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Intracrystalline Reactivity of Phyllodisilicic Acid (H2Si2O5).

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fluoroethanol stabilizes mainly the conformation (1 a ) . As
expected, the Cotton effect of the n-n* amide transition is
shifted hypsochromically with increasing polarity of the solvent.
In contrast, the Cotton effect at 305nm is less temperature
dependent and not to be ascribed to the disulfide group;
a dependence of its position and/or ellipticity on the solvent
can hardly be established. This previously unobserved Cotton
effect can certainly not arise from an impurity, for highly
purecrystals were employed in the investigations. It is conceivable that a positive Cotton effect above 300nm (possibly
a CT transition analogous to that in epidithiopiperazinedionesI"l) is superimposed by the negative amide Cotton effect
such that it gives an apparent positive maximum above 300 nm.
r rci
Conformational calculations on L-cysteinylcysteine disulfide
indicate a slightly nonplanar cis-amide group and give similar
bond lengths and angles as in open chain cystine peptides.
The total energies of the P- and-M-conformations should
differ only slightly (0.6 kcal/mol)lxl. In contrast to the C D
spectrum of ( I 1, the spectra of L-cysteinylcysteine disulfide
hydrochloride (2) and its methyl ester ( 3 ) show strongly
reduced ellipticities and a reversal of sign, thus indicating
lack of interaction between the amide groups and an increased
flexibility of the disulfide groupiy1.Hence, together with ( I ),
compounds (2) and ( 3 ) are the only examples known so
far of compounds with inherent dissymmetrical disulfide
groups without optical activity in the region of the longwave
disulfide absorption.
Received. August I . 1974 [Z 91 IF.]
G e r m a n version' Angew. Chem. NO. 856 (1974)
Fig. 2. Temperature dependence of the C o t t o n effect at about 225nm in
trtfliioroethanol (o --.I, ethanol l96",,) (0--o). a n d 0.1 N HCI (o--o)
The "C-NMR spectrum of ( I ) in D6-DMS0 at temperatures
below 45°C shows three weak signals besides the three intense
peaks (Fig. 3). The stronger signal of the carbonyl carbon
lies at low field, which, independently of the CD, indicates
the P-conformation for the disulfide bridge in which the sulfur
atoms and the carbonyl group are closely proximateisT,the
cdrbonyl carbon atom being more strongly deshielded than
that in the M-helical molecule, whose "C signal was previously
not observed1''.
cys - co
~. .~
B. l k n i x / , B. Kumhev. K . Mirhvirh, a n d R. S(.hu I :PI'. Helv Chim. Acta
5 5 . 947 ( 1972).
[2] R M,. W ~ O ~Tetrahedron
2Y. 1273 11973).
[3] a) L . FIohP, H. Ch. Ben%r, H . Sies. H. D. Wulkr, a n d A . Wendel. Glutathione. Thieme, Stuttgart 1974; b) M .Ortnad, C. Olmad, P . Hurrrer, a n d G.
Jifny in [,a],
p 20ff.. c) G . Junq. M . Oirriad, and M . Ktnipltv, Eur. .I
Biochem. 35, 436 11973): d ) M. O r r n d , C Orlnod. P M U I ' I I P ~and
. G . Jitiiy,
Tetrahedron, in press: e) 7 7>kayi a n d N. Iro, Biochim. Biophys. Acfa
757. I (1972): 0 7: lukugt. R. Okano,a n d N. 110, ihid 311). I1 (1973).
[4] K. Nugor(ijurt a n d R. U: Woot/~,J Amer. Chem Soc. YS. 7212 (1973).
[ S ] C J i t t i y . E. Bretrmuiw, a n d M: RWIIW,Fur. 1. Biochem. 24. 438 ( 1972):
G Jitny. E. Bwirniuwv, U A Gtiiiz/w, M . Orinuil, U L ' i w I r ~ ~a. n d 1.. F l o h i
in [3a]. p. I f f .
[6] S. Bergo-, Dissertation. Universrtiit Tubingen 1973, p 58ff.: D. K . D d l t n y .
D. M. Gram, a n d L. F . John,mn, J. Anier. Chem. Soc. 93, 3678 1197 t ) :
0.A . Gonvoii, J . Ktlloiigli. a n d A . K. Bttrhe, thid. Y3. 4297 (1971).
[7] H . K c ~ l o a. n d M: Rtni(/d. Chem. Ber 101, 3350 (1968)
R. C h ~ n d r ~ . ~ r haun~d . ~X .~ Bu/u.~tth,-iitnoiiiun.
Biochim. Hiophys. Acta
1 N 8 , I ( 1969).
G. Jting a n d M Orrt7ud. unpublished.
Intracrystalline Reactivity of Phyllodisilicic Acid
1-ig. 3.1-emperaturedependenceo f t h e '.'C-NMR stgnals of ( I ) In D , -1)MSO.
Despite the weakness of the coalescence-point method in the
determination of energy barriers from "C-NMR spectral"!
the lower limit of AG+ for rearrangement of the P-helical
conformation of the disulfide bridge into the M-helical form
can be estimated. Values of 15.6-16.0 kcal/mol are obtained.
The highest previously observed rotation barriers about the
disulfide group, which were measured on sterically very hindered diary1 disulfides, amounted to 15.7 kcal/m01['~ and likewise can only be considered as a lower limit value for this
process. The intensities of the 'C-NMR signals of ( I u ) and
( I b ) give the proportion of the less stable M-helical conformers ( I b ) at 25°C as 15-20'%,. Since the relaxation times
of the aliphatic C atoms of ( I u ) and ( I h ) are comparable,
this estimation is acceptable.
Angcw. C'hom. i n r c ~ n o t tdir.
J Vol. 1 3 f 1974) J No. 12
By Gerharil Luguij, K . Beneke, P. Dietz, and Armin Wrisd'l
It is generally difficult to characterize solid silicic acids. The
groups are often of low thermal stability, so that
even slight heating causes the structure to change by condensation to siloxane groups >Si-O-Sic.
Their acidity is low;
in attempts to determine the amount of >Si-OH
in aqueous media cleavage of siloxane groups cannot always
be excluded with certainty and many reagents do not yield
the correct value if the density of silanol groups is high.
[*] Prof. Dr. G . Lagaly a n d K. Beneke
Instttut fiir Anorgdnische Chemie d e r Universiliit
23 Kiel, Olshausenstrasse ( G e r m a n y )
Dipl.-Chem. P. Dietz a n d Prof. D r . Armin Weiss
Inscitut fiir Anorganische Chemie der Universitit
X Munchen 2, Meiserstrasse I - - 3 (Germany)
An exception is provided by the crystalline phyllosjlicic acids
which form characteristic intercalation complexes. This property is shown most markedly by the natural and synthetic
silicic acid "H-magadiite" ( H & I +O,~.5.4
We report below about "phyllodisilicic acid" ( H 2 S i 2 0 5 ).,
According to X-ray diagrams three forms can be disting ~ i s h e d ' ~ but
- ~ ~ we
, investigated mainly form 11. This is
obtained by reaction of 80% sulfuric acid at 0°C with powdered cr-Na?Si?O< ' ?{.
After refinement the relatively sharp powder diagram of form
I1 has the axes (cf.[31)a,=5.6+, bo= 14.63, and c0=29.7,
According to the structure determination by Liehair, the SiOJ
tetrahedra are linked to form layers in such a way that twelvemembered siloxane rings are obtained. But unlike the "tetrahedral layers" in clay minerals, the free corners of the tetrahedrons (>Si-OH groups) project alternately above and below
the layer. In the free acid the layers are folded; the basal
spacing ill,= b/2 is 7.3 A.
The phyllodisilicic acids are considerably less reactive than
H-magadiite. They do not form intercalation complexes by
direct reaction with formamide, acetamide, urea, pyridine,
pyridine N-oxide, or their methyl or ethyl derivatives. It is
impossible to distinguish whether simple intercalation complexes have been formed or whether new silicates have arisen
by acid-base reactions with retention of the layer structure.
Reaction with aqueokis hvdrazine solutions increases the basal
spacing d,, from 7.3 A to 9.8-10.5 A, depending on the water
content (Table 1). The increase in the basal spacing is
of the same order of magnitude as in kaoiinite (from 7.1,
to 10.4.&1('1).
By washing with water the phyllodisilicic acid
is reformed. Methylhydrazine ( p K t ~ =
7.9) increases the basal
spacing to lO.OA, but with NJ-dimethylhydrazine (pK13=7.5)
there is no reaction. This makes i t clear that base strength
is not alone decisive, and that steric effects play an appreciable
increasing from 10.9 to 17.1 A. The butylamine compound
can be obtained analogouslj from the propylamine compound,
and therefrom the pentylamine compound, erc'. ("propping
open"l*I). The displacement reactions are reversible.
Table I . Basal spacings il, and methods of preparation of intercalation
compounds of phyllodisilicic acid ( H : S i ? O; ) ,
__ .....
-. ........................
10. I i
I I .o
- ....... - ...
Dii-ect reaction Mirh
N ? H , - I H.0
N,H,. 2H:O
N.H,- 4 H ? O
N:H, 6 H . 0
N?H, IOH-0
N .€I,- 50 H ?O
Mcthq Ihqdrarinc
Ammonia 1 I N [a])
Methylamine (40 "<, [a])
Fthylamine (33 ":, [a])
Piperazine (sat. [a])
N > HK H
P K I Ll a 1
B! displacement of
Pq ridinc
Clclohexb larnine
22 0
Butqlarnine or
Ethyl-, buty1-, or
Fig. I . Basal spacings d , of intercalation compounds of phqllodis~lic~c
uith primary n-alk)lamines as dependent on rhe number i? of C atoms
- - - calculated for bimolecuinthealkql chain. - - 0 experimental values. ~-~
lar layers of alkyl chains arranged perpendicularly to the layers according to
therelationdi=9.8+2x1.26xn+3[~](9.X=basalspacingofthe NH,compound; 1.26 =projection of the C-C bond on the cham long axis: 3 =van der
Waals radius of the methyl terminal group).
Figure 1 shows the basal spacings of the n-alkylamine compounds with n = 1 to 18 C atoms in the alkyi chain. For
n > 2 they increase linearly with chain length. The average
increase is 2.8 AL/CH2; this value is distinctly greater than
the maximal value 2.5 that would be expected for a bimolecular arrangement of the alkylamine molecules in the interlayer
spaces with their long axes standing perpendicular to the
silicate layers. I t must be assumed that the chains are tilted
at an angle to the silicate layers and that the tilting angle
increases with chain length up to 90". This is shown also
in the absolute values: Starting from the NH3 compound
( d , = 9.8 A)one calcukites for perpendicularly arranged chains
values of 33.0 and 58.2 A for, respectively, 8 and 18 C atoms
in the alkyl chain; observed values are 30.0 and 58.4.k Fitting
the NH? groups to the puckered silicate layer probably forces
an inclined orientation on the shorter alkyl chains. Increasing
van der Waals energy with increasing chain length cause
the tilting angle to approach 90". A similar change in orientation was found in the complexes of transition-metal disulfides
with alkylamines[8! The inclination of the shorter alkyl chains
is indicated also by the alternation of the basal spacings: the
increase Adl,=dl.(n+ l)-dI.(n) is larger for odd than for even
n ; and this hints to a specific orientation ( b ) of the N H 2
groups with respect to the silicate 1ayer''l'.
[a] Aqueous solution
Aqueous NH3, methylamine,and ethylamine r y c t with expansion of the basal spacing to 9.8, 10.0, and 10.9 A, respectively.
Amines with longer chains do not react directly. If an excess
of propylamine is allowed to react with the ethylamine compound, the ethylamine is displaced from the interlayer spaces
and the propylamine compound is formed, the basal spacing
Shortening of the shorter alkyl chains by formation of gauche
bonds is presumably excluded, since this effect is normally
favored with long alkyl chainsf1"'.
AnyPw. Ckrm. infernal. Edit.
1 Vol 13
1 No. 12
The ethylamine or but>laminc compound can be converted
into other amine complexes (Table I ) too.
The amine can be hashed out of rt-alkylamine compounds
by anhydrous ethanol. which is an indication in favor of
existence of true intercalation compounds and against formation ofn-alkylammonium silicates by direct acid-base reaction.
The free d-orbitals of the Si atoms probably function as acceptors for the intercalated Lewis bases. I t is possible that intercalation cornpounds o f crystalline silicic acids may come to
be used as models of adsorption systems with amorphous
SiO preparations.
The majority of the intercalation compounds are well ordered
and the original silicic acid can be reformed in more or less
well ordered state by cautious evaporation of the intercalated
component 01- by its extraction with an inert solvent.
In some cases, e.g. with dimethyl sulfoxide, formation of intercalation compounds of phyllodisilicic acid is accompanied
by large broadening of the (OkO) interferences, sometimes even
by production of amorphous materials. Presumably the strong
interactions between the intercalated molecules and the silicic
acid layers change the folding and destroy the parallel orientation over large areas: if the intercalated molecules are removed
the original order cannot be restored and hitherto unknown
paracrystalline silicic acids result.
The intracrystalline reactivity of phyllodisilicic acid and the
structural stability during the intercalation processes proved
to be strongly dependent on the mode of preparation of the
disilicic acid. Disilicicacid can be prepared not only by reaction
of r - N a z S i 2 0 5 with 80", HzSOI at 0"C1", but also with
40 H ,SOA, I N HCI, 01- H +-ionexchangers at room temperature. The preparations at room temperature give nearly identical X-I-aydiagrams with only minor differences in the sharpness
of the reflections in comparison with preparations at 0"C,
but amorphous products with hydrazine hydrate. Probably
at room temperature the folding of the layers becomes less
regular and the regions ofequal folding direction less extended.
Aging phenomenal-'-I'
connected with condensation of silanol
groups play an important role.
spectrometric investigations of the crystalline solids suggest
a structure for the (HgI)+ cation[21consisting of planar chains
with angular bonding at the iodine atom, as has been found for
the isoelectronicA~I[~~
The determination of the crystal structure of (Hg1j2TiFi,(HgI)?ZrF,,and (HgI)?SnF<,
are isotypic-was based on 490
independent reflections (255 with I < 3 o ) measured with a
four circle diffractometer (Mo,, radiation, graphite monochromator)in the range O"<$<22"'i'. Refinement of the structural
model obtained by Fourier methods led, after absorption
correction['l, and with anisotropic temperature factors, to a
final R factor of 0.083 (coordinates in Table 1).
Table I . Atoinic coordinate&of (HgI):TiF,
0 3583
0. 1092
0 237 I
0 9x2 I
0 2s
I1 25
. _.
Crystallographic data: Space group Cmcm-Di;: (1 = 762.2
k0.6, b= 1492.0+0.9, ~=761.3+0.9pm: Z = 4 ; t/,~,,,=6.27,
dexp=6.1 5gcm- '.
Zigzag chains &[IHg,,,]
pass through the lattice parallel
to the u axis (line group No. 10 of the Bhagavantam classification"], factor group isomorphic to C,,-mm) ; coplanar pairs
of chains lie in planes with ;=0.25 and z=0.75 (Fig. I).
Inderatomic distances and bond angles are listed in Table
Receivcd. Ma? 17. 1974 [Z 96 I f ]
Gci-man version: Angch. Chem. Nh. 893 (1974)
4. Lki\$. 2. Naturforsch. X h . 234 11973).
(;, /.mgdi.
R . S ~ / i u m : and E. M c m i ~ r . Bei. Drut Chem. Gcs 57. 1177 i1914).
[i] E.
5 c i i c 4 ~ .a n d
Z.Ki-istallogi. 120. 427 (1964).
[J] / l i o d i < , k c and I- Lichiii. Z. Anorg. Allg. Chem. 335, 178 (1965).
[ 5 ] .!.I.-/ /I. 1.1, Biiiuil. A. Kuli. and R . l l c i . Bull.Soc. t i - Mineral. Cristallogr.
YJ. 1.((1971)
. 11.
Riirn-. II .SIIiofc,r-. a n d (; <;orin$/. 2 Anorg
[7] G. I i . 5rim//(,i and S. Koi. Amer. Mineral 4Y. 106 11964).
4. I l c i \ \ and K Riit/iori/i. 2. Naturforsch. ?Xh. 249 11973).
/.uqiil~ a n d 1. Lt
Kolloid Z 2.Polym. 23X. 485 119701.
[ I 0J (;. L o ; g r i / i and .A I
. A n g e ~Chem. X3. 5x0 (1971): NS. 915 (1973).
Angc\\. Chem inlcinat. Edit. I O . 55X 11971): 12. 8.50 (1973).
t.ig. I . Striictui-e of iHgl):TiF,,: projection onto 1001).
Table 2. Interatomic distances [pm] and bond angles (standard deviation
in units of last decimal place given in parenthesis).
Crystal Structure of (HgI)2TiFh[**]
By K l i m Kiihlw, Diririch Brritingrr, and Grrharrl Thiele[*l
Mercurioiodonium complexes of the composition (HgI)::. X"are formed as reaction products in the systems Hg'-/I -/X"
(X"- = TiFi-, ZrFi-, SnFi-, NO;, and BF;)"'. Vibrational
[*] Prof. Dr. D. Breitinger, Dr. K. Kohler, and Prof. Dr. G. Thiele
I n s t i l u l f u r Anorganische Chemie der Univcrsitiii Erlangen-Nurnberg
852 Erlangen. Fgerlandstrasse I (German))
[**I This u o r k h a s supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
Anynt. Chein. infrrnuf. E d i t .
1 V'l. 13 f 1974) 1 No. 12
Hg- I '
H g - 1'
Hg I"
Ti- F '
Ti .I.?
TI- t '
26 I.N4)
167 (4)
264 ( 4 )
2 x 2 6 2 (4)
H g - 1 ' - Hg
Hg-- 1'- Hg
] I ..
X91(2)"- 1.56013)rdd
97 2(2)"=- 1.69613)rad
175 8" -3.068
.- .- .. ...--
_ _ __ .-.-.
The chains are linked together in various ways cia slightly
deformed TiFg- octahedra, such that the mercury atoms
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acid, intracrystalline, h2si2o5, reactivity, phyllodisilicic
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