Intramolecular d10-d10 interactions in a Ni 6C(CO)9(AuPPh3)4 bimetallic nickel-gold carbide carbonyl cluster

Article abstract of DOI:10.1021/ic401540s

The Ni₆C(CO)₉(AuPPh₃)₄ bimetallic carbide carbonyl cluster was obtained from the reaction of [Ni ₉C(CO)₁₇]^2- with Au(PPh₃)Cl. It contains a rare carbon-centered (distorted) Ni₆C octahedral core decorated by four Au(PPh₃) fragments. These are μ₃- bonded to four contiguous Ni₃-triangular faces and display weak intramolecular Au···Au d¹⁰-d¹⁰ interactions. The cluster has been characterized in the solid state on two different solvato crystals, i.e., Ni₆C(CO)₉(AuPPh ₃)₄·THF and Ni₆C(CO) ₉(AuPPh₃)₄·THF·0.5C ₆H₁₄. The two solvates show some interesting differences concerning the weak Au···Au contacts. Density functional theory calculations have demonstrated that the presence of the two isomers is related to solid-state packing effects and not to the existence of two double minima in the potential energy surface. This, in turn, confirms that Au···Au d¹⁰-d¹⁰ interactions are rather soft and thus influenced also by weak van der Waals forces because of the interaction of the cluster with the cocrystallized solvent molecules.

Full text of DOI:10.1021/ic401540s

Article
pubs.acs.org/IC
Intramolecular d10−d10 Interactions in a Ni6C(CO)9(AuPPh3)4
Bimetallic Nickel−Gold Carbide Carbonyl Cluster
Iacopo Ciabatti,† Cristina Femoni,† Maria Carmela Iapalucci,† Andrea Ienco,‡ Giuliano Longoni,†
Gabriele Manca,‡ and Stefano Zacchini*,†
†Dipartimento di Chimica Industriale “Toso Montanari”, Universita
̀
di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
‡Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organo Metallici, Via Madonna del Piano 10, 50019 Sesto
Fiorentino, Florence, Italy
S
* Supporting Information
ABSTRACT: The Ni6C(CO)9(AuPPh3)4 bimetallic carbide carbon-
yl cluster was obtained from the reaction of [Ni9C(CO)17]2− with
Au(PPh3)Cl. It contains a rare carbon-centered (distorted) Ni6C
octahedral core decorated by four Au(PPh3) fragments. These are μ3-
bonded to four contiguous Ni3-triangular faces and display weak
intramolecular Au···Au d10−d10 interactions. The cluster has been
characterized in the solid state on two different solvato crystals, i.e.,
Ni6C(CO)9(AuPPh3)4·THF and Ni6C(CO)9(AuPPh3)4·THF·
0.5C6H14. The two solvates show some interesting differences
concerning the weak Au···Au contacts. Density functional theory calculations have demonstrated that the presence of the two
isomers is related to solid-state packing effects and not to the existence of two double minima in the potential energy surface.
This, in turn, confirms that Au···Au d10−d10 interactions are rather soft and thus influenced also by weak van der Waals forces
because of the interaction of the cluster with the cocrystallized solvent molecules.
The M6C octahedral framework present in several
monocarbide carbonyl clusters seems to be an interesting
platform to test aurophilicity.11−15 In these clusters, the
[AuPPh3]+ fragment might be coordinated to an edge or a
face of the octahedron. Moreover, when a second fragment is
added, several options arise because it can coordinate to a site
close or far from the first one. Aurophilicity favors the
proximity of the two AuI centers and the formation of
intramolecular d10−d10 interactions, as exemplified in Rh6C-
(CO)13(AuPPh3)2 and Co6C(CO)13(AuPPh3)2.16,17
It was, thus, of interest to investigate analogous octahedral
M6C carbonyl clusters containing more than two [AuPPh3]+
fragments, in order to see whether more extended Au···Au
interactions were formed and to evaluate the importance of
such interactions in larger clusters. Herein, we report the
synthesis and structural characterization of the neutral Ni6C-
(CO)9(AuPPh3)4 cluster, which contains four of these
fragments. Its structure has been determined on two different
solvate crystals, i.e., Ni6C(CO)9(AuPPh3)4·THF and Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14 (THF = tetrahydrofuran),
showing some interesting differences regarding the weak Au···
Au contacts. Density functional theory (DFT) calculations have
been performed in order to establish whether the presence of
two isomers is related to solid-state packing effects or the
existence of two double minima in the potential energy surface.
In addition, Ni6C(CO)9(AuPPh3)4 represents the first example
1. INTRODUCTION
Weak d10−d10 metal−metal interactions are now widely
documented in the chemistry of gold(I) complexes and
clusters, and the term “aurophilicity” is commonly used to
refer to such interactions.1−4 Although positively charged AuI
ions could be expected to repel each other on the basis of
electrostatics, the attractive interactions between these closed-
valence-shell ions result in interatomic distances typically in the
range between 2.7 and 3.3 Å, often shorter than the sum of the
van der Waals radii.1−4 This phenomenon could not be
explained by conventional descriptions of chemical bonding but
is now well described as dispersion-driven and enhanced by
relativistic effects.1−5 However, the conditions for the
occurrence of aurophilicity and its structural, physical, and
chemical consequences remain difficult to predict; hence,
further experimental and theoretical studies on d10−d10
interactions are needed, whether in homo- or in heterometallic
systems.1−6
Some interesting examples of aurophilic interactions are
documented also for metal carbonyl clusters containing two or
more [AuPPh3]+ fragments.3b,7 On the basis of the isolobal
analogy between [AuPPh3]+ and H+,8,9 the former has been
widely employed in metal carbonyl cluster chemistry in order to
get structural information on the location of hydrides.
Nonetheless, the occurrence of aurophilic interactions often
invalidates these considerations when two or more AuI ions are
present. For instance, intramolecular AuI···AuI interactions
cause structural differences between Fe3S(CO)9(AuPPh3)2 and
H2Fe3S(CO)9.10
Received: June 18, 2013
Published: September 5, 2013
© 2013 American Chemical Society
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of an octahedral monocarbidonickel carbonyl cluster. Thus, the
octahedral M6C framework is very common for carbonyl
clusters of group 8 and 9 metals, whereas up to now, it was
completely unknown for carbonyls of group 10 metals.11−15
2. RESULTS AND DISCUSSION
2.1. Synthesis of Ni6C(CO)9(AuPPh3)4. The neutral cluster
Ni6C(CO)9(AuPPh3)4 was obtained in low yield from the
reaction of [Ni9C(CO)17]2−18 with Au(PPh3)Cl (ca. 2 equiv)
in THF. The formation of Ni6C(CO)9(AuPPh3)4 is accom-
panied by several byproducts, such as Ni(CO)4, Ni2+,
Ni(CO)3(PPh3), [Ni8C(CO)16]2−, gold metal, and unreacted
[Ni9C(CO)17]2−. All of the carbonyl byproducts [i.e., Ni(CO)4,
Ni(CO)3(PPh3), [Ni8C(CO)16]2−, [Ni9C(CO)17]2−] have been
identified through IR spectroscopy by comparison with the
spectra reported in the literature. The presence of Ni2+ salts was
confirmed by the typical green color of the water solution used
to wash the residue (see below) and confirmed using
dimethylglyoxime. The formation of gold metal was confirmed
by the typical gold mirror.
Purification was accomplished by removal of the solvent in
vacuo and washing of the residue with water (to remove NiII
salts) and toluene (to remove neutral mononuclear species).
The residue was then extracted in THF and recrystallized from
THF/toluene and THF/n-hexane, resulting in X-ray-quality
crystals of Ni6C(CO)9(AuPPh3)4·THF and Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14, respectively. Under these
conditions, anionic species such as [Ni8C(CO)16]2− and
[Ni9C(CO)17]2− preferentially remained in solution or
precipitated as amorphous solids. Crystals for X-ray analyses
were, therefore, mechanically separated from the amorphous
material before proceeding further with analysis. The crystals
show ν(CO) in a Nujol mull at 2027(ms), 1984(vs), 1970(s),
1851(m), and 1832(ms) cm−1. These crystals are almost
insoluble in all organic solvents, hampering any further
chemical, spectroscopic, or physical study.
Figure 1. Molecular structure of Ni6C(CO)9(AuPPh3)4 as found in
Ni6C(CO)9(AuPPh3)4·THF (a) and Ni6C(CO)9(AuPPh3)4·THF·
0.5C6H14 (b). Color code: green, Ni; yellow, Au; orange, P; gray, C;
white, H.
2.2. Crystal Structures of Ni6C(CO)9(AuPPh3)4·THF and
Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. The structure of the
neutral cluster Ni6C(CO)9(AuPPh3)4 has been determined on
two different solvato solids, i.e., Ni6C(CO)9(AuPPh3)4·THF
and Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. The cluster displays
a similar structure in both solvates, even if there are some
differences especially regarding the weak Au···Au contacts. The
molecular structure of the cluster, as found in the two solvates,
is represented in Figure 1, whereas the most relevant bond
lengths are compared in Table 1.
Table 1. Comparison of the Most Relevant Bond Lengths
(Å) in Ni6C(CO)9(AuPPh3)4·THF and
Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14
Ni6C(CO)9(AuPPh3)4·THF·
Ni6C(CO)9(AuPPh3)4·THF
0.5C6H14
Ni−Ni
2.3891(12)−2.8687(12)
average 2.678(4)
2.3847(18)−2.9875(18)
average 2.682(6)
Ni−
1.811(6)−1.931(6)
1.816(9)−1.920(9)
a
Ccarbide
The Ni6C(CO)9(AuPPh3)4 cluster contains a carbon-
centered distorted Ni6C octahedral core (Figure 2). The four
Au(PPh3) fragments are μ3-bonded to four contiguous
triangular faces (related by 4-fold) of the octahedron, formally
reducing the symmetry from Oh to C4v. Actually, the cluster
displays C1 symmetry in view of its heavy distortions. For what
concerns the nine CO ligands, six are terminally coordinated
one per each Ni atom, whereas the remaining three carbonyls
are edge bridging, one in the equatorial plane of the cluster and
the other two on two edges spanning from the equatorial plane
toward the apical Ni atom nonbonded to any Au atom.
The four Ni atoms in the equatorial plane of the cluster as
well as the carbide atom are almost coplanar [mean deviation
from the least-squares plane 0.0551 and 0.0466 Å for the two
solvates, respectively], whereas the other two Ni atoms are in
apical positions [Niap−C−Niap 163.6(4) and 159.7(6)°], one
bonded to four Au atoms and the other to none. The cluster
average 1.893(16)
2.5625(8)−2.9323(9)
average 2.696(3)
average 1.89(2)
Ni−Au
Au−P
2.5738(12)−2.8615(14)
average 2.702(5)
2.287(3)-2.298(3)
average 2.294(6)
2.2836(19)-2.2914(19)
average 2.289(4)
b
Au···Au
3.5922(5), 3.0509(5),
4.2721(5), 3.6648(5)
3.1701(7), 2.9889(7),
4.3230(7), 4.0611(7)
average 3.6450(10)
average 3.6358(14)
a
b
Ccarbide refers to the interstitial carbide atom. All contacts (bonding
and nonbonding) have been considered.
may be partitioned into an anionic [Ni6C(CO)9]4− moiety
decorated by four cationic [AuPPh3]+ units.
The Ni−Ni contacts are rather spread [2.3891(12)−
2.8687(12) Å, average 2.678(4) Å for Ni6C(CO)9(AuPPh3)4·
THF; 2.3847(18)−2.9875(18) Å, average 2.682(6) Å for
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Ni−Ccarbide contacts in Ni6C(CO)9(AuPPh3)4 [1.811(6)−
1.931(6) Å, average 1.893(16) Å, and 1.816(9)−1.920(9) Å,
average 1.89(2) Å, for the two solvates, respectively] compare
very well to the octahedral cages of [Ni36C8(CO)36(Cd2Cl3)]5−
and [Ni36−yC8(CO)34−y(MeCN)3(Cd2Cl3)]3− [1.874(8)−
1.956(8) Å, average 1.90 Å, and 1.865(7)−2.003(8) Å, average
1.90 Å, respectively], whereas the Ni−Ccarbide contacts in
19
Ni6C(Cp)6 are more scattered [1.767(4)−2.109(4) Å,
average 1.897(9) Å].
Each Au atom is tetracoordinated to a Ni3 face of the
octahedron and a PPh3 ligand. The Ni−Au contacts
[2.5625(8)−2.9323(9) Å, average 2.696(3) Å; 2.5738(12)−
2.8615(14) Å, average 2.702(5) Å] are rather spread but in
keeping with those previously reported for other nickel−gold
3 −
carbonyl clusters such as [Ni1 2 Au(CO)2 4
]
,
[Ni32Au6(CO)44]6−, and [Ni12Au6(CO)24]6−.22,23
Four Au···Au contacts are present in the cluster, displaying
similar average values in the two solvates [3.6450(10) and
3.6358(14) Å, respectively] but distributed in a rather different
manner (Figure 3). Thus, in Ni6C(CO)9(AuPPh3)4·THF, only
Figure 2. Ni6C(CO)9 core of Ni6C(CO)9(AuPPh3)4 as found in
Ni6C(CO)9(AuPPh3)4·THF (a) and Ni6C(CO)9(AuPPh3)4·THF·
0.5C6H14 (b). Color code: green, Ni; gray, C.
Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14] and may be divided
into three sets: (a) four Ni−Ni contacts in the equatorial plane
[2.3891(12)−2.8687(12) Å, average 2.682(2) Å; 2.3847(18)−
2.9875(18) Å, average 2.685(4) Å], (b) four Ni−Ni contacts
from the equatorial plane toward the apical Ni atom
nonbonded to any Au atom [2.4521(11)−2.8989(12) Å,
average 2.644(2) Å; 2.4616(18)−2.8492(17) Å, average
2.635(4)Å], and (c) four Ni−Ni contacts capped by the four
Au(PPh3) fragments [2.5830(12)−2.7918(11) Å, average
2.707(2) Å; 2.5371(17)−2.8817(17) Å, average 2.726(4) Å].
The resulting octahedral cages are very distorted, with the 12
Ni−Ni edges very different, in virtue of the fact that the
interstitial carbide atom is rather big to be accommodated in a
regular octahedron.
Figure 3. Ni6CAu4 core of Ni6C(CO)9(AuPPh3)4 as found in
Ni6C(CO)9(AuPPh3)4·THF (a) and Ni6C(CO)9(AuPPh3)4·THF·
0.5C6H14 (b).
Ni6C(CO)9(AuPPh3)4 represents a very rare case of a nickel
cluster containing a carbide atom within an octahedral cage and
the first case for monocarbidonickel carbonyl clusters. As far as
we are aware, the only monocarbide species displaying a
(heavily distorted) octahedrally coordinated carbide is the
cyclopentadienyl cluster Ni6C(Cp)6.19 Focusing our attention
on carbonyl clusters, all nickel monocarbides reported to date
displayed larger cages, such as trigonal-prismatic or square-
antiprismatic, i.e., [Ni7C(CO)12]2−, [Ni8C(CO)16]2−, [Ni9C-
(CO)17]2−, and [Ni10C(CO)18]2−.18,20 Only in the case of the
one contact may be considered at bonding distance [3.0509(5)
Å], whereas the other three contacts [3.5922(5), 3.6648(5),
and 4.2721(5) Å] are well above the sum of the van der Waals
radii of gold [sum of the covalent radii 2.72 Å; sum of the van
der Waals radii 3.32 Å].24 Conversely, in Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14, two contiguous Au···Au
contacts are at bonding distances [2.9889(7) and 3.1701(7)
Å], whereas the other two are nonbonding [4.0611(7) and
4.3230(7) Å].
Interestingly, the four Au atoms as well as the apical Ni atom
bonded to them lie in the same plane in Ni6C(CO)9(AuPPh3)4·
THF·0.5C6H14 [mean deviation from the least-squares plane
0.0219 Å], whereas they significantly deviate from the common
octacarbides [Ni36C8(CO)36(Cd2Cl3)]5− and [Ni36−yC8-
21
(CO)34−y(MeCN)3(Cd2Cl3)]3−
were four of the eight
carbide atoms contained within distorted octahedral cages,
whereas the other four carbides were located in two trigonal-
prismatic and two monocapped trigonal-prismatic cages. The
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plane in Ni6C(CO)9(AuPPh3)4·THF [mean deviation from the
least-squares plane 0.1059 Å]. Moreover, these planes form
rather different angles with the equatorial plane [the one
comprising the four equatorial Ni atoms and the carbide] in
Ni6C(CO)9(AuPPh3)4·THF [6.6°] compared to Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14 [11.0°].
state of this structure may be justified by assuming that packing
effects compensate for its minor stability as an isolated
molecule.
In the optimized structure, the Ni−Ni contacts spread over a
large range (2.39−3.04 Å), and they can be divided into three
different sets: the in-plane ones (2.42−3.04 Å), Niap−Nieq not
involved in interactions with Au centers (2.39−2.80 Å), and the
one in the gold-capping half (2.59−2.92 Å). The calculated
Ni−Ccarbide distances are 1.93 Å with the only exception of the
one between the apical Ni atoms, interacting with the Au atoms
(1.83 Å). Although there is some overestimation by the
calculations, likely imputed to the usage of a pseudopotential for
the metal atoms and a simplified model, the computed
structure satisfactorily reproduces the Ni6C core. Interestingly,
the four capping Au atoms and the apical Ni atom lie all in the
same plane as Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. The Au···
Au distances are in pairs: two short (3.14 Å) and two long
(4.22 Å), quite resembling the structure of Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14.
2.3. Theoretical Investigation. In order to better
understand the factors that rule such a dichotomy found in
the solid state, a theoretical investigation was performed at the
B3LYP-DFT/6-31+G(d,p) level of theory with the Stuttgart−
Dresden pseudopotential for both Au and Ni centers. Two
simplified models were built from the X-ray structures upon
substitution of the bulky PPh3 with the simpler PH3 and by
neglect of the cocrystallized solvent molecule. Single-point-
energy calculations on the structure models revealed that the
structure found in Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14 is
more stable by 4.95 kcal mol−1 than the one present in
Ni6C(CO)9(AuPPh3)4·THF. This difference in stability is
consistent either with a solid-state packing effect or with
weak Au−Au interactions. Optimization of both of these
models converged to the same structure with an angle Niap−
C−Niap of 159.5° and very similar to the one found in
Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14 (see Figure 4 and Table
The highest occupied molecular orbital (HOMO)−lowest
unoccupied molecular orbital (LUMO) gap was estimated to be
2.54 eV. The HOMO (Figure 5a) is calculated to be mainly
Figure 5. Graphical plots of the (a) HOMO and (b) LUMO orbitals
of Ni6C(CO)9(Au(PH3)4.
Figure 4. Optimized structure of Ni6C(CO)9(AuPPh3)4 at the B3LYP-
DFT level of theory.
localized on the Ni6 core; in contrast, the LUMO (Figure 5b)
has a strong contribution from the Au and apical Ni centers.
The main contributions to metal bonding come from the
interaction between fully occupied d orbital combinations of
the Ni atoms with the empty sp hybrids on the Au centers.
In principle, a functional with inclusion of the dispersion
forces as B97D could help to reproduce the two isomers in the
case that structural differences between the two experimental
2). This suggests that the more stable geometry is the one
found in Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14, with two short
and two long Au···Au distances. Conversely, the one present in
Ni6C(CO)9(AuPPh3)4·THF with a single short Au···Au contact
is less stable (by ca. 5 kcal mol−1). The presence in the solid
Table 2. Experimental and Calculated Bond Lengths (Å) and Angles (deg) of Ni6C(CO)9(AuPPh3)4
Ni6C(CO)9(AuPPh3)4·THF
Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14
calcd B3LYP-DFT/6-31+G(d,p)
Nieq−Nieq
2.3891(12)−2.8687(12)
2.4521(11)−2.8989(12)
2.5830(12)−2.7918(11)
1.880(6)−1.920(7)
1.931(6)
2.3847(18)−2.9875(18)
2.4616(18)−2.8492(17)
2.5371(17)−2.8817(17)
1.901(10)−1.919(9)
1.920(9)
2.42−3.04
2.39−2.80
2.59−2.92
1.93
Nieq−Niap (no-Au)
Nieq−Niap (Au)
Ccarbide−Nieq
Ccarbide−Niap (no Au)
Ccarbide−Niap (Au)
Ni−Au
1.93
1.811(6)
1.816(9)
1.83
2.5625(8)−2.9323(9)
2.2836(19)−2.2914(19)
3.5922(5)
2.5738(12)−2.8615(14)
2.287(3)−2.298(3)
3.1701(7)
2.60−2.87
2.38−2.40
3.14
Au−P
Au···Au
3.0509(5)
2.9889(7)
3.14
4.2721(5)
4.3230(7)
4.22
3.6648(5)
4.0611(7)
4.22
Niap−C−Niap
163.6(4)
159.7(6)
159.5
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structures are given by variable Au···Au interactions. As
occurred for the B3LYP functional, the calculations converged
into the same structure with quite short Au···Au distances
between 3.59 and 3.85 Å. Although there are some slight
differences in the obtained Ni−Ni distances, especially for those
involving the Ni atom bonded to Au atoms, the other main
features remain quite unaltered. The HOMO−LUMO gap
calculated with the B97D functional was 1.58 eV. Because also
inclusion of the dispersion corrections is not able to reproduce
the double minimum features of the potential energy surface,
such behavior could be reasonably imputed to solid-state
packing in the crystal because of weak interaction with the
cocrystallized solvent molecules.
The experimental IR spectrum in a Nujol mull displays five
main peaks at 2027, 1984, 1970, 1851, and 1832 cm−1,
respectively. Through frequency calculations, performed within
the Gaussian 09 package on the optimized geometries, we
attempted assignment of the different carbonyl stretchings
(Table 3). In fact, although slightly different in position (2114,
distribution of the four Au···Au contacts. DFT calculations
clearly point out that these deformations arise from packing
effects due to van der Waals interactions of the neutral clusters
with the cocrystallized solvent molecules. The fact that the Au
atoms are the ones more affected by these weak forces confirms
that Au···Au d10−d10 interactions are rather soft and, thus,
influenced also by weak forces. Finally, the present work
demonstrates that the M6C octahedral framework present in
some monocarbide carbonyl clusters may be an interesting
platform to test aurophilicity.
4. EXPERIMENTAL SECTION
4.1. General Procedures. All reactions and sample manipulations
were carried out using standard Schlenk techniques under nitrogen
and in dried solvents. All of the reagents are commercial products
(Aldrich) of the highest purity available and were used as received,
except [NEt4]2[Ni9C(CO)17]18 and Au(PPh3)Cl26, which have been
prepared according to the literature. Analyses of nickel and gold were
performed by atomic absorption on a Pye-Unicam instrument.
Analyses of carbon, hydrogen, and nitrogen were obtained with a
ThermoQuestFlashEA 1112NC instrument. IR spectra were recorded
on a Perkin-Elmer SpectrumOne interferometer in CaF2 cells.
Structure drawings have been performed with SCHAKAL99.27
4.2. Synthesis of Ni6C(CO)9(AuPPh3)4·THF. Au(PPh3)Cl (0.52 g,
1.04 mmol) was added in solid to a solution of [NEt4]2[Ni9C(CO)17]
(0.664 g, 0.520 mmol) in THF (30 mL) over a period of 2 h. The
resulting mixture was further stirred at room temperature for 6 h and
then the solvent removed in vacuo. The residue was washed with water
(40 mL) and toluene (40 mL), dried in vacuo, and extracted with THF
(20 mL). Crystals of Ni6C(CO)9(AuPPh3)4·THF suitable for X-ray
analysis were obtained after layering toluene (40 mL) on the THF
solution (yield 0.24 g, 12% based on nickel).
Anal. Calcd for C86H68Au4Ni6O10P4 (2525.41): C, 40.90; H, 2.71;
Au, 31.20; Ni, 13.94. Found: C, 40.71; H, 2.94; Au, 31.35; Ni, 14.09.
IR (Nujol, 293 K): ν(CO) 2027(ms), 1984(vs), 1970(s), 1851(m),
1832(ms) cm−1.
4.3. Synthesis of Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. Au(PPh3)
Cl (0.57 g, 1.15 mmol) was added in solid to a solution of
[NEt4]2[Ni9C(CO)17] (0.730 g, 0.572 mmol) in THF (30 mL) over a
period of 2 h. The resulting mixture was further stirred at room
temperature for 6 h and then the solvent removed in vacuo. The
residue was washed with water (40 mL) and toluene (40 mL), dried in
vacuo, and extracted with THF (20 mL). Crystals of Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14 suitable for X-ray analysis were
obtained after layering n-hexane (40 mL) on the THF solution
(yield 0.22 g, 10% based on nickel).
Table 3. Experimental and Calculated ν(CO) Stretchings
(cm−1) of Ni6C(CO)9(AuPPh3)4
assignment
multiplicity experimental (Nujol mull) calculated
t-CO Niap (no Au)
t-CO Nieq
1
4
1
1
2
2027(ms)
1984(vs)
1970(s)
2114
2062
2038
1972
1935
t-CO Niap (Au)
μ-CO Nieq
1851(m)
1832(ms)
μ-CO Niap
2062, 2038, 1972, and 1935 cm−1) and sometimes derived from
a complex vibrational pattern, they can be simply attributed to
the different carbonyl moieties. The first three peaks could be
assigned to the terminal CO: the high-energy one to CO
bonded to the apical Ni atom without interaction with the Au
centers, the second to the in-plane ones, and the last to the
remaining apical one. The calculated stretchings of the bridging
CO ligands occur at 1935 and 1970 cm−1 respectively for the
in-plane and out-of-plane carbonyl ligands.
3. CONCLUSIONS
A new bimetallic Ni6C(CO)9(AuPPh3)4 monocarbide cluster
has been synthesized and structurally characterized. It may be
viewed as composed of an octahedral [Ni6C(CO)9]4− core
capped by four [AuPPh3]+ fragments. It represents the first
example of an octahedral monocarbidonickel carbonyl cluster
because, due to steric effects, C atoms are usually lodged into
larger cavities in nickel monocarbide clusters, i.e., trigonal-
prismatic or square-antiprismatic.18,20 This results in heavy
distortion of the octahedral geometry, as was recently found in
the (heavy distorted) octahedral Ni6C(Cp)6cyclopentadienyl
monocarbide cluster.19
Anal. Calcd for C89H74Au4Ni6O10P4 (2567.49): C, 41.64; H, 2.91;
Au, 30.69; Ni, 13.72. Found: C, 41.51; H, 3.02; Au, 30.81; Ni, 13.64.
IR (Nujol, 293 K): ν(CO) 2027(ms), 1984(vs), 1970(s), 1851(m),
1832(ms) cm−1.
4.4. X-ray Crystallographic Study. Crystal data and collection
details for Ni6C(CO)9(AuPPh3)4·THF and Ni6C(CO)9(AuPPh3)4·
THF·0.5C6H14 are reported in Table 4. The diffraction experiments
were carried out on a Bruker APEX II diffractometer equipped with a
CCD detector using Mo Kα radiation. Data were corrected for
Lorentz polarization and absorption effects (empirical absorption
correction SADABS).28 Structures were solved by direct methods and
The [Ni6C(CO)9]4− core of Ni6C(CO)9(AuPPh3)4 pos-
sesses 86 cluster valence electrons (CVEs), as expected for an
octahedral cluster.25,26 Conversely, Ni6C(Cp)6 is considerably
electron-richer and displays 94 CVEs. This increase in CVEs
results in the opening of the octahedral cage of Ni6C(Cp)6 by
breaking two Ni−Ni edges.19 Conversely, in the case of
Ni6C(CO)9(AuPPh3)4, even if the Ni6C octahedron is rather
distorted, the 12 Ni−Ni contacts are all at bonding distances, in
keeping with its electron count.
refined by full-matrix least squares based on all data using F2.29
H
atoms were fixed at calculated positions and refined by a riding model.
All non-H atoms in the cluster molecules were refined with anisotropic
displacement parameters, whereas solvent molecules were treated
isotropically.
Ni6C(CO)9(AuPPh3)4·THF. The asymmetric unit of the unit cell
contains one cluster and one THF molecule (all located on general
positions). Similar U restraints (s.u. 0.01) were applied to the C and O
atoms. Two CO ligands in the cluster are disordered and, therefore,
they have been split into two positions each and refined with one
occupancy factor per disordered group. Restraints to bond distances
The structure of Ni6C(CO)9(AuPPh3)4 has been determined
in two different solvate salts, which mainly differ in the
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dx.doi.org/10.1021/ic401540s | Inorg. Chem. 2013, 52, 10559−10565

Inorganic Chemistry
Article
Table 4. Crystal Data and Experimental Details for
Ni6C(CO)9(AuPPh3)4·THF and Ni6C(CO)9(AuPPh3)4·THF·
0.5C6H14
AUTHOR INFORMATION
Corresponding Author
*E-mail: stefano.zacchini@unibo.it. Fax: +39 0512093690.
■
Notes
Ni6C(CO)9(AuPPh3)4·
Ni6C(CO)9(AuPPh3)4·
THF·0.5C6H14
THF
The authors declare no competing financial interest.
formula
fw
C86H68Au4Ni6O10P4
2525.41
C89H74Au4Ni6O10P4
2567.49
ACKNOWLEDGMENTS
Financial support of Universita
■
T, K
293(2)
295(2)
̀
di Bologna is gratefully
λ, Å
0.71073
0.71073
acknowledged. Funding by Fondazione CARIPLO (Project
2011-0289) is heartily acknowledged. A.I. and G.M. acknowl-
edge ISCRA-CINECA HP Grant HP10BNL89W for computa-
tional resources.
cryst syst
space group
a, Å
monoclinic
P21/n
monoclinic
P21/n
15.4746(9)
24.3295(14)
22.3941(13)
91.8920(10)
8426.5(8)
4
15.493(2)
22.922(4)
24.490(4)
90.978(2)
8696(2)
b, Å
c, Å
REFERENCES
■
β, deg
cell volume, Å3
(1) (a) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2012, 41, 370.
(b) Chen, Z. N.; Zhao, N.; Fan, Y.; Ni, J. Coord. Chem. Rev. 2009, 253,
1. (c) Laguna, A. Modern supramolecular gold chemistry: gold−metal
interactions and applications; Wiley-VCH: Weinheim, Germany, 2008.
Z
4
Dc, g cm−3
μ, mm−1
F(000)
1.991
1.961
8.374
8.117
(d) Pyykko, P. Chem. Rev. 1997, 97, 597.
̈
4832
4928
(2) (a) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2008, 37, 1932.
(b) Katz, M. J.; Sakaib, K.; Leznoff, D. B. Chem. Soc. Rev. 2008, 37,
1884. (c) Schmidbaur, H. Gold Bull. 2000, 33, 3. (d) Kim, P.-S. G.;
Hu, Y.; Brandys, M.-C.; Burchell, T. J.; Puddephatt, R. J.; Sham, T. K.
Inorg. Chem. 2007, 46, 949.
cryst size, mm3
θ limits, deg
index ranges
0.16 × 0.13 × 0.10
1.24−25.03
0.18 × 0.16 × 0.12
1.54−25.03
−18 ≤ h ≤ 18, −28 ≤ k ≤ −18 ≤ h ≤ 18, −27 ≤ k ≤
28, −26 ≤ l ≤ 26 27, −29 ≤ l ≤ 29
(3) (a) Voβ, C.; Pattacini, R.; Braunstein, P. C. R. Chim. 2012, 15,
229. (b) Zank, J.; Schier, A.; Schmidbaur, H. J. Chem. Soc., Dalton
Trans. 1998, 323. (c) Fackler, J. P. Inorg. Chem. 2002, 41, 6959.
(4) (a) Schmidbaur, H. Gold: Progress in Chemistry, Biochemistry and
Technology; Wiley: Chichester, U.K., 1999. (b) Scherbaum, F.;
reflns collected
indep reflns
80483 82307
14881 (Rint = 0.0542)
15347 (Rint = 0.0915)
completeness to
θmax, %
100.0
99.9
data/restraints/
param
GOF on F2
14881/574/1004
15347/514/990
Grohmann, A.; Huber, B.; Kruger, C.; Schmidbaur, H. Angew.
̈
1.007
1.005
Chem., Int. Ed. Engl. 1988, 27, 1544. (c) Schmidbaur, H. Chem. Soc.
Rev. 1995, 24, 391.
R1 [I > 2σ(I)]
wR2 (all data)
0.0340
0.0804
0.0451
(5) (a) Muniz, J.; Wang, C.; Pyykko, P. Chem.Eur. J. 2011, 17, 368.
̃
̈
0.1173
(b) Pyykko, P. Chem. Soc. Rev. 2008, 37, 1967. (c) Pyykko, P. Angew.
̈
̈
largest diff peak/ 1.103/−0.609
2.952/−1.324
hole, e Å−3
Chem., Int. Ed. 2004, 43, 4412. (d) Pyykko, P.; Li, J.; Runeberg, N.
̈
Chem. Phys. Lett. 1994, 218, 133.
(6) Sculfort, S.; Braunstein, P. Chem. Soc. Rev. 2011, 40, 2741.
(7) Braunstein, P., Oro, L. A., Raithby, P. R., Eds. Metal Clusters in
Chemistry; Wiley-VCH: New York, 1999.
were applied as follows (s.u. 0.02): 1.43 Å for C−O and 1.53 Å for C−
C in THF.
Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. The asymmetric unit of the unit
cell contains one cluster, one THF molecule (all located on general
positions), and half of a C6H14 molecule (on a 2 axis). The latter is
disordered over two symmetry-related positions and has been refined
isotropically with 0.5 occupancy factor. Similar U restraints (s.u. 0.005)
were applied to the C and O atoms. The O atoms of the CO ligands
have been restrained to isotropic behavior (ISOR line in SHELXL; s.u.
0.01). Restraints to bond distances were applied as follows (s.u. 0.02):
1.43 Å for C−O and 1.53 Å for C−C in THF; 1.53 Å for C−C in
C6H14.
4.5. Computational Details. The models were optimized at the
hybrid DFT using B3LYP30 and B97D31 functionals within the
Gaussian 09 program.32 For all of the fully optimized structures,
calculations of the vibrational frequencies were performed to confirm
their nature as stationary points. The effective Stuttgart−Dresden core
potential33 was adopted for the Au and Ni atoms, while for the
remaining atomic species, the basis set used was 6-31G, with the
important addition of the polarization functions (d and p) for all s,
including the H atoms. The coordinates of the optimized structure
have been reported in the Supporting Information.
(8) (a) Lauher, J. W.; Wald, K. J. Am. Chem. Soc. 1981, 103, 7648.
́
(b) Braunstein, P.; Rose, J.; Dusausoy, Y.; Mangeot, J.-P. C. R. Chim.
1982, 294, 967. (c) Li, X.; Kiran, B.; Wang, L.-S. J. Phys. Chem. A 2005,
109, 4366.
(9) (a) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711.
(b) Mingos, D. M. P. Gold Bull. 1984, 17, 5. (c) Braunstein, P.; Rose,
́
J.
Gold Bull. 1985, 18, 17.
(10) (a) van Hal, J. W.; Whitmire, K. H. Organometallics 1998, 17,
5197. (b) Roland, E.; Fischer, K.; Vahrenkamp, H. Angew. Chem., Int.
Ed. Engl. 1983, 22, 326. (c) Fischer, K.; Deck, W.; Schwarz, M.;
Vahrenkamp, H. Chem. Ber. 1985, 118, 4946. (d) Albano, V. G.;
Castellari, C.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Monari, M.;
Rauccio, M.; Zacchini, S. Inorg. Chim. Acta 1999, 291, 372.
(11) (a) Albano, V. G.; Braga, D.; Martinengo, S. J. Chem. Soc., Dalton
Trans. 1986, 981. (b) Albano, V. G.; Braga, D.; Martinengo, S. J. Chem.
Soc., Dalton Trans. 1981, 717. (c) Heaton, B. T.; Strona, L.;
Martinengo, S. J. Organomet. Chem. 1981, 215, 415. (d) Martinengo,
S.; Strumolo, D.; Chini, P.; Albano, V. G.; Braga, D. J. Chem. Soc.,
Dalton Trans. 1985, 35. (e) Albano, V. G.; Sansoni, M.; Chini, P.;
Martinengo, S. J. Chem. Soc., Dalton Trans. 1973, 651. (f) Albano, V.
G.; Chini, P.; Ciani, C.; Sansoni, M.; Martinengo, S. J. Chem. Soc.,
Dalton Trans. 1980, 163.
ASSOCIATED CONTENT
* Supporting Information
■
S
(12) (a) Adams, R.; Wu, W. J. Cluster Sci. 1991, 2, 271. (b) Saha, S.;
Zhu, L.; Captain, B. Inorg. Chem. 2010, 49, 3465. (c) Adams, R. D.;
Layland, R.; McBride, K. Organometallics 1996, 15, 5425. (d) Lange,
A.; Meier, W.; Wachter, J.; Zabel, M. Inorg. Chim. Acta 2006, 359,
1006. (e) Chihara, T.; Yamaaki, H. J. Organomet. Chem. 1994, 473,
273.
CIF files giving X-ray crystallographic data for the structure
determination of Ni6C(CO)9(AuPPh3)4·THF and Ni6C-
(CO)9(AuPPh3)4·THF·0.5C6H14 and Cartesian coordinates of
the optimized structure of Ni6C(CO)9(AuPH3)4. This material
is available free of charge via the Internet at http://pubs.acs.org.
10564
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Inorganic Chemistry
Article
(13) (a) Braga, D.; Grepioni, F.; Dyson, P. J.; Johnson, B. F. G.;
Frediani, P.; Bianchi, M.; Piacenti, F. J. Chem. Soc., Dalton Trans. 1992,
2565. (b) Khimyak, T.; Johnson, B. F. G.; Hermans, S.; Bond, A. D.
Dalton Trans. 2003, 2651. (c) Johnson, B. F. G.; Lewis, J.; Sankay, S.
W.; Wong, K.; McPartlin, M.; Nelson, W. J. H. J. Organomet. Chem.
1980, 191, 63. (d) Lewis, J.; Morewood, C. A.; Raithny, P. R.; Ramirez
de Arellano, M. C. J. Chem. Soc., Dalton Trans. 1997, 3335. (e) Dyson,
P. J.; Hearley, A. K.; Johnson, B. F. G.; Khimyak, T.; McIndoe, J. S.;
Langride-Smith, P. R. R. Organometallics 2001, 20, 3970. (f) Berin-
ghelli, T.; D’Alfonso, G.; Molinari, H.; Sironi, A. J. Chem. Soc., Dalton
Trans. 1992, 689.
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
revision B.01; Gaussian, Inc.: Wallingford, CT, 2010.
(33) Dolg, M.; Stoll, H.; Preuss, H.; Pitzer, R. M. J. Phys. Chem. 1993,
97, 5852.
(14) (a) Churchil, M. R.; Wormald, J. J. Chem. Soc., Dalton Trans.
1974, 2410. (b) Koshevoy, I. O.; Haukka, M.; Pakkanen, T. A.; Tunik,
S. Dalton Trans. 2006, 5641. (c) Slovokhotov, Yu. L.; Struchkov, Yu.
T.; Lopatin, V. E.; Gubin, S. P. J. Organomet. Chem. 1984, 266, 139.
(d) Nakajima, T.; Konomoto, H.; Ogawa, H.; Wakatsuki, Y. J.
Organomet. Chem. 2007, 692, 4886. (e) Tachikawa, M.; Sievert, A. C.;
Muetterties, E. L.; Thompson, M. R.; Day, C. S.; Day, V. W. J. Am.
Chem. Soc. 1980, 102, 1725.
(15) (a) Alami, M. K.; Dahan, F.; Mathieu, R. J. Chem. Soc., Dalton
Trans. 1987, 1983. (b) Hrijac, J. A.; Holt, E. M.; Shriver, D. F. Inorg.
Chem. 1987, 26, 2943. (c) Kamiguchi, S.; Chihara, T. J. Cluster Sci.
2000, 11, 483. (d) Jensen, M. P.; Henderson, W.; Johnston, D. H.;
Sabat, M.; Shriver, D. F. J. Organomet. Chem. 1990, 394, 121. (e) Hsu,
G.; Wilson, S. R.; Shapley, J. R. Inorg. Chem. 1991, 30, 3881.
(16) Fumagalli, A.; Martinengo, S.; Albano, V. G.; Braga, D.;
Grepioni, F. J. Chem. Soc., Dalton Trans. 1989, 2343.
(17) Reina, R.; Riba, O.; Rossell, O.; Seco, M.; de Montauzon, D.;
Pellinghelli, M. A.; Tiripicchio, A.; Font-Bardía, M.; Solans, X. J. Chem.
Soc., Dalton Trans. 2000, 4464.
(18) Ceriotti, A.; Longoni, G.; Manassero, M.; Perego, M.; Sansoni,
M. Inorg. Chem. 1985, 24, 117.
́
(19) Buchowicz, W.; Herbaczynska, B.; Jerzykiewicz, L. B.; Lis, T.;
Pasynkiewiicz, S.; Pietrzykowski, A. Inorg. Chem. 2012, 51, 8292.
(20) Ceriotti, A.; Piro, G.; Longoni, G.; Manassero, M.; Masciocchi,
N.; Sansoni, M. New J. Chem. 1988, 12, 501.
(21) Bernardi, A.; Femoni, C.; Iapalucci, M. C.; Longoni, G.;
Zacchini, S.; Fedi, S.; Zanello, P. Eur. J. Inorg. Chem. 2010, 4831.
(22) Ciabatti, I.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini,
S.; Fedi, S.; Fabrizi de Biani, F. Inorg. Chem. 2012, 51, 11753.
(23) (a) Whoolery, A. J.; Dahl, L. F. J. Am. Chem. Soc. 1991, 113,
6683. (b) Whoolery Johnson, A. J.; Spencer, B.; Dahl, L. F. Inorg.
Chim. Acta 1994, 227, 269.
(24) (a) Cordero, B.; Gom
Echevarría, J.; Cremades, E.; Barragan
2008, 2832. (b) Bondi, A. J. Phys. Chem. 1964, 68, 441.
́
ez, V.; Platero-Prats, A. E.; Reves
́
, M.;
́
, F.; Alvarez, S. Dalton Trans.
(25) Wade, K. J. Chem. Soc. D 1971, 792. (b) Wade, K. Adv. Inorg.
Chem. Radiochem. 1976, 18, 1.
(26) Kowala, C.; Swan, J. M. Aust. J. Chem. 1966, 19, 547.
(27) Keller, E. SCHAKAL99; University of Freiburg: Freiburg,
Germany, 1999.
(28) Sheldrick, G. M. SADABS, Program for empirical absorption
correction; University of Gottingen: Gottingen, Germany, 1996.
̈
̈
(29) Sheldrick, G. M. SHELX97, Program for crystal structure
determination; University of Gottingen: Gottingen, Germany, 1997.
̈
̈
(30) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(31) Grimme, S. J. Comput. Chem. 2006, 27, 1787.
(32) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.;Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.;
Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.;
Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.;Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand,
J.;Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
10565
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