Bimetallic nickel-cobalt hexacarbido carbonyl clusters [H 6-nNi22Co6C6(CO)36] n- (n = 3-6) possessing polyhydride nature and their base-induced degradation to the monoacetylide [Ni9CoC2(CO) 16- x]3- (x = 0, 1)

Article abstract of DOI:10.1021/om300412d

The reaction of [Ni₁₀C₂(CO)₁₆] ^2- with Co₃(μ₃-CCl)(CO)₉ results in the new bimetallic Ni-Co hexacarbido carbonyl clusters [H _6-nNi₂₂Co₆C₆(CO)₃₆] ^n- (n = 3-6), which possess polyhydride nature and can be interconverted by means of acid-base reactions. The tetra-anion [H ₂Ni₂₂Co₆C₆(CO)₃₆] ^4- and the hexa-anion [Ni₂₂Co₆C ₆(CO)₃₆]^6- have been isolated in a crystalline state and structurally characterized via X-ray crystallography. The six carbide atoms are lodged into Ni₇CoC square antiprismatic cages. Addition of strong bases to [Ni₂₂Co₆C₆(CO) ₃₆]^6- affords mixtures of the monoacetylides [Ni ₉CoC₂(CO)₁₆]^3- and [Ni ₉CoC₂(CO)₁₅]^3-, which have been cocrystallized as [NEt₄]₃[Ni₉CoC ₂(CO)_16-x] (x = 0.58-0.84) salts, displaying tightly bonded interstitial C₂ units.

Full text of DOI:10.1021/om300412d

Article
pubs.acs.org/Organometallics
Bimetallic Nickel−Cobalt Hexacarbido Carbonyl Clusters
[H6−nNi22Co6C6(CO)36]n− (n = 3−6) Possessing Polyhydride Nature and
Their Base-Induced Degradation to the Monoacetylide
[Ni9CoC2(CO)16−x]3− (x = 0, 1)
Iacopo Ciabatti, Cristina Femoni, Maria Carmela Iapalucci, Giuliano Longoni, and Stefano Zacchini*
̀
Dipartimento di Chimica Fisica e Inorganica, Universita di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
S
* Supporting Information
ABSTRACT: The reaction of [Ni10C2(CO)16]2− with Co3(μ3-CCl)(CO)9 results in the new
bimetallic Ni−Co hexacarbido carbonyl clusters [H6−nNi22Co6C6(CO)36]n− (n = 3−6), which
possess polyhydride nature and can be interconverted by means of acid−base reactions. The
tetra-anion [H2Ni22Co6C6(CO)36]4− and the hexa-anion [Ni22Co6C6(CO)36]6− have been
isolated in a crystalline state and structurally characterized via X-ray crystallography. The six
carbide atoms are lodged into Ni7CoC square antiprismatic cages. Addition of strong bases to
[Ni22Co6C6(CO)36]6− affords mixtures of the monoacetylides [Ni9CoC2(CO)16]3− and
[Ni9CoC2(CO)15]3−, which have been cocrystallized as [NEt4]3[Ni9CoC2(CO)16−x] (x =
0.58−0.84) salts, displaying tightly bonded interstitial C2 units.
isolation and structural characterization of the new hexacarbides
1. INTRODUCTION
[H6−nNi22Co6C6(CO)36]n− (n = 3−6), which represent more
than twice an increase of the maximum nuclearity of Co−Ni−C
clusters. Their reactions with strong bases, such as [NBu4]-
[OH], besides revealing the polyhydride nature of these
Several bimetallic Ni−Co carbide and acetylide carbonyl
clusters are known, i.e., [Co2Ni10C(CO)20]2−, [Co3Ni9C-
(CO)20]2−,1 [Co3Ni9C(CO)20]3−,2 [Co3Ni7C2(CO)15]3−,
[Co3Ni7C2(CO)16]n− (n = 2, 3),3 and [Co6Ni2C2(CO)16]2−.4
Their highest nuclearity is 12, and the Ni/Co ratio ranges from
0.33 to 5. The wide variability of the Ni/Co composition of
these clusters is due to the fact that both metals form
homometallic as well as carbido carbonyl clusters, and thus,
several carbonyl precursors are available for the synthesis of
bimetallic Ni−Co carbides via redox condensation.5
Bimetallic carbonyl clusters are useful precursors for the
preparation of metal nanoparticles with controlled composi-
tion.6−13 Thus, the possibility to prepare bimetallic Ni−Co
molecular clusters with very different Ni/Co compositions
makes these clusters quite attractive for the preparation of
bimetallic magnetic Ni−Co nanoparticles, allowing a gradual
variation of their properties. A fine control of the composition
of the resulting bimetallic nanoparticles might result in a better
understanding of the relationships existing between composi-
tion and properties of the nanoparticles.
In addition, bimetallic and heteronuclear clusters often
display rather different properties than the analogous
homometallic species and can more easily reach higher
nuclearities. This point makes bimetallic carbido carbonyl
clusters attractive also from a molecular point of view.14−18
Thus, we started a reinvestigation of Ni−Co carbide carbonyl
clusters, aiming at obtaining higher nuclearity species. Herein,
we report on the study of the reaction between
[Ni10C2(CO)16]2− and Co3(μ3-CCl)(CO)9 and the consequent
c l u s t e r s , a ff o r d e d t h e n e w m o n o a c e t y l i d e
3−
[Ni9CoC2(CO)16−x
[Ni10C2(CO)16]2−.
]
(x = 0, 1), structurally related to
2. RESULTS AND DISCUSSION
2.1. Synthesis of [H6−nNi22Co6C6(CO)36]n− (n = 3−6)
3−
and [Ni9CoC2(CO)16−x
]
(x = 0, 1). The slow addition of an
acetone solution of Co3(μ3-CCl)(CO)9 to [Ni10(C2)(CO)16]2−
dissolved in acetone results in the formation of a considerable
amount of Ni(CO)4 together with a new brown species, which
has been isolated after removal of the solvent in vacuo, washing
with water and toluene, and extraction of the residue in
CH3CN. In this solvent, the new brown cluster displays ν(CO)
at 2008(vs) and 1849(m) cm−1. After layering n-hexane and di-
isopropyl ether on the CH3CN solution, crystals suitable for X-
ray analysis of [NEt4]4[H2Ni22Co6C6(CO)36] were obtained.
The formation of [H2Ni22Co6C6(CO)36]4− is formally in
agreement with eq 1:
Received: May 15, 2012
Published: June 12, 2012
© 2012 American Chemical Society
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Scheme 1
3[Ni10C2(CO)16]2− + 2Co3(μ ‐CCl)(CO)9 + 2H2O
(E°′5−/6− = −0.961 V; E°′6−/7− = −1.293 V; E°′7−/8−
=
3
−1.666 V, in CH3CN). Therefore, the changes in ν(CO)
reported in Scheme 1 cannot be due to redox reactions.
Unfortunately, all attempts to directly confirm the hydride
→ [H2Ni22Co6C6(CO)36]4− + 2C + 2Cl− + +Ni2+
+ 2OH− + 7Ni(CO)4 + 2CO
1
(1)
nature of these clusters via H NMR failed. We have recently
discussed the problems of detecting hydrides in high-nuclearity
carbonyl clusters, showing that above a nuclearity of ca. 22 all
1H NMR resonances disappear since they become so broad as
to get blurred in the baseline of the spectrum.6,19−25 Thus, as
already reported, the hydride nature of large metal carbonyl
clusters can be only indirectly inferred from joined chemical
and electrochemical experiments.
The crystals of [NEt4]4[H2Ni22Co6C6(CO)36] are slightly
soluble in thf, where they display ν(CO) at 2023(vs) and
1859(m) cm−1, corresponding to the dihydride tetra-anion
[H2Ni22Co6C6(CO)36]4−. The same species is completely
soluble in acetone, where it displays ν(CO) at 2018(vs) and
1 8 5 7 ( m ) c m − 1
.
T h e d i h y d r i d e t e t r a - a n i o n
[H2Ni22Co6C6(CO)36]4− is deprotonated to the monohydride
penta-anion [HNi22Co6C6(CO)36]5− after dissolution in the
more basic CH3CN (Scheme 1), as shown by a significant
lowering of its IR carbonyl absorptions. Thus, the penta-anion
displays ν(CO) at 2008(vs) and 1849(m) cm−1 in CH3CN,
corresponding to the species observed in solution before
The nature of the [H6−nNi22Co6C6(CO)36]n− (n = 3−6)
anions has been confirmed also by means of ESI-MS analyses.
For example, crystals of [NEt4]4[H2Ni22Co6C6(CO)36] dis-
solved in CH3CN display ES− peaks (relative intensity in
parentheses) at m/z 889 (70), 880 (100), 870 (30), 862 (25),
and 850 (35) attributable to stepwise CO loss from the
molecular anion, i.e., [M − 2CO]3−, [M − 3CO]3−, [M −
4CO]3−, [M − 5CO]3−, and [M − 6CO]3−, respectively. A
further peak at 932 (25) is due to the adduct {[M −
2CO][NEt4]}3−. Since Ni and Co have very similar atomic
masses (i.e., 58.69 and 58.93 g mol−1), it is not possible to
completely support the metal composition of the cluster on the
basis only of ESI-MS analyses. Thus, we have analyzed different
crystals via EDS coupled to a scanning electron microscope
(SEM), resulting in a Ni/Co ratio of ca. 22/6.
c r y s t a l l i z a t i o n . F u r t h e r d e p r o t o n a t i o n o f
5−
[HNi2 2Co6 C6(CO)36
]
to yield the hexa-anion
[Ni22Co6C6(CO)36]6− occurs in CH3CN only upon addition
of solid Na2CO3. Its nature and charge have been confirmed
since it has been possible to isolate it as crystals of
[NMe4]6[Ni22Co6C6(CO)36]·4CH3CN by slow diffusion of n-
hexane and di-isopropyl ether on the basified solution. The
hexa-anion displays ν(CO) at 1996(vs) and 1844(m) cm−1 in
dmso and at 1988(vs) and 1824(m) cm−1 in Nujol mull.
Conversely, addition of strong acids such as HBF4 to an
acetone solution of the dihydride tetra-anion
[H2Ni22Co6C6(CO)36]4− results in the formation of the
trihydride trianion [H3Ni22Co6C6(CO)36]3−, which displays
ν(CO) at 2033(vs) and 1868(m) cm−1 in acetone.
The [H6−nNi22Co6C6(CO)36]n− (n = 3−6) anions are not
stable under CO atmosphere, being completely decomposed,
yielding Ni(CO)4 and [Co(CO)4]− as the only carbonyl
species detected in solution, in accordance with eq 2:
The hydride nature of the [H6−nNi22Co6C6(CO)36]n− (n =
3−6) anions is suggested by the observed shifts of their ν(CO)
bands as a function of the basicity of the solvent and/or after
addition of acids or bases to their solutions in accordance with
Scheme 1 and by the isolation of both the tetra- and hexa-
anion. Such a suggestion is further implemented by electro-
chemical studies, which clearly point out that
[H2Ni22Co6C6(CO)36]4− and [HNi22Co6C6(CO)36]5− display
different voltammetric profiles. If they were the same species in
a different oxidation state, they would have, conversely, shown
the same electrochemical behavior, as previously dis-
cussed.6,19−24 In particular, [H2Ni22Co6C6(CO)36]4− displays
two reduction processes with features of chemical reversibility
(E°′4−/5− = −0.533 V; E°′5−/6− = −0.833 V, in acetone),
whereas [HNi22Co6C6(CO)36]5− displays three reductions
[H6−nNi22Co6C6(CO)36]n− + 76CO
→ 22Ni(CO)4 + 6[Co(CO)4]− + 6C + (6 − n)H+
(2)
The hexa-anion [Ni22Co6C6(CO)36]6− reacts with excess
[NBu4 ][OH], yielding the new monoacetylide
3−
[Ni9CoC2(CO)16−x
]
(x = 0, 1). The fact that
[Ni22Co6C6(CO)36]6− is not further deprotonated can be
taken as an indirect proof of the number of hydride ligands in
[H6−nNi22Co6C6(CO)336−]n− (n = 3−6).
[Ni9CoC2(CO)16−x
]
(x = 0, 1) has been isolated in good
yields after removal of the solvent in vacuo, washing the residue
with water, thf, and acetone, and, then, extracting in CH3CN.
C r y s t a l s s u i t a b l e f o r X - r a y a n a l y s e s o f
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[NEt4]3[Ni9CoC2(CO)16−x] were obtained by slow diffusion of
n-hexane and di-isopropyl ether on the CH3CN solution. The
Ni/Co composition has been ascertained by EDS-SEM analyses
of different crystals, showing very similar results.
The fractionary index of [NEt4]3[Ni9CoC2(CO)16−x] is due
to the fact that, within the same crystals, mixtures of structurally
related [Ni9CoC2(CO)16]3− and [Ni9CoC2(CO)15]3− clusters
are present. Their ratio varies from batch to batch, probably
because, depending on the experimental conditions, a different
amount of CO may be lost during the synthesis. This has been
confirmed by analyzing several crystals obtained from different
batches. Four different CIF files are included with this paper
corresponding to crystals of [NEt4]3[Ni9CoC2(CO)16−x
]
obtained from three different reaction batches (a−c) and in
particular (a) x = 0.84 and x = 0.82 (two crystals from the same
batch a); (b) x = 0.58; and (c) 0.70. Crystals from the same
batch show the same composition, as expected from the
statistical crystallization of the [Ni9CoC2(CO)16]3− and
[Ni9CoC2(CO)15]3− mixtures present in solution. Conversely,
crystals from different batches display different compositions,
indicating that the two species are formed in different ratios
depending on slight variations of the experimental conditions.
[Ni9CoC2(CO)16]3− and [Ni9CoC2(CO)15]3− may be
formally interchanged by reaction 3:
[Ni9CoC2(CO)16]3− ⇄ [Ni9CoC2(CO)15]3− + CO
(3)
Nonetheless, [Ni9CoC2(CO)16]3− is stable under N2, and
even under vacuum eq 3 is not observed. Thus, the two
products are likely formed in parallel during the reaction of
[Ni22Co6C6(CO)336−]6− with [NBu4][OH]. Moreover,
Figure 1. Molecular structure (a) and the metal framework (b) of
[H6−nNi22Co6C6(CO)36]n− (n = 4, 6) (green, Ni; blue, Co; gray, C;
red, O).
[Ni9CoC2(CO)16−x
]
is decomposed under CO atmosphere,
resulting in the formation of Ni(CO)4 and [Co(CO)4]−.
The crystals of [NEt4]3[Ni9CoC2(CO)16−x] show ν(CO) at
2043(w), 2005(w), 1958(vs), 1920(m), 1832(ms), and
1772(m) cm−1 in Nujol mull. They are insoluble in thf, slightly
soluble in acetone [ν(CO) 1976(vs), 1942(sh), 1840(br)
cm−1] and completely soluble in CH3CN [ν(CO): 1979(vs),
1948(sh), 1874(ms), 1829(m) cm−1].
Table 1. Main Bond Distances (Å) for
[H6−nNi22Co6C6(CO)36]n− (n = 4, 6)
[H2Ni22Co6C6(CO)36]4−
[Ni22Co6C6(CO)36]6−
Ni−Ni
2.330(16)−3.2680(10)
2.337(3)−3.298(5)
average 2.613(8)
average 2.617(2)
a
Ni−Ni (interstitial)
Ni−Co
2.330(16)
2.337(3)
2.2. Crystal Structures of [NEt4]4[H2Ni22Co6C6(CO)36],
[ N M e 4 ] 6 [ N i 2 2 C o 6 C 6 ( C O ) 3 6 ] · 4 C H 3 C N , a n d
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58). The molecular
structures of the tetra-anion [H2Ni22Co6C6(CO)36]4− and the
hexa-anion [Ni22Co6C6(CO)36]6− have been determined
crystallographically on their [NEt4]4[H2Ni22Co6C6(CO)36]
and [NMe4]6[Ni22Co6C6(CO)36]·4CH3CN salts, respectively.
In both cases, only half of a cluster anion is present within the
asymmetric unit of the unit cell, the whole anions being
generated by an inversion center. The molecular structures of
the two cluster anions are almost identical (Figure 1 and Table
1) with respect to the geometry of the metal core, the
stereochemistry of the CO ligands, and all bonding distances.
The cluster comprises 28 metal atoms, and the relative
composition (22 Ni, 6 Co) has been independently confirmed
by elemental and EDS-SEM analyses. The assignment of the
positions to Ni and Co have been based on the fact that there
are six similar sites displaying the lowest M−M connectivity
and highest M−CO coordination, and these have been labeled
as the six Co atoms. Free refinement of all positions as
disordered Co/Ni confirmed the above assignment and
suggests that no site disorder is present, even if X-ray
crystallography is not the best way to distinguish between Ni
and Co.
2.4283(11)−2.6315(11)
2.398(3)−2.652(3)
average 2.524(4)
average 2.525(9)
Ni−C
Co−C
1.881(6)−2.328(6)
1.911(12)−2.368(13)
average 2.08(3)
average 2.09(5)
1.925(6)−1.968(6)
1.858(13)−1.910(14)
average 1.952(15)
average 1.892(19)
a
This refers to the two fully interstitial Ni atoms.
The metal core of the [H6−nNi22Co6C6(CO)36]n− (n = 4, 6)
clusters is rather complex and formally results from the
condensation of six Ni7CoC distorted square antiprismatic C-
centered cages. Two of these Ni7CoC polyhedra are so highly
distorted that the two Ni atoms along the diagonal on one of
the square faces are at bonding distance 3.03−3.05 Å, and
therefore, they may be alternatively described as two Ni5CoC
trigonal prisms capped by two further Ni atoms. In all cases,
each interstitial carbide atom is octa-coordinated, with rather
spread Ni−C contacts [range 1.881(6)−2.328(6) Å, average
2.08(3) Å for n = 4; range 1.911(12)−2.368(13) Å, average
2.09(5) Å for n = 6], whereas the Co−C distances are
distributed in a narrower range [range 1.925(6)−1.968(6) Å,
average 1.952(15) Å for n = 4; range 1.858(13)−1.910(14) Å,
average 1.892(19) Å for n = 6]. For comparison, the sum of the
covalent radii is 1.92 Å for Ni−C and 1.94 Å for Co−C.26
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The Ni22Co6 metal core of the cluster presents 83 M−M
contacts that can be considered within bonding distances: 59
Ni−Ni [range 2.330(16)−3.2680(10) Å, average 2.613(8) Å
for n = 4; range 2.337(3)−3.298(5) Å, average 2.617(2) Å for n
= 6] and 24 Co−Ni [range 2.4283(11)−2.6315(11) Å, average
2.524(4) Å for n = 4; range 2.398(3)−2.652(3) Å, average
2.525(9) Å for n = 6].
The average M−M connectivity is 5.93, resulting from very
different situations. Thus, the six Co atoms display the lowest
number of M−M bonds, i.e., 4, plus one Co−C(carbide) bond.
Conversely, there are two fully interstitial Ni atoms (non-
bonded to any CO) that display nine Ni−M bonding contacts
and four Ni−C(carbide) bonds. It must be remarked that these
two fully interstitial Ni atoms are tightly bonded together,
showing the shortest Ni−Ni contact [2.330(16) Å for n = 4;
2.337(3) Å for n = 6]. The remaining 20 Ni atoms display
intermediate situations. A M−M connectivity of nine is close to
that found in bulk close-packed metals (12) and similar to
body-centered cubic (8), suggesting (at least morphologically)
metalization of these two atoms. Conversely, the situation for
Co (4 M−M bonds) is similar to that found in lower nuclearity
molecular clusters (e.g., Co6(CO)16).27
Figure 2. Frontier region (in the −11 to −9 eV interval of energy) of
the EHMO diagram of [Ni22Co6C6(CO)36]6−.
The surface of the cluster is completed by 36 CO ligands, 16
terminal and 20 edge bridging. The CO/M ratio is 1.286,
which, by considering the two interstitial Ni atoms, corresponds
to a surface coverage CO/Msurface of 1.385. The six Co atoms
display the highest number of CO ligands, one terminal and
two edge bridging. This is a further (indirect) confirmation of
our assignment of these sites as Co. Moreover, the addition of a
further CO ligand formally results in the formation of
[Co(CO)4]−, suggesting a possible pathway for the CO-
induced decomposition of the cluster.
The [H6−nNi22Co6C6(CO)36]n− (n = 3−6) clusters possess
376 cluster valence electrons (CVE) corresponding to 188 (6N
+ 20; N = number of metal atoms) cluster valence orbitals
(CVO). This electron count is in keeping with other Ni
polycarbide clusters, which are usually electron rich, i.e.,
[Ni32C6(CO)36]6− and [Ni38C6(CO)42]6− (6N + 19 CVO),28
[Ni36C8(CO)36(Cd2Cl3)]5− (6N + 19 CVO), and
[Ni42C8(CO)44(CdCl)]7− (6N + 22 CVO).24
The electronic properties of [Ni22Co6C6(CO)36]6− have
been investigated by means of extended Huckel molecular
̈
orbital (EHMO) analysis, using the program CACAO29 with its
crystallographic coordinates. The frontier regions (in the −11
to −9 eV interval of energy) of the EHMO diagrams of
[Ni22Co6C6(CO)36]6− are represented in Figure 2.
The diagram shows the presence of four closely spaced
molecular orbitals (MOs 231−234) in an otherwise wide gap
(ΔMO(230−235) = 0.676 eV). The HOMO (MO 233)−
LUMO (MO 232) gap is, thus, very small (0.114 eV), and the
LUMO (MO 232) and LUMO+1 (MO 231) are almost
degenerate (0.048 eV). The small HOMO−LUMO gap and
the presence of a very low energy LUMO+1 explain the
propensity of these clusters toward reduction, as indicated by
electrochemical studies (see Section 2.1).
Figure 3. Molecular structure of (a) [Ni9CoC2(CO)16]3− and (b)
[Ni9CoC2(CO)15]3− (green, Ni; blue, Ni/Co; gray, C; red, O).
3−
Table 2. Main Bond Distances (Å) for [Ni9CoC2(CO)16−x
(x = 0, 1)
]
a
The molecular structure of the [Ni9CoC2(CO)16−x]
3− (x = 0,
M−M
M−C
2.3393(8)−2.8029(9)
1 ) t r i a n i o n h a s b e e n d e t e r m i n e d i n i t s
[NEt4]3[Ni9CoC2(CO)16−x] salt (Figure 3 and Table 2). As
described in the previous section, four crystals showing
different values of the index x (0.58, 0.70, 0.84, 0.82) have
been analyzed in order to shed some light on the composition
of this cluster. A mixture of the two [Ni9CoC2(CO)16]3− and
[Ni9CoC2(CO)15]3− trianions, which differ only for the number
average 2.5957(18)
1.927(6)−2.159(6)
average 2.078(13)
C−C
1.455(12)
a
M denotes Ni and Co.
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of CO ligands, is present within each crystal. Crystals from the
same reaction batch display almost identical compositions (e.g.,
x = 0.84 and 0.82 for the two crystal data herein included as an
example). Conversely, the ratio of the two clusters slightly
v a r i e s f r o m b a t c h t o b a t c h . F o r i n s t a n c e ,
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58) contains 42%
[Ni9CoC2(CO)16]3− and 58% [Ni9CoC2(CO)15]3−, whereas
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.70) is composed of 30%
[Ni9CoC2(CO)16]3− and 70% [Ni9CoC2(CO)15]3−. This
indicates that the two species are formed together within the
same reaction (see Section 2.1) and their exact ratio is affected
by minor variations of the experimental conditions. For
simplicity, only the data of [NEt4]3[Ni9CoC2(CO)16−x] (x =
0.58) will be used in the following discussion, whereas the other
CIF files are included as Supporting Information.
Within the crystal, the two different trianions are generated
by the fact that two edge-bridging CO ligands related by a
mirror plane and bonded to a common atom are partially
vacant and replaced by a single terminal CO bonded to the
same metal atom. The metal composition of the crystals has
been determined by means of EDS coupled to a SEM,
indicating the presence of nine Ni and one Co. Even if Ni and
Co are not well distinguished by X-ray crystallography, the
single Co atom has been assigned as disordered over two
symmetry-related positions (see Experimental Section) in the
central square of the cluster. Indeed, also the above-mentioned
disordered bridging-terminal CO ligands are bonded to these
Figure 4. Frontier region (in the −12 to −8.5 eV interval of energy) of
the EHMO diagrams of (a) [Ni9CoC2(CO)16]3− and (b)
[Ni9CoC2(CO)15]3−.
3. CONCLUSIONS
The new bimetallic Ni−Co hexacarbido carbonyl clusters
[H6−nNi22Co6C6(CO)36]n− (n = 3−6) have been prepared, and
the tetra- and hexa-anions structurally characterized. These
results confirm the capability of interstitial heteroatoms, among
which are carbides, to stabilize larger metal carbonyl
clusters.16,31,32 Moreover, this enhanced stability contributes
also to the development of peculiar physical properties, such as
multivalence.6,14 Thus, the [H6−nNi22Co6C6(CO)36]n− (n = 4,
5) anions display some redox processes that are reversible
under electrochemical control. These redox properties are in
keeping with the EHMO diagrams, which display a very small
HOMO−LUMO gap and the presence of several MOs in the
frontier region with rather similar energies.
atoms.
The [Ni9CoC2(CO)16−x
3−
]
(x = 0, 1) trianions are closely
related to the previously reported [Ni10C2(CO)16]2−,30
[Co3Ni7C2(CO)15]3−, and [Co3Ni7C2(CO)16]n− (n = 2, 3).3
Their common metal polyhedron may be seen as being derived
from the condensation of two (distorted) capped trigonal
prisms sharing a common square face. Overall, the metal
framework consists of a 3,4,3 stack of metal atoms of C2h
idealized symmetry. The interstitial C atoms are lodged within
monocapped trigonal prismatic cavities, showing seven M−C
contacts each. As a result of the fact that these two M7C prisms
share a common square face, the interstitial C atoms display a
very short C−C distance [1.455(12) Å], suggesting the
presence of tightly bonded C2 units. For what concerns the
stereochemistry of the CO ligands, [Ni9CoC2(CO)16]3−
contains six terminal and 10 edge-bridging carbonyls, whereas
[Ni9CoC2(CO)15]3− possesses seven terminal and eight edge-
bridging ligands.
In addition, joined electrochemical and chemical experiments
result as being the only tools available to elucidate the
polyhydride nature of such large carbonyl clusters, since their
hydride atoms are 1H NMR silent. This point has already been
discussed in the literature, even if a satisfactory explanation of
this phenomenon is still missing.6,19−25
The [Ni22Co6C63(−CO)36]6− hexa-anion is degraded to
[Ni9CoC2(CO)16−x
]
(x = 0, 1) after treatment with an
EHMO calculations with CACAO29 (Figure 4) show that
[Ni9CoC2(CO)15]3− displays a rather wide HOMO−LUMO
gap (1.416 eV) and possesses a closed-shell electronic
configuration. The addition of a further CO in
[Ni9CoC2(CO)16]3− introduces an additional MO within this
gap, reducing the HOMO−LUMO gap to 0.88 eV. The latter is
isoelectronic with [Ni10C2(CO)16]2−,30 possessing 142 CVE
(6N + 11 CVO). Conversely, [Ni9CoC2(CO)15]3− contains
140 CVE (6N + 10 CVO), being isoelectronic to
[Co3Ni7C2(CO)16]3−.3 Finally, the previously reported
excess of a strong base, indirectly confirming the number of
hydride atoms in the parent cluster. [Ni9CoC2(CO)16−x
3− (x =
0, 1) is structurally related to the previously reported
]
3 0
2 −
3 −
[Ni1 0 C2 (CO)1 6
]
,
[Co3 Ni7 C2 (CO)1 5
]
, and
[Co3Ni7C2(CO)16]n− (n = 2, 3).3 They are all based on the
condensation of two distorted monocapped C-centered trigonal
prisms sharing a common square face, which allows the
formation of a direct C−C bond. Nonetheless, their electron
counts range from 6N + 9 CVO for [Co3Ni7C2(CO)15]3− to
3 −
6N
+
10 for [Co3 Ni7 C2 (CO)1 6
]
as well as
[Ni9CoC2(CO)15]3− and, eventually, 6N + 11 in the cases of
[Ni10C2(CO)16]2− and [Ni9CoC2(CO)16]3−. This results in
deformations of their metal cages and loosening of some M−M
bonds, even though the overall structures are rather similar.
Thus, even for relatively small clusters such as these
decanuclear species, the assignment of their structures based
3
[Co3Ni7C2(CO)15]3− displays only 138 CVE (6N + 9 CVO)
even if the metal cages are very similar. The different electron
count of these decanuclear monoacetylide clusters possessing
similar metal frameworks is probably due to distortions and
loosening of the metal interactions.
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Table 3. Crystal Data and Experimental Details for [NEt4]4[H2Ni22Co6C6(CO)36], [NMe4]6[Ni22Co6C6(CO)36]·4CH3CN, and
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58)
[NEt4]4[H2Ni22Co6C6(CO)36]
[NMe4]6[Ni22Co6C6(CO)36]·4CH3CN
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58)
formula
fw
C74H80Co6N4Ni22O36
3246.62
C74H84Co6N10Ni22O36
3334.71
C41.42H60CoN3Ni9O15.42
1434.00
T, K
100(2)
100(2)
293(2)
λ, Å
0.71073
0.71073
0.71073
cryst syst
space group
a, Å
orthorhombic
Pbca
triclinic
orthorhombic
Pnnm
P1
̅
18.233(2)
21.495(3)
24.119(3)
90
14.578(3)
14.582(3)
15.213(4)
62.964(3)
63.929(3)
87.386(3)
2539.1(10)
1
12.0473(12)
12.2173(12)
18.4801(18)
90
b, Å
c, Å
α, deg
β, deg
90
90
γ, deg
cell volume, Å3
90
90
9453(2)
2720.0(5)
2
Z
4
Dc, g cm−3
μ, mm−1
F(000)
cryst size, mm
θ limits, deg
index ranges
2.281
2.181
1.751
5.364
4.997
3.398
6472
1664
1464
0.21 × 0.16 × 0.12
1.69−26.00
−22 ≤ h ≤ 22
−26 ≤ k ≤ 26
−29 ≤ l ≤ 29
93 522
0.18 × 0.15 × 0.12
1.58−25.03
−17 ≤ h ≤ 17
−17 ≤ k ≤ 17
−18 ≤ l ≤ 18
23 617
0.21 × 0.16 × 0.12
2.00−25.55
−14 ≤ h ≤ 14
−14 ≤ k ≤ 14
−22 ≤ l ≤ 22
25 873
reflns collected
indep reflns
9285 [Rint = 0.0924]
100.0%
8910 [Rint = 0.0574]
99.3%
2637 [Rint = 0.0351]
99.9%
completeness to θ max
data/restraints/params
goodness on fit on F2
R1 (I > 2σ(I))
9285/0/640
1.075
8910/253/623
1.061
2637/205/278
1.225
0.0420
0.0885
0.0407
wR2 (all data)
largest diff. peak and hole, e Å−3
0.1171
0.2653
0.1027
1.154/−0.912
2.002/−1.194
0.559/−0.432
interferometer in CaF2 cells. ESI mass spectra were recorded on a
Waters Micromass ZQ4000 instrument. The electrochemical experi-
ments were performed with a PGSTAT302N (Autolab) potentiostat
equipped with a nitrogen-purged three-electrode cell containing a
platinum working electrode, a saturated calomel electrode (SCE) as
the reference, and a Pt wire as the counter electrode; [NBu4][BF4]
(0.1 M) was used as supporting electrolyte. Structure drawings have
been performed with SCHAKAL99.36
4.2. Synthesis of [NEt4]4[H2Ni22Co6C6(CO)36]. A solution of
Co3(μ3-CCl)(CO)9 (0.224 g, 0.471 mmol) in acetone (15 mL) was
added dropwise to a solution of [NEt4]2[Ni10(C2)(CO)16] (1.05 g,
0.818 mmol) in acetone (25 mL). An evolution of gas was
immediately observed, and the solution was further stirred under
nitrogen for 2 h. Then, the solvent was removed in vacuo, and the solid
was washed with water (40 mL) and toluene (40 mL) and extracted in
CH3CN (20 mL). Crystals of [NEt4]4[H2Ni22Co6C6(CO)36] suitable
for X-ray analyses were obtained by slow diffusion of n-hexane (5 mL)
and di-isopropyl ether (40 mL) (yield 0.62 g, 52% based on Ni, 82%
based on Co).
solely on their electron count might be taken always with some
care.
Finally, this work further confirms the capacity of carbide
atoms in Ni, Co, and Ni−Co carbonyl clusters to be lodged in
rather different cavities such as square antiprismatic, trigonal
prismatic, monocapped trigonal prismatic, and octahedral, as
well as to form tightly bonded C2 units.1−4,19,20,23,24,28,30,33,34
Also, the greater stabilizing effect of isolated interstitially
located carbide atoms with respect to C2 moieties23,34 enables
obtaining higher nuclearity molecular clusters and approaching
t h e n a n o s i z e r e g i m e . T h u s , t h e b i m e t a l l i c
[H6−nNi22Co6C6(CO)36]n− (n = 3−6) cluster displays a
diameter (measured at the outer Co atoms) of ca. 0.9 nm,
and the whole molecular ion has a diameter of ca. 1.5 nm once
measured from the outer oxygen atoms.
4. EXPERIMENTAL SECTION
Anal. Calcd for C74H80Co6N4Ni22O36 (3228.63): C 27.50, H 2.50,
N 1.73, Co 10.95, Ni 39.48. Found: C 27.68, H 2.50, N 1.59, Co 11.12,
Ni 39.64. IR (thf, 293 K) ν(CO): 2023(s), 1859(m) cm−1. IR
(acetone, 293 K) ν(CO): 2018(vs), 1857(m) cm−1.
4.3. Synthesis of [NMe4]6[Ni22Co6C6(CO)36]·4CH3CN. A sol-
ution of Co3(μ3-CCl)(CO)9 (0.224 g, 0.471 mmol) in acetone (15
mL) was added dropwise to a solution of [NMe4]2[Ni10(C2)(CO)16]
(0.958 g, 0.818 mmol) in acetone (25 mL). An evolution of gas was
immediately observed, and the solution was further stirred under
nitrogen for 2 h. Then, the solvent was removed in vacuo, and the solid
was washed with water (40 mL) and toluene (40 mL) and extracted in
CH3CN (20 mL). Solid Na2CO3 was added and the solution stirred
4.1. General Procedures. All reactions and sample manipulations
were carried out using standard Schlenk techniques under nitrogen
and in dried solvents. All the reagents were commercial products
(Aldrich) of the highest purity available and used as received, except
[NR4]2[Ni10(C2)(CO)16] (R = Me, Et)30 and Co3(μ3-CCl)(CO)9,35
which have been prepared according to the literature. Analysis of Ni
and Co were performed by atomic absorption on a Pye-Unicam
instrument. The content of Ni and Co on single crystals was
determined using an EVO 50 EP (ZEISS) scanning electron
microscope with an Oxford INCA 350 EDS. Analyses of C, H, and
N were obtained with a ThermoQuest FlashEA 1112NC instrument.
IR spectra were recorded on a Perkin-Elmer SpectrumOne
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overnight at room temperature. The solid was, then, removed by
filtration, and crystals of [NMe4]6[Ni22Co6C6(CO)36]·4CH3CN
suitable for X-ray analyses were obtained by slow diffusion of n-
hexane (5 mL) and di-isopropyl ether (40 mL) (yield 0.68 g, 55%
based on Ni, 87% based on Co).
Anal. Calcd for C74H84Co6N10Ni22O36 (3316.68): C 27.77, H 2.55,
N 4.22, Co 10.66, Ni 38.43. Found: C 27.52, H 2.71, N 4.07, Co 10.87,
Ni 38.61. IR (dmso, 293 K) ν(CO): 1996(vs), 1844(m) cm−1. IR
(Nujol, 293 K) ν(CO): 1988(vs), 1824(m) cm−1.
center), three [NMe4]+ cations, and two CH3CN molecules (located
on general positions). Two carbonyl ligands in the anion are
disordered, and therefore they have been split into two positions
each and refined isotropically using one occupancy parameter per
disordered group. Similar U restraints (su 0.005) were applied to the C
and O atoms. The geometries of the [NMe4]+ cations and the CH3CN
molecules were restrained to be similar (SAME line in SHELXL; su
0.02). Restraints to bond distances were applied as follow (su 0.01):
1.47 Å for C−C and 1.14 Å for C−N in CH3CN.
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58). The structure of
[NEt4]3[Ni9CoC2(CO)16−x] has been determined on four isomor-
phous crystals obtained from three different reaction batches, showing
different values of x (0.58, 0.70, 0.84, 0.82). The asymmetric unit of
the unit cell contains one fourth of a cluster anion (located on 2/m)
and one-half (located on 2) and one forth (located on 2/m) of a
[NEt4]+ cation. The half [NEt4]+ cation located on 2 is disordered
over two independent positions, which have been refined anisotropi-
cally using one occupancy parameter per disordered group.
Conversely, the [NEt4]+ cation located on 2/m (present as one
forth in the asymmetric unit) is disordered over four symmetry-related
positions and has been refined anisotropically using a 0.25 occupancy
factor. The M(2) position of the cluster anion has been assigned as
disordered Ni/Co. Since this position is repeated twice on the same
anion by symmetry and on the basis of EDS analyses, which indicate
the presence of a single Co atom within the cluster, this position has
been assigned 50% to Ni and 50% to Co. The CO ligand bonded to
M(2) is disordered over two positions, one in general position and one
on a mirror plane. Thus, the disordered CO has been split into two
positions and refined anisotropically using one occupancy parameter
per disordered group. Because of symmetry, this disorder originates
two different anions, one containing 16 and the other 15 CO ligands.
Similar U restraints (su 0.005) were applied to the C and O atoms.
The geometries of the [NEt4]+ cations were restrained to be similar
(SAME line in SHELXL; su 0.02). Restraints to bond distances were
applied as follow (su 0.01): 1.53 Å for C−C and 1.47 Å for C−N in
[NEt4]+.
(a)
4.4. Deprotonation/Protonation Studies of
n−
[H6−nNi22Co6C6(CO)36
]
(n = 3−6). The tetra-anion
[H2Ni22Co6C6(CO)36]4− [ν(CO) 2018(vs), 1857(m) cm−1 in
acetone] is protonated to the trianion [H3Ni22Co6C6(CO)36]3−
[ν(CO) 2033(vs), 1868(m) cm−1 in acetone] after addition of
HBF4·Et2O in acetone. In detail, HBF4·Et2O (42.5 μL, 0.310
mmol) was added dropwise with a micropipet to a solution of
[NEt4]4[H2Ni22Co6C6(CO)36] (0.868 g, 0.269 mmol) in
acetone (20 mL). The reaction was monitored by IR after
each addition up to complete conversion.
(b) The tetra-anion [H2Ni22Co6C6(CO)36]4− [ν(CO) 2018(vs),
1857(m) cm−1 in acetone] was deprotonated to the penta-
anion [HNi22Co6C6(CO)36]5 [ν(CO) 2008(vs), 1849(m) cm−1
in CH3CN] by simple dissolution in CH3CN.
(c) The hexa-anion [Ni22Co6C6(CO)36]6− [ν(CO) 1996(vs),
1844(m) cm−1 in dmso] was obtained by deprotonation of
the penta-anion [HNi22Co6C6(CO)36]5− [ν(CO) 2008(vs),
1849 (m) cm−1 in CH3CN] after treatment in CH3CN with
Na2CO3 as described in Section 4.4. Alternatively, it may be
obtained by treating the penta-anion [HNi22Co6C6(CO)36]5−
in CH3CN with [NBu4][OH]. In this case, the hydroxide must
be added very slowly, monitoring by IR the reaction after each
3−
addition, in order to avoid formation of [Ni9CoC2(CO)16−x
as described in Section 4.5.
]
4.5. Synthesis of [NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58). A
solution of [NBu4][OH] (0.348 g, 1.34 mmol) in CH3CN (15 mL)
was added dropwise to a solution of [NEt4]4[H2Ni22Co6C6(CO)36]
(0.868 g, 0.269 mmol) in CH3CN (20 mL) over a period of 3 h. Then,
the solvent was removed in vacuo, and the solid was washed with water
(40 mL), thf (20 mL), and acetone (20 mL) and extracted in CH3CN
(20 mL). Crystals of [NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58) suitable
for X-ray analyses were obtained by slow diffusion of n-hexane (5 mL)
and di-isopropyl ether (40 mL) (yield 0.59 g, 63% based on Ni, 25%
based on Co).
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving X-ray crystallographic data for the structure
determinations of [NEt4]4[H2Ni2 2Co6C6(CO)36],
[ N M e 4 ] 6 [ N i 2 2 C o 6 C 6 ( C O ) 3 6 ] · 4 C H 3 C N , a n d
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58, 0.70, 0.82, 0.84). This
material is available free of charge via the Internet at http://
pubs.acs.org.
The value of x varies from batch to batch. The CIF files of other
three crystals obtained from different reaction batches are included to
support this point. They show x = 0.70, 0.84, and 0.82.
Anal. Calcd for C41.42H60CoN3Ni9O15.42 (1434.00): C 34.70, H 4.22,
N 2.93, Co 4.11, Ni 36.74. Found: C 34.55, H 4.40, N 2.78, Co 4.02,
Ni 36.85. IR (Nujol, 293 K) ν(CO): 2043(w), 2005(w), 1958(vs),
1920(m), 1832(ms), 1772(m) cm−1. IR (acetone, 293 K) ν(CO):
1976(vs), 1942(sh), 1840(br) cm−1. IR (CH3CN, 293 K) ν(CO):
1979(vs), 1948(sh), 1874(ms), 1829(m) cm−1.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: +39 0512093690. E-mail: stefano.zacchini@unibo.it.
Notes
4.6. X-ray Crystallographic Study. Crystal data and collection
The authors declare no competing financial interest.
d e t a i l s f o r [ N E t 4
] 4 [ H 2 N i 2 2 C o 6 C 6 ( C O ) 3 6 ] ,
[ N M e 4 6 [ N i 2 2 C o 6 C 6 ( C O ) 3 6 ] · 4 C H 3 C N , a n d
]
ACKNOWLEDGMENTS
■
[NEt4]3[Ni9CoC2(CO)16−x] (x = 0.58) are reported in Table 3. 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).37 Structures were solved
by direct methods and refined by full-matrix least-squares based on all
data using F2.38 Hydrogen atoms were fixed at calculated positions and
refined by a riding model. All non-hydrogen atoms were refined with
anisotropic displacement parameters, unless otherwise stated.
The financial support of MIUR (PRIN2008) and the University
of Bologna is gratefully acknowledged. Funding by Fondazione
CARIPLO, Project No. 2011-0289, is heartily acknowledged.
REFERENCES
■
(1) Ceriotti, A.; Della Pergola, R.; Longoni, G.; Manassero, M.;
Masciocchi, N.; Sansoni, M. J. Organomet. Chem. 1987, 330, 237.
(2) Ceriotti, A.; Della Pergola, R.; Longoni, G.; Manassero, M.;
Sansoni, M. J. Chem. Soc., Dalton Trans. 1984, 1181.
(3) (a) Arrigoni, A.; Ceriotti, A.; Della Pergola, R.; Longoni, G.;
Manassero, M.; Sansoni, M. J. Organomet. Chem. 1985, 296, 243.
(b) Longoni, G.; Ceriotti, A.; Della Pergola, R.; Manassero, M.;
[NEt4]4[H2Ni22Co6C6(CO)36]. The asymmetric unit of the unit cell
contains half of a cluster anion (located on an inversion center) and
two [NEt4]+ cations (both located on general positions).
[NMe4]6[Ni22Co6C6(CO)36]·4CH3CN. The asymmetric unit of the
unit cell contains half of a cluster anion (located on an inversion
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Perego, M.; Piro, G.; Sansoni, M. Philos. Trans. R. Soc. London A 1982,
308, 47.
(4) Arrigoni, A.; Ceriotti, A.; Della Pergola, R.; Manassero, M.;
Masciocchi, N.; Sansoni, M. Angew. Chem., Int. Ed. Engl. 1984, 23, 322.
(5) Chini, P. J. Organomet. Chem. 1980, 200, 37.
(23) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S.; Fedi, S.;
Fabrizi de Biani, F. Dalton Trans. 2012, 41, 4649.
(24) Bernardi, A.; Femoni, C.; Iapalucci, M. C.; Longoni, G.;
Zacchini, S.; Fedi, S.; Zanello, P. Eur. J. Inorg. Chem. 2010, 4831.
(25) Ciabatti, I.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini,
S.; Zarra, S. Nanoscale, DOI: 10.1039/C2NR30400G.
(6) Zacchini, S. Eur. J. Inorg. Chem. 2011, 4125.
(26) (a) Cordero, B.; Gom
Echevarría, J.; Cremades, E.; Barragan
2010, 2832. (b) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(27) (a) Chini, P. Chem. Commun. 1967, 440−441. (b) Albano, V.;
Chini, P.; Scatturin, V. Chem. Commun. 1968, 163−164.
(28) (a) Calderoni, F.; Demartin, F.; Fabrizi de Biani, F.; Femoni, C.;
Iapalucci, M. C.; Longoni, G.; Zanello, P. Eur. J. Inorg. Chem. 1999,
663. (b) Calderoni, F.; Demartin, F.; Iapalucci, M. C.; Longoni, G.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2225. (c) Ceriotti, A.; Fait, A.;
Longoni, G.; Piro, G.; Demartin, F.; Manassero, M.; Sansoni, M. J. Am.
Chem. Soc. 1986, 108, 8091.
́
ez, V.; Platero-Prats, A. E.; Reves
́
, M.;
(7) (a) Adams, R. D.; Trufan, E. Philos. Trans. R. Soc. A 2010, 368,
1473. (b) Johnson, B. F. G.; Reynor, S. A.; Brown, D. B.; Shephard, D.
S.; Mashmeyer, T.; Thomas, J. M.; Hermans, S.; Raja, R.; Sankar, G. J.
Mol. Catal. A 2002, 182−183, 89.
(8) (a) Shephard, D. S.; Maschmeyer, T.; Sankar, G.; Thomas, J. M.;
Ozkaya, D.; Johnson, B. F. G.; Raja, R.; Oldroyd, R. D.; Bell, R. G.
Chem.Eur. J. 1998, 4, 1214. (b) Adams, R. D.; Blom, D. A.; Captain,
B.; Raja, R.; Thomas, J. M.; Trufan, E. Langmuir 2008, 24, 9223.
(c) Jones, M. D.; Duer, M. J.; Hermans, S.; Khimyak, Y. Z.; Johnson,
B. F. G.; Thomas, J. M. Angew. Chem., Int. Ed. 2002, 41, 4726.
(9) (a) Albonetti, S.; Bonelli, R.; Epoupa Mengou, J.; Femoni, C.;
́
, F.; Alvarez, S. Dalton Trans.
(29) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 66, 399.
(30) Ceriotti, A.; Longoni, G.; Manassero, M.; Masciocchi, N.;
Resconi, L.; Sansoni, M. Chem. Commun. 1985, 181.
(31) (a) King, R. B. New J. Chem. 1988, 12, 493. (b) Halet, J. F.;
Evans, D. G.; Mingos, D. M. P. J. Am. Chem. Soc. 1988, 110, 87.
(32) (a) Hughes, K.; Wade, K. Coord. Chem. Rev. 2000, 197, 191.
(b) Sironi, A. Dalton Trans. 1993, 173.
(33) (a) Masters, A. F.; Meyer, J. T. Polyhedron 1995, 14, 339.
(b) Battie, J. K.; Masters, A. F.; Meyer, J. T. Polyhedron 1995, 14, 829.
(34) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S. Chem.
Commun. 2008, 3157.
(35) (a) Ercoli, R.; Santambrogio, E.; Casagrande, G. T. Chim. Ind.
(Milan, Italy) 1962, 44, 1344−1349. (b) Dent, W. T.; Duncanson, L.
A.; Guy, R. G.; Reed, H. W. R.; Shaw, B. L. Chem. Ind. 1961, 169−170.
(36) Keller, E. SCHAKAL99; University of Freiburg: Germany, 1999.
(37) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Tiozzo, C.; Zacchini, S.; Trifiro,
(b) Albonetti, S.; Bonelli, R.; Delaigle, R.; Femoni, C.; Gaigneaux, E.
M.; Morandi, V.; Ortolani, L.; Tiozzo, C.; Zacchini, S.; Trifiro, F. Appl.
Catal., A 2010, 372, 138. (c) Bonelli, R.; Albonetti, S.; Morandi, V.;
Ortolani, L.; Riccobene, P. M.; Scire, S.; Zacchini, S. Appl. Catal., A
2011, 395, 10. (d) Bonelli, R.; Lucarelli, C.; Pasini, T.; Liotta, L. F.;
Zacchini, S.; Albonetti, S. Appl. Catal., A 2011, 400, 54. (e) Bonelli, R.;
Zacchini, S.; Albonetti, S. Catalysts 2012, 2, 1.
̀
F. Catal. Today 2008, 137, 483.
̀
̀
(10) (a) Schweyer-Tihay, F.; Estournes
Paillaud, J. L.; Richard-Plouet, M.; Rose,
2006, 8, 4018. (b) Schweyer, F.; Braunstein, P.; Estournes
J.; Kessler, H.; Paillaud, J. L.; Rose, J. Chem. Commun. 2000, 1271.
(c) Schweyer-Tihay, F.; Braunstein, P.; Estournes, C.; Guille, J. L.;
Lebeau, B.; Paillaud, J. L.; Richard-Plouet, M.; Rose, J. Chem. Mater.
2003, 15, 57.
̀
, C.; Braunstein, P.; Guille, J.;
J. Phys. Chem. Chem. Phys.
, C.; Guille,
́
̀
́
̀
́
(11) Robinson, I.; Zacchini, S.; Tung, L. D.; Maenosono, S.; Thanh,
N. T. K. Chem. Mater. 2009, 21, 3021.
(12) Rutledge, R. D.; Morris, W. H.; Wellons, M. S.; Gai, Z.; Shen, J.;
Bentley, J.; Wittig, J. E.; Lukehart, C. M. J. Am. Chem. Soc. 2006, 128,
14210.
Correction; University of Gottingen: Germany, 1996.
̈
(38) Sheldrick, G. M. SHELX97, Program for Crystal Structure
Determination; University of Gottingen: Germany, 1997.
̈
(13) (a) Adams, R. D.; Cotton, F. A., Eds. Catalysis by Di- and
Polynuclear Metal Cluster Complexes; Wiley-VCH: New York, 1998.
(b) Braunstein, P.; Oro, L. A.; Raithby, P. R., Eds. Metal Clusters in
Chemistry; Wiley-VCH: New York, 1999.
(14) Femoni, C.; Iapalucci, M. C.; Kaswalder, F.; Longoni, G.;
Zacchini, S. Coord. Chem. Rev. 2006, 250, 1580.
(15) (a) Longoni, G.; Iapalucci, M. C. In Clusters and Colloids;
Schmid, G., Ed.; Wiley-VCH: New York, 1994; p 91. (b) Fumagalli,
A.; Della Pergola, R. In Metal Clusters in Chemistry; Braunstein, P.;
Oro, L. A.; Raithby, P. R., Eds.; Wiley-VCH: New York, 1999; p 323.
(c) Lewis, J.; Raithby, P. R. In Metal Clusters in Chemistry; Braunstein,
P.; Oro, L. A.; Raithby, P. R., Eds.; Wiley-VCH: New York, 1999; p
348.
(16) (a) Johnson, B. F. G.; Martin, C. M. In Metal Clusters in
Chemistry; Braunstein, P.; Oro, L. A.; Raithby, P. R., Eds.; Wiley-VCH:
New York, 1999; p 877. (b) Longoni, G.; Femoni, C.; Iapalucci, M. C.;
Zanello, P. In Metal Clusters in Chemistry; Braunstein, P.; Oro, L. A.;
Raithby, P. R., Eds.; Wiley-VCH: New York, 1999; p 1137.
(17) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Wolowska, J.;
Zacchini, S.; Zanello, P.; Fedi, S.; Ricco,
J. Am. Chem. Soc. 2010, 132, 2919.
̀
M.; Pontiroli, D.; Mazzani, M.
(18) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S. Eur. J.
Inorg. Chem. 2009, 2487.
(19) Bernardi, A.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Ranuzzi,
F.; Zacchini, S.; Zanello, P.; Fedi, S. Chem.Eur. J. 2008, 14, 1924.
(20) Bernardi, A.; Femoni, C.; Iapalucci, M. C.; Longoni, G.;
Zacchini, S. Dalton Trans. 2009, 4245.
(21) Collini, D.; Fabrizi de Biani, F.; Dolznikov, D. S.; Femoni, C.;
Iapalucci, M. C.; Longoni, G.; Tiozzo, C.; Zacchini, S.; Zanello, P.
Inorg. Chem. 2011, 50, 2790.
(22) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S.; Fedi, S.;
Fabrizi de Biani, F. Eur. J. Inorg. Chem. 2012, 2243.
4600
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