. Blume, Physic. Rev. Letters 14, 96 (1963).
[271 A. M. Afanas’ev and Yu. M. Kagan,
eksper. teoret. Fiz.
45, 1660 (1963); 47, 1108 (1964).
[281 Yu. M. Kagan and A. M. Afanas’ev, a)
eksper. teoret. Fiz.
48, 327 (1965); b) 50, 271 (1966); c) 2. eksper. teoret. Fiz., Pis’ma
v Redakciju 2, 130 (1965).
I291 M. I. Podgoretzkii and I. I. Rojzen, 2. eksper. teoret. Fiz. 39,
1473 (1960).
z.
z.
834
Fig. 4. Elements for which the Mossbauer effect has been observed
(shaded squares).
A light top right-hand corner in a shaded square means that the
effect has been detected even at room temperature. The effect is to be
expected for almost all lanthanides and actinides; chemical symbols
in respective squares show for which elements of these series the effect
has already been observed. Silver is not shaded since its ratio r/Eis
very low (= 10-22) and therefore the experiments with Doppler shift
of gamma-quanta absorption have not been carried out.
Angew. Chem. internat. Edit. 1 Vol. 6 (I967) f No. I0
vanishingly small. At present potassium is the lightest
of the elements observed to give the Mossbauer effect.
Despite the absence of such common elements as carbon, nitrogen, oxygen, and silicon in the "Mossbauer
list", the field of application of gamma-resonance is
extremely wide since gamma-resonance nuclei are frequently introduced as observers to elucidate the properties of other systems. In the following sections, a
selection of important and impressive examples illustrate the successful application of gamma-resonance
spectroscopy in various fields of chemistry and biology.
111. Some Applications of Nuclear Gamma
Resonance (NGK) in Solid-state Physics
Brjuclzanov, Deljagin, and Kagan 1301 introduced tin into
vanadium and compared the temperature dependence of the
gamma-resonance probability (Fig. 5a) with that estimated
by means of the theory of impurity nucleus vibrations in the
cubic lattice 1131. The spectrum of the host-lattice vibrations
required for such a theory had been found independently in
experiments with sub-thermal neutrons [30a,30bl. The perfect
spectra, since the magnetic moment of the absorbing nucleus
(i.e. the nucleus in the ground state) is generally known from
other experiments. Fig. 5b shows the temperature dependence
of the field (recently obtained [311 at the Kurchatov Institute
of atomic energy) for impurity nuclei of dysprosium (161DV)
formed in the metallic gadolinium lattice by neutron capture
and two subsequent beta-decay events. At a temperature of
5 "K the local magnetic field attains a value of 7.3 MOe. The
nature of the diminution o f the field with decreasing temperature indicates that two states of dysprosium occur
(for the first the local field disappeared a t about 20°K, for
the second - simultaneously with the disappearance of the
ferromagnetism of gadolinium - at a Curie temperature of
about +290 OK).
A clear correlation between a macroscopic magnetic property, such as the spontaneous magnetization of the sublattices of anti-ferromagnetic FeSnz, and the local magnetic fietds
at nuclear sites was demonstrated a t the same Institute[321.
In this work, the magnitudes of magnetic fields were determined both for iron and for tin (Fig. 5c); for iron directly
from the line splitting, for tin from the width of the line with
the unresolved hyperfine structure (this width decreases with
diminishing local field at the nuclear sites).
Randomization of electron spins through their continuous
fast flipping certainly leads to disappearance of the magnetic
hyperfine structure of N G R spectra, since in this case the
local field o n the nucleus averaged over time becomes zero.
The general theory of gamma resonance in systems %ith
unpaired electrons, which allows for all these circumstances,
has been verified for numerous examples. Only two obvious
cases of alteration of the nature of N G R spectra in such
systems will be given here.
100
I
v
Og 9 I
0 98
77°K
t 0.99t
=
T
(OK)-
22°K
I
1
I ("K)-
Fig. 5. Application of the Mossbauer effect in solid-state physics.
a) Temperature dependence of the effect probability f " ( T ) for 119%
nuclei in vanadium;
b) temperature dependence of the magnitude of the local magnetic field
on 161Dy nuclei in gadolinium: HN(O) = 7.3 MOe;
c) temperature dependence of the local magnetic field on XlFe nuclei (in
kOe) and the width of the gamma-resonance spectrum line of 1W.n in
FeSn2.
agreement between theory and experiment shows the broad
potentialities of quantitative gamma-resonance spectroscopy
of simple and complex crystal lattices.
Interaction of unpaired electrons of external shells with
internal s electrons of the atom may lead, under certain
conditions, to very strong local magnetic fields in the vicinity
of the atomic nucleus. The magnitude of these fields is
determined directly from the hyperfine structure of N G R
[30] W. A. Brjuchanov, N . N . Deljagin, and Yu. M . Kagan, 2.
eksper. teoret. Fiz. 45, 1372 (1963).
[30a] A. T. Stewart and B. N . Brockhouse, Rev. mod. Physics 30,
250 (1958).
[30b] N. A . CernopGokov, M . G . Zendjanov, and A . G . C%erin, 2.
eksper. teoret. Fiz. 43, 2080 (1962).
Angew. Chem. internat. Edit.
I Vol. 6 (1967) 1 No. 10
I
J
100 -
09909BI
m
-20
-10
0
V(crn/sec)
10
20
I
Fig. 6. Application of the Mossbauer effect i n solid-state physics.
a) Gamma-resonance of 161Dy in a Dy-AI garnet at different
temperatures;
[31] I . I . LukaieviC, V . V . Skljarevskii, B. N . Samojlov, E. P . Stepanov, K . P . Alesin, and N . 1. Filippov, 2. eksper. teoret. Fiz.,
Pis'ma v Redakciju 3, 81 (1966).
[32] V . I . Nikolaev, Yu. I. Sterbina, and S.S.Yakimov, 2. eksper.
teoret. Fiz. 45, 1372 (1963).
835
-8
-I
0
I
V(rnm/sec)b) Gamma-resonance spectra of 57Fe in a nickel-zinc-ferrite spine! for
different degrees ( x ) of replacement of iron by zinc in the tetrahedral
lattice (ZnxFet-x) [ N i t _ x F e ~ + ~ l O(Ordinate:
+
number of counts in
arbitrary units.);
100 -
t
92-
76
50
100
T("C)+
150
c) Mossbauer effect probability diminishing as a result of increasing
mobility of atoms in the ferrielectric lattice of Pb21FeNb102 near the
Curie temperature (1 14 "C).
Fig. 6a shows dysprosium (161Dy) spectra [331 for a dysprosium-aluminum garnet, which is anti-ferromagnetic at a
temperature below 2.49 OK, and becomes paramagnetic at a
temperature above this point (the NCel point), Here, the
transition to the paramagnetic state does not cause abrupt
disappearance ot'the hyperfine structure.The latter disappears
only gradually with diminishing electron-relaxation time, i.e.
with more frequent flipping of spin with increasing temperature. Such a n increase in flipping entails broadening of
the hyperhie structure lines in accordance with the theory.
Fig. 6b shows spectraf341 of the ferrite spinels (Zn,Fel_,)
[Nil_,Fel+,]04. Here, iron is incorporated in the tetrahedral
sublattice (together with zinc) and in the octahedral sublattice
[331 I. Nowik and H. H. Wickmart, Physic.Rev.140, A 869 (1965).
[34] V. I. Goldanskii, V. F. Belov, M . N. Deviieva, and V.A.Truchtanov, 2. eksper. teoret. Fiz. 49, 1681 (1965).
836
(together with nickel). The interaction between these sublattices induces the occurrence of uncompensated antiferromagnetism (so-called ferrimagnctism). As iron is dislodged
in the tetrahedral sublattice by the zinc ions, interaction
between the sublattices weakens, and the ferromagnetic
material is converted into a paramagnetic material with a
very short spin-lattice relaxation time; the magnetic splitting
of the spectrum line disappears.
It should be mentioned that the properties of ferrites are not
only of theoretical interest but are also of practical interest
since their magnetization is not accompanied by substantial
loss of energy by eddy currents, even at ultra-high frequencies.
Of similar dual interest is the application of the Mossbauer
effect to the study of ferroelectrics, which display dielectric
polarization even in the absence of a n external electric field.
The electrical properties of ferroelectrics are in many respects
similar to ferromagnetic magnetization. In both cases there
is a certain critical temperature (Curie temperature) above
which thermal motion destroys the ordering of electrical
and magnetic moments, and thus eliminates ferroelectric and
ferromagnetic properties.
V. V. Skljarevskii et aZ. 1351 observed a sharp increase in the
mobility of atoms in a ferroelectric lattice at a temperature
close to the temperature of transition from the ferroelectric
state to the paraeiectric state i.e. phase transition of the
second kind. Indeed, Fig. 6c shows that an abrupt decrease in
the probability of the Mossbauer effecr on iron in the ferroelectric Pb?[FeNb]Os was observed close to the Curie
temperature (114 "C).
Observations of the Mossbauer effect led also to the discovery of new magnetic phenomena. For example, Borg et
aZ.[361 as well as Craig et aZ.[371 found a magnetic ordering
of electron spins in highly diluted solid solutions of iron (5 %)
in gold (95 %). The conservation of the same magnetic hyperfine structures -. the number of lines, their width and splitting
values (Fig. 7a) -- a t an imposed external axial magnetic
field of about 30 kOe, indicates that the variant of spin
ordering effected in this alloy is antiferromagnetic. Thus, the
so-called indirect or super-exchange interaction of unpaired
electrons takes place here through the conduction electrons
rather than through homopokdr valence bonds as, for example
in various magnetic oxides or ferrites.
Quantitative analysis of indirect interaction between 3d
electrons of iron via 4s conduction electrons was carried out
by another research group 138~38a3in experiments with iron
containing small amounts of aluminum. Fig. 7b shows the
variations in the field strength at the iron nuclei according to
the distance between the iron atoms and the closest admixed
aluminum atoms.
The magnetic field is proportional to the electron-spin
density at a 57Fe nucleus. The electron spin density is made
up of contributions of core s electrons and conduction s
electrons. I t was shown experimentally that in Fe-A1
alloys the core contribution remains constant over a wide
range of solute concentrations. It was concluded that the
change in the field, as obtained with the help of a computer
from the GR spectra of Fe at different concentrations of A1
(see Fig. 7b), is caused by the changes in the spin densities
of conduction electrons. Thus it was shown that the nearestneighbor and second-neighbor A1 atoms decrease the field on
iron, i.e. the indirect exchange reaction between the localized
3d spins via the 4s conduction band is antiferromagnetic in
these cases.
1351 V. V. Skljarevskii, I . I . LukaSeviE, V . N. Romanov, N . I.
Fifippov, Yu. N. Venevtzkev, and A . S. Viskov, Z . eksper. teoret.
Fiz., Pis'ma v Redakciju 3, 212 (1966).
[36] R. J . Borg, R. Booth, and C. E. Violet, Physic. Rev. Letters
11, 463 (1963).
1371 P. P. Craig and W. A . Steyer, Physic. Rev. Letters 13, 802
(1964).
1381 M . B. Stearns and S . S . Wilson, Physic. Rev. Letters 13,313
(1964).
[38a] A . W . Overhauser and M . B. Stearns, Physic. Rev. Letters
13, 316 (1964).
Angew. Chem. internat. Edit. 1 Vol. 6 (1967) 1 No. 10
N1N2
002t
N3 NLNS N6
' '
i
-8
-4
0
8
1
TIT,
V(rnrn/sec)+
4
190000
(c)
-8
6
-10
f
z
I
2
180000'
-;S
,
0
V (rnm/sec)
15
0
+
02
04
i'/Tt+
Fig. 7. Application of the Mossbauer effect in solid-state physics.
a) GR spectra of 57Fe in iron-gold alloys (Feo.osAuo.95) in the absence
of and in the presence of an external axial magnetic field;
b) the local magnetic field at 5lFe nuclei as a function of the average
distance between iron atoms and their nearest-neighbor aluminum
atoms (role of the indirect effect via conduction electrons);
c ) the GR spectrum of 119Sn in the yttric ferrite garnet
{ Y ~ L ~ [C
S n~~ F~e }
z-~l(Fe3)01~;
d) temperature dependence of local magnetic field on iron nuclei in
two sublattices and o n tin nuclei, and of electroconductivity of the
ferrite garnet (top right).
A still more peculiar example of indirect magnetic interaction
is the super-exchange induction of the magnetic fields on
nuclei of diamagnetic tin atoms introduced into yttric ferrite garnets {Y3-xCax} [Sn,Fe2-,] (Fe3)012, This effect was
observed independently by Goldanskii et a1.[391 and by Belov
et a1.[401 about three years ago. Fig. 7c shows the Mossbauer
spectrum of the tin in this garnet. The spectrum parameters,
the chemical shift (equal to the shift for SnOz), quadrupole
splitting (absent in this case, which means that all Sn bonds
are equal), the effect probability and its temperature dependence (characteristic of tin with a coordination number
of 6 ) , warranted the conclusion that, in this yttric ferrite, tin
is not directly bound with iron, but is connected with it
through oxygen: Sn-0-Fe.
hevertheless, a considerable
magnetic field - over 200 kOe at 77°K - was observed at
the nucleus of a diamagnetic tin atom as indicated by Zeeman
splitting of the spectrum line into six components; at the
Curie point it disappeared, as did the field on the iron
nuclei (see Fig. 7c). Later measurements[39al showed that the
sign of the local magnetic field at the tin nucleus (similarly
to that at the iron nuclei in the same octahedral sublattice)
coincides with the sign of the imposed external magnetic
field. Rather low values are obtained for the electrical conductivity of ferrite: 10-10 to 10-8 ohm-1 cm-* (upper righthand corner of Fig. 7d). The conductivity increases with
decreasicg field.
[39] V. I. Goldanskii, V . A . Truchtanov, M . N. DeviSeva, and V. F.
Belov, 2. eksper. teoret. Fiz., Pis'ma v Redakciju I , 31 (1965);
Physics Letters 15, 317 (1965).
[39a] V . I . Goldanskii, M . N . Devisheva, E. F. Makarov, G . V .
Novikov, and V . A . Truchtanov, 2. eksper. teoret. Fiz., Pis'ma v
Redakciju 4, 63 (1966).
[40] K . P. Belov and I. S . Lyubutin, 2. eksper. teoret. Fiz., Pis'ma
v Redakciju 1, 26 (1965).
Angew. Chem. internat. Edit.
/ Vol. 6 (1967) 1 No. 10
06
08
10
Thus, it was ascertained that the unpaired electron of iron
polarizes the internal s electrons of tin at the expense of
super-exchange interaction through two chemical bonds Fe-0
and 0-Sn. In other words, dclocalization of the unpaired
electron of iron was observed in an inorganic system having
only G bonds and it was found that this delocalization
manifests itself by the polarizing exchange interaction between
the unpaired electron and internal s shells.
IV. Examples of the Application of
Gamma-Resonance Spectroscopy in Chemistry
Work on the development and the application of
gamma-resonance spectroscopy in chemistry began in
our laboratory some seven years ago. The results obtained in our first experiments, which were carried out
mainly with organotin compounds, provided general
substantiation of the applicability of gamma-resonance
spectroscopy to the elucidation of chemical problems.
For instance, the Mossbauer effect was observed in
polymers and amorphous materials. It appeared that,
due to optical branches of vibrational spectra, recoilless gamma-resonance was best displayed in systems
consisting mostly of light atoms, e.g. H, C, N, 0.
Further, it was shown that it is possible to investigate
the influence of chemical bonds in the immediate neighborhood of, and more distant from, the "Mossbauer
atom". Finally, the asymmetric doublet structure in
a quadrupole splitting for a polycrystalline specimen
was investigated and interpreted.
Some applications of gamma-resonance spectroscopy
in structural chemistry are illustrated by Fig. 8 and 9.
The marked difference of the SnF4 spectrum from the
spectra of other tin halides (Fig. 8) and the study of
data on chemical shift, quadrupole splitting, and the
Mossbauer effect probability led to the conclusion that
the SnF4 structure is octahedral, that here the coordination number of tin is 6 , and that the coplanar bonds
837
between the tin and the four fluorine bridge atoms,
which are responsible for formation of the inorganic
polymer, are different from the bonds with the other
two fluorine atoms. It is of interest that all six Sn-F
bonds in salts of the K2SnF6 type become equivalent,
and quadrupole splitting of the lines vanishes [413. Tin
coordination numbers of 5 and 6 were found from
Mossbauer spectra for many organotin compounds.
!-?/""I
v
SnCI,
side the complex occurs in the form of Fe(II), and in the
external coordination sphere in the form of Fe(m).
The nuclear gamma-resonance spectra of xenon (129Xe
and 131Xe) made it possible to ascertain the electronic
structures of XeFz and XeF4 146-481 (see Fig. 9a). Quadrupole splittings that are identical in magnitude (but
with opposite signs) must correspond to these two
structures. Moreover, by using the radioactive iodine
compound K129IC14 as emitter of resonance gammaquanta it was shown that a chlorine xenon compound
XeC14, which was previously unknown, is formed in
the process of P-decay of iodine (to 129Xe); it was identified by its gamma-resonance spectrum (see Fig. 9 b).
In a similar way, P-decay of K129103 and K129104
gives rise to the formation of xenon oxides, XeO3 and
XeO4.
The elucidation of the structure of iron dodecacarbony1 Fe3(CO)12 also serves as characteristic example
,2151
0
-2
-1
-3
A = 17rnrnisec
A=O
SnF,
K,SnF,
-4
v(rnrn/sec)-
I
l3OI
120
lI0l
f loo
26 5
XeF,
I
I
-60
-LO
I
I
I
I
-20
0
20
LO
60
v(rnrn/sec)F
I
,
,
-1
-05
I
I
I
0
05
1
v(rnrn/sec)Fig. 8. Chemical gamma-resonancespectroscopy.
.I.
F
a) GR spectra of tin halides and their structures;
+
[Fe(CN)@
b) GR spectra of Prussian blue Fefm)
Turnbull's blue Fe(rr) [Fe(CN)@ (below);
1: singlet [Fe(CN).@; 2.3: doublet F e h ) .
+
XeF,
XeF,
(above) and
a
The structure of both Prussian blue and Turnbull blue is
fFe(n0Ix 1Fe(1r)(CN)61y.
The spectra of two well-known iron complexes, i.e.
Prussian blue and Turnbull blue, are shown in Fig. 8.
It has been shown in a number of laboratories [5,42-451
that the spectra of these two compounds are identical.
As a rule (for an exception, see 1451) these spectra were
regarded as superpositions of the Fe3 Q-doublet and the
single line of the complex hexacyanoferrate(I1) anion
[Fe(CN)6]4e. Thus, both Prussian blue and Turnbull
blue turned out to be the same compound, and it is
now considered that in these compounds the iron in[41] V . I . Goldanskii, E. F. Makarov, R . A . Stukan, T. N. Sumarokova, V. A . Truchtanov, and V. V . Chrapov, Doklady Akad. Nauk
SSSR 156, 400 (1964).
[42] L. M . Epstein, J. chem. Physics 36. 2731 (1962).
[43] J. F. Duncan and P . W. R. Wigley, J. chem. SOC.(London)
1963, 1120.
[44] W . Kerler, W. Neuwirth, E. Fluck, P. Kuhn, and B. Zimmermann, Z . Physik 173, 321 11963).
[45] K. Otto and A. Ito, Rev. mod. Physics 36, 459 (1964).
838
260"
-60
"
-40
"
-20
'
I
0
'
I
20
'
'
LO
'
"
60
v(rnrn/sec)+
Fig. 9. Chemical gamma-resonancespectroscopy.
a) GR spectra of XeFz and XeF4 and their structures:
b) GR spectra of XeF4 and XeClr obtained on beta-decay of Klz91C14.
1461 C. L:Chernick, C . E. Johnson, Y. G . Malon, G . Y.Perlow, and
M . R. Perlow, Physics Letters 5 , 103 (1963).
[47] G. J. Perlow and M . R. Perlow, Rev. mod. Physics 36, 353
(1 964).
1481 G. J. Perlow and M . R. Perlow, J. chem. Physics 41, 1157
(1964).
Angew. Chem. internat. Edit. 1 Vot. 6 (1967) / No. I0
of the fruitful application of nuclear gamma-resonance in structural chemistry.
Three variants of the structure of iron dodecacarbonyl
have been discussed previously in various papers (see,
e . g . , the references 13,9, 113): the linear structures
(C0)4Fe(C0)2Fe(C0)2Fe(C0)4 and
(CO)3Fe(CO)3Fe(CO)3Fe(CO)3designated as 4.2.2.4
and 3.3.3.3, and the cyclic one
all three having bridge bonds between the iron atoms
via carbonyl groups.
X-ray structural analysis [491 resulted in selection of the
cyclic structure (1 ) . However, all three iron atoms
would be equivalent in this structure, whereas observations of the Mossbauer effect had shown a complex
gamma-resonance spectrum of iron, shaped as a trident formed by superposition of the singlet and the
quadrupole-split doublet. This spectrum rules out the
above cyclic structure, and of the two linear variants it
is more consistent with that of 3.3.3.3. However, this
structure could not be allotted since it contradicted
X-ray analysis indications. On the basis of a repeated
X-ray analysisr501 the cyclic structure (f) was corrected - the structure of iron dodecacarbonyl is now
assumed to be (2).
(CO)4FeyFe(C0)3
I ,co I
(2)
(C0)3Fe-CO
Naturally, there are many cases in which a full interpretation
of results requires complicated calculations, as for example in
the use of the molecular orbital method. In this connection
one might mention the various explanations of differences in
ferrocene and ferricinium spectra [4*511.
The application of gamma-resonance spectroscopy in
chemical kinetics and physical chemistry of surface
phenomena is illustrated by a number of examples in
Figures 10 and 11. Curves describing the kinetics of
oxidation of solid dibutyltin in air with formation of
dibutyltin oxide[521 are shown in Fig. 1 0 a ; these
curves were obtained by observation of variations in
the intensity of nuclear gamma-resonance (NGR)
spectra of initial compounds and reaction products as
a function of time. The example that is of more common interest is that in which the tin atoms serve as observers in the characterization of the properties of dipolar aprotic solvents [531. Dimethyl formamide and
tetrahydrofuran are widely used as solvents in organic
chemistry, and strongly affect the kinetics of nucleo[49] L . Dahl and P . Rundle, J. chem. Physics 26, 1751 (1957).
[SO1 L . Dahl and J . Blount, Inorg. Chem. 4, 1373 (1965).
[51] U.Zahn, P. Kienle, and H . Eicher, Z . Physik 166,220 (1962).
[52] V . I. Goldanskii, V.Ya. RoEev, and V. V. Chrapov, Doklady
Akad. Nauk SSSR 156,909 (1964).
[53] V . I . Goldanskii, 0.Yu. Ochlobystin, V. Ya. Rochev, and V. V .
Chrapov, 3 . organometallic Chem. 4, 160 (1965).
Angew. Chem. internal. Edit. I VoI. 6 (1967)
No. 10
philic heterolytic reactions. It appears that the quantitative aspect of the solvent properties may be defined
from the increase in quadrupole splitting of the NGR
spectra of solutions of polar compounds, such as dibutyltin dichloride (cf. Fig. 10b).
0
8
L
12
RFig. 10. Chemical gamma-resonance spectroscopy.
(a) Curves depicting kinetics of the decrease in the dibutyltin (BuzSn)n
content and increase in its oxidation product (BuzSnOh: obtained by
analysis of G R spectra of tin (ordinate: intensity of Mossbauer effect
in arbitrary units).
(b) Increasing quadrupole splitting of the GR-spectrum line of tin
in dibutyltin dichloride, the latter dissolved in various dipolar aprotic
solvents (abscissa: molar ratio of solvent to (C4HdzSnC12).
Indeed, both the increase in quadrupole splitting and
the kinetic effects [53a,53bl are of the same origin; they
are caused by strong reactions of the solvents with the
cationoid, but not with the anionoid parts of molecules. In contrast to the strongly solvated cations, the
weakly solvated anions appear to be extremely reactive [53c,53d].
Gamma-resonance spectra supply information both
on the chemical state (chemical shifts, quadrupole
splitting) and on the dynamics of surface atoms (asymmetry of quadrupole splitting). For example, the spectra of tin on a silicagel[s41 surface shows two oxide
forms - SnO and SnO2. (The silica gel surface was
prepared in the following way: (i) Ion exchange between CaC12 and the H Q ions of the silica gel OH
groups, (ii) ion exchange between SnCll and Gaze.)
On the basis of the stronger temperature dependence
of the Mossbauer effect probabilityf' for the adsorbate
SnO2 (Fig. l l a ) , it may be inferred that the oxide SnO
is chemisorbed while the dioxide SnO2 is attached to
the surface by van der Waals forces only. Root mean
[53a] L . I. Zacharkin, 0.Yu. Ochlobystin, and K . A.Toilevic, Izvest.
Akad. Nauk SSSR, Ser. Chim. 7, 1347 (1964).
[53b] L . I . Zucharkin, and 0 .Yu. Ochlobysfin, J. organometallic
Chem. 3,257 (1965).
[53c] A. J. Parker, Quart. Rev. 16, 163 (1962).
[53d] 0 . Y u . Ochlobysrin, Uspechi Chim. 36, 34 (1967).
[54] I . P. Suzdnlev, V. I. Goldanskii, E. F. Makarov, A . S . PlaPinda, and L.A.Korytko, i.eksper. teoret. Fiz. 49, 1424 (1965).
839
square amplitudes of thermal vibrations along the surface (0.07 A) and normal to it (0.13 A) were established
from the quadrupole splitting asymmetry of SnO. In
the case of Sn02 it is possible to distinguish two factors
of the Mossbauer effect probability, namely the role of
atomic vibrations inside the molecule and that of
molecular vibrations on the surface of the silica gel.
suggestion [561 that two types of adsorption centers
exist, localized and non-localized. It was found that
only Fe(II1) ions had been localized before adsorption,
while localization of Fe(I1) was induced only by filling
of zeolite channels with various adsorbed compounds
(for example, hexane). Accordingly, a doublet in the
gamma-resonance spectrum of trivalent iron was observed before adsorption whilst after adsorption another doublet arising from Fe(I1) with much larger
quadrupole splitting appeared.
Spectroscopy has proved to be of immense value in the
elucidation of problems in polymer science.
/
100097-
93°K
"V
,
00
00
C
l
-0
,
T= 300°K
I
i
l
i
l
i
i
i
23 -
22 21
-
20 -
1
I
-1
,
0
1
v(rnrn/sec)+
2
I
I
3
L
Fig. 11. Chemical gamma-resonance spectroscopy.
I
(a): Temperature dependence of the Mossbauer eiTect probabilityf' for
two oxidized forms of tin (SnO and SnOz) on the surface of silicagel;
(b): GR spectra of iron in mordenite before adsorption (I and 11; at
93 OK and 293 "K) and after adsorption of hexane (111; 93 OK).
The gamma-resonance spectra of synthetic zeolites
have also been obtained 1551. At present, zeolites attract general attention as efficient separating and drying agents for mixtures. For the investigation of the
structures and the adsorption properties of faujasite
( Y ) and mordenite (M), the sodium in these compounds was replaced by iron, which was highly enriched in 57Fe. The basic structural unit of these zeolites is an octahedron consisting of silicon-oxygen and
aluminum-oxygen tetrahedrons. The octahedrons are
connected with one another via oxygen bridges forming the channels which form the internal surface of
zeolites. The spectra given in Fig. l l b confirmed the
-I
-2
v
0
(mmisec)
2
i,
--3
Fig. 12. ChemicaI gamma-resonance spectroscopy.
(a): The first NGR-spectrum of a polymer (polyrnethylmethacrylate
with triethyl tin introduced into side groups).
(b): The G R spectrum of ferrocene (I), of soluble (II), and of insoluble
(111) polyferrocenes.
Fig. 1 2 a shows the spectrum of tin in polymethyl methacrylate, in which a number of methyl groups are replaced by triethyltin. This represents an example of
one of the first Mossbauer spectra of polymers to
be obtained 1573. A comparison was made of the spec___.
[56] M . M . Dubinin, Doklady Akad. Nauk SSSR 159,166(1964).
[ 5 5 ] V . I. Goldanskii, I . P. Suzdalev, A, S. Platinda, and L. G.
styrkov, Doklady Akad. Nauk SSSR 169, 827 (1966).
840
[ 5 1 ] V. A. Bryuchanov, Y. I . Goldanskii, N . N . Delyagin, E. F.
Makarov, and Y.S. spinel, 2. eksper. teoret. Fiz. 42,631 (1962).
Angeiv. Chem. internat. Edit. / lfol. 6 (1967) / No. I0
tra [5*1 of soluble polyferrocenes and insoluble polyferrocenes, i.e. of linear polymers ( 3 ) whose chains
involve only one of the two cyclopentadienyl rings
bonded toeach iron atom, and polymers in which both
cyclopentadienyl rings are involved in a continuous
three-dimensional network. The spectrum of such an
insoluble polymer ( 4 ) (Fig. 12b) consists of two doublets; the cross-linked regions exhibit a weaker quadrupole splitting and a relatively high Mossbauer effect
probability. At room temperature, gamma-resonance is
observed only for these cross-linked regions. The spectra
may therefore be used to determine directly the extent of
cross-linking in polyferrocene, and moreover provide
information about the removal of electrons to the conduction levels of the cross-linked regions - such knowledge is important in the description of the properties
of organic semiconductors.
Fe
Fe
v
(3)
000
0
d"
,-@
1.000
(4)
0.960
-2
2
0
4
6
v(mm/sec)-
Fe
Very curious results were obtained in the study of radiation damage in polyethylene, to which stabilizers, such
as dibutyltin dimaleate, had been added. The strong,
Co-y-radiation-induced change of the chemical shift in
the NGR spectra of tin in this compound (Fig. 13a)
shows the detachment of two butyl radicals, tetravalent tin being converted to the divalent species. Obviously it is this reaction that is responsible for the
effect of organotin stabilizers as inhibitors of oxidative
aging of polymers 1591.
A number of papers on kinetics of chemical conversions (e.g. solid-phase polymerization 1601) contain reports of sudden accelerations of reactions in the vicinity of a melting point or other phase transitions in
the solid state. Such accelerations are assumed to be
connected with an increase in the mobility of atoms in
a solid under these conditions. In this connection, great
interest attaches to the temperature dependence of the
Mossbauer effect probability for different iron salts in
ice [GI]. It may be seen from Fig. 13, that within a certain temperature range close to -90 OC, the recoil-less
nuclear-gamma resonance of iron atoms in Fe(C104)~
and FeC12 simply disappears, which is a direct indication of the sharp increase in mobility of the iron atoms
in ice near the point of its phase transition.
[58] V. F. Belov, T . P. Viinyakova, V . I. Goldanskii, E . F. Makarov,Ya. M . Pauskin, T . A. Sokolinskaya, R. A . Stukan, and V. A.
Truchtanov, Doklady Akad. Nauk SSSR 159, 831 (1964).
1591 A.Yu. Aleksandrov, S. M . Berlyant, V . L. Karpov, S . S.
LeStenko, 0 .Yu. Ochlobystin, E . E. Finkel, and V. S . spinel, Vysokornolekuljarnye Soedineniya 6, 2105 (1964).
[60] V. A. Kargin and V . A . Kabanov,
vses. chim. ObSi-. im.
D. I. Mendeleeva 9, 602 (1964).
[61] I . Derci, L . Keszthelyi, B. Molnar, and L. Poes, Physics
Letters 18, 28 (1965).
z.
Angew. Chem. internat. Edit.
I
Po
@
Fe
This result is similar t o that obtained later in the study of
ferroelectrics for a second-order phase transition (cf. Section 111).
1 Vol. 6 (1967) 1 No. I0
-180
-100
-1lO
- 60
t ("C)Fig. 13. Chemical gamma-resonance spectroscopy.
(a): GR spectra of dibutyltin dimaleate in polyethylene before and after
irradiation by a 6*Co gamma source. Decomposition follows the scheme:
(C,tH9)2Sn(C02CH)2 + 7 C4H9
Sn(C02CH)z.
+
(b): Temperature dependence of the Mossbauer effect probabililyf' for
iron in frozen aqueous solutions of Fe(C104)z and FeC12 within the
range of -196 "C to -40°C (the phase transition point for ice is close
to -90 "0.
V. Nuclear Gamma-Resonance as a Method
of Chemical Analysis
First of all let us consider a specialized but highly promising application of the Mossbauer effect in trace
analysis[62,631.Since gamma resonance is observed only
for certain isotopes of certain elements (for example,
57Fe), a new technique suggests itself for the study
of the kinetics and mechanism of complicated reactions, and the structures of many chemical compounds.
To this end it is necessary to study the dependence of
the nuclear gamma-resonance spectrum upon the chemical state of the Mossbauer isotope in the system.
Even the first attempts to combine the Mossbauer effect with the tracer technique disclosed electron exchange between Fe(I1) and Fe(In) ions in solid salts at
[62] R . A. Stukan, V. I . Goldanskii, and E. F. Makarov, Doklady
Akad. Nauk SSSR 165, 1347 (1965).
[63] R . A. Stukan and L. P. Yur'evn, Doklady Akad. Nauk SSSR
167, 1311 (1966).
841
0
A
.c1
78 'K[62J. Assignment of the first of the two possible
structures ( 5 ) and (6) to ferricinium ferrichloride thus
became possible 1631.
L
l
I
0500.47 028
I
0
FeTiO,
,
$
1
L
!
I
,
/
I
I
028 0 4 7 0 5 0 108 091 041 0 041 091 1.08
v (crnisec)
-
Fe,O,
Fig. 14. Analytic applications of gamma-resonance spectroscopy.
GR spectra of two iron minerals-ilmenite FeTiO3 and magnetite Fe304,
Figure 14 shows the Mossbauer spectra of two minerals - ilmenite (FeTi03) and magnetite - at room temperature 1641. Magnetic splitting of the resonance line
is observed for magnetite but not for ilmenite. Thus, it
is possible to distinguish between the two minerals
solely on the basis of the scattering of gamma-quanta
by their surfaces. A given ore can be rapidly classified
as iron (Fe:Ti > 10) or titanium (Fe:Ti < 10) ore, by
determining the ilmenite-magnetite ratio in this way.
There are indications in scientific literature[65.6sal that the
Mossbauer effect has been proposed for use in distant analysis (from a spacecraft) of the mineral composition of the
surfaces of the moon and of Mars.
R
Fig. 15. (a): MAK-1 gamma-resonance tin detectors operating for
absorption (left) and scattering (right).
(b): Arrangement of detector f o r absorption (top) and for scattering
(bottom).
164) V . 1. Goldanskii, B. G . Egiazurov, V. M . Zuporoietz,Yu. M.
OstaneviE; and I. D. Cuprova, Priklad. Geofizika 44, 202 (1965).
[651 P . J . Klass, Aviation Week and Space Technology 9, 89
(1963).
[65a] Angew. Chem. 77, 263, 265 (1965); Angew. Chem. internat. Edit. 4, 248 (1965).
842
Since 1962 Soviet scientists have been working on various designs of gamma-resonance devices for determining the tin content (in the form of cassiterite
(SnOz)) of ores and minerals. From 1963 t o 1965 these
devices were tested under field conditions for different
tin deposits, and in the summer of 1965 our device
(MAK-I) was accepted for serial manufacturing.
Figure 15 shows the principles of its operation both for
absorption and for scattering of gamma-quanta by the
objects tested. A picture of the MAK-1 portable
gamma-resonance tin detector weighing about 3.5 kg
is also shown in Figure 15.
Instead of delivering the ore t o the laboratory for chemical
investigation, it is sufficient t o determine whether or not the
counting rate for gamma-quanta changes with a slight
movement of the resonance source. In a few minutes the tin
content is known as accurately as can be determined by
chemical analysis. Geologists and economists claim that
every such instrument saves over 7000 roubles a year.
VI. Some Applications of Gamma-Resonance
Spectroscopy in Riology
Application of the Mossbauer effect in biology [66,66a]
is favored at present mainly because iron -- one of the
principal elements showing this effect - is a component of hemoglobin and a number of ferments (see
e.g. 1711). Moreover, it is present in all native nucleic
acids, in which it evidently plays an essential, though
not yet established, biological role.
The tobacco mosaic virus contains merely 0.01 wt.- "/o
iron. However, removal of this very small amount of
iron deprives the virus of its infectious properties and
causes decomposition of the RNA molecule into
smaller subunits, as has been shown by sedimentation
measurements. Reintroduction of iron regenerates the
RNA and the infectious nature of the virus is reestablished 1671. Before elucidating the role of iron in
this system, it was necessary to ascertain the nature of
its bonding in nucleic acids. By comparison of the
spectrum of FeC13 and those of its complexes with
nitrogeneous bases such as guanine and guanosine,
with sugars such as ribose and deoxyribose and finally,
with nucleic acids such as RNA and DNA, (Fig. 16a)
it was demonstrated 168,691 that incorporation of iron
into RNA and DNA takes place via formation of coordinate bonds between Fe(n1) ions and sugars. The
latter act as electron donors in RNA and reduce the
iron to Fe(Ir); in DNA they d o not display donor properties. It is quite possible that these data might help to
explain the essential difference in the biological roles
of DNA and RNA.
[661 U. Gonser and R . W. Grant: Mossbauer Effect Methodology. Plenum Press, New York 1965, p. 21.
[66al A. J. Bearden, T. H. Moss, W. S. Caughey, and C. A.
Beaudreau, Proc. nat. Acad. Sci. USA 53, 1246 (1965).
[67] H. S. Loring, Y. Fujinioto, and L. F. Eng, Proc. nat. Acad.
Sci. USA 45, 287 (1959).
[681 R. A. Srukan, A. N. Il'ina, Yu.
Moikovskii, and V. I. Goldanskii, Biofizika 10,343 (1965).
[691 Yu. S. MoSkovskii, A. N. Il'ina, R . A. Stukun, and V. I. Goldanskii, Biofizika 11, 524 (1966).
s.
Angew. Chern. internat. Edit. / Vol. 6 (1967) J No. 10
states, i . p . Fe(I1) and Fe(ir1) are apparently present
in the cytochrome system of these bacteria. A change
in the valence state of iron during the fixation of nitrogen by azobacteria has recently been observed and
investigated '711.
'
6000"
-L
'
'
-2
I
"
"
0
2
i,
0
2
L
'
6oool
4000
-4
-2
v(rnrn/sec)Fig. 16. Gamma-resonance spectroscopy in biology.
G R spectra of iron bound t o R N A and t o D N A . In case of RNA the
complexity of the spectrum is caused by the t wo valence states of iron:
(I) Fe3@ coordinated with ribose and (II)Fez@ coordinated with ribose;
in the case of D N A the spectrum represents superposition of the sinslet
due to Fe3@ coordinated with deoxyribose and that due t o Fe3@ coordinated with bases.
A gamma-resonance spectrum 1701 has recently been
obtained of a living object, the hydrogeneous bacteria Hydrogenomonas Z-I grown in a ferric chloride
medium that had been enriched in 57Fe. This spectrum
exhibits components due to both major iron valence
I701 Yu. 3. MoSkovskii, E. F. Makarov, G. A. Zavarsin, I.Ya.
Vedenina, S . S . Mardanyan, and V. 1. Goldanskii, Biofizika 11,
357 (1966).
Angew. Chem. internat. Edit.
!Vol. 6 (1967) I No. 10
Interesting research in biomechanics has been conducted by Hillman et al. 1721: A miniature 57Co source
(57Fe served as absorber) was attached to the ear tympanum and the latter made to vibrated under the influence of acoustic oscillations. Since the oscillation
frequency (103-104 sec-1) was preset, and the tympanum velocity (of the order of 10-4 cmjsec) could be
determined by the Doppler shift of the absorption
maximum in the gamma-resonance spectrum, it was
possible to ascertain the amplitude of oscillation of
several Angstrom at an accuracy of 1- 2 A. There are
a number of analogous applications of the Mossbauer
effect in engineering where one wishes to measure and
control e.g. speeds, shifts, and accelerations. Pressure
measurements can be based on the dependence of both
chemical shifts and of Mossbauer effect probability on
compression of matter; changes in component population of the hyperfine structures of gamma-resonance
spectra, namely when the magnitude of kT becomes
commensurable with the difference in energies of individual HFS lines ( k T 5 10-5 eV, /. e . T 5 0.1 OK),
allow precise measurement of very low temperatures.
Received: Ausust 4th, 1966; revised: July 241h, 1967
[A 598 IE]
German version: Angew. Chem. 79, 844 (1967)
[71] Yu. S . MoSkovskii, I . D. Ivanov, R . A . Stukan, C. 1. Marchanov, s. S. Mardanyan, Yu. M . Belov, and V. l. Goldansltii,
Doklady Akad. Nauk SSSR 174, 215 (1967).
[72] P . Hillman, H . Schechter, and M . Rubinstein, Rev. mod.
Physics 36, 360 (1964).
843
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