close

Вход

Забыли?

вход по аккаунту

?

Chloromolybdate(VI) A Halomolybdate Having Tetrahedral Coordination.

код для вставкиСкачать
b= 86.98,y=94.88 ";duxp=1.98,d,.,,,=2.00gcm-3). Preliminary results of an X-ray structure analysis['] performed on
single crystals show that the two terminal tungsten atoms
W-1 and W-3 are tetrahedrally coordinated while the central
W-2 is in a strongly distorted square pyrimidal environment.
The WS, polyhedra are edge linked (see Fig. 116]).
Fig. 1. Structure of the anion W,S;-. (The statistical distribution of W-2
is symbolized with broken lines; see Fig. 1 in Ref. [6].)
The WS stretching vibrations are unambiguously compatible with the proposed structure of the anion. The IR solid
state spectra of ( I ) and ( 2 ) show bands at 525 [v(W(2)=S)],
,]
490, 485 [v(W(1,3)=S)], 465 and 435cm-' [v,,(W--S--U
(concerning the frequency of v(WS) vibrations see ref. [7]).
Procedure.
a) 40 % H F (40 ml) is added to a vigorously stirred solution
of (NH4),WS4 (1.2g) in H 2 0 (360ml). After addition of a
solution of [(C6H5)4P]C1 (0.4g) in H 2 0 (50ml) there results
a reddish brown precipitate of ( I ) which is filtered off, washed
with alcohol and ether, and recrystallized from nitromethane.
M. W. in CH,Cl,: 1452 (calc. 1519).
b) Alternatively, (1) is formed on heating (250°C, 0.5 h)
of a thoroughly stirred mixture of (NH4),WS4 and
[(C,H,),P]CI (molar ratio 3:2) under N,. The reaction product is recrystallized as above.
c) Compound (2) can be obtained in analogous manner
from [(C6H5)4A~]C1.M.W. in CH2C12: 1624 (calc. 1602).
Received: January 27, 1975
revised: July 18. 1975 [Z 193a IE]
German version: Angew. Chem. 87. 598 (1975)
CAS Registry numbers:
( I ) , 54844-39-2; (2). 54823-22-2; (NH4)2WS,, 13862-78-1
[ l J D . L. Kepert, Progr. Inorg. Chem. 4, 199 (1962); 0.Glemser, H. Holznagel,
W Hiiltje, and E . Schwarzmann, Z. Naturforsch. 206, 725 (1965).
[2] P. Souchuy; Polyanions and Polycations. Gauthier-Villars, Paris 1963.
[3] F . A . Cotton and G. Wilkinson: Advanced Inorganic Chemistry. Wiley-
[4]
[5]
[6]
[7]
574
Interscience, New York 1972; Anorganische Chemie. Verlag Chemie,
Weinheim 1974.
E. Diemann and A. Miiller, Coord. Chem. Rev. 10, 79 (1973).
A . Miiller, E. Diemann, and C. K . Jsrgensen, Struct. Bonding 14, 23
(1973).
We are grateful t o Dr. Prrut, Dortmund, for his assistance. The crystal
structure determination is very complicated because of the statistical distribution of W-2 over two different lattice sites. When accurate results
become available we shall report the structure of ( I ) jointly with Dr.
Preut.
K. H. Schmidt and A..Muller, Coord. Chem. Rev. 14, 115 (1974).
Chloromolybdate(vi) : A Halomolybdate Having Tetrahedral Coordination
By E. Koniger-Ahlborn and Achim Miiller[*]
While halochromates of type Cr03X- (X = F, C1, Br) having
isolated tetrahedral anions have been known for some time
and are readily accessible by reaction in solution['*21, the
corresponding molybdates and tungstates are not formed in
analogous manner since the central atoms prefer the coordination number 6, as for example in the compounds containing
the anions [MO2F3];- (fluorine bridging)[31,M02X2-[41,and
M03F:-[51 (M=Mo, W; X = F , Cl).
Our studies on halovanadates(v) showed that the size of
the cation exerts a decisive influence on the coordination
number of the anion. Thus isolated V02F: units are present
in [ ( C ~ H S ) ~ P ] V O
prepared
~ F ~ in solution[61,whereas the corresponding alkali metal salts exhibit oxygen and fluorine
bridges['! We have now succeeded in the first preparation
of a halomolybdate, the analog of chlorochromate, having
tetrahedral coordination by a simple and novel method, and
in its unequivocal characterization by vibrational spectra and
X-ray studies. If tetraphenylphosphonium or tetraphenylarsonium chloride is sintered with stoichiometric amounts of
M o o 3 at 250-280°C in an H20-free atmosphere of N 2 for
1 h (process repeated several times with thorough mixing of
product between each repetition and with rigorous exclusion
of moisture) there results [(C6H5)4P]Mo03C1 ( I ) or
[(C6H5)&]Mo03C1 (2). The Mo03CI- ion is isoelectronic
with Tc03CI. Compounds ( 1 ) and (2) are expectedly prone
to hydrolysis and colorless. While the electronic spectrum
of the anion could not be measured (the longest wave band
corresponding to a 'AI+'E (a2+e) transition should lie at
40000cm-1[81) because the cations absorb at relatively long
wavelengths, all the characteristic modes of the anion, which
can beclassifiedaccordingtor(CsV)=3A1+3E,wereobserved
(cf. Table 1). The frequencies are in approximate agreement
with those of TcO3CI.
Table 1. Fundamental modes of Mo0,CI- [b] in c m - ' (the frequencies of
C r 0 3 C I - and Tc03CI are gwen for the sake of comparison)
-
Cr0,CI
~
MoO,CI-
t.1
Tc03CI
Cal
[a] Cf. ref. 191.
[bJ From IR and Raman solid state spectra.
We have recently reported on the assignment of vz(A1)
and v3(A1)and the problem of distinguishing between them['].
The valence force constants calculated by the L Tatrix
method["] amount to fMca = 6.67, fMlC,= 2.40 mdyn/A and
are thus expectedly somewhat smaller than in neutral
TcO~CI'~'.
Powder diagrams (Cu-K, radiation) show that ( I ) and (2)
are isostructural with the corresponding salts of the ions
MnOi[''], FeC1i[121,and Cr03X-[131.The systematic extinctions (hkl only with h + k + 1 = 2 n) reveal a pseudotetragonal
structure (a complete crystal structure determination is available for [(C6H5)&h]FeC14[t ,]; space group S i - 13).The lattice
dimensions [ ( I ) , U O = 12.48, co=7.36A; (2), U O = 12.66,
[*] Prof. Dr. A. Muller and Dipl.-Chem. E. Koniger-Ahlborn
Institut fur Chemie der Universitat
46 Dortmund 50, Postfach 500500 (Germany)
Anyew. Chem. internat. Edit.
Vol. 14 ( 1 9 7 5 )
Nu. 8
c o = 7.23
a] are comparable with
those of the compounds
cited.
Received: January 27, 1975 [Z 193b I€]
German version: Angew. Chem. X7, 599 (1975)
CAS Registry numbers:
( I ) . 54823-26-6: ( 2 ) . 54823-27-7; MOO,. 1313-27-5:
[(C,H 5 ) 4 PICI, 2001- 4 5 4 : [(C,H ,),As]CI, 507-28-8
[ 11 G. Bruuer: Handbuch der praparativen anorganischen Chernie. F. EnkeVerlag, Stuttgart 1960.
121 E. Ahlhorn, E . Diemann, and A. Muller, Z. Naturforsch. 27h, 1108
(1972).
[3] R. Maftes, C . Miiller, and H. J. Brcher, Z. Anorg. Allg. Chem. 389,
I77 ( 1972).
141 Y A . Buslaec and R . L. Dacidotitch, Russ. J. Inorg. Chem. 10, 1014
(1965); W P. Criffifh and 7: D. Wickins, J. Chem. SOC. A 1967, 675.
[S] G . Pausewzng and W Riidorfi Z. Anorg. Allg. Chem. 364, 69 (1969).
[6] E . Ahlhorn, E . Diemann, and A. Muller, J. C . S. Chem. Comm. 1972,
378.
[7] R . Muttes and H . Rieskamp, Z. Anorg. Allg. Chem. 399, 205 (1973).
181 A. Miiller, E . Diemann, and C . K. Joryensen, Struct. Bonding 14. 23
(1973).
[9] A . Muller. K . H . Schmidt, E . Ahlborn, and C. J. L. Lock, Spectrochim.
Acta 2 9 A , 1773 (1973); see also K . H. Schmidt and A . Miiller, Coord.
Chem. Rev. 14, I14 (1974).
[lo] A. Miiller, 2.Phys. Chem. (Leipzig) 238, 116 (1968).
[ I l l E . J. Baran, Z. Anorg. Allg. Chem. 382, 80 (1971).
[12] B . Za.slou and R . E. Rundle. J. Phys. Chem. 61. 490 (1957).
[13] E . Diemann, E . Ahlborn, and A. Muller, Z. Anorg. Allg. Chem. 3Y0,
217 (1972).
The distortion is carried out in such a manner as to preserve
a plane of symmetry (plane of the paper) for the molecule.
Under these conditions the odd orbitals belong to different
symmetry representations (heterosymmetric diradical)['! The
ground singlet is a purely covalent diradical state ID, while
the two excited singlets Z I and Z2 are purely ionic. The
energies and charge distributions of these three singlet states
can be calculated by the Nesbet restricted open-shell SCF
technique, augmented by configuration interaction between
the three lowest singlet state configuration^'^^.
I
1
12 15
I
,
20
30
Sudden Polarization in the Zwitterionic Z, Excited
States of Organic Intermediates. Photochemical Implications
Fig. 1. Charge separation Aq in 2 ,excited singlet state of 9O-tw1sted ethylene
as a function of the pyramidalization angle @. The number Aq has been
corrected for the intrinsic charge separation in the ground state (which
never exceeds 0.04e).
By Vlasta BonaCiC-Kouteckj, Peter Bruckmann, Philippe
Hiberty, Jaroslav Kouteckj, Claude Lrforestier, and Lionel
Salem ['I
In 1971, in a relatively unnoticed paper['], Wulfman and
Kumei pointed out that the two lowest excited singlet states
of 90"-twisted olefins should show a remarkably large polarizability. These states are the zwitterionic[*I Z1 ( 1 ) and Z2 (2)
excited states of the twisted olefin diradical; the ( - ) and
(+)signs refer to out-of-phase and in-phase resonance interactions respectively. Since numerous bitopic photochemical reactions, in which two radical sites are created in the primary
photochemical step, are expected to involve the lowest such
excited state, ZlC3l,it appears important to study the extent
of charge separation which can be created in Z, by chemical
perturbations.
Figure 1 shows the charge separation Aq between the two
carbon atoms in the Z1excited state, as a function of pyramidalization angle 4, calculated with an extended basis set (4-31G)
of Gaussian orbitals[5! The curve has an interesting sigmoid
shape. Remarkably, the charge separation reaches 0.72 e for
a pyramidalization of only 15". It then increases slowly towards
a limit of0.87efor a full sp3 carbon atom ($= 55"). Throughout
the pyramidalization process the energy of Z I remains constant, within 4 kcal/mol. This is confirmed by a 271-configuration interaction calculation, constructed on a limited basis
set (STO-3G) of Gaussian orbitals[51,which shows the energy
to decrease by only 8 kcal/mol in the full pyramidalization
process.
The large polarization of the CC bond can also be obtained
by simple chemical substitution. Thus, a similar calculation
for 90O-twisted propene molecule, with the same symmetry
plane, yields a large charge separation (Aq=0.84e) without
any pyramidalization.
Let us first consider the effect of a slight distortion of the
molecule at one end of the CC bond on the charge separation
in Z,. In a 90"-twisted ethylene molecule one CH2 group
is slowly pyramidalized:
As a first application of these results, let us consider the
photocyclization of 1,3,5-hexatrienes to bicyclo[3.1 .O]hexenes16]. Formally, a typical such reaction can be writtenC3]:
[*I
Dr. P. Bruckmann (Deutsche Forschungsgemeinschaft Scholarship), Dr.
P. Hiberty, Mr. C. Leforestier and Prof. L. Salem [ + ]
Laboratoire de Chimie Thkorique (E. R. A. N" 549)
Universit; de Paris-Sud, 91405 Orsay (France)
Dr. V. BonaEiC-Kouteckq and Prof. J. Kouteckf (Exchange Professorship,
UniversitC de Paris-Sud)
lnstitut fur Physikalische Chemie und Quantenchemie der Freien Universitit
1 Berlin 33. Thielallee 63-67 (Germany)
[ +] Author to whom correspondence should be addressed.
Angew. Chem. inrernar. Edit.
1 Val. 14 (1975) 1 N o . 8
We have performed a similar open-shell, calculation of the
charge distribution in the Z, state of s-cis,s-trans diallyl (1,3,5hexatriene) as a function of twist angle 0. (The starting planar
conformation (3) corresponds to 0 =On.)
575
Документ
Категория
Без категории
Просмотров
2
Размер файла
223 Кб
Теги
halomolybdate, chloromolybdate, coordination, tetrahedral
1/--страниц
Пожаловаться на содержимое документа