close

Вход

Забыли?

вход по аккаунту

?

The Recoil-Free Fraction of the Resonance in 197Au Mssbauer Spectroscopy; Findings from Measurements of Polynuclear Mixed-Valent Ylide Complexes.

код для вставкиСкачать
achieved. The structure of the side products, which may
involve isomers, were not investigated further.
Experimental Procedure
Each type of complex is exemplified by one preparation
2c: l c (220 mg, 0.21 mmol) was dissolved in T H F (50 mL) and the resulting
solution was treated at -35 "C with a solution of Ph,PCH2 (58 mg,
0.21 mmol) in the same solvent. After the reaction mixture had warmed to
room temperature, the orange-yellow precipitate was filtered off, washed
with diethyl ether, and dried under vacuum (yield 210 mg, 75%); m.p.= 174177 "C (dec.), soluble in CH2C12,CHCl,/CH,OH; the solutions in CHCIJ/
CH,OH are yellow at 20 "C, green at -30 "C.--)'P-NMR(CD,CI,): 6=44.5,
29.1 (each s, int. 2 : I ) . 'H-NMR (CD2C12): 6= 1.02, 1.76 (each virtual d,
N = 10.99 and 9.89 Hz, ring CHZ),3.18 (d, J= 11.4, CHZPPh,), 7.37-7.73 (m,
Ph). "C-NMR (CD2C12):6=4.3, 4.5, 11.1 (all d, J=51.3, 41.5, and 54.8 Hz,
CH2); 128.9, 130.4, 132.0, 133.5 (Ph,); 121.7, 129.8, 133.8, 134.3 (Ph,). I9'Au
Mossbauer spectrum: IS 2.92 and 3.26 mm s - ' , QS 6.26 and 6.94mm s - '
(4 K, int. 1 : 1).
Zb: yield 81%, m.p.= 186-190°C (dec.).
[71 H. Schmidbaur, P. Jandik, Inorg. Chrm. Acta 74 (1983) 97; P. Jandik, U.
Schubert, H. Schmidbaur, Angew. Chem. 94 (1982) 74;Angew. Chem. Int.
Ed. Engl. 212 (1982) 73; Angew. Chem. Suppl. 1982. I.
[81 D. S . Dudis, J. P. Fackler, Inorg. Chem. 24 (1985) 3758; H. H. Murray, J.
P. Fackler, L. C. Porter, A. M. Mazany, J. Chem. Soc. Chem. Commun.
1986, 321; H. H. Murray, J. P. Fackler, L. C. Porter, D. A. Briggs, M. A.
Guerra, R. J. Lagow, Inorg. Chem. 26 (1987) 357.
[91 H. Schmidbaur, W. Tronich, Chem. Ber. 101 (1968) 595.
[I01 H. Schmidbaur, H. Stiihler, W. Vornberger, Chem. Ber I05 (1972)
1084.
[ I 11 Za: Enraf-Nonius CAD4 diffractometer, MoK,, radiation, A=0.71069
graphite monochromator, T=22 "C; triclinic, space group Pi,
a = 10.563(1), b = 11.2 l5[1), c = 15.132(2) A, a=93.55(1), 8=89.83( I),
y=92.33(1)",
V= 1787.7 A',
Z=2,
p,,,,,=2.162 gcm-',
,u(MoKa)= 100.3 cm-'. 6988 unique reflections, 5659 "observed" with
12 2.00(I) (+ h, fk, fI, [sin 8/d)m4x
= 0.6 16). Lp and empirical absorption correction; solution by Patterson methods (SHELXS-86).
R(R,)=0.029(0.031), w = l/02(Fo) for 352 refined parameters (SHELX76). Aprrn=0.82/- 1.32 e/A' at Au.-4c-4CH2C12: Syntex P2, diffractometer, T = -4O"C, monoclinic, space group PZ,/c. a = 10.160(1),
b=19.981(3), ~=35.540(5)A, /?=98.48(1)", V=7136.0 AJ, 2 = 4 ,
pC.,zEd=
1.778 g cm-', p(MoKn)=69.8 cm-'. 10544 reflections, 8188 with
I Z 2.00(0 (+ h,
k, 2 I, (sin8/A),,,dr =0.561). Patterson methods,
R(R,)=0.054 (0.056) for 493 refined parameters. bf,.
= 1.76/- 2.09 e/A'
at the disordered CH2C12.-Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Energie,
Physik, Mathematik GmbH, D-7514 Eggenstein-Leopoldshafen 2
(FRG), on quoting the depository number CSD-52624, the names of the
authors, and the journal citation.
I121 H. Schmidbaur, C. Hartmann, F. E. Wagner, Angew. Chem. 99 (1987)
1191; Angew. Chem. int. Ed. Engl. 26 (1987) 1148.
[13] H. Schmidbaur, M. Heimann, 2. Narurforsch. B 29 (1974) 485.
A,
+
2 a : yield 77%, m.p.= 170-173 "C (dec.) (see Fig. 1)
3 a : l c (184 mg, 0.17 mmol) was dissolved in T H F (50 mL) and the resulting
solution was treated at -100°C with a solution of Me3PCH2 (31 mg,
0.34 mmol) in THF. The color became lighter. At -90 "C, after further disappearance of the color, an almost colorless precipitate formed, which was
filtered off, washed with ether, and recrystallized from CH2CIZ(yield 146 mg
(68%), m.p.= 166-174°C (dec.), soluble in CH2C12, CHCI,).--)'P-NMR
(CDCI,):6=26.9, 31.1 (eachs,int. 1 : I ) . "C-NMR(CDC13):6=11.34, 18.11,
18.82 (all "d," N = 56.2.69.9 and 55.7 Hz, int. 1 : 1 : 1, CHI); 14.65 (d, J= 54.8,
CH,); 129.0-134.6 (m. Ph). 'H-NMR (CDCI,): 6=0.84, 1.34, 2.23 (all "d,"
N=13.9, 12.9, and 14.6 Hz, CH,); 1.95 (d, 5=13.3, CH3); 7.2-8.1 (m, Ph).
'"Au Mossbauer spectrum: IS 3.59 and 3.69mm s - ' , QS 6.49 and
9 . 4 0 m m s - ' ( 4 K , int.: 2:l).
3b: yield 82%, m.p.= 181-184°C [dec.).
k:yield 89%. m.p.=173-176T (dec.).
4c: Ic (464 mg, 0.432 mmol) was dissolved in T H F (60 mL) and treated at
- 105 "C with a solution of MePh2PCH2 (643 mg, 3 mmol, large excess) in
T H F ( 5 mL). After the solution had warmed to room temperature, the colorless precipitate was filtered off, washed with ether, and dried under vacuum.
Significant losses occurred upon recrystallization from CH2C12 (yield 165 mg
(48%). m.p.= 195-197 "C (dec.), see Fig. ?;)).-,'P-NMR (CDCI,): 6=31.4 (s).
"C-NMR (CDCI,/CH,OH): 6=7.45 and 11.37 ("d," N=50.7 and 49.4 Hz,
CH,); 129.5, 132.1, 132.6, 133.1 (Ph). 'H-NMR (CDCIJCH3OH): 6 = 1.26
and 1.33 (d, J = 12.2 and 12.7 Hz, CH,); 7.36-7.57 (Ph). I9'Au Mossbauer
spectrum: IS 3.43 and 3.79 mm s - ' , QS 5.61 and 9.67 mm s - ' (4 K ; int. 1 : 1).
Solutions in CH2C12 exhibit the electrical conductivity of a 1 : 1 electrolyte
such as 2c.
4b: decomposition temperature 198-204 "C
4a: decomposition temperature 200-206 "C
Satisfactory elemental analyses were obtained for all compounds.
Received: June 29, 1987 [ Z 2317 IE]
German version: Angew. Chem. 99 (1987) 1189
[I] H. Schmidbaur, R. Franke, Angew. Chem. 85 (1973) 449; Angew. Chem.
Int. Ed. Engl. 12 (1973) 416; Inorg. Chim. Acra 13 (1975) 84; H. Schmidbaur, Inorg. Synth. 18 (1978) 136.
[2] H. Schmidbaur, Angew. Chem. 95 (1983) 980; Angew. Chem. l n t . Ed.
Engl. 22 (1983) 907; Acc. Chem. Res. 8 (1975) 62; Gmelin Handbook of
Inorganic Chemistry, Organogold Compounds. Springer, Berlin 1980; H.
Schmidbaur, P. Jandik, Inorg. Chim. Acta 74 (1983) 97; H. Schmidbaur,
C. Hartmann, Angew. Chem. 98 (1986) 573; Angew. Chem. Int. Ed. Engl.
25 (1986) 575 (and references cited therein).
[3] Y. Yamamoto, Z. Kanda, Bull. Chem. SOC.Jpn. 52 (1979) 2560; Y. Yamamoto, Chem. Lett. 1980. 31 I ; w. Ludwig, w. Meyer, Helu. Chim. Acta
65 (1982) 934; R. Uson, A. Laguna, M. Laguna, A. Uson, M. C. Gimeno,
Inorg. Chim. Acta 116 (1986) 91; R. Uson, A. Laguna, M. Laguna, A.
Uson, ibid. 73 (1983) 63.
[4] J . P. Fackler, ACS Symp. Ser. 211 (1983) 201 ; J. P. Fackler, H. H. Murray, J. Basil, Organometallics 3 (1984) 821; H. H. Murray, A. M. Mazany. J. P. Fackler, ibid. 4 (1985) 154; H. H. Murray, J. P. Fackler, B.
Trzcinska-Bancroft, ibid. 4 (1985) 1633; J. P. Fackler, B. Trzcinska-Bancroft, ibid. 4 (1985) 1891; H. H. Murray, J. P. Fackler, D. A. Tocher, J.
Chem. SOC.Chem. Commun. 1985. 1278.
[S] Y . Jiang, S. Alvarez, R. Hoffmann, Inorg. Chem. 24 (1985) 749.
[6] H. Schmidbaur, J. R. Mandl, W. Richter, V. Bejenke, A. Frank, G.
Huttner, Chem. Ber. I10 (1977) 2236; H. Schmidbaur, J. R. Mandl, A.
Frank, G. Huttner, ibid. 109 (1976) 466.
1148
0 VCH Verlagsgesellschafi mbH. 0-6940 Weinherm, 1987
The Recoil-Free Fraction of the y Resonance in
197
Au Mossbauer Spectroscopy;
Findings from Measurements of Polynuclear,
Mixed-Valent Ylide Complexes**
By Hubert Schmidbaur, * Christoph Hartmann, and
Friedrich E. Wagner*
I9'Au Mossbauer spectroscopy provides a useful
method for elucidating the structure and bonding of gold
compounds.['] Progress in the interpretation of the spectra
has resulted, in particular, from the availability of increasingly reliable correlations of the parameters for the isomeric shift (IS) and the quadrupole coupling (QS) with
chemical characteristics such as the oxidation state and
coordination number of gold as well as with the electronic
influence of the ligands.[2-61On the other hand, the interpretation of the absolute and relative intensities of the
Mossbauer lines remains a problem, since-in contrast to
N M R spectroscopy, for example-the intensities often d o
not agree with expectations based on stoichiometry. These
discrepancies are ascribed to variations in the recoil-free
fraction (RFFJ[',61of the y resonance, which depends on
the "intermolecular" lattice vibrations as well as on the
"intramolecular" vibrational motions of the gold
atom^.",^.^]
Our investigations were prompted by the following observations:[81The newly prepared trinuclear gold complex
1 exhibits two quadrupole doublets in its Mossbauer spec[*] Prof. Dr. F. E. Wagner
Physik-Department der Technischen Universitgt Mijnchen
Lichtenbergstrasse 4, D-8046 Garching (FRG)
Prof. Dr. H. Schmidbaur, Dr. C. Hartmann
Anorganisch-chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, 0-8046 Garching (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
(Leibniz Progam), the Fonds der Chemischen Industrie, and Degussa
AG.
05~0-0833/87/1111-1148!$ 02.50/0
Angew Chem. Int Ed. Engl. 26 (1987) No. 11
trum, each doublet being composed of two equal-intensity
components (Fig. 1). In the binuclear complex 2, in contrast, the components of the doublet appear in an intensity
ratio of 1 : 2 (Fig. 2). Thus, there seems to be no relationship to the stoichiometry, an observation that resulted initially in the proposal of incorrect structures.
100.0-
-10
99.5.
t
s
0
-5
v [mm s-']
-
5
10
Fig. 3. '"Au Mossbauer spectrum of a mixture of the digold compounds 3
and 4 in a molar ratio of 1 : I .
I
99.0-
-
-10
-5
-
,
-
0
v [mm s-']
.
5
10
Fig. 1. ""Au Mossbauer spectrum of the trigold compound 1 recorded at
4 K.
2, it should exhibit the same intensity as the Au"' resonance.
In contrast, binuclear gold compounds in which the gold
atoms are in similar (but not identical) environments, e. g.,
5 and 6J''Jgive rise to two equal-area doublets (Fig. 4; the
IS and QS values correspond to those of other di- and trivalent gold corn pound^^^-^^).
1
I
100.0~
r
99.0-
f
99.6.
-10
-5
0
v [mm s'l
-
,
5
10
Fig. 2. '"Au Mossbauer spectrum of the digold compound 2
Examination of the other measured values then showed
that the "'Au Mossbauer intensities are also strongly dependent on the oxidation state, and thus on the coordination number, since, at least for organogold compounds, an
increase in the oxidation state is generally associated with
an increase in the coordination n ~ m b e r . 1 ~ '
This conclusion is established by a simple control experiment. The simultaneous measurement of exactly equimolar amounts of the crystalline reference compounds 3"'
and 4"01 affords a Mossbauer spectrum (Fig. 3) in which
the components of the two doublets d o not exhibit a 1 : 1
intensity ratio but rather a 1 : 1.25 ratio, the higher intensity
being assigned to the gold(ir1) complex. With respect to the
problem discussed above, this means that the RFF of the y
resonance of both 1 and 2 is larger for the Au'" centers
than for the Au' centers, so that the resonances of the Au'
centers are less intense. Otherwise, in the case of 1, the Au'
resonance, which is assigned on the basis of the large QS
value, should exhibit twice the intensity and, in the case of
Angew. Chem. Inr. Ed. Engl. 26 (1987) No. I 1
100.0
-st
-
9950
99 0 0
98.50
-5
v [mm s-']
-
7 1 1 - - - - ? -
5
Fig. 4. "'Au Mossbauer spectrum of the digold compounds a ) 5 and b) 6 .
0 VCH Verlugsgeseilschuft mbH. 0-6940 Weinheim, 1987
0570-0833/87/1111-1149 $ 02.50/0
1149
The significance of the new data for cations such as 1
and 2 lies in the fact that two gold atoms having different
configurations are each present in a common structural
unit. RFF values are usually broken down in a reasonable
way into the aforementioned inter- and intramolecular
components, provided that the solid is composed of larger
individual structural units!"
f=A.
Received: June 29, 1987 [Z 2318 IE]
Ge'rman version: Angew. Chem. 99 (1987) I191
'
f M
and fM are the Debye-Waller factors of the lattice and
molecular effects, respectively."' In the mixed-valent gold
compounds reported so far, Au' and Au"' were present in
separate species, for example in cation and anion, so that
the two RFF terms for the individual units were not separable."] In the case of 1 and 2, however, fL can be assumed
to be similar, to a good approximation, for each of the two
types of gold atoms, particularly since 1 and 2 are loosely
packed in the crystal without discrete interactions between
the ions.IX1The dramatic increase in the RFF values of the
gold atoms in the complexes under consideration on going
to higher oxidation states/coordination numbers (C.N.)
(Au'/C.N. 2; Au'"/C.N. 4) is thus a direct consequence of
the change in the immediate environment of the metal
atoms and therefore off,.
These results clearly revealed that, in contrast to earlier
assurnptions,["lf, is not the dominant RFF term; instead,
f M is primarily responsible for determining the relative intensities of the Mossbauer lines.
The vibrational motions of simple organogold compounds have been the subject of numerous investigations."21 Normal mode analyses show how the energies
and amplitudes of the fundamental vibrations change on
going from the one-dimensional (linear) to the two-dimensional (square) coordination. These changes differ particularly in their strong anisotropy from those observed on going to a tetrahedral or a pseudo trigonal-bipyramidal coordination. The situation in ylide complexes is complicated
further in that the neighboring gold atoms appreciably approach each other perpendicular to the C-Au-C axis to
within distances of under 3.00 AT1 resulting in a further
increase in the effective coordination number at each gold
atom. Although these interactions, indicated by dotted
lines in the formulas, are weaker than normal coordinative
bonds, they are sufficient, for example, to influence the
conformations of complexes and their packing in the crysta1.14.51
This phenomenon, which is the result of a relativistic effect/131presumably also affects the recoil behavior
and thus enters into the RFF values.
These components are no longer present for 4 owing to
the Au-CH2-Au linkage, so that it is not surprising that the
intensity ratio for 413 is smaller (Fig. 3) than for 1 or 2
(internal in each case).
It is noteworthy that the ellipsoids of thermal vibration
of the gold atoms in 1, determined by X-ray analysis, also
directly reveal the stronger motion of the two Au' atoms.
Obviously, however, a quantitative evaluation is not possible.I9l
Overall, the data show that, in the case of 1 and 2, the
coordinative bonding of the gold atom in a square array of
ligands with secondary bonding to further gold atoms
causes the RFF parameter f M to increase strongly and
thereby results in considerable shifts in the intensities of
the Mossbauer lines. Owing to the special geometries of 1
and 2, these shifts are much larger than analogous effects
in other complexes.
f L
1150
In one of the few reported studies in this area, the Debye-Waller factorsf,, were correlated with the molecular
weight; however, satisfactory results were obtained for
only some of the compounds
Apparently, the
contribution of coordination number and coordination
geometry['21discussed above is still considerably underestimated.
0 VCH Verlagsgesellschaf mbH, 0-6940 Wemherm. 1987
[I] R. V. Parish in G. J. Long (Ed.): Mossbauer Spectroscopy Applied 10 Inorganrc Chemistry, Plenum, New York 1984, Chap. 17.
[2] H. Schmidbaur, J. R. Mandl, F. E. Wagner, D. F. van d e Vondel, G.P.
van der Kelen, J. Chem. Soc. Chem. Commun. 1976. 170.
131 R. V. Parish, Gold Bull. I5 (1982) 51; M. Melnik, R. V. Parish, Coord.
Chem. Reu. 70 (1986) 157.
141 H. Schmidbaur in Gmelin Handbook of Inorganic Chemistry. Organogold
Compounds, Springer, Berlin 1980.
[5] R. J. Puddephatt: The Chemistry of Gold. Elsevier, Amsterdam 1980.
[6] N. G. Greenwood, T. C. Gibb: Mossbauer Spectroscopy, Chapman and
Hall, London 1971, p. 9ff.
171 A. J. Rein, R. H. Herber, J . Chem. Phys. 63 (1975) 1021; and earlier
references cited therein.
[8] H. Schmidbaur, C. Hartmann, G. Reber, G. Miiller, Angew. Chern. 99
(1987) 1189; Angew. Chem. Int. Ed. Engl. 26 (1987) 1146.
[9] J. D. Basil, H. H. Murray, J. P. Fackler, J. Tocher, A. M. Mazany, B.
Trzcinska-Bancroft, H. Knachel, D. Dusis, T. J. Delord, D. 0. Marler, J.
Am. Chem. SOC.107 (1985) 6908.
[lo] P. Jandik, U. Schubert, H. Schmidbaur, Angew. Chem. 94 (1982) 73;
Angew. Chem. Int. Ed. Engl 21 (1982) 73; Angew. Chem. Suppl. 1982, 1.
I l l ] H . Schmidbaur, C. Hartmann, J . Riede, B. Huber, G. Miiller, Organometallics 5 (1986) 1652.
[I21 T. P. A. Viegers, J. M. Trooster, P. Bouten, T. P. Rit, J . Chem. Soc. Dnlton Trans. 1977. 2074.
[I31 P. Pyykko, J. P. Desclaux, Acc. Chem. Res. 12 (1979) 276.
Conformational Transitions between
Enantiomeric 3,,,-Helices
By Rolf-Peter Hummel, Claudio Toniolo, and
Giinther Jung*
Dedicated to Professor Manfred Rothe on the occasion of
his 60th birthday
In the following we report on the 13C-NMR study of an
enantiotopomerization of 3 lo-helices. This conformational
change of a peptide, which occurs rapidly at room temperature, has been detected by us on a decapeptide consisting
of a-aminoisobutyric acid (Aib), Me2C(NH2)C02H residues. Our results are of relevance for those engaged in
conformational energy calculations, molecular modeling,
o r the dynamics of peptides o r who, for example, wish to
use enzyme-resistant, nontoxic a-amino acid residues such
as Aib in drug design.
In proteins 310-helicesare found rarely and usually as
short segments at the end of a-helices."' On the other
hand, partial sequences of the peptaibol antibiotics"] from
tri- to octapeptides containing L-amino acids and a large
amount of a,a-dialkylated, achiral Aib residues strongly
prefer the right-handed 3;o-helical c o n f ~ r m a t i o n . [ ~ ~ . ~ ~ - ~ ~
When the N-terminal -X-Aib sequence is in the type-I1 pbend conformation, the adjacent segment of the peptide
[*I
Prof. Dr. G. Jung, DipLChem. R.-P. Hummel
Institut fur Organische Chernie der Universitat
Auf der Morgenstelle 18, D-7400 Tubingen (FRG)
Prof. Dr. C. Toniolo
Centro di Studi sui Biopolymeri, C N R
Dipartimento di Chimica Organica, Universita di Padova
Via Martolo I, 1-35131 Padova (Italy)
0570-0833/87/1111-1150$ 0250/0
Angew. Chem. Int. Ed Engl 26 (1987) N o I 1
Документ
Категория
Без категории
Просмотров
2
Размер файла
354 Кб
Теги
valenti, complexes, mixed, findings, fractional, polynuclear, recoil, 197au, measurements, spectroscopy, free, mssbauer, resonance, ylide
1/--страниц
Пожаловаться на содержимое документа