A decagallane(6) cluster Ga10[Si(CMe3) 3]6 with an unprecedented structure

Article abstract of DOI:10.1039/b802959h

The decagallane(6) Ga₁₀R′₆ [R′ = Si(CMe₃)₃] adopts a quite unusual structure, which might be described as being derived from a pentagonal bipyramidal core, which is threefold capped. An alternative description is that of a conjuncto-cluster. The structure of the anionic cluster [Ga₁₀R′₆] ^- as well as that of Ga₁₀R″₆ [R″ = Si(SiMe₃)₃] are described as being built of fused octahedra. Thus, this family of decagallanes is unique in showing structural isomers in the cluster core, giving hints to the pathways of formation of these clusters, too. The novel cluster compound is characterized by X-ray crystallography. Isomeric decagallanes(6) and structural changes on reduction are studied by DFT methods.

Full text of DOI:10.1039/b802959h

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A decagallane(6) cluster Ga10[Si(CMe3)3]6 with an unprecedented structure†
Gerald Linti*a and Annekathrin Seifertb
Received 20th February 2008, Accepted 18th April 2008
First published as an Advance Article on the web 2nd June 2008
DOI: 10.1039/b802959h
The decagallane(6) Ga10Rꢀ6 [Rꢀ = Si(CMe3)3] adopts a quite unusual structure, which might be described
as being derived from a pentagonal bipyramidal core, which is threefold capped. An alternative
description is that of a conjuncto-cluster. The structure of the anionic cluster [Ga10Rꢀ6]− as well as that
of Ga10Rꢀꢀ [Rꢀꢀ = Si(SiMe3)3] are described as being built of fused octahedra. Thus, this family of
6
decagallanes is unique in showing structural isomers in the cluster core, giving hints to the pathways of
formation of these clusters, too. The novel cluster compound is characterized by X-ray crystallography.
Isomeric decagallanes(6) and structural changes on reduction are studied by DFT methods.
Introduction
The clusters of gallium, characterized until now, can be divided
into two series1 (Scheme 1). The first, comprising compounds
of the type [GanRn]x− (x = 0, 1, 2; n = 4, 6, 8, 9), might
be looked upon as classical polyhedral clusters. Examples are
4
Ga4R4 1 [a R = C(SiMe3)3,2 b Si(SiMe3)3,3 c Si(CMe3)3 ] precloso-
Ga6[SiMe(SiMe3)2]6 2,5 closo-[Ga6{Si(CMe3)3}4(CH2Ph)2]2− 3,5
the formally closo cluster [Ga8(fluorenyl)8]2− 4,6 and precloso-
[Ga9(CMe3)9] 5.7,8 The dianionic compounds fit the Wade–
Williams rules.9–14
Tetragallanes(4) 1 with a tetrahedral structure and four skeleton
electron pairs are cluster compounds, where the cluster bonding
is described as four three-centre two-electron (3c2e)-bonds. 3 is an
octahedral closo-cluster with seven skeleton electron pairs, while
2 has only six cluster electron pairs. Here a Jahn–Teller distortion
of a regular polyhedron is observed.
The second series are gallium-rich cluster compounds [GanRm]x−
(m < n). Some prominent examples are [Ga8{Si(CMe3)3}6]x−
(x = 0, 2) 6,15 [Ga9{Si(SiMe3)3}6]− 7,16 [Ga12fluorenyl10]2− 8,17 and
[Ga13{Si(CMe3)3}6] 9.18 Even higher clusters with up to 84 gallium
atoms are known, for a recent review see ref. 19.
Whilst 6 and 7 might be understood as closo-clusters with a six
or seven vertex core, respectively, which are substituted by four
R groups and two GaR units, the higher clusters show structures
which resemble sectors of structures observed in modifications of
gallium.1
Of special interest are Ga22 clusters. In addition to the
Scheme 1 Survey of gallium cluster compounds of types [GanRn]x− and
[Ga22R8] clusters [R = Si(SiMe3)3,20 Ge(SiMe3)3,21 Si(CMe3)322],
[GanRm]x−
.
Ga22 clusters with different numbers of substituents and
consequently different core structures are known. These
are [Ga22{N(SiMe3)2}10]2−,23 [Ga22{N(SiMe3)2}10Br10]2−24 and
Ga22(PtBu2)12.25 The first with eight and ten substituents have core
structures of 14 and 12 gallium atoms, respectively, which are
surrounded by eight or ten GaR units. The Ga14 core is a centered
Ga13 polyhedron, the Ga12 core a centered Ga11 polyhedron. In
contrast, those clusters which have more substituents possess
icosahedral Ga12 cores without a central atom. This structural
diversity seemed to be unique in cluster chemistry.
We want to focus now on Ga10 cluster compounds. Two clusters
[Ga10R6]n− have been prepared.18 A neutral Ga10[Si(SiMe3)3]6
cluster 10 and an anionic [Ga10{Si(CMe3)3}6]− 11 have cluster
cores of fused octahedra. They differ in the distribution of the
six substituents on the cluster atoms. That means in 10 a 4/2, in 11
aUniversity of Heidelberg, Institute of Inorganic Chemistry, Im Neuenheimer
Feld 270, D-69120, Heidelberg, Germany. E-mail: Gerald.linti@aci.uni-
heidelberg.de; Fax: +49-6221-546617; Tel: +49-6221-548468
bAnorganisch-Chemisches Institut, Universita¨t Heidelberg, Im Neuenheimer
Feld 270, D-60120, Heidelberg, Germany
† Electronic supplementary information (ESI) available: Table with SEN
and plots of MOs for 12a. CCDC reference number 602531. For ESI
or crystallographic data in CIF or other electronic format see DOI:
10.1039/b802959h
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a 3/3 distribution of substituents is observed. In 11 the octahedra
are severely distorted. Thus, a description of a trigonal antiprism
of GaR units with an intercalated Ga4 ring was used. Here we
describe a novel Ga10R6 cluster with a different cluster structure.
The cluster 12 is composed of ten gallium atoms, six of them
bearing silyl groups (Fig. 1). The cluster core is difficult to
describe, because no regular polyhedron is present. 12 might be
viewed as having a flat, distorted pentagonal bipyramidal core of
gallium atoms. The equatorial plane exhibits three rather short and
two long Ga–Ga distances which are bridged by gallium atoms.
That means Ga(8) bridges the Ga(1)–Ga(5) edge, with Ga(8)–Ga
Results and discussion
In the reaction of “GaI”,26 prepared from the elements in an ultra-
distances of 243 pm (averaged). The bridged edge [dGa(1)–(5)Ga
=
27
306 pm] is the longest in this cluster. Alternatively, 12 might be
described as made up of fused Ga8 and Ga4 polyhedra, sharing
the Ga(1)–Ga(2) edge. DFT calculations (see Table 5) indicate
a large three-center bonding contribution to the Ga(1)–Ga(8)–
Ga(5) triangle. This is in support of a description of the cluster as
a bridged pentagonal bipyramid.
sonic bath, with Na(thf)2Si(CMe3)3 several cluster compounds
are formed. Recently, we reported on one of the products, namely
11.18 In addition, the tetragallane [Ga4{Si(CMe3)3}4] 1c is formed.
From a toluene solution of the crude products of this reaction
black crystals could be isolated, which were analyzed to be co-
crystals of clusters 1c and [Ga10{Si(CMe3)3}6] 12 (eqn (1)).
(1)
This reaction involves a lot of redox reactions, leading to the
formation of elemental gallium and other cluster compounds like
[Ga13{Si(CMe3)3}6] 9 in low yields. In addition various silanes like
(Me3C)3SiH and [(Me3C)3Si]2 are observed.
1c and 12 crystallize together in prisms of the monoclinic system,
space group Cc (see Table 1). Here clusters 12 form approximately
close packed hexagonal layers with a layer of the tetrahedral cluster
1c and thf in between. 1c shows Ga–Ga distances averaging to
253.6 pm [dGaGa = 252.2(1)–254.4(1) pm]. This is shorter than
reported for 1c (dGaGa = 257.2 pm), crystallized separately.4 Thus
the tetrahedron is slightly compressed, which might be due to
incorporation in the crystal structure of 12.
Table 1 Crystallographic data for 12·1c
Empirical formula
Mr/g mol−1
T/K
Ga10Si6C72H162·Ga4Si4C48H108·OC4H8
3042.4
150
˚
k/A
0.71073
Monoclinic
Cc
4727(1)
2117.4(4)
1666.3(3)
107.54(3)
15903(5)
4
1.27
2.44
6416
3–45
Crystal system
Space group
a/pm
b/pm
c/pm
b/◦
3
˚
V /A
Z
qcalc/g cm−3
l/mm−1
F(000)
Fig. 1 View of cluster molecule 12. tert-Butyl groups have been omit-
ted for clarity. (a) polyhedral view, (b) view down the Si3–Ga6–Ga7
axis. Selected distances [pm]: Ga(1)–Ga(2) 284.0(1), Ga(1)–Ga(6)
270.1(1), Ga(1)–Ga(7) 289.1(1), Ga(1)–Ga(8) 244.1(1), Ga(1)–Ga(9)
253.3(1), Ga(1)–Ga(10) 287.8(1), Ga(2)–Ga(3) 256.9(1), Ga(2)–Ga(6)
280.1(1), Ga(2)–Ga(7) 275.6(1), Ga(2)–Ga(9) 246.5(1), Ga(2)–Ga(10)
291.4(1), Ga(3)–Ga(4) 255.1(1), Ga(3)–Ga(6) 277.8(1), Ga(3)–Ga(7)
273.1(1), Ga(4)–Ga(5) 253.4(1), Ga(4)–Ga(6) 278.0(1), Ga(4)–Ga(7)
261.0(1), Ga(5)–Ga(6) 265.2(1), Ga(5)–Ga(7) 267.6(1), Ga(5)–Ga(8)
241.5(1), Ga(6)–Ga(7) 295.3(1), Ga(7)–Ga(10) 252.4(1), Ga(9)–Ga(10)
246.6(1), Ga(3)–Si(1) 249.7(2), Ga(4)–Si(2) 250.2(2), Ga(6)–Si(3) 246.9(2),
Ga(8)–Si(4) 242.1(2), Ga(9)–Si(5) 241.0(2), Ga(10)–Si(6) 245.5(2).
2h range/◦
Index range
50, 22, 17
1427
44359
Parameters
Reflections, collected
Reflections, unique
GOOF on F2
20193 (Rint = 0.0524)
0.883
Final R indices [I > 2r(I)]a
R indices (all data)
R1 = 0.046, wR2 = 0.095
R1 = 0.069, wR2 = 0.10
a Weighting scheme: w = 1/[r2(Fo2) + (0.0504P)2 + 0.0000P] where P =
2
(Fo + 2Fc2)/3.
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The remaining edges in the pentagonal bipyramidal core range
between 253.3(1) and 289.1(1) pm. Ga(9) is bridging the long
Ga(1)–Ga(2) edge with Ga(9)–Ga distances of 246.5(1) and
253.3(1) pm, respectively. Ga(9) is additionally bonded to Ga(10)
[dGaGa = 246.6(1) pm]. Ga(10) itself is bridging the face Ga(1),
Ga(2), Ga(7) unsymmetrically [dGaGa = 252.4(1)–291.4(1) pm].
The bipyramid is quite flat with a Ga–Ga distance of 295.3(1)
pm between the apical atoms. This is similar to the lengths of
edges in this cluster and hints to an additional interaction and is
consistent with the results of the DFT calculations.
Looking for structural analogies (disregarding different R
substituents), 10 can be viewed upon as derived from an anionic
cluster with a core like 7 by addition of Ga+, shown to attack at
Ga(*) (Scheme 2). Similarly, 7 might be derived from addition of
a Ga+ ion to [Ga8R6]2−. If Ga+ is added to 7 not at the Ga3(GaR)2
site but via an opposite triangular face, 12 is formed instead of 10.
Three gallium atoms, making up one triangular face of this poly-
hedron, are connected to silicon atoms of Si(CMe3)3 groups. The
remaining three gallium atoms, which are bonded to silyl groups,
are in bridging positions, either bridging an edge or a face. This
broad distribution of Ga–Ga distances is typical for gallium rich
cluster compounds.1 The Ga–Si distances show a broad variability,
too. The Ga–Si bonds [dGaSi = 240.9(2)–245.5(2) pm] to the
bridging gallium atoms are shorter than the gallium–silicon bonds
of the bipyramidal core atoms [dGaSi = 246.9(2)–250.2(2) pm].
The structure of 12 resembles somewhat that of the nonagallane
7, in which two RGa units bridge two neighbouring edges of
a pentagonal bipyramid with Ga–Ga distances of 234.4(1) and
237.7(1) pm. The edges in the bipyramidal core range between
242.5(1) and 289.8(1) pm. The pentagonal bipyramid is less flat
(dGaGa = 344 pm) than that in 12. 715 can be explained as a closo-Ga7
cluster with four silyl and two bridging RGa substituents.
Scheme 2 Possible formation pathways for clusters with cores of types 7,
10 and 12.
The isomeric, neutral clusters Ga10(SiMe3)6 10a and 12a have
been studied by DFT-methods (RI-DFT, BP86 functional, def
SV(P)-base)34 (Fig. 2 and 3, Tables 2 and 3). 10a, with a core
structure similar to 10, is the most stable isomer. 12a is less stable
by 56.6 kJ mol−1, based on total electronic energies.
Starting from the calculated structure 12a the apical Ga atom
An electron count for 12, built formally by 6 RGa units and
4 Ga atoms, is not unambiguous, since it is not obvious which of
the bare gallium atoms contribute the usual three orbitals to the
cluster skeleton and which provide four orbitals. The usual count
would result in eight skeleton electron pairs, which, according
to the Wade–Mingos rules,9–14 is in line with a three-capped seven
vertex polyhedron. Obviously, 12 seems to have far too few skeletal
electrons for a polyhedral cluster. Therefore, 12 is not a polyhedral
cluster of this type. We find a flattened, irregular polyhedral core
with several cappings. The short Ga(6)–Ga(7) distance suggests
that the bare vertex atom Ga(7) contributes not only one, but
three electrons and four orbitals to the cluster bonding. This
should be the case for Ga(1) and Ga(2), too, which would give
11 skeletal pairs for 12. The structures and electron count in
bare indium clusters have been discussed similarly, on the basis
of flattening vertices as a result of the contribution of four orbitals
(Ga(7) in Fig. 3) was removed as Ga+. Optimization of the
Table 2 Selected distances [pm] for 10a
Ga(3)–Ga(4)
Ga(2)–Ga(3)
Ga(1)–Ga(2)
Ga(1)–Ga(7)
Ga(7)–Ga(8)
Ga(4)–Ga(8)
Ga(2)–Ga(8)
Ga(4)–Ga(5)
Ga(3)–Ga(5)
Ga(2)–Ga(5)
Ga(5)–Ga(8)
Ga(4)–Ga(10)
Ga(3)–Ga(10)
Ga(2)–Ga(10)
Ga(8)–Ga(10)
Ga(6)–Ga(8)
255.6
259.8
267.9
259.7
268.2
259.9
310.8
270.3
270.1
277.0
276.3
270.3
269.9
276.0
277.5
279.4
Ga(2)–Ga(6)
Ga(1)–Ga(6)
Ga(7)–Ga(6)
Ga(8)–Ga(9)
Ga(2)–Ga(9)
Ga(1)–Ga(9)
Ga(7)–Ga(9)
Ga(5)–Ga(6)
Ga(9)–Ga(10)
278.0
264.7
266.1
277.9
279.4
266.0.
264.7
254.5
254.4
Ga(4)–Si(3)
Ga(3)–Si(2)
Ga(5)–Si(4)
Ga(1)–Si(1)
Ga(7)–Si(5)
Ga(10)–Si(6)
244.2
244.1
244.7
243.8
243.9
244.8
7−
to cluster bonding by some of the vertex atoms.28,29 Thus, In11
has three flattened vertices, which allows for 12 skeletal electron
pairs, required for a closo-cluster.30
Table 3 Selected distances [pm] for 12a
A comparison of 12 with the structural isomeric cluster 10 seems
appropriate.18 Here, a description as a three capped cluster is
not obvious. Cluster 10 was rationalized as being a conjuncto-
cluster31 according to the Jemmis counting rules.32,33 But this
implies a different counting of electrons for some of the naked
Ga atoms (3 cluster electrons instead of 1), too. According to
this, 24 skeleton electrons in 10 allow a conjuncto cluster made
up of two subpolyhedra; i.e. two octahedra in 10. Therefore,
22 skeleton electrons in 12 are consistent with a tetrahedron
and a hexagonal bipyramid (or bridged pentagonal bipyramid).
The latter is severely distorted (see above). Obviously, both
counting rules roughly give explanations for the structure of
this hypoelectronic cluster but are near their limits. Therefore,
a forecast of structures on this basis is not possible at all.
Ga(3)–Ga(4)
Ga(2)–Ga(3)
Ga(1)–Ga(2)
Ga(1)–Ga(5)
Ga(4)–Ga(5)
Ga(4)–Ga(6)
Ga(3)–Ga(6)
Ga(1)–Ga(6)
Ga(5)–Ga(6)
Ga(2)–Ga(6)
Ga(4)–Ga(7)
Ga(3)–Ga(7)
Ga(2)–Ga(7)
Ga(1)–Ga(7)
Ga(5)–Ga(7)
Ga(2)–Ga(9)
261.6
254.7
295.7
318.6
254.7
261.7
269.0
290.1
259.7
285.1
265.2
274.9
310.8
296.7
283.4
250.0
Ga(1)–Ga(9)
Ga(1)–Ga(8)
Ga(5)–Ga(8)
Ga(7)–Ga(10)
Ga(7)–Ga(8)
Ga(1)–Ga(10)
Ga(9)–Ga(10)
Ga(6)–Ga(7)
256.6
249.2
247.7
248.5
297.9
292.0
251.8
300.9
Ga(3)–Si(1)
Ga(4)–Si(2)
Ga(6)–Si(3)
Ga(8)–Si(4)
Ga(9)–Si(5)
Ga(10)–Si(6)
244.0
244.8
244.7
245.0
242.7
244.4
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Fig. 2 RI-DFT calculated structure for 10a. For selected distances see
Fig. 4 RI-DFT calculated structure for 7a. For selected distances see
Table 2.
Table 4.
12. If the calculations are done with smaller substituents like
SiH3, the deviations are much larger and interactions of Si–H
bonds with the cluster core occur. A population analysis using the
Ahlrichs–Heinzmann method35,36 for 12a reveals intensive multi
center bonding based on shared electron numbers (SEN) (see
ESI†). An electron–orbital balance makes a description of the
bonding in the cluster core of two Ga–Ga 2c2e bonds and ten
3c2e GaGaGa bonds plausible. Three of them are on the faces of
the tetrahedral part of the cluster. High two-centre [Ga(6)–Ga(7)
0.91] and three-centre SENs [Ga(1)–Ga(6)–Ga(7) 0.43] indicate
interaction between the apical atoms of the core. The small SEN
for the Ga(6)–Si bond (1.0 compared to 1.2 for the others) is due to
the high coordination number of seven for the apical gallium atom.
Inspecting the HOMO for 12a (Fig. 5), the different contribution
of the bare gallium atoms becomes apparent. Whilst Ga(1), Ga(2)
and Ga(7) are engaged in cluster bonding, at Ga(5) the MO has
lone pair character. This justifies the electron count applied above.
The variation in the bond lengths of the Ga–Si bonds is smaller
than in the experimental structure. This is explained by the more
bulky substituents and the disorder in the cluster (Experimental
section).
Fig. 3 RI-DFT calculated structure for 12a. For selected distances see
Table 3.
structure of this open [Ga9(SiMe3)6]− cage resulted in 7a (Fig. 4,
Table 4). This represents a structure found for 7. An assumed
formation of 12a from 7a (eqn (2))
7a + Ga+ → 12a DE = −606.5 kJ mol−1
(2)
is exothermic.
Thus, the postulated formation pathways of Ga10 clusters
(Scheme 2) seem possible. The calculated distances in 10a, 12a
and 7a resemble those observed for 10, 12 and 7 very well. Slight
differences are due to the more bulky substituents in 7 and 10–
Table 4 Selected distances [pm] for 7a
Ga(3)–Ga(4)
Ga(2)–Ga(3)
Ga(1)–Ga(2)
Ga(1)–Ga(5)
Ga(4)–Ga(5)
Ga(4)–Ga(6)
Ga(3)–Ga(6)
Ga(2)–Ga(6)
Ga(1)–Ga(6)
Ga(5)–Ga(6)
Ga(4)–Ga(7)
Ga(3)–Ga(7)
Ga(2)–Ga(7)
250.0
245.4
287.4
287.7
245.5
277.1
269.8
289.7
270.5
282.5
268.7
276.5
283.8
Ga(1)–Ga(7)
Ga(5)–Ga(7)
Ga(2)–Ga(8)
Ga(1)–Ga(8)
Ga(1)–Ga(9)
Ga(5)–Ga(9)
274.7
291.2
240.5
244.0
243.9
240.7
Ga(4)–Si(2)
Ga(3)–Si(1)
Ga(6)–Si(3)
Ga(7)–Si(4)
Ga(8)–Si(5)
Ga(9)–Si(6)
243.6
243.7
244.6
243.8
243.9
244.4
Fig. 5 HOMO for 12a.
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A formally one electron reduction of 12a gives anionic 13− (eqn
(3)).
ring of gallium atoms. A comparison with the experimental values
for 11 is difficult, because in 11 the cluster core is severely
disordered. Bearing in mind the difference in the steric demand
of the substituents, 13− and 11 are in good agreement (atom
numbering according to Fig. 1). The transition from 12a to 13−
may be described as moving atom Ga1 out of the equatorial plane
of the pentagonal bipyramid, which results in a elongation of the
Ga(1)–Ga(6) bond and shortening of the Ga–Ga bonds between
the GaR units.
12a + e− → 13− DE = −203.0 kJ mol−1
(3)
This is accompanied by a drastic structural change (Fig. 6,
Table 5). Further reduction (eqn (4))
13− + e+ → 132− DE = +46.0 kJ mol−1
(4)
is accompanied by minor structural changes, only.
13− and 132− have core structures that differ only in detail
and are very similar to 11. This means six GaR units form an
elongated trigonal antiprism with an intercalated four-membered
Experimental
All experiments were performed under purified nitrogen or in
vacuum with Schlenk techniques. NMR: Bruker AXS 200. Mass
spectra: Finnegan MAT 8400. X-Ray crystallography: a suitable
crystal was mounted with a perfluorinated polyether oil on the tip
of a glass fibre and cooled immediately on the goniometer head.
Data collection was performed on a STOE IPDS diffractometer
˚
with MoKa radiation (k = 0.71073 A). The structure was solved
and refined with the Bruker AXS SHELXTL 5.1 program package.
Refinement was full matrix against F2. All hydrogen atoms were
included as riding models with fixed isotropic U values in the
final refinement. For further data see Table 1. The relatively high
residual electron density (2.29/−0.81) may be explained by a
disorder in the cluster core. Refinement in a split model gave
10 occupation factors of 0.86/0.14 for the gallium positions, but
did not result in a significant change in R values. The crystals
of 12 were weakly diffracting and no intensity was observed at
angles higher than 2h = 45◦. Quantum chemical calculations: All
DFT calculations have been performed with the TURBOMOLE
package36 using RI approximation with BP86 functional and a
def-SV(P) basis, as well as Gaussian 03.37
Fig. 6 RI-DFT calculated structure for 13− [132−]−. For distances see
Table 5.
Table 5 Selected distances [pm] for 13−, 132− (experimental values for 11)
13−
132−
11
C72H162Ga10Si6 · C48H108Ga4Si4 (12·1c)
Ga(3)–Ga(4)
Ga(2)–Ga(3)
Ga(1)–Ga(2)
Ga(1)–Ga(5)
Ga(4)–Ga(5)
Ga(4)–Ga(6)
Ga(3)–Ga(6)
Ga(2)–Ga(6)
Ga(1)–Ga(6)
Ga(5)–Ga(6)
Ga(4)–Ga(7)
Ga(3)–Ga(7)
Ga(2)–Ga(7)
Ga(2)–Ga(5)
Ga(5)–Ga(7)
Ga(2)–Ga(8)
Ga(1)–Ga(9)
Ga(1)–Ga(8)
Ga(5)–Ga(8)
Ga(7)–Ga(10)
Ga(2)–Ga(10)
Ga(9)–Ga(10)
Ga(8)–Ga(10)
Ga(7)–Ga(8)
Ga(8)–Ga(9)
Ga(4)–Si(2)
Ga(3)–Si(1)
Ga(6)–Si(3)
Ga(10)–Si(6)
Ga(9)–Si(5)
Ga(8)–Si(4)
254.4
267.3
270.7
249.6
264.5
257.5
274.5
265.2
280.1
277.7
280.7
272.9
268.7
350.2
266.5
270.9
254.5
276.9
299.6
262.3
284.0
263.8
255.7
266.6
263.7
243.3
245.0
243.6
244.7
243.2
243.4
276.4
264.3
310.8
299.2
266.2
250.6
261.7
357.5
252.2
301.6
259.7
260.1
310.7
298.6
299.2
265.5
251.0
261.8
289.9
253.9
312.9
253.7
259.0
268.0
280.6
243.5
246.0
243.7
244.5
243.1
245.6
(269.7)
(250.2)
(253.8)
(245.3)
(253.7)
(271.1)
(269.7)
(312.2)
(287.5)
(321.0)
(260.6)
(262.9)
(245.3)
(407.7)
(253.8)
(253.7)
(260.6)
(262.9)
(250.2)
(287.5)
(321.0)
(271.1)
(269.7)
(269.7)
(269.7)
(247.5)
(249.2)
(247.5)
(247.5)
(247.5)
(249.2)
A solution of Na(thf)2Si(CMe3)3 (3.0 g, 8.0 mmol) in 40 ml of
toluene was added dropwise to a suspension of “GaI” (1.47 g,
7.5 mmol) in 30 ml of toluene at −78 ◦C. The mixture was warmed
to ambient temperature and stirred for further 12 h. All volatiles
were removed in vacuo and the residue was extracted with 50 ml
of pentane. The remaining solid was treated with 40 ml of toluene.
From the pentane solution violet crystals of 1c (NMR, mass
spectra are in agreement with those reported in the literature4)
could be obtained at −30 ◦C. From the toluene solution, after
reduction of the volume to 10 ml, black prisms of 12·1c crystallized
at −30 ◦C, yield: 0.15 g (together with crystals of 1c, 9, 11), mp: 70–
130 ◦C (decomp.). NMR (C6D6) : d1H = 1.37 (s, CMe3, 1c); d13C =
32.7 (CMe3), 26.6 (CMe3); signals for 12 could not be observed.
(Crystals of 12·1c are of low solubility in common solvents, which
was observed for many other higher gallium clusters, too. Thus,
NMR spectra are dominated by the soluble 1c.) MS (EI): m/z
•
•
+
1216 ({12 − Ga4[Si(CMe3)3]2} ), 1076/100, 1c+ ), 1015 (20, {12 −
+
+
Ga4[Si(CMe3)3]3} ), 877 (50, {1c − Si(CMe3)3} ).
Conclusions
During the past decade gallium rich cluster compounds, some-
times apostrophied as metalloidal clusters, have been prepared
with cluster cores of 7 to 84 gallium atoms. With the structural
3692 | Dalton Trans., 2008, 3688–3693
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characterization of the neutral decagallane(6) 12 the family of
[Ga10R6]n− clusters [n = 0, 1, R = Si(SiMe3)3, C(SiMe3)3] became
unique in showing polymorphism of the cluster core structure
keeping the number of substituents constant.
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