Synthesis and structure of Tri- and octaindium compounds

Article abstract of DOI:10.1039/b908450a

The reactions of InCp* with alkali metal silanides M(thf) _nSiRPh₂ (R = Me, Ph) resulted in the triindanate [(Ph ₃Si)₃In-In-In(SiPh₃)]^- with a linear arrangement of In atoms and the octaindi

Full text of DOI:10.1039/b908450a

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www.rsc.org/dalton | Dalton Transactions
Synthesis and structure of Tri- and octaindium compounds†
Gerald Linti,* Martina Bu¨hler, Kirill Yu. Monakhov and Thomas Zessin
Received 28th April 2009, Accepted 14th July 2009
First published as an Advance Article on the web 12th August 2009
DOI: 10.1039/b908450a
The reactions of InCp* with alkali metal silanides M(thf)nSiRPh2 (R = Me, Ph) resulted in the
triindanate [(Ph3Si)3In–In–In(SiPh3)]- with a linear arrangement of In atoms and the octaindium
clusters [(In8(SiPh3)8]m- (m = 0, 2) amongst others, which were characterized by X-ray crystallography.
The neutral cluster has a bisphenoidal core similar to that of B8Cl8, whilst the anionic one adopts a
distorted square antiprismatic structure. In addition, the tri- and octaindium compounds were studied
by DFT calculations.
Introduction
Cluster compounds of indium seem to be less common than those
of the lighter element homologues boron, aluminium and gallium,
whose chemistry has developed widely during the last decade.1,2
Simple inorganic indium compounds featuring oxidation state +1
are expected to be more stable than gallium(I) or aluminium(I)
derivatives. However, organic derivatives InCp*3 exhibits lower
stability and higher reactivity than GaCp*.4,5 It was possible
(1)
In the reaction of InCp* with equimolar amounts of the less
bulky [Li(thf)3SiMePh2]16 (eqn (2)) in toluene solution elemental
indium precipitated, accounting for at least 90% of the starting
material. From the solution grew some colourless crystals of the
diindanate 9. The origin of the OH groups is an impurity of the
lithium silanide.
to synthesize tetrahedral clusters [In4R4] (1) [a: R = C(SiMe3)3,
C(SiMe3)2X with X = Me, Et;6–8 b: R = Si(SiMe3)3 ] as well as
9
the metalloid clusters [In8R*6] (2),10 [In12R*8] (3)11 (R* = SitBu3)
and [In8Aryl4] (4)12 (Aryl = C6H3-2,6-mesityl2). Clusters of type
[InxRx]n- (x > 4), which are part of the closo- (n = 2) or hypercloso-
series (n = 0) according to Wade–Mingos rules13–15 are not yet
known.
Here, we describe the reactions of InCp* (InCl3) with bulky
silanides [M(thf)3SiPh2R] (M = Li, Na; R = Me, Bu, Ph),16–18
t
(2)
which afford a triindanate and octaindium clusters among other
products.
If the more bulky silanide [Li(thf)3SitBuPh2]18 was reacted with
indium(III) chloride, [In(SitBuPh2)3] (10) was obtained (eqn (3)).
The formation of [SitBuPh2]2 hints to redox reactions, but no other
indium species could be detected.
Results and discussion
Synthesis
(3)
By the reaction of InCp* with [Na(thf)3SiPh3] (eqn (1)) in toluene
at 195 K a blackish solution and elemental indium were obtained.
Upon workup colourless crystals [In(SiPh3)3(thf)] (5) were isolated
from a pentane extract of the reaction mixture. The neutral
octaindane cluster [In8(SiPh3)8] (6) crystallized from a toluene
solution. If the residue was treated with thf a dark solution
forms again. Upon cooling to 253 K more 5 and black needles
of the triindanate [Na(thf)6]+[In3(SiPh3)6]- (7) precipitated. If
[Li(thf)3SiPh3] was used instead of the sodium salt, 5 and 6 were
obtained, too. From a thf extract of the reaction mixture several
crystals of the ionic cluster 8 could be isolated.
Crystal structure analysis
In the following, the crystal structure analyses are presented
grouped to related compounds. The monoindane 5 crystallizes
¯
from pentane in crystals of the triclinic sytem, space group P1
(Table 1). The central indium atom is coordinated distorted
tetrahedral by three triphenylsilyl groups and a thf molecule
(Fig. 1). The Si–In–Si angles are wide [115.3(1)–119.4(1)◦]. This
is due to the space filling silyl groups and as a consequence,
the indium atom is only 44 pm above the Si3-plane. The In–Si
bond lengths (263.8 pm) are similar to those in [In{Si(SiMe3)3}3]
(264.6 pm)9 and [In2{Si(SiMe3)3}4] (265.5 pm).19 The In–O dis-
tance is comparable to that found in other adducts.9
Universita¨t Heidelberg, Anorganisch-Chemisches Institut, Im Neuenheimer
Feld 270, D-69120 Heidelberg, Germany. E-mail: gerald.linti@aci.uni-
heidelberg.de; Fax: 049-6221-546617
† Electronic supplementary information (ESI) available: Information on
the crystal structure of 8. CCDC reference numbers 728993–728998. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/b908450a
¯
10 forms yellow prisms of the triclinic system, space group P1.
The indium atom is a surrounded trigonal planar (In(1) resides
only 16 pm above the plane through the Si atoms) (Fig. 2). The
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Table 1 Crystallographic data of 5–10
5
6
7
9
10
Empirical formula
Formula weight/g mol-1
Crystal size/mm3
Crystal system
Space group
a/pm
C58H53InOSi3
965.09
0.36 ¥ 0.21 ¥ 0.13 0.19 ¥ 0.14 ¥ 0.05
C144H120Si8In8·3C7H8 C132H138O6Si6In3Na·4thf·C6H6 C54H72In2Li2O6Si3 InSi3C48H57
3270.1
2722.9
1144.91
833.0
0.57 ¥ 0.34 ¥ 0.20
0.47 ¥ 0.45 ¥ 0.43
0.42 ¥ 0.23 ¥ 0.22
Triclinic
Triclinic
Triclinic
Triclinic
Triclinic
¯
P1
¯
P1
¯
P1
¯
P1
¯
P1
993.9(2)
1134.2(2)
2215.3(4)
81.25(3)
85.93(3)
85.45(3)
2456.1(9)
2
1625.1(3)
1675.5(3)
3059.9(4)
79.02(2)
85.71(2)
63.59(2)
7325(2)
2
1.483
1370.8(3)
1411.5(3)
1974.9(4)
72.28(3)
79.83(3)
81.56(3)
1416.0(3)
1420.0(3)
1468.8(3)
81.40(3)
81.72(3)
89.42(3)
2889(1)
999.9(2)
1189.3(2)
1865.1(4)
87.01(3)
86.06(3)
78.24(3)
2164.8(8)
2
b/pm
c/pm
a/◦
b/◦
g /◦
V/A
3
˚
3565.1(12)
1
Z
2
D
calc/g cm-3
1.305
1.268
0.591
1.316
0.904
1.278
0.660
mMo Ka/mm-1
0.594
1000
1.352
3276
F(000)
1422
3–48
1180
3–48
872
5–55
q range for data collection/◦
Index ranges
4–48
11 12 25
15 607
3–45
17 17 32
38 433
15 16 22
22 330
10 322/56/832
0.918
15 16 16
18 260
8387/0/619
0.911
12 15 24
20 226
9234/0/478
0.834
Reflections collected
Data/restraints/parameters
Goodness-of-fit (S) on F2
Final R indices [I > 2s(I)]
7182/6/568
0.809
17 693/1373/1660
0.627
R1 = 0.0901;
wR2 = 0.1941
R1 = 0.1853;
wR2 = 0.2254
+1.53/-1.10
R1 = 0.0567;
wR2 = 0.0800
R1 = 0.2018;
wR2 = 0.1101
+1.04/-0.49
R1 = 0.0554;
wR2 = 0.1304
R1 = 0.0932;
wR2 = 0.1410
+2.38/-0.84
R1 = 0.0492;
wR2 = 0.1162
R1 = 0.0694;
wR2 = 0.1209
+0.94/-0.66
R1 = 0.0378;
wR2 = 0.0788
R1 = 0.0584;
wR2 = 0.0827
+0.64/-0.64
R indices (all data)
-3
˚
Largest diff. peak and hole/e A
Fig. 1 View of a molecule of 5 (hydrogen atoms have been omitted
for clarity). Selected distances [pm] and angles [◦]: In(1)–Si(1)
264.0(4), In(1)–Si(2) 263.8(4), In(1)–Si(3) 263.6(4), In(1)–O(1)
231.7(10); Si(1)–In(1)–Si(2) 119.4(1), Si(2)–In(1)–Si(3) 117.4(1),
Si(3)–In(1)–Si(1) 115.3(1), Si(1)–In(1)–O(1) 95.5(2), Si(2)–In(1)–O(1)
105.7(3), Si(3)–In(1)–O(1) 97.0(3).
Fig. 2 View of a molecule of 10 (hydrogen atoms have been omit-
ted for clarity). Selected distances [pm] and angles [◦]: In(1)–Si(1)
257.9(1), In(1)–Si(2) 261.4(1), In(1)–Si(3) 262.7(1), Si(1)–C(1) 188.8(4),
Si(2)–C(17) 190.4(3), Si(3)–C(33) 191.4(3); Si(1)–In(1)–Si(2) 123.14(3),
Si(2)–In(1)–Si(3) 116.35(4), Si(3)–In(1)–Si(1) 119.39(4), In(1)–Si(1)–C(1)
118.4(1), In(1)–Si(2)–C(17) 114.9(1), In(1)–Si(3)–C(33) 119.1(1).
average In–Si distance is 260.7 pm, which is shorter than in 5 and
[In{Si(SiMe3)3}3]. This is due to the higher coordination number
in 5 and the even more bulky substituent in [In{Si(SiMe3)3}3],
respectively. The steric strain imposed by the SitBuPh2 substituents
is visible in the different In–Si distances. Variations in the Si–C
distances and In–Si–C angles to the tbutyl groups are in line with
this too. The Si–C bonds involving the ipso-carbon atoms of the
phenyl groups are all nearly equal [188.1(3)–188.8(4) pm]. This
might be due to the orientation of these substituents. The butyl
groups are in the InSi3 plane (with regard to the In–C bonds),
whilst the phenyl rings are oriented topside and below this plane.
centrosymmetric dimer, the central unit of which is a cage made
up by two indium atoms, four lithium atoms and six oxygen
atoms from hydroxy groups. This cage contains two Li2O3In
rings in a boat conformation, which are linked by two Li–O
[dLi(2)–O(2) = 207(2) pm] and two In–O [dIn(2)–O(4) = 213.7(5)] bonds.
The lithium atoms Li(1) and Li(1)(A) are coordinated by two
additional thf molecules. In(2) is bonded to another indium atom,
In(2) [dIn(1)–In(2) = 279.5(1) pm]. Whilst, In(1) bears three OH
groups, In(2) is bonded to three SiMePh2 substituents. The In–In
distance between the tetra-coordinated indium atoms is shorter
than that in other diindanes with three-coordinated indium atoms;
i.e. R2In–InR2 [R = Si(SiMe3)3 [dIn–In = 286.80(6) pm],20 R = CH-
(SiMe3)2 [dIn–In = 282.8(1) pm],21 R = SitBu3 [dIn–In = 292.2(1) pm]22
¯
9 is obtained as colourless rod-like crystals, space group P1,
from a thf solution. This anionic diindanate (Fig. 3) forms a
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Fig. 4 View of the anion of 7 (for clarity the hydrogen atoms have
been omitted). Selected bond lengths [pm] and angles [◦]: In(1)–In(2)
282.69(8), In(2)–Si(1) 264.1(2), In(2)–Si(2) 263.5(2), In(2)–Si(3)
263.6(2); In(2)–In(1)–In(2)(A) 180.00(1), Si(1)–In(2)–Si(2) 113.77(6),
Si(2)–In(2)–Si(3) 113.27(7), Si(3)–In(2)–Si(1) 113.18(6), Si(1)–In(2)–In(1)
104.87(6), Si(2)–In(2)–In(1) 103.44(5), Si(3)–In(2)–In(1) 107.27(5).
[Ga3(GePh3)6]- 26 That means, two Lewis acidic In(SiPh3)3 units
are attached to a Lewis base In-, formally isoelectronic to a tin
atom. Thus, 7 might be an intermediate on the way to metalloidal
clusters. Compared to 5, similiar In–Si bond lengths (263.8 pm on
average) are observed.
Fig.
3 View of a molecule of 9 (carbon hydrogen atoms have
6 (Fig. 5) is an octanuclear cluster, where the indium atoms
occupy the corners of a distorted triangle dodecahedron, a so-
called “snub disphenoid”.27 Each of the indium atoms is bonded
to a triphenylsilyl group with indium–silicon distances of 260 pm
on an average [dIn–Si = 257.0(5)–262.2(5) pm]. This is similar to
those in 1b and 7, but shorter than those in clusters with the more
bulky tri(tert-butyl)silyl groups as substituents [dIn–Si = 265 pm
(2), 268 pm (3)]. The indium–indium distances in the cluster vary
between 285.5(2) and 328.2(2) pm. The deviation of ideal D2d
symmetry is significant (Table 1). This spreading is comparable
to that in 2 (277–330 pm) and 3 (280–330 pm). In the tetrahedral
cluster 1b indium–indium distances of 290 pm are observed.
been omitted for clarity). Selected distances [pm] and angles
[◦]: In(1)–In(2) 279.6(1), In(2)–O(2) 216.1(5), In(2)–O(3) 212.9(5),
In(2)–O4 213.7(5), O(1)–Li(1) 202(2), O(2)–Li(1) 186(2), O(2)–Li(2)(A)
207(2), O(3)–Li(2) 187(2), O(4)–Li(1)(A) 188(2), O(4)–Li(2)(A)
198(2), O(5)–Li(1) 227(3), O(6)–Li(2) 203(2), In(1)–Si(1) 260.1(2),
In(1)–Si(2) 259.8(2), In(1)–Si(3) 260.0(2); Si(2)–In(1)–Si(3) 110.00(6),
Si(2)–In(1)–Si(1) 110.99(6), Si(3)–In(1)–Si(1) 113.19(6), Si(2)–In(1)–In(2)
107.03(4), Si(3)–In(1)–In(2) 110.49(4), Si(1)–In(1)–In(2) 104.87(4),
O(2)–In(2)–O(3) 88.0(2), O(2)–In(2)–O(4) 85.1(2), O(3)–In(2)–O(4)
91.9(2),
O(2)–In(2)–In(1)
127.4(1),
O(3)–In(2)–In(1)
125.5(2),
O(4)–In(2)–In(1) 126.4(2), Li(1)–O(2)–Li(2)(A) 110.1(7), Li(1)–O(2)–In(2)
115.8(10), Li(2)(A)–O(2)–In(2) 89.6(5), Li(2)–O(3)–In(2) 130.4(7),
Li(1)(A)–O(4)–Li(2)(A)
94.2(10),
Li(1)(A)–O(4)–In(2)
130.7(7),
Li(2)(A)–O(4)–In(2) 92.7(7).
and R = SitBu2Ph)2 [dIn–In = 293.8(1) pm)22]. This is due to the elec-
tronegative substituent atoms at In(1) and the less electronegative
ones at In(2) and is in line with the rule of Bent.23,24
The In–Si distances are similar to those in the compounds
described above.
The triindanate 7 (Fig. 4) is obtained as pale green crystals of the
+
¯
[Na(thf)6] salt, triclinic space group P1 with Z = 1. In addition
the crystal contains four equivalents of interstitial thf molecules.
The three indium atoms of the anion form a linear chain with
In–In distances of 282.7(1) pm, with the central two-coordinated
indium atom residing on a center of inversion. The In–In bond
lengths are shorter than those observed for diindanes R4In2.
For [In(NArylCMe)2CH]6I2 (Aryl = 3,5-Me2C6H3)25 with a chain
of six tetra-coordinate indium atoms, indium–indium distances
[281.2(1)–285.4(1) pm] similar to those in 7 are observed. The
terminal indium atoms in 7 are coordinated by three Ph3Si groups,
each. The Si–In–Si bond angles are 113.4◦, on average. This is
wider than the tetrahedral angle, due to the steric requirements. 7
might be described similar to the homologous gallium derivative
Fig. 5 View of the cluster molecule 6 (hydrogen atoms have been omitted
for clarity). Selected distances [pm]: In(1)–In(2) 293.2(2), In(1)–In(3)
285.5(2), In(1)–In(4) 298.1(2), In(1)–In(5) 299.2(2), In(2)–In(3) 326.3(2),
In(2)–In(5) 310.7(2), In(2)–In(6) 291.3(2), In(2)–In(7) 296.3(2), In(3)–In(4)
300.3(2), In(3)–In(7) 290.8(2), In(3)–In(8) 326.2(2), In(4)–In(5) 288.6(2),
In(4)–In(8) 292.3(2), In(5)–In(6) 295.5(2), In(5)–In(8) 328.2(2), In(6)–In(7)
297.3(2), In(6)–In(8) 294.0(2), In(7)–In(8) 291.2(2).
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Table 2 Interatomic distances dIn–In and dB–B [pm]: average of the symme-
try related distances with assumed D2d symmetry
8 is a dianionic octanuclear cluster. This is supported by an
ESI mass spectrometric study. Here a minor peak at m/z =
1497 (M2-) with a spacing of 0.5 mass units in the isotopic pattern
is observed. The crystal structure analysis reveals a distorted
Archimedes antiprism of eight [InSiPh3] units. As counter ions
severely disordered [Li(thf)n]+ cations are found. These and several
thf molecules fill the holes between the large cluster ions, which
have a diameter of 1.8 nm. This disorder influences the quality
of the X-ray structure determination badly and does not allow
discussing the structure properly (see ESI†). For a fuller discussion
see the Quantum chemical section. Therefore, it was attempted
to crystallize cluster 8 with other cations by adding Me4N+Cl-
or Ph4P+Cl- into reaction solutions according to Scheme 1 and
reduction of 6 with C8K. These efforts did not result in single
crystals.
a
6a
[B8H8]2a
B8Cl8
a
b
c
298(1)
293(2)
323(5)
293(1)
156(2)
176(2)
193(2)
172(2)
168(1)
175(1)
200(3)
181(2)
d
a For definitions of a, b, c, d see Table 8.
Jahn–Teller-distorted regular (x)-polyhedron. This was observed
for [Ga6{SiMe(SiMe3)2}6]31 and [Ga9 Bu9].32,33
t
8 has a similar structure to [Ga8(fluorenyl)8]2-,34 which is
described as a square antiprismatic. For this cluster, the cationic
charge could not be located unambiguously in the crystal structure.
On the basis of a Lipscomb electron/orbital balance35 a cluster
molecule 6 can be described by eight 2c2e and eight 3c2e bonds.
The former represent the indium–silicon bonds and the latter are
located on eight of the twelve triangular faces. A similar balance
for 8 results in six 3c2e and three 2c2e bonds for the In8-core.
Quantum chemical calculations
A series of linear and bent [In3Xn]m compounds (X = H, SiH3; n =
4, 5, 6; m = 0, -1, Scheme 1) was examined with DFT calculations
(BP86-functional, def-SV(P)-base).36–38 For X = H the minimum
structures of [In3H4]0,1- (11a–d) (Table 3) are bent. With decreasing
In–In–In angle the indium–indium distances get longer. This is
in line with a smaller orbital overlap and is expressed by lower
2c-SEN (shared electron number) resulting from an Ahlrichs–
Heinzmann population analysis.39 For the neutral radical species
the energetic difference between linear and bent structure is
neglectible.
In the monoanion [In3H4]- the lone pair is located at the central
indium atom. This implies a strongly bent molecule 11d, which is
more stable by 47 kJ mol-1 compared to a linear one. The In–In–In
bond angle is 74◦, making the indium–indium distance of the
Table 3 Results of DFT calculations on [In3X4]m compounds (X = H,
SiH3)
[In3X4]m
m
0
0
1-
1-
X = H
11a
176.1
282.3
179.7
0
0.8
—
11b
176.6
284.6
152.6
-1
11c
11d
d
d
In–H/pm
In–In/pm
178.8
274.5
180.0
-162
0.9
182.3
293.3 (353.0)
74.0
Angle In–In–In/◦
Scheme 1 DFT calculated structures of [In3Xn]m.
E
relative/kJ mol-1
DEHOMO–LUMO/eV
-209
1.6
1.27
1.56
0.8
We observe a structural change in transition from neutral 6 to
anionic 8. Cluster 6 has eight skeletal electron pairs and should
be addressed as hypercloso-cluster. 8, with nine skeletal electron
pairs, is expected to be a closo-cluster. An eight vertex closo-
SEN In–H
—
—
—
1.29
1.96
—
SEN In–In
SEN In–In–In
—
—
0.38
X = SiH3
11e
262.3
283.5
179.7
0
0.7
—
11f
262.4
284.1
176.0
2
0.7
—
11g
11h
d
d
In–Si/pm
In–In/pm
262.3
274.3
180.0
-211
0.8
268.1
292.6 (348.5)
73.1
cluster in borane chemistry adopts a disphenoidal structure, as
29,30
is observed for [Zn(NH3)4][B8H8].28 B8Cl8
with eight skeletal
Angle In–In–In/◦
electron pairs is a disphenoidal cluster, too. It’s structure is similar
to that of 6, regardless of the shorter boron–boron distances
(Table 2). Even the closo-octaboranate shows a similar distortion.
From common cluster rules a ExRx cluster with x skeletal electron
pairs is expected to have a capped (x - 1)-polyhedral structure or a
E
relative/kJ mol-1
DEHOMO–LUMO/eV
-259
1.4
1.30
1.47
SEN In–Si
1.37
1.82
—
SEN In–In
SEN In–In–In
—
—
—
—
0.37
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Table 4 Results of DFT calculations on dimers [In6X8]m
Table 6 Results of DFT calculations on In3X5
[In6X8]m
In3X5
m
0
2-
X = H
14a
15a
d
d
In–H/pm
In–In/pm
177.5
303.3; 304.6
179.8
0
177.4
287.1
124.2
-27
X = H
12a
175.9
See Table 5
0
1.1
1.26
12b
Angle In–In–In/◦
d
d
In–H/pm
In–In/pm
E
181.3
See Table 5
-180
E
relative/kJ mol-1
DEHOMO–LUMO/eV
relative/kJ mol-1
1.5
1.29
1.16; 0.86
2.5
1.29
1.34
DEHOMO–LUMO/eV
SEN In–H
0.7
1.25
SEN In–H
SEN In–In
X = SiH3
12c
12d
X = SiH3
14b
15b
d
d
In–Si/pm
In–In/pm
262.1
264.6
See Table 5
-353
d
d
In–Si/pm
In–In/pm
263.1
294.7; 303.8
175.8
0
263.8
286.9
123.4
-18
See Table 5
0
0.9
1.32
relative/kJ mol-1
DEHOMO–LUMO/eV
Angle In–In–In/◦
E
E
relative/kJ mol-1
DEHOMO–LUMO/eV
0.9
1.31
SEN In–Si
1.3
1.30
1.10; 0.94
2.0
1.29
1.26
SEN In–Si
SEN In–In
Table 5 DFT calculated indium–indium distances and SEN for dimers
of type [In6X8]m
(eqn (4)) on the left side.40 For the lighter homologues boron and
aluminium the closo-cluster species are preferred.
D/pm
12a
12b
12c
12d
In(1)–In(1)(A)
In(1)–In(2)
In(1)–In(3)
In(1)–In(2)(A)
In(2)(A)–In(3)
333.6
291.4
288.1
327.3
335.3
325.1
313.8
301.0
344.5
290.1
326.1
290.9
287.8
324.1
335.5
334.9
304.4
293.1
346.6
289.6
(4)
SEN
In(1)–In(1)(A)
In(1)–In(2)
0.54
1.13
1.22
0.88
0.79
0.30
0.17
0.89
0.99
1.28
0.80
1.48
0.29
0.27
0.53
1.04
1.11
0.86
0.68
0.26
0.15
0.66
0.99
1.19
0.68
1.30
0.23
0.20
In(1)–In(3)
For In3X5 isomers 14 and 15 (Table 6) were calculated. 14 is a
linear molecule. The In–InX2 bond is shorter than the In–InX3
bond by 1 pm (X = H) and 9 pm (X = SiH3). Isomer 15 is more
stable than 14 by 27 kJ mol-1 (X = H) and 18 kJ mol-1 (X = SiH3),
respectively. The In–In distances are shortened by 17 pm.
Isomers 16 of [In3X6]- ions (Table 7) with the topology of 7,
have linear In3 chains. The four bonding electrons are involved in
two dative In–In bonds. 16 is more stable than the other isomers,
considered. 17a,b with three coordinate central indium atoms are
less stable by 9 kJ mol-1 (X = H) and 22 kJ mol-1 (X = SiH3).
Isomers 18 with a tetra-coordinate central indium atom are less
stable by 6 and 22 kJ mol-1, respectively. The In–In distances
decrease in the row 16 to 18.
In(1)–In(2)(A)
In(2)(A)–In(3)
In(1)–In(2)(A)–In(3)
In(1)–In(1)(A)–In(2)
InH2 units short (353 pm). A 3c-SEN of 0.38 indicates delocalized
bonding. For X = SiH3 similar results are obtained.
Table 7 Results of DFT calculations on [In3X6]-
Dimerisation of In3X4 leads to hexaindanes 12a–d. It has been
postulated, that higher clusters of group 13 elements form via
E3 species.1 In the dianionic species 12b and 12d (Table 4, 5)
the 3c-SEN for the In3 triangles indicate extensive multicenter
bonding. On transition from In6X8 to [In6X8]2- the In(1)–In(2)
and In(1)–In(2)(A) distances increase, the In(1)–In(1)(A) and
In(2)(A)–In(3) distances get shorter. Formally, due to shorter
In–In distances the neutral species In6X8 are considered as
dimers of linear In3X4 units. [In6X8]2- is then the dimer of bent
[In3X4]- units. By elimination of X2 from [In6X8]2-, closo-cluster
of type [In6X6]2- (13) are formed (eqn (4)). Based on electronic
energies this reaction is endothermic (X = H, DE = +32 kJ mol-1;
X = SiH3, DE = +82 kJ mol-1). In the structurally characterized
hexagallanate [Ga6(SitBu3)4(CH2Ph)2]2-,31 a octahedral cluster is
observed, as calculated for [In6X8]2-. Quantum chemical calcula-
tions for [Ga6X8]2- and octahedral [Ga6X6]2- show an equilibrium
[In3X6]-
X = H
16a
17a
18a
d
d
In–H/pm
In–In/pm
180.1
298.1
179.9
0
181.2
294.1
130.3
+9
181.2
288.7
98.3
+6
Angle In–In–In/◦
E
relative/kJ mol-1
DEHOMO–LUMO/eV
1.5
1.30
1.21
2.0
1.28
1.19
1.8
1.27
1.28
SEN In–H
SEN In–In
X = SiH3
16b
17b
18b
d
d
In–Si/pm
In–In/pm
263.3
292.8
180.0
0
265.7
290.5
130.2
+22
266.0
287.2
99.1
+22
1.7
Angle In–In–In/◦
E
relative/kJ mol-1
DEHOMO–LUMO/eV
1.7
1.32
1.16
1.8
1.30
1.16
SEN In–Si
1.29
1.23
SEN In–In
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Table 8 Results of DFT calculations on 19–21
19
192-
20
202-
21-
212-
Symm dIn–In/pm D2d
D2d
C4
C4
C4
Oh
310.3a
305.5a
363.4b
306.9c
287.1d
182
311.0e
307.2f
295.1e
315.2f
301.0e 302.0
311.0f
326.3b
297.1c
307.3d
176
dIn–H/pm
E
relativ/kJ mol-1
177
+118
0.15
182
-220
1.97
179
-222
0.19
186
-76
1.16
0
-210
2.0
DEHOMO–LUMO/eV 1.09
Scheme 2 Results of DFT calculations for clusters 22a–c. Selected
distances [pm]: 22a: a 307.7, b 330.4, c 299.0, d 300.6, In–Si 263.6; 22b2-: a
291.4, b 308.5, c 337.9, d 288.0, In–Si 266.1; 22c2-: e 295.0, f 310.1, In–Si
265.0.
DFT calculations (BP86-functional, def-SV(P)-base)36–38 were
performed for [In8H8]n- (Table 8) in disphenoidal structure (n = 0:
19, 2: 192-), square antiprismatic structure (n = 0: 20, 2: 202-, 1:
20-) and cubic arrangement (n = 2: 212-) in order to get insight
into the structural change observed from 6 to 8.
For neutral In8-clusters the disphenoidal structure 19 is more
stable than 20. For dianionic species this is inverted, but the energy
difference—at least for hydrogen substituted clusters—is small. An
alternative cubic structure 21 is the least stable of all. By reduction
of 19 to 202- more than 200 kJ mol-1 are gained. By comparison
of the indium–indium distances in 8 with those calculated for 202-
and 20- a monoanionic 8 can be excluded.
On reduction of 19 a significant change in indium–indium
distances is observed, which means increase of distances b and
c and a shrinking of a and d. In case of reduction of 20 to 202-
the distances in the quadratic faces (e) get shorter than those
of the triangular ones, which is in line with the findings for 8.
Shared electron numbers (SEN), as resulting from an Ahlrichs–
Heinzmann population analysis, are a valuable tool for evaluating
bonding properties. For 19 2c-SENs of 0.94 to 1.27 are calculated
which correspond to long (b) and short edges (c). On eight faces
of the disphenoid, namely those not adjacent to edges a, high
3c-SENs of 0.35 are found. This is in line with the eight 3c2e
bonds expected, as described above. In 202- 2c-SENs on edges
of the square faces are higher (1.41) than on edges f . The 3c-
SENs (1.41) on the triangular faces are larger than on the square
faces (0.16). This hints to delocalized bonding preferentially
there.
In order to evaluate the influence of larger substituents
[In8(SiMe3)8] cluster 22a–c have been investigated (Scheme 2).
Reduction of the neutral disphenoidal cluster 22a to the dian-
ionic square antiprismatic 22c2- is exothermic by 190 kJ mol-1.
A dianionic disphenoidal cluster 22b2- is less stable by only
15 kJ mol-1. The calculated distances for 22a and 22c2- corre-
spond well with the average ones of 6 and 8. Furthermore, the
structures of [InSiPh3]8 (5 calc.) and [InSiPh3]2- (8 calc.) (Fig. 6)
were calculated using a ONIOM model (In, Si: DFT BP/def-
SV(P); C,H: UFF-Forcefield).41 Here, only minor shortening of
the In–In and In–Si distances is observed compared to 22a
and 22c2-.
Fig. 6 Results of a ONIOM calculation on 8 calc. Selected averaged
distances [pm]: e 293.7, f 308.7, In–Si 265.5.
Experimental
Allexperiments were performedunder purified argonor 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
to 200 K. Data collections were performed on a STOE IPDS
˚
diffractometer with Mo Ka radiation (l = 0.71073 A). The
structure was solved and refined with the Bruker AXS SHELXTL
5.1 program package. Refinement was in 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
and CCDC reference numbers 728993 (5), 728994 (6), 728995 (7),
728995 (8), 728997 (9) and 728998 (10). The crystals of 6 and
especially of 8 were extremely weakly diffracting and no intensity
was observed at angles higher than 2q = 45◦. This might be due
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to a high solvent content in the crystal. 6 crystallizes together
with three toluene molecules, which are partially disordered,
which was modelled using part -1 instructions. 8 has several thf
molecules incorporated in the crystal structure, which could only
partially resolved (see ESI†). Crystals 5 were weakly diffracting,
too. Consequently the ratio measured/observed data is low. The
coordinated thf molecule is disordered, but was refined in averaged
positions, which gave high thermal parameters for the thf carbon
atoms. Crystals of 7 contain 4 thf and a benzene molecule in the
elementary cell. The disordered thf moecule was modelled in split
positions (occupation 1 : 1).
Compound 6
MS (4.5 kV, ESI, thf, 4 ml min-1) m/z = 1497 (M2-, 0.05%), 1151
([In(SiPh3)4]-, 4%), 551 ([Si2Ph6]-, 13%), 275 ([SiOPh3]-, 100%),
259 ([SiPh3]-, 13.5%).
Synthesis of 9
Into a solution of freshly sublimed InCp* (2.70 g, 10.8 mmol)
in 20 ml of toluene at 215 K with stirring Li(thf)3SiMePh2
(5.5 g; 13.1 mmol) in 20 ml of toluene were added rapidly. The
mixture turned black at once. After slow warming up to ambient
temperature all volatiles were removed in vacuum. The dark
residue was insoluble in hexane and toluene. With thf a pale
maroon solution was obtained, but most of the material remained
undissolved (elemental In). From the thf solution crystallized upon
cooling to 243 K several crystals of colourless 9, which could be
used for X-ray structure determination.
Quantum chemical calculations: All DFT calculations have
been performed with the TURBOMOLE package37–39,42–46 using
RI approximation with BP86 functional and a def-SV(P) basis, as
well as Gaussian 03 (B3LYP or BP; LANL2DZ, SV(P)).41
Synthesis of 5, 6, 7
Synthesis of 10
Into a solution of 3.25 g (13.0 mmol) InCp* in 20 ml of toluene
a solution of NaSiPh3 (13.0 mmol, freshly prepared from Si2Ph6
and sodium powder) in 35 ml thf was added dropwise at 215 K
with stirring. After slow warming to ambient temperature and
continued stirring for 18 h all volatiles were removed in vacuum.
The residue was washed with pentane, toluene and finally thf.
All solutions were reduced in volume. From the pentane solution
some colourless crystals of 5 precipitated upon cooling. From the
toluene extract black needles of 6 (0.10 g; 2%) were obtained.
At first colourless crystals of 5 (1.5 g; 12.1%) grew from the thf
solution, then, after cooling to 253 K, green, prismatic crystals of
7 (0.18 g; 1.5%) formed. 5 C58H53OSi3In (965.09 g mol-1): calcd. C
72.18, H 5.54; found C 75.99, H 6.03%. 1H NMR (C6D6) d = 7.57
(m, 9H, p-H of SiPh3), 7.47 (m, 18H, o-H), 7.09 (m, 18H, m-H),
3.47 (m, thf), 1.28 (m, thf). 13C NMR (C6D6) d = 139.8 (s, o-C),
137.0 (s, p-C), 128.16 (s, m-C), 68.6 (s, thf), 25.6 (s, thf). 29Si NMR
A suspension of Li(thf)3SitBuPh2 (7.0 g, 15.2 mmol) in 15 ml thf
was added dropwise to a stirred solution of 1.12 g (5.07 mmol)
InCl3 in 35 ml thf at 215 K. The dark-coloured reaction mixture
was stirred for additional 3 h at low temperature and was then
slowly warmed to ambient temperature. After stirring for 16 h
all volatile reaction components were removed under oil pump
vacuum and the residue was extracted with 60 ml of toluene. After
filtration a reddish-brown solution was obtained, from which 10
was isolated as brownish powder. The powder was dissolved in the
mixture of 20 ml toluene and 10 ml hexane, reduced to a volume
15 ml and cooled to 253 K, resulting in the formation of pale
yellow crystals. Yield: 0.93 g, 22.1%.
InSi3C48H57 (832.1): calcd. C 69.22%, H 6.85%; found C 69.78%,
1
H 7.04. H NMR (400 MHz, C6D6, iTMS): d = 1.04 (s, CMe3),
7.5 (m, o-Ph), 7.7 (m, p-Ph), 7.8 (m, m-Ph). 13C NMR (400 MHz,
C6D6, iTMS): d = 27.7 (s, CMe3), 31.9 (s, CMe3), 129.7 (m-
(eTMS) d = -47.2 (s, SiPh3). MS (70 eV, EI) m/z = 815 ([M -
∑
thf - Ph]+ , 0.2%), 633 ([In(SiPh3)2]+, 28%), 518 ([SiPh3]2 ∑ , 9.5%),
+
Ph), 134.1 (p-Ph), 136.5 (o-Ph), 139.7 (i-Ph). 29Si{ H}-NMR
1
336 ([SiPh4]+∑ , 13%), 259 ([SiPh3]+, 100%), 182 ([SiPh2]+∑ , 42%),
115 (In+, 15%), 105 ([SiPh]+, 16.5%).
(400 MHz, C6D6, eTMS): d = 24.5 (s, SitBuPh2), -2.19 (s, SitBuPh2,
disilane). MS (EI, 70 eV): m/z = 593 {[In(SitBuPh2)2]+, 26.4%},
∑
Due to the low yields and bad solubility of 6, 7 and 8 no NMR
spectra could be obtained for these compounds. Under EI-MS
conditions 6 fragments unspecifically, giving raise to signal at
m/z = 1112 ([In2(SiPh3)2(SiPh2)2]+., 0.9%). The most intense signal
corresponds to m/z = 517 ([In2(SiPh2)(SiPh)]+, 98.0%).
478 ([SitBuPh2]2 , 7.9%), 239 ([SitBuPh2]+, 100%), 115 (In+, 18%).
+
Conclusions
In3 and In8 compounds were accessible via reaction of InCp*
with silanides. Compounds with chained indium atoms are very
rare. The triindanate 7 incorporates formally a highly reduced In-
between two InR3 units. This In- is one of the building elements of
higher anionic metalloidal In cluster compounds which have not
been known up to now. Only a few neutral metalloidal In clusters
have been reported.10–12 This is in contrast to the flourishing cluster
chemistry of the element homologues aluminium and gallium.1
The couple of octanuclear clusters 6 and 8 exhibits a structural
change with the number of skeletal electrons. 6 adopts a dodeca-
hedral structure analogous to that of B8Cl8. In the reduced species
8 the indium atoms are at the corners of a distorted Archimedes
antiprism, which is in analogy to the structure of a dianionic
octanuclear gallium cluster.34 Those novel indium clusters may
open a fruitful chemistry of indium as it is known with the lighter
homologues.
Synthesis of 5, 6, 8
A solution of [Li(thf)3SiPh3] (7.0 g, 14.5 mmol) in 35 ml of toluene
was added slowly into a solution of InCp* (3.4 g, 13.5 mmol)
in 70 ml of toluene at 195 K. After slow warming to ambient
temperature and stirring for 18 h all volatiles were removed
under reduced pressure. The residue was washed successively with
hexane, toluene and thf. All extracts were reduced in volume. Upon
standing at room temperature 6 (0.2 g, 4%) crystallized as black
plates from the toluene solution, 8 (some crystals) as black rods
from the thf solution. From all of the three extracts 5 (1.5 g,
36%) was isolated as colourless crystals. 6 and 8 are very poorly
soluble in common solvents, both, which did not allow NMR
measurements.
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8078 | Dalton Trans., 2009, 8071–8078
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