Icosahedral Ga-centred nickel carbonyl clusters: Synthesis and characterization of [H3-nNi12 (μ12-Ga)(CO) 22]n- (n = 2, 3) and [Ni14.3(μ12- Ga)(CO)24.3]3- anions

Article abstract of DOI:10.1002/ejic.200900904

The reaction of [Ni₅(CO)₁₂]^2- or [Ni ₆(CO)₁₂]^2- with GaCl₃ in dichloromethane under a nitrogen atmosphere affords a mixture of [Ni _12+x(μ₁₂-Ga)(CO)_22+x]^3- (x = 0-3) clusters. Short exposure of the above mixture to a carbon monoxide atmosphere leads to the green icosahedral [Ni₁₂(μ₁₂-Ga)(CO) ₂₂]^3- trianion, which was isolated and characterized as its [NnBu₄]⁺ salt. In contrast, crystallization of the above mixture in the presence of Ni(CO)₄ enabled isolation of a cocrystallized mixture of [Ni₁₄(μ₁₂-Ga)(CO) ₂₄]^3- (70%) and [Ni₁₅(μ₁₂-Ga)(CO) ₂₅]^3- (30%). As inferable from its structure, the additional three Ni(CO) moieties condense onto interlayer faces of the icosahedron. Protonation of [Ni₁₂(μ₁₂-Ga)-(CO) ₂₂]^3- affords the corresponding [HNi₁₂(μ ₁₂-Ga)(CO)₂₂]^2- hydride derivative, which was isolated in a pure state and fully characterized. All of the above compounds conform to the cluster-borane analogy, by the inclusion principle, and none exhibits relevant redox behaviour.

Full text of DOI:10.1002/ejic.200900904

FULL PAPER
DOI: 10.1002/ejic.200900904
Icosahedral Ga-Centred Nickel Carbonyl Clusters: Synthesis and
Characterization of [H3–nNi12 (µ12-Ga)(CO)22]n– (n = 2, 3) and
[Ni14.3(µ12-Ga)(CO)24.3]3– Anions
Cristina Femoni,[a] Maria Carmela Iapalucci,*[a] Giuliano Longoni,[a] and Stefano Zacchini[a]
Keywords: Cluster compounds / Carbonyl ligands / Nickel / Gallium / Hydrides
2–
2–
3–
The reaction of [Ni5(CO)12
dichloromethane under a nitrogen atmosphere affords a mix-
ture of [Ni12+x(µ12-Ga)(CO)22+x
3– (x = 0–3) clusters. Short ex-
]
or [Ni6(CO)12
]
with GaCl3 in
[Ni15(µ12-Ga)(CO)25
]
(30%). As inferable from its structure,
the additional three Ni(CO) moieties condense onto inter-
layer faces of the icosahedron. Protonation of [Ni12(µ12-Ga)-
]
3–
2–
posure of the above mixture to a carbon monoxide atmo- (CO)22
sphere leads to the green icosahedral [Ni12(µ12-Ga)(CO)22
trianion, which was isolated and characterized as its
[NnBu4]+ salt. In contrast, crystallization of the above mixture
in the presence of Ni(CO)4 enabled isolation of a cocrys-
tallized mixture of [Ni14(µ12-Ga)(CO)24
]
affords the corresponding [HNi12(µ12-Ga)(CO)22]
3–
]
hydride derivative, which was isolated in a pure state and
fully characterized. All of the above compounds conform to
the cluster-borane analogy, by the inclusion principle, and
none exhibits relevant redox behaviour.
3–
]
(70%) and
distorted and slightly more stable than the [Ni12(µ12-
Sn)(CO)22]2– congener.[6]
Introduction
Several metal carbonyl clusters adopting an icosahedral
geometry are known. The great majority is based on a
noncentred icosahedron having the 12 vertices constituted
by 10 nickel metal atoms and a pair of trans main-group
elements (E).[1–5] A few of them display 12 metal vertices
and are centred by an interstitial E atom, for example,
In an attempt to implement such suggestions and eventu-
ally find new examples of icosahedral metal carbonyl clus-
ters making exception to the cluster-borane analogy, we
started an investigation of bimetallic Ni–Ga clusters, mainly
on the basis of the consideration that Ga is comparable in
size to Ge and features a minor Pauling electronegativity.
These properties could eventually lead to undistorted icosa-
hedral architectures and, consequently, to a more robust
[Ni12(µ12-Ga)] metal core.
As a result, we report here a new series of icosahedral Ni
carbonyl clusters, which represent the first examples of
metal carbonyl clusters containing Ga as an interstitial ele-
ment.[12]
[Ni12(µ12-E)(CO)22]2– (E
=
Ge, Sn),[6] [Rh12(µ12-Sn)-
(CO)27]4–[7] and [Rh12(µ12-Sb)(CO)27]3–.[8] All formally fea-
ture 13 skeletal electron pairs, so fuelling through the in-
clusion principle[9] the cluster-borane analogy.[10] However,
it was shown that [Rh12(µ12-Sn)(CO)27]4– can reversibly lose
carbon monoxide to give the electron-poor [Rh12(µ12-
Sn)(CO)26]4– and [Rh12(µ12-Sn)(CO)25]4– icosahedral clus-
ters.[11] This exceptional behaviour probably descends from
the fact that Rh and Sn belong to the same fifth period.
Besides, the relatively low electronegativity of Sn could
probably favour its shrinking to the point to fill a Rh12
icosahedron without need of swelling the cage. Indeed, un-
der a rigid sphere model, the icosahedron would only allow
lodging of a sphere having 95% of the size of the outer
spheres. The above considerations were thought to impart
a particular stability to the Rh12(µ12-Sn) metallic core. In
partial agreement with the above reasoning, the [Ni12(µ12-
Ge)(CO)22]2– dianion, which requires lodging in the icosa-
hedral cavity of a smaller Ge atom, was reported to be less
Results and Discussion
Synthesis and Spectroscopic Characterization
The reaction of either [Ni5(CO)12]2– or [Ni6(CO)12]2–
with GaCl3 in dichloromethane under a nitrogen atmo-
3–
sphere leads to a mixture of [Ni12+x(µ12-Ga)(CO)22+x
]
(x
= 0–3) trianions, formally according to Equation (1).
3–
3[Ni5(CO)12]2– + 4GaCl3 Ǟ [Ni12+x(µ12-Ga)(CO)22+x
]
+
(3 – x)Ni(CO)4 + (2 – x)CO + 3[GaCl4]– (1)
[a] Dipartimento di Chimica Fisica ed Inorganica, Università di
Bologna,
The presence of x = 0, 1, 2 and 3 derivatives is suggested
by ESI-MS analysis of the mixture, as well as the 1H NMR
spectra of the protonated mixture, which display four major
Viale Risorgimento 4, 40136 Bologna, Italy
Fax: +39-0512093690
E-mail: iapa@ms.fci.unibo.it
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Icosahedral Ga-Centred Nickel Carbonyl Clusters
hydride signals. Owing to limited differential solubility in yet uncharacterized Ni–Sn species.[6] Conversely, [Ni12(µ12-
all solvents, the mixture could not be separated. However, Ga)(CO)22]3– is unaffected by short exposure to carbon
3–
the [Ni12+x(µ12-Ga)(CO)22+x
]
mixture is converted into monoxide at atmospheric pressure, although it is completely
pure [Ni12(µ12-Ga)(CO)22]3– trianion, according to Equa- degraded by long exposures.
tion (2), by short exposure to a carbon monoxide atmo-
sphere. The resulting green [Ni12(µ12-Ga)(CO)22]3– trianion
X-ray Structures of [Ni12(µ12-Ga)(CO)12(µ-CO)6(µ3-CO)4]3–,
was crystallized in its [NnBu4]+ salt by layering isopropyl
alcohol on top of its dichloromethane solution. It shows
infrared carbonyl absorptions in dichloromethane at
1999(s) and 1790(m) cm–1.
[HNi12(µ12-Ga)(CO)12(µ-CO)8(µ3-CO)2]2– and [Ni14.3(µ12-
3–
Ga)(CO)24.3
]
[NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2
3–
The unit cell of [NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2 con-
tains 4 anions, 12 cations and 8 dichloromethane molecules
separated by normal contacts. The structure of the
[Ni12(µ12-Ga)(CO)12(µ-CO)6(µ3-CO)4]3– trianion is shown
in Figure 2; the adopted numbering scheme and the most
significant bond lengths are collected in Table 1. Its metal
framework may be described as a Ga-centred icosahedron
of Ni atoms. Owing to a slight elongation along the pseudo
C5 axis passing through Ni2, Ga and Ni6, the metal frame-
work is more precisely described as a bicapped pentagonal
antiprism. It is likely that the above distortion is due to the
CO ligands, which are layered in a 1-5-5-5-5-1 sequence
of terminal-bridge-terminal-terminal-bridge-terminal CO
groups describing a fused double icosahedron missing the
shared vertex. As a result of the above sequence, there are
no CO ligands spanning the interlayer edges or faces and
shortening the bonding interlayer contacts between the two
pentagonal rings of the inner Ni10 pentagonal antiprism.
Indeed, six CO bridging ligands span three out of five edges
of each pentagonal ring of the antiprism. Four carbonyl
groups cap the triangular faces individuated by the remain-
ing pentagonal edges and the apical Ni2 and Ni6 atoms.
Finally, the CO ligand shell is completed by 12 terminal
ligands, 1 per each Ni atom. As a whole, the carbonyl ste-
reochemistry is very similar, though not identical, to the
one displayed by the [Ni12(µ12-E)(CO)22]2– (E = Ge, Sn)
congeners.[6]
[Ni12+x(µ12-Ga)(CO)22+x
]
+ 3xCO p
[Ni12(µ12-Ga)(CO)22]3– + xNi(CO)4
(2)
Conversely, we only succeeded in isolating a cocrys-
tallized mixture of [Ni14(µ12-Ga)(CO)24]3– and [Ni15(µ12-
Ga)(CO)25]3– in a 70:30 ratio, by crystallization in dichloro-
methane/isopropyl alcohol of the [NnBu4]3[Ni12+x(µ12-
Ga)(CO)22+x] mixture in the presence of deliberately added
Ni(CO)4.
A
first difference between the new [Ni12(µ12-Ga)-
(CO)22]3– cluster and the [Ni12(µ12-E)(CO)22]2– (E = Ge, Sn)
congeners resides in its aptitude toward protonation to its
corresponding hydride derivative. As shown by Equa-
tion (3), the protonation is reversible and the trianion is
partially or completely regenerated by dissolving the hy-
dride derivative in basic solvents such as DMF or DMSO.
(3)
The [HNi12(µ12-Ga)(CO)22]2– dianion has been isolated
in a pure state by crystallization of its [NnBu4]+ salt from
acetone/isopropyl alcohol mixtures. It shows infrared car-
bonyl absorptions in acetone at 2025(s) and 1826(m) cm–1.
Its H NMR spectrum (Figure 1) displays a signal at δ =
–13.56 ppm, which corresponds to one of the hydride sig-
1
2–
nals of the [HNi12+x(µ12-Ga)(CO)22+x
]
mixture.
Figure 1. 1H NMR spectrum of the [HNi12(µ12-Ga)(CO)22]2– di-
anion in [D6]acetone.
The relatively enhanced stability of [Ni12(µ12-Ga)-
(CO)22]3– under carbon monoxide represents a second dif-
ference with [Ni12(µ12-Ge)(CO)22]2– and [Ni12(µ12-Sn)-
(CO)22]2–. Indeed, the first of the two latter compounds
promptly reacts with CO to give the stable pentagonal anti-
prismatic [Ni10(µ10-Ge)(CO)20]2– by loss of the apical Ni
atoms, whereas the second is more extensively degraded to Figure 2. The structure of [Ni12(µ12-Ga)(CO)12(µ-CO)6(µ3-CO)4]3–.
Eur. J. Inorg. Chem. 2010, 1056–1062
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C. Femoni, M. C. Iapalucci, G. Longoni, S. Zacchini
FULL PAPER
Table 1. Range and average bond lengths [Å] in the title Ni–Ga clusters.
3–
Distance
[Ni12(µ12-Ga)(CO)22]3–
[HNi12(µ12-Ga)(CO)22]2–
[Ni14.3(µ12-Ga)(CO)24.3]
Ga–Ni range
Average
Ni–Ni icosahedron range
Average
2.4641(7)–2.6747(8)
2.524
2.4762(8)–2.8564(9)
2.653
2.4994(14)–2.6848(15)
2.542
2.509(2)–2.884(2)
2.656
2.4547(7)–2.6082(7)
2.532
2.4634(7)–2.8393(8)
2.643
Caps range
Average
–
–
–
–
2.4384(7)–2.7351(7)
2.502
Ni–C terminal range
Average
Edge-bridging range
Average
1.767(5)–1.785(5)
1.778
1.888(5)–1.924(5)
1.902
1.736(15)–1.782(14)
1.757
1.889(14)–2.034(13)
1.925
1.754(7)–1.794(4)
1.776
1.84(3)–2.25(3)
1.918
Face-bridging range
Average
C–O range
1.923(5)–2.083(5)
2.000
1.133(6)–1.189(5)
terminal 1.141
edge-bridging1.168
face-bridging 1.183
1.939(13)–2.098(13)
2.023
1.121(15)–1.182(13)
terminal 1.146
edge-bridging 1.158
face-bridging 1.182
–
–
1.128(5)–1.184(5)
terminal 1.139
edge-bridging 1.167
Average
[NnBu4]2[HNi12Ga(CO)22]
a slight shrinking of the metal core. However, examination
of Table 1 argues against it and points out that the metal
core of [HNi12(µ12-Ga)(CO)12(µ-CO)8(µ3-CO)2]2– un-
dergoes a slight swelling with respect to that of the parent
trianion. In particular there is a small but significant elong-
ation of the Ni2–Ni5 and Ni5–Ni6 edges (which have been
arbitrarily omitted in Figure 3) and the Ni2–Ni6 bond.
It seemed reasonable that the hydride hydrogen atom
could be located and disordered over the above two crystal-
lographically equivalent faces or edges. Theoretical calcula-
tions with Xhydex[13] were carried out. The preliminary out-
put resulted in three possible face-bridging hydrides with
similar potential energy, respectively located on the Ni2–
Ni5–Ni6, Ni3–Ni4–Ni6 and Ni3–Ni5–Ni6 faces and
equally disordered on their correspondent centrosymmetric
images. However, after refinement, only the hydride atom
on the Ni2–Ni5–Ni6 face remained stable and displayed
Ni–H bond lengths in the 1.70–2.06 Å range of values. As
expected, the preferred hydride position is where the longest
Ni–Ni bond lengths [Ni3–Ni6 2.820(2) and Ni5–Ni6
2.884(2) Å] are found.
The unit cell contains one [HNi12(µ12-Ga)(CO)12(µ-CO)8-
(µ3-CO)2]2– dianion and two [NnBu4]+ cations, whereas in
the asymmetric unit only one half of the cluster and one
cation are present, as the Ga atom lies on the crystallo-
graphic centre of symmetry. The structure of the dianion is
reported in Figure 3; the adopted numbering scheme and
the most relevant bonding interactions are collected in
Table 1. As a whole, the structure is very similar to that of
the parent trianion, the only difference being represented
by a lengthening of the Ni7–C2 contact [2.213(14) Å] be-
yond the usual bond length. Owing to that, the C2–O2
carbonyl has been somehow arbitrarily shown as edge-
bridging in Figure 3.
[NnBu4]3[Ni14.3Ga(CO)24.3]·2CH2Cl2
The unit cell of [NnBu4]3[Ni14.3Ga(CO)24.3]·2CH2Cl2
contains 4 anions, 12 cations and 8 dichloromethane molec-
ules separated by normal contacts. The structure of the
[Ni14.3Ga(CO)24.3]
3– trianion is shown in Figure 4; the most
relevant bonding contacts are collected in Table 1. The cen-
tral core of the cluster anion is again a distorted icosahe-
dron slightly elongated along both the Ni3–Ga–Ni8 and
Ni2–Ga–Ni6 axes. The icosahedron is capped by three
Ni(CO) moieties on two contiguous (Ni7 and Ni12) and
one opposite (Ni16) interlayer triangular faces. However,
the third cap, namely, Ni16–CO25, shows a refined occu-
Figure 3. The structure of [HNi12(µ12-Ga)(CO)12(µ-CO)8(µ3-
CO)2]2–.
This slight change is probably a consequence of the re- pancy fraction of 0.29, arising from the presence in the crys-
duced negative charge of the anion, which decreases the tals of both [Ni14(µ12-Ga)(CO)24]3– (ca. 70%) and [Ni15(µ12-
need of back-donation from the Ni12Ga core towards the Ga)(CO)25]3– (ca. 30%) trianions. This disorder justifies the
CO ligand shell. A second difference is present in the indi- given fractional composition. Moreover, the presence of
vidual Ni–Ga and Ni–Ni bond contacts. In general, on re- Ni(CO) moieties binding two interlayer Ni5 rings opposes
ducing the negative charge of the anion one should expect the deformation shown by both [Ni12Ga(CO)22]3– and
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Icosahedral Ga-Centred Nickel Carbonyl Clusters
[HNi12Ga(CO)22]2–. As a result, the average Ni–Ni distance 4p AOs is antibonding. As a result, these interactions
of the icosahedral moiety is the shortest of this series of feature the least Ni–Ga overlap population, in agreement
compounds (see Table 1).
with the slight elongation of the icosahedron along the
Ni2–Ga–Ni6 axis. Practically identical features are also
shown by the previously reported [Ni12(µ12-Ge)(CO)22]2–
and [Ni12(µ12-Sn)(CO)22]2–, which are both isoelectronic
and isostructural. In contrast, EHMO simulations of hypo-
thetical [Ni12(µ12-E)(CO)22]n– (E = Sb or Bi, n = 1; E = Se
or Te, n = 0) isoelectronic and isostructural clusters suggest
that interstitial group 15 and 16 elements should only
feature a wide HOMO–LUMO gap of ca. 1.6–1.8 eV.
3–
Figure 4. Structure of [Ni12+x(µ12-Ga)(CO)22+x
]
[x = 2 (70%), 3
(30%) based on occupancy fraction of Ni16 and CO25, which re-
fines to ca. 0.3].
As a further difference, no more symmetrical face bridg-
ing carbonyl groups are present, even if five carbonyl
groups (represented as edge-bridging in Figure 4) lean to-
ward a third Ni atom and display contacts shorter than the
sum of their van der Waals radii [namely, Ni12–C20
2.203(4), Ni4–C8 2.322(4), Ni5–C13 2.433(5), Ni9–C1
2.272(4) and Ni15–C4 2.434(4) Å].
Finally, the two contiguous caps reciprocally interact, as
inferable by a bonding contact of 3.074 Å, whereas the Ni–
Ni interactions between the caps and the Ni atoms of the
inner icosahedral core are in the range 2.4384(7)–
2.4724(7) Å. Though weak, the above additional interaction
probably favours such contiguity, rather than the capping
of nonadjacent faces. Conversely, the subsequent addition
of a third contiguous Ni(CO) cap is likely disfavoured by
the unavoidable crowding of the carbonyl ligands.
Figure 5. Frontier region of the EHMO diagram (top) calculated
with CACAO[14] and picture of the quasidegenerate 116 and 117
HOMOs of [Ni12Ga(CO)22]3– (bottom).
The presence of a pair of quasidegenerate filled MOs as
HOMO, falling almost in the middle of a wide gap, is also
displayed by the Ni-centred [Ni11(µ6-E)2(CO)18]4– (E = Sb,
EHMO Calculations and Redox Behaviour of [Ni12(µ12-
Ga)(CO)22]3–
According to the EHMO (extended Hückel molecular Bi)[15,16] and [Ni13(µ7-Sb)2(CO)24]4– multivalent clus-
orbital) method, the frontier region of [Ni12(µ12-Ga)- ters.[17,18] Both display two reversible oxidations and the re-
(CO)22]3– (see Figure 5) displays a pair of quasi degenerate sulting tri- and dianions are even more easily workable than
filled molecular orbitals as HOMO, which fall almost in the the corresponding tetraanions.
middle of a wide gap of ca. 1.6 eV between the LUMO and
In spite of the similarities between the EHMO diagrams
the third HOMO. The stabilization of the above two MOs of E-centred [Ni12(µ12-Ga)(CO)22]3– and Ni-centred
is due to the bonding character of the interaction between [Ni11(µ6-E)2(CO)18]4– (E = Sb, Bi),[15,16] the cyclic voltam-
the px and py atomic orbitals (AOs) of Ga with one or a metry of the former species only discloses irreversible redox
pair of contiguous Ni atoms belonging to the two pentago- changes. In particular, at the highest scan rate (1 Vs–1), it
nal faces of the inner antiprism (see bottom part of Fig- shows two well-defined oxidation steps at +0.75 and
ure 5). All other Ni–Ga and Ni–Ni contributions are either +1.26 V (vs. SCE), accompanied in the back scan by ill-
weakly bonding or nonbonding, whereas the C–O interac- reproducible and less-intense reduction signals at ca. +1.0
tions are mainly antibonding. In particular, the interaction and +0.4 V. Upon a decrease in the scan rate to 0.1 and
of the apical Ni atoms (Ni2 and Ni6 of Figure 2) with Ga 0.01 Vs–1 the back waves become almost unnoticeable.
Eur. J. Inorg. Chem. 2010, 1056–1062
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C. Femoni, M. C. Iapalucci, G. Longoni, S. Zacchini
FULL PAPER
trumOne interferometer in CaF2 cells. 1H NMR spectra were re-
corded with a Varian Mercury 400 MHz spectrometer, and refer-
enced to internal TMS. The structure figures were drawn with
Concluding Remarks
The calculated average radius of the interstitial Ga atoms
in the title icosahedral compounds is comprised in the nar- SCHAKAL99.[21] EHMO calculations have been carried out with
CACAO.[14]
row 1.20–1.21 Å range of values, which is very close to the
accepted covalent radius of Ga (1.22 Å)[19] and corresponds
[NnBu4]3[Ni14.3Ga(CO)24.3]:
A
solution of GaCl3 (0.37 g,
to ca. 91% of the radii of the surrounding Ni atoms. There-
fore, both steric and electronic (viz. the above EHMO dia-
gram) factors seemed favourable but turned out to be not
sufficient to grant multivalence, as well as stability in a dif-
2.10 mmol) in dichloromethane (20 mL) was added in portions to
[NnBu4]2[Ni6(CO)12] (1.85 g, 1.58 mmol) dissolved in dichlorome-
thame (50 mL) with stirring. The mixture was left to react for 24 h,
until IR monitoring showed disappearance of [Ni6(CO)12]2– from
ferent ligand shell, to the [Ni12(µ12-Ga)(CO)22]3– icosahe- solution. The resulting dark-brown suspension was evaporated to
dral cluster, as it instead occurs for [Ni11(µ6-E)2(CO)18]4– (E
dryness and washed with water (3ϫ15 mL) and isopropyl alcohol
= Sb, Bi) and [Rh12(µ12-Sn)(CO)25]4–.
(2ϫ20 mL). The residual brown material was extracted in dichlo-
romethane (20 mL) and Ni(CO)4 (0.2 mL) was added. Precipitation
The difference between Ni-centred and E-centred Ni
by slow diffusion of isopropyl alcohol (60 mL) gave dark-brown
clusters is particularly striking. In spite of their different
crystals of [NnBu4]3[Ni14.3Ga(CO)24.3]·2CH2Cl2 (yield 0.654 g,
compositions, the two architectures feature identical num-
bers of Ni–Ni (30, dotted bonds in Figure 6) and Ni–E (12,
blackened bonds) interactions and similar EHMO dia-
grams. The only noticeable difference between the two
architectures in EHMO calculations is represented by a sig-
39.7% based on Ni). The salt is soluble in CH2Cl2, THF, acetone,
acetonitrile, DMF and DMSO, sparingly soluble in alcohols and
insoluble in nonpolar solvents. IR (CH Cl ): ν = 2009 (s), 1879
˜
CO
2
2
(m, br.), 1822 (sh.) cm–1. [NnBu4]3[Ni14.3Ga(CO)24.3]·2CH2Cl2:
calcd. Ni 33.76, C 35.89, H 4.51, N 1.69; found Ni 33.89, C 35.71,
nificant increase in the average overlap population (OP) of H 4.46, N 1.71.
Ni–E bonds, on going from group 13 or 14 (OP ca. 0.2) to
[NnBu4]3[Ni12Ga(CO)22]: Solid [NnBu4]3[Ni14.3Ga(CO)24.3] (0.521 g,
group 15 (OP ca. 0.3) elements. Besides, in all cases, the
umbrella sticks of geometry A in Figure 6 show ca. 45% of
the rib’s OP, whereas the opposite trend is observed in B.
0.21 mmol) was dissolved in dichloromethane (30 mL) in a 200-mL
flask and stirred under a static carbon monoxide atmosphere. The
initial dark red-brown colour of the solution slowly turned green-
brown. The resulting solution was evaporated to dryness to elimin-
ate Ni(CO)4, and the residue was dissolved in dichloromethane
(15 mL). Precipitation by diffusion of isopropyl alcohol (30 mL)
gave [NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2 within a few days as brown
crystals (0.39 g, 68.2% based on Ni). The salt is soluble in CH2Cl2,
THF, acetone, acetonitrile, DMF and DMSO, sparingly soluble or
insoluble in alcohols and insoluble in nonpolar solvents. IR
(CH Cl ): ν
= 1999 (s), 1790 (m) cm–1. [NnBu4]3[Ni12Ga-
˜
CO
2
2
(CO)22]·2CH2Cl2: calcd. Ni 30.78, C 37.80, H 4.89, N 1.84; found
Ni 30.91, C 37.73, H 4.72, N 1.82.
Figure 6. Schematic structure of [Ni12(µ12-E)(CO)22]n– and [Ni11(µ6-
E)2(CO)18]n– (E as black spheres), pointing out the Ni–E bonds
acting as sticks and ribs of the two differently oriented (head–head
in A and tail–tail in B) Ni6(µ6-E) umbrella.
[NnBu4]2[HNi12Ga(CO)22]: Solid [NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2
(0.32 g, 0.14 mmol) was dissolved in THF and treated dropwise
whilst stirring with a solution of dilute acid (1 mL of 20% H2SO4
in 5 mL of THF) monitoring the reaction by IR spectroscopy. The
Such a trend formally explains the greater reactivity of resulting brown solution was evaporated under vacuum. The pre-
[Ni12(µ12-E)(CO)22]n– species under a CO atmosphere in
cipitate was washed several times with water and dried. The residue
was extracted in acetone (10 mL) and precipitated by diffusion of
comparison with [Ni11(µ6-E)2(CO)18]n–. In particular,
[Ni12(µ12-Ge)(CO)22]2– is quantitatively degraded by CO at
isopropyl alcohol (20 mL) to obtain black crystals of [NnBu4]2-
[HNi12Ga(CO)22] (0.28 g). The salt is soluble in CH2Cl2, THF, ace-
atmospheric pressure to
a pentagonal antiprismatic
tone, acetonitrile, DMF and DMSO and insoluble in nonpolar sol-
[Ni10(µ10-Ge)(CO)20]2–.[6] It may therefore be speculated
that the trend of Ni–E OP and the opposite orientation of
their umbrella concur in tightening geometry B and explain
the different stability of the above geometries also upon a
redox change.
vents. The compound is deprotonated to [Ni12Ga(CO)22]3– both in
1
DMF and DMSO. H NMR ([D6]acetone, 293 K): δ = –13.5 ppm.
IR (acetone): ν
= 2025 (s), 1826 (m) cm–1. [NnBu4][HNi12-
˜
CO
Ga(CO)22]: calcd. Ni 37.53, C 34.56, H 3.89, N 1.49; found Ni
37.46, C 34.49, H 3.91, N 1.47.
X-ray Crystallographic Studies: Crystal data and collection details
for [NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2, [NnBu4]2[HNi12Ga(CO)22]
and [NnBu4]3[Ni14.3Ga(CO)24.3]·2CH2Cl2 are reported in Table 2.
The diffraction experiments were carried out with a Bruker APEX
II diffractometer equipped with a CCD detector by using Mo-Kα
radiation. Data were corrected for Lorentz polarization and ab-
sorption effects (empirical absorption correction SADABS).[22]
Structures were solved by direct methods and refined by full-matrix
least-squares based on all data using F2.[23] Hydrogen atoms were
fixed at calculated positions and refined by a riding model. All
Experimental Section
General: All reactions and sample manipulations were carried out
by using standard Schlenk techniques under a nitrogen atmosphere
and in dried solvents. The [Ni6(CO)12]2– salts were prepared accord-
ing to literature methods.[20] Analysis of Ni were performed by
atomic absorption on a Pye-Unicam instrument. Analyses of C,
H and N were obtained with a ThermoQuest FlashEA 1112NC
instrument. IR spectra were recorded with a Perkin–Elmer Spec-
1060
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1056–1062

Icosahedral Ga-Centred Nickel Carbonyl Clusters
Table 2. Crystal data and experimental details for [NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2, [NnBu4]2[HNi12Ga(CO)22] and [NnBu4]3[Ni14.3
Ga(CO)24.3]·2CH2Cl2.
-
[NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2
[NnBu4]2[HNi12Ga(CO)22]
[NnBu4]3[Ni14.3Ga(CO)24.3]·2CH2Cl2
Formula
Fw
T [K]
C72H112Cl4GaN3Ni12O22
2287.69
100(2)
C54H72GaN2Ni12O22
1875.38
296(2)
C74.29H112Cl4GaN3Ni14.29O24.29
2486.06
100(2)
λ [Å]
0.71073
monoclinic
P21/n
18.6475(15)
21.3024(18)
23.3035(19)
90
99.8230(10)
90
9121.3(13)
4
1.666
2.887
4704
0.71073
0.71073
monoclinic
P21/n
13.3235(14)
33.238(4)
21.338(2)
90
93.022(2)
90
9436.3(17)
4
1.750
3.238
5088
Crystal system
Space group
a [Å]
b [Å]
c [Å]
triclinic
¯
P1
11.241(2)
13.908(3)
14.287(3)
61.497(2)
68.815(2)
68.798(2)
1780.8(6)
1
α [°]
β [°]
γ [°]
Cell Volume [Å3]
Z
Dcalcd. [gcm–3]
µ [mm–1]
F(000)
1.749
3.530
953
Crystal size [mm]
θ limits [°]
Index ranges
0.21ϫ0.14ϫ0.11
1.46–26.00
–23 Յ h Յ 23
–26 Յ k Յ 26
–28 Յ l Յ 28
92429
17895 [Rint = 0.0555]
99.9
17895/440/1055
1.086
0.15ϫ0.10ϫ0.08
1.67–25.00
–13 Յ h Յ 13
–16 Յ k Յ 16
–16 Յ l Յ 16
17002
6251 [Rint = 0.0952]
99.7
6251/174/412
0.968
0.22ϫ0.14ϫ0.11
1.55–27.00
–17 Յ h Յ 17
–42 Յ k Յ 42
–27 Յ l Յ 27
103831
20591 [Rint = 0.0725]
100.0
20591/365/1191
1.030
Reflections collected
Independent reflections
Completeness to θ = 25.03°
Data/restraints/parameters
Goodness on fit on F2
R1 [IϾ2σ(I)]
0.0368
0.0714
0.0365
wR2 (all data)
0.1064
0.957/–0.783
0.2100
1.240/–0.479
0.0852
0.987/–0.752
Largest diff. peak/hole [eÅ–3]
non-hydrogen atoms were refined with anisotropic displacement
parameters, unless otherwise stated.
0.01): 1.47 Å for C–N and 1.53 Å in [NnBu4]+; 1.75 Å for C–Cl in
CH2Cl2.
CCDC-741742 (for [NnBu4]2[HNi12Ga(CO)22]), -741743 (for
[NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2) and -741744 (for [NnBu4]3-
[Ni14.3Ga(CO)24.3]·2CH2Cl2) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[NnBu4]3[Ni12Ga(CO)22]·2CH2Cl2: The asymmetric unit contains
one cluster anion, three [NnBu4]+ cations and two CH2Cl2 molec-
ules all located in general positions. One of the two CH2Cl2 molec-
ules appears to be disordered; its atoms have been split into two
positions and refined isotropically with one independent occupancy
factor. Similar U restraints were applied to the C (s.u. 0.003), O
and Cl (s.u. 0.005) atoms. Restraints to bond lengths were applied
as follow (s.u. 0.01): 1.47 Å for C–N and 1.53 Å in [NnBu4]+;
1.75 Å for C–Cl in CH2Cl2.
Acknowledgments
We wish to thank the University of Bologna (CLUSTERCAT) and
Ministero dell’Università e della Ricerca (PRIN) for financial as-
sistance.
[NnBu4]2[HNi12Ga(CO)22]: The asymmetric unit contains one half
of the cluster anion and one [NnBu4]+ cation; the rest of the unit
cell can be generated thanks to the centre of symmetry, located on
the Ga atom. Similar U restraints were applied to the CO ligands
and the cation (s.u. 0.01). Distance restraints of 1.54 Å (s.u. 0.02)
were also applied to C–C bonds in the latter.
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1061

C. Femoni, M. C. Iapalucci, G. Longoni, S. Zacchini
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Received: September 11, 2009
Published Online: January 19, 2010
1062
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Eur. J. Inorg. Chem. 2010, 1056–1062