Anionic Cadmium Complexes Containing the Bulky Tris(trimethylsilyl)germyl and Tris(trimethylsilyl)silyl Ligands

Article abstract of DOI:10.1021/ic951061e

The first triiodo-bridged tris(trimethylsilyl)silyl- and tris(trimethylsilyl)germyldicadmium anionic complexes were prepared from CdI₂ and 2 equiv of LiE(SiMe₃)₃ (E = Si and Ge) in hexane. The crystal structure of the germyl derivative 1 was determined. It crystallizes as a lithium salt from pentane in the Cmcm space group (orthorhombic) with a = 14.494(2), b = 16.334(3), and c = 27.361 ?, V = 6478 ?³, and Z = 4. The complex anion of 1, [(Me₃Si)₃GeCd(μ-I₃)CdGe(SiMe ₃)₃^-], exhibits two approximately tetrahedrally coordinated cadmiums with three iodides in trigonal bridging positions between the cadmiums. Efforts to prepare similar chloride-bridged structures were not fruitful.

Full text of DOI:10.1021/ic951061e

Inorg. Chem. 1996, 35, 745-748
745
Anionic Cadmium Complexes Containing the Bulky Tris(trimethylsilyl)germyl and
Tris(trimethylsilyl)silyl Ligands
Siva P. Mallela, Frank Schwan,† and R. A. Geanangel*
Department of Chemistry, University of Houston, Houston, Texas 77204-5641
ReceiVed August 11, 1995X
The first triiodo-bridged tris(trimethylsilyl)silyl- and tris(trimethylsilyl)germyldicadmium anionic complexes were
prepared from CdI2 and 2 equiv of LiE(SiMe3)3 (E ) Si and Ge) in hexane. The crystal structure of the germyl
derivative 1 was determined. It crystallizes as a lithium salt from pentane in the Cmcm space group (orthorhombic)
with a ) 14.494(2), b ) 16.334(3), and c ) 27.361 Å, V ) 6478 Å3, and Z ) 4. The complex anion of 1,
[(Me3Si)3GeCd(µ-I3)CdGe(SiMe3)3-], exhibits two approximately tetrahedrally coordinated cadmiums with three
iodides in trigonal bridging positions between the cadmiums. Efforts to prepare similar chloride-bridged structures
were not fruitful.
Table 1. Data Collection and Processing Parameters
Li+‚C18H54Si6Ge2Cd2I3-‚4C4H8O Cmcm (orthorhombic)
Introduction
The development of a variety of metal-silicon reagents as
silylating agents has generated increasing interest in sterically
demanding substituents of the form -E(SiMe3)3 (E ) C, Si,
and Ge). In some cases, these bulky groups kinetically stabilize
metal centers through the protective influence of their large
“umbrella” of methyl groups.1 In other cases, however, the
steric strain they produce seems to cause structural rearrange-
ments such as phenyl migration in the case of -C(SiMe3)3 with
Ph2PbCl22 and trimethylsilyl group migration in the case of Ge-
(II).3 Group 12 complexes with metal-silicon bonds were
shown to be useful silylating agents.4 Homoleptic tellurolates
containing Te-Cd bonds can act as single-source precursors
for thin films.5
Bis(tris(trimethylsilyl)silyl)cadmium and its zinc and mercury
counterparts were among the early examples of metal-silyls
with the bulky substituents.6 To determine how substitution of
Ge for the central Si affects the structure and stability of the
complexes, we prepared several -Ge(SiMe3)3 analogues of
known metal-Si(SiMe3)3 compounds.1e,f Our initial objective
in the present work was to prepare Cd(Ge(SiMe3)3)2 from CdCl2
or CdI2 and (THF)2.5LiGe(SiMe3)3. In this paper we describe
the results of those reactions along with that between CdI2 and
(THF)3LiSi(SiMe3)3.
fw ) 1485.36
a ) 14.494(2) Å
b ) 16.334(3) Å
c ) 27.361(6) Å
V ) 6478 Å3
Z ) 4
T ) -50 °C
λ ) 0.710 73 Å
F(calcd) ) 1.52 g cm-3
µ ) 31.04 cm-1
R ) Σ||Fo| ) |Fc||/Σ|Fo| ) 0.049
Rw ) [Σw2(|Fo| - |Fc|)2/
2
Σ|Fo| ]1/2 ) 0.042
use. The reagents (THF)2.5LiGe(SiMe3)3 and (THF)3LiSi(SiMe3)3 were
prepared according to literature methods7,8 using low-halide (chloride)
methyllithium from Aldrich. Elemental analyses were done by Atlantic
Microlabs. All manipulations were conducted under argon dried with
P4O10. NMR and IR spectra were recorded as described earlier.1e,f
Syntheses of Tetrakis(tetrahydrofuran)lithium Tris(-µ-iodo)bis-
[tris(trimethylsilyl)germylcadmate](1-), [Li(THF)4][(Me3Si)3GeCdI3-
CdGe(SiMe3)3] (1). To a hexane suspension (50 mL, -78 °C) of CdI2
(947.9 mg, 2.588 mmol) was slowly added 150 mL of a hexane solution
of (THF)2.5LiGe(SiMe3)3 (2481.8 mg, 5.176 mmol). The mixture was
stirred at -78 °C for 4 h and allowed to warm slowly to room
temperature where stirring continued for 15 h, and then the hexane
was removed in Vacuo. The residue was stirred for 1 h with pentane
(50 mL) and filtered and the filtrate concentrated to about 40 mL and
held at 0 °C for 30 min affording colorless, transparent, hygroscopic,
needle crystals of 1 (1271 mg, isolated yield 60%). Mp: 150 °C dec.
Anal. Calcd for C26H70Cd2Ge2I3LiO2Si6 (bis(THF) solvate, Vide
infra): C, 23.28; H, 5.2. Found: C, 22.19; H, 4.94. 1H NMR (C6D6):
δ 0.558 (s, 54 H, Ge(SiMe3)3), 1.425 (mult) and 3.467 (mult 32 H, 4
THF). 13C NMR (C6D6): δ 4.889 (Ge(SiMe3)3), 25.54, 68.42 (THF).
IR (Nujol and neat, cm-1): 3380 s br, 2960 s br, 2900 s br, 1920 w,
1745 m, 1600 s br, 1450 s, 1410 sh, 1285 w, 1250 vs, 1230 w, 1055
vs, 970 s, 850 vs br, 775 w, 695 m, 645 m, 635 sh, 425 w.
Experimental Section
Cadmium iodide and chloride were from Baker and Aldrich. Ethyl
ether and tetrahydrofuran (THF) were distilled from LiAlH4 under dry
nitrogen. Pentane and hexane were distilled from sodium just before
† University of Saarbru¨cken, Germany.
X-ray Structure Determination of 1. A colorless thick plate having
approximate dimensions 0.40 × 0.45 × 0.12 mm was mounted in a
random orientation on a Nicolet R3m/V automatic diffractometer. Since
the crystals began to decompose in less than 1 min when exposed to
the air at room temperature, all handling was done on a glass slide in
constant contact with a block of dry ice, and the sample was then placed
in a stream of dry nitrogen gas at -50 °C. The radiation used was
Mo KR monochromatized by a highly ordered graphite crystal. Final
cell constants, as well as other information pertinent to data collection
and refinement, are listed in Table 1. The Laue symmetry was
determined to be mmm, and from the systematic absence noted the
space group was shown to be either Cmc21, C2cm, or Cmcm. Intensities
X Abstract published in AdVance ACS Abstracts, January 15, 1996.
(1) (a) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1990, 29, 3525. (b)
Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1991, 30, 1480. (c)
Mallela, S. P.; Bernal, I.; Geanangel, R. A. Inorg. Chem. 1992, 31,
1626. (d) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1993, 32,
5623. (e) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1994, 33,
1115. (f) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1994, 33,
6357.
(2) Mallela, S. P.; Myrezek, J.; Bernal, I.; Geanangel, R. A. J. Chem.
Soc., Dalton Trans. 1993, 2891.
(3) Heine, A.; Stalke, D. Angew. Chem., Intl. Ed. Engl. 1994, 33, 113.
(4) (a) Newmann, W. P.; Reuter, K. J. Organomet. Chem. Libr. 1979, 7,
229. (b) Hoefler, F. Top. Curr. Chem. 1974, 50, 129.
(5) (a) Bonasia, P.; Arnold, J. Inorg. Chem. 1992, 31, 2508. (b) Arnold,
J.; Walker, J. M.; Yu, K.; Bonasia, P.; Seligson, A. L.; Bourret, E. D.
J. Crystal Growth 1992, 124, 647.
(7) Brook, A. G.; Abderaken, F.; So¨llradl, H. J. Organomet. Chem. 1986,
299, 9.
(8) Gutekunst, G.; Brook, A. G. J. Organomet. Chem. 1982, 225, 1.
(6) Arnold, J.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J. Inorg. Chem.
1987, 26, 2106.
0020-1669/96/1335-0745$12.00/0 © 1996 American Chemical Society

746 Inorganic Chemistry, Vol. 35, No. 3, 1996
Mallela et al.
were measured using the ω scan technique, with the scan rate depending
on the count obtained in rapid prescans of each reflection. Two standard
reflections were monitored after every 2 h or every 100 data collected,
and these showed no significant change. During data reduction, Lorentz
and polarization corrections were applied, as well as a semiempirical
absorption correction based on ψ scans of 10 reflections having ø angles
between 70° and 90°. Since the unitary structure factors displayed
centric statistics, space group Cmcm was assumed from the outset. The
structure was solved by the SHELXTL Patterson interpretation program
which revealed the positions of the I and Cd atoms in the asymmetric
unit, consisting of one-quarter anion situated about an m2m site, one-
quarter Li cation situated on an m2m site, and two independent half-
THF molecules situated about mirror planes. Remaining atoms were
located in subsequent difference Fourier syntheses. The usual sequence
of isotropic and anisotropic refinement was followed, after which some
of the methyl hydrogens were entered in ideal calculated positions and
constrained to riding motion, with a single variable isotropic temperature
factor for all of them. One of the two unique SiMe3 groups in the
anion was found to be disordered over two slightly different positions,
and this was treated by introducing an ideal rigid body at this position
having 50% occupancy, with the nearby mirror plane generating the
other orientation. Both of the two independent THF molecules were
found to be heavily disordered, and this was treated by refining atoms
with partial occupancies at several different positions.
At this point, properly adjusted models were refined in both of the
noncentrosymmetric space groups in order to see if any of the extensive
disorder would disappear. Refinement in Cmc21 was very difficult due
to extensive correlations between variables and resulted in no less
disorder than in Cmcm. Refinement in C2cm proceeded smoothly, but
again none of the disorder noted in the Cmcm refinement disappeared,
and the bond distances seemed unrealistic compared to literature values.
The R values were little changed despite the additional variables. Since
no discernible improvement was achieved by refinement in either of
the noncentrosymmetric space groups, the assumption was made that
Cmcm is the best choice, and this was used for the final refinement.
After all shift/ESD ratios were <0.1 (excepting the rigid group),
convergence was reached at the agreement factors listed in Table 1.
No unusually high correlations were noted between any of the variables
in the last cycle of full-matrix least-squares refinement, and the final
difference density map showed a maximum peak of about 0.7 e/A3.
All calculations were made using Nicolet’s SHELXTL PLUS (1987)
series of crystallographic programs.
Figure 1. View of the cation and anion structures of 1. Thermal
ellipsoids are 40% equiprobability envelopes, with hydrogens omitted
for clarity. Only one orientation of the disordered groups is shown.
Results and Discussion
Arnold, Tilley, Rheingold, and Geib6 obtained bis(tris-
(trimethylsilyl)silyl)cadmium as a moderately stable solid from
reaction of CdCl2 with 2 equiv of (THF)3LiSi(SiMe3)3 in diethyl
ether. The more stable zinc and mercury silyls were similarly
prepared and the former shown by X-ray crystallography to have
the expected linear Si-Hg-Si backbone connecting the bulky
“super silyl” groups. Seeking to prepare the analogous cadmium
tris(trimethylsilyl)germyl derivative, we conducted the reaction
of CdI2 with 2 equiv of (THF)2.5LiGe(SiMe3)3. The unexpected
result, shown in eq 1, was the formation of the lithium salt of
Reaction of CdCl2 with (THF)2.5LiGe(SiMe3)3 in Hexane.
A
hexane (-78 °C, 50 mL) suspension of CdCl2 (553.8 mg, 3.02 mmol)
and 150 mL of a hexane solution of (THF)2.5LiGe(SiMe3)3 (2896.7 mg,
6.04 mmol) were combined as described in the synthesis of 1. Workup
in pentane produced copious quantities of metallic powder, presumably
cadmium, along with decomposition products of the lithium germyl
reagent including (Me3Si)3Ge-Ge(SiMe3)3, HGe(SiMe3)3, and Ge-
(SiMe3)4. No cadmium-containing product was isolated.
Reaction of CdCl2 with (THF)2.5LiGe(SiMe3)3 in Diethyl Ether.
An ether solution (150 mL) of (THF)2.5LiGe(SiMe3)3 (4550 mg, 9.48
mmol) was added to a cold ether suspension of CdCl2 (870 mg, 4,74
mmol), as described for 1 in hexane. Workup in pentane gave only
metallic powder and lithium germyl decomposition products. No
cadmium-containing product was isolated.
an unusual dicadmium anion.
Synthesis of Tetrakis(tetrahydrofuran)lithium Tris(µ-iodo)bis-
[tris(trimethylsilyl)silylcadmate](1-), [Li(THF)4][(Me3Si)3SiCdI3-
CdSi(SiMe3)3] (2). A hexane (150 mL) solution of (THF)3LiSi(SiMe3)3
(3435.7 mg, 7.29 mmol) was added to a hexane suspension (-78 °C,
50 mL) of CdI2 (1330 mg, 3.647 mmol). After workup as described
for 1, colorless, transparent, hygroscopic crystals (2010 mg, isolated
yield 79%) formed from pentane. Mp: 135 °C dec. Anal. Calcd for
C26H70Cd2I3LiO2Si8 (bis(THF) solvate, Vide infra): C, 24.94; H, 5.63.
Found: C, 25.18; H, 5.62. 1H NMR (C6D6): δ 0.538 (s, 54 H, Si-
(SiMe3)3), 1.451 (mult) and 3.481 (mult) (32 H, 4THF). 13C NMR
Description of the Structure of 1. The anion in 1 (Figure
1) consists of two, approximately tetrahedral RCdI3 (R ) (Me3-
Si)3Ge) complexes sharing three trigonally disposed iodines
(Table 2 gives atomic coordinates). The I-Cd-I angles average
only about 91°, while the average of the Ge-Cd-I angles is
near 125° (Table 3). This distortion of the expected tetrahedral
angles around Cd is attributable, at least in part, to crowding of
the iodines by the bulky R group. Figure 2 shows a CPK model
of the anion where the steric demands of the group can be seen.
The large space requirements of the iodines in the Cd(µ-I)3Cd-
bridging framework also favor small I-Cd-I angles. The Cd-
Cd distance (3.345 Å) exceeds that in metallic cadmium (3.04
Å),10 indicative of minimal interaction between the cadmiums.
The Cd-Cd distance in 1 falls in the range of values recently
(C6D6): δ 4.266 (Si(SiMe3)3), 25.63 and 68.41 (THF). IR9 (Nujol cm-1
)
3460 s br, 1910 w, 1620 m, 1410 s sh, 1370 sh, 1325 m, 1270 sh,
1260 vs, 1205 w, 1070 sh, 1065 vs, 940 s sh, 920 sh, 870 vs br, 785
m, 770 sh, 720 s, 660 s, 650 s, 595 m, 445 s.
(9) Both 1 and 2 reacted with the AgBr windows of the infrared cells.

Anionic Cadmium Complexes
Inorganic Chemistry, Vol. 35, No. 3, 1996 747
Table 2. Atomic Coordinates (×104) and Equivalent Isotropic
Displacement Parameters (Å2, ×103)
x
y
z
U (eq)a
I(1)
I(2)
1466(1)
0
2791(1)
609(1)
7500
7500
92(1)
73(1)
Cd
Ge
0
0
2099(1)
2162(1)
1469(3)
1964(9)
1405(9)
399(8)
3550(3)
3972
3618
6889(1)
5964(1)
5702(2)
5964(6)
5036(5)
5958(6)
5703(2)
5997
74(1)
64(1)
91(2)
154(9)
146(9)
165(10)
76(4)
106(7)
106(7)
106(5)
100(18)
113(8)
104(7)
89(10)
116(6)
125(10)
129(12)
107(11)
123(16)
121(19)
276(34)
Si(1)
C(1)
C(2)
C(3)
Si(2)
C(4)
C(5)
C(6)
Li
O(1)
O(2()
C(7)
C(8)
C(9)
C(10)
C(7′)
C(9′)
C(10′)
C(24)
1330(3)
2397(10)
1413(10)
1318(10)
-170(7)
-1224
-287
5027
5903
2500
854
0
4150
3359(32)
4052(9)
2611(9)
4212(17)
4893(9)
2041(18)
1412(18)
4649(18)
2561(25)
1708(25)
272(34)
1079(11)
150(25)
1734(20)
2267(10)
834(19)
542(20)
1214(22)
468(27)
-267(36)
5842(25)
2572(17)
1952(6)
2091(11)
2220(5)
1867(11)
1533(13)
2057(12)
1511(16)
1329(14)
4811(64)
Figure 2. Space-filling (CPK) view of the anion of 1.
of RCdI (R ) (Me3Si)3Ge) that has formed a complex with an
iodide. Sharing three bridging iodides relieves the coordinate
unsaturation around the cadmiums in the putative dimer while
2-
achieving the tetrahedral coordination familiar in CdX4
complex ions. RCdI (R ) alkyl) compounds are known in the
solid phase14 but may decompose in solution unless stabilized
by complex formation with either neutral ligands15 or anions.13
A possible pathway to 1 (eq 2) involves, first, formation of (Me3-
a Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor.
Table 3. Selected Bond Lengths (Å), Bond Angles (deg), and
Torsion Angles (deg) for 1
Bond Lengths
Cd-I(1)
Cd-Ge
Ge-Si(1)
Si(1)-C(2)
Li-O(1)
2.931(2)
2.533(2)
2.348(5)
1.830(16)
1.940(35)
Cd-I(2)
2.953(2)
3.345(1)
1.887(16)
1.884(15)
1.947(36)
Si)3GeCdI, second, its dimerization, and, finally, its complex-
ation with iodide from the reaction mixture. Although we did
not see spectroscopic evidence for the RCdI dimer, the low
complexing ability of the hexane solvent favors its formation.
An alternate pathway in which RCdI first combines with I- to
form an intermediate cadmate ion, RCdI2-, and then this reacts
with another RCdI giving the anion of 1 does not seem as likely
Cd-CdA
Si(1)-C(1)
Si(1)-C(3)
Li-O(2)
Bond Angles
69.6(1)
89.7(1)
126.8(1)
106.6(1)
116.8(3)
110.7(15)
Cd-I(1)-CdA
I(1)-Cd-I(2)
I(2)-Cd-Ge
Cd-Ge-Si(1)
Si(1)-Ge-Si(2)
O(1)-Li-O(2)
Cd-I(2)-CdA
I(1)-Cd-Ge
I(1)-Cd-I(1A)
Cd-Ge-Si(2)
Si(1)-Ge-Si(1A)
O(1)-Li-O(1B)
69.0(1)
123.7(1)
92.9(1)
109.7(2)
110.4(2)
108.6(26)
-
since known RCdX2 salts, even with large cations, are
substantially insoluble in organic solvents.13
The novel structure of 1 prompted us to carry out the reaction
of CdI2 with 2 equiv of (THF)2.5LiSi(SiMe3)3 to determine
whether the disubstituted product, reported by Tilley et al.,6
formed or if it would follow the course of the synthesis of 1.
The product (2) is assigned by its NMR spectra and elemental
analyses16 to be the -Si(SiMe3)3 counterpart of 1. Although 2
was not structurally characterized, the major differences in
spectra, melting point,17 and composition between it and Cd-
(Si(SiMe3)3)2, the other plausible product, support the assign-
ment of its structure as also involving a triiodide-bridged
dicadmium anion (eq 3). A small NMR peak at δ 0.330, as
Torsion Angles
-46.7
46.4
60.5
178.4
174.6
CdA-I(1)-Cd-I(2)
CdA-I(2)-Cd-I(1)
I(1)-Cd-Ge-Si(1)
I(1)-Cd-Ge-Si(1)A
I(2)-Cd-Ge-Si(2)
CdA-I(1)-Cd-Ge
CdA-I(2)-Cd-Ge
I(1)-Cd-Ge-Si(2)
I(2)-Cd-Ge-Si(1)
177.5
180.0
-66.0
-59.0
I(2)-Cd-Ge-Si(1)A
59.0
found in three dicadmium complexes with tetrakis(µ-carboxy-
late-O,O′) dimetal cores.11 Both the two Ge atoms and the two
Cd atoms are colinear. The trimethylsilyl groups on the two
Ge atoms are in an eclipsed conformation, probably due to steric
interactions with the iodines. Taking into account the slight
disorder found in the trimethylsilyl positions, the Si-Ge-Cd-I
angles average about 60°. The THF positions in the cation of
1 were heavily disordered.
expected for Cd(Si(SiMe3)3)2,6 was observed in the reaction
mixture, but isolation of that product was not attempted.
The presence of THF was necessary for the purification of
both products. Repeated crystallizations of either from pentane
-
2-
Cadmium iodide complexes such as CdI3 and CdI4 are
known,12 as are organodihalocadmates, RCdX2- 13 but bridged
,
dicadmium complexes appear to be uncommon, and we were
unable to find examples of tribridged, dicadmates related to the
anion of 1. In principle, the anion can be regarded as a dimer
(14) Sheverdina, N.; Paleeva, I. E.; Deinskaya, E. D.; Kocheskov, K. Dokl.
Akad. Nauk. SSSR 1959, 125, 348.
(15) Habeeb, J. J.; Tuck, D. G. J. Organomet. Chem. 1978, 146, 213.
(16) Crystals of both 1 and 2 lost THF readily. Vacuum drying of analytical
samples for 30 min gave results which correspond reasonably well to
bis(THF) solvates. Crystals dried for only 1-2 min for NMR spectra
gave integrations consistent with tetrakis(THF) solvation if the spectra
were obtained immediately after preparation. After about 15 min, the
C6D6 solutions became turbid.
(10) Wells, A. F. Structural Inorganic Chemistry; Oxford University
Press: London, 1962; p 984.
(11) Li, S.-L.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 1995, 1519.
(12) (a) Ackerman, J. J. H.; Orr, T. V.; Bartuska, V. J.; Maciel, G. E. J.
Am. Chem. Soc. 1979, 101, 341. (b) Trofimchuck, A. K.; Nizel’skii,
Y. N. Zh. Neorg. Khim. 1974, 19, 2308.
(17) The mp of Cd(Si(SiMe3)3)2 was reported to be 154-160 °C, whereas
(13) Osman, A.; Tuck, D. G. J. Organomet. Chem. 1979, 169, 255.
2 melted with decomposition at 135 °C.

748 Inorganic Chemistry, Vol. 35, No. 3, 1996
Mallela et al.
alone caused loss of THF and decomposition forming insoluble
materials. Fortunately, conditions were found whereby one
crystallization gave single crystals suitable for an X-ray structure
determination.
stability. The rather striking difference in products obtained
from different cadmium halides has led us to examine the
behavior of other metal iodides with the silyl and germyl
reagents.
Seeking a chloro-bridged, dicadmium anion analogous to the
anion in 1, we carried out reactions between CdCl2 and 2 equiv
of (THF)2.5LiGe(SiMe3)3, both in hexane, as done in the other
syntheses, and in diethyl ether. Unfortunately, both reactions
gave only metallic powder, presumably cadmium, and decom-
position products of the reagent, HGe(SiMe3)3, (Me3Si)3Ge-
Ge(SiMe3)3, and Ge(SiMe3)4. There was no indication in NMR
spectra of either Cd(Ge(SiMe3)3)2 or [Li(THF)4][(Me3Si)3-
GeCdCl3CdGe(SiMe3)3]. The facile reduction of CdCl2 by the
germyl reagent was unexpected. Reduction was not reported
when CdCl2 and the silyl reagent were combined in ether and
extracted into pentane.6 Since chloro-bridged anions were not
observed by the earlier workers either, it may be that the
tribridged dicadmium anion core requires the large iodides for
Acknowledgment. The authors gratefully acknowledge the
support of this investigation by the Robert A. Welch Foundation
under Grant E-1105. We are also grateful to J. Korp for carrying
out the X-ray structure determinations and to the University of
Saarbru¨cken for partial support of one of us (F.S.).
Supporting Information Available: Tables listing full data col-
lection and processing parameters, full bond lengths and angles,
anisotropic displacement parameters, and H atom coordinates (9 pages).
Ordering information is given on any current masthead page. Observed
and calculated structure factors (11 pages) are available from the
corresponding author.
IC951061E