Synthesis and characterization of new paramagnetic nickel carbonyl clusters containing antimony atoms: X-ray structure of [NEt3CH2Ph](2)[Ni-15(mu(12)-Sb)(CO)(24)] and [NEt4](3)[Ni10Sb2(mu(12)-Ni)(CO)(18)]
Vg. Albano et al., Synthesis and characterization of new paramagnetic nickel carbonyl clusters containing antimony atoms: X-ray structure of [NEt3CH2Ph](2)[Ni-15(mu(12)-Sb)(CO)(24)] and [NEt4](3)[Ni10Sb2(mu(12)-Ni)(CO)(18)], J ORGMET CH, 594, 2000, pp. 325-334
The reaction of the [Ni-6(CO)(12)](2-) dianion with SbCl3 in a 2.5:1 molar
ratio leads to formation of the new [Ni-15(mu(12)Sb)(CO)(24)](2-), 1(2-), c
luster with good selectivity. This has been conveniently separated from [Ni
-9(CO)(18)](2-), [Ni-10(SbNi(Co)(3))(2)(mu(12)-Ni)(CO)(18)](n-), 2(n-), (n
= 2, 3) and other side-products by differential solubility of their [NEt4](
+) salts and isolated in 50-60% yields. The corresponding [NEt3CH2Ph](2)[1]
salt was obtained from [NEt4](2)[1] by metathesis in acetonitrile with [NE
t3CH2Ph]Cl and has been structurally characterized. The structure of 12- co
nsists of a distorted Sb-centered Ni-12(mu(12)-Sb) icosahedral moiety, capp
ed by three Ni atoms on three adjacent triangular faces. The 1(2-) dianion
is moderately stable to oxidation and has been electrochemically reduced to
the corresponding tri-, tetra- and penta-anion; these electrogenerated spe
cies are stable only on the timescale of cyclic voltammetry. The 1(2-) dian
ion is readily degraded upon exposure to an atmosphere of carbon monoxide t
o a mixture of Ni(CO)(4) and a yet uncharacterized red-violet intermediate,
which has been tentatively formulated as the [Ni6Sb(CO)(x)](2-) dianion on
the basis of its spectroscopic features. The above mixture converts under
nitrogen into the known 2(n-) (n = 3, 4), through the intermediate formatio
n of the new [Ni10Sb2(mu(12)-Ni)(CO)(18)](n-), 3(n-), (n = 3, 4) species. P
ure 3(3-) has been obtained by degradation of 2(3-) with two equivalents of
triphenylphosphine by elimination of two equivalents of Ni(CO)(3)(PPh3) an
d has been structurally characterized in its tetraethylammonium salt. The N
i-centered icosahedral 3(3-) trianion shows a chemical and electrochemical
redox propensity comparable to that of the parent 2(3-) compound and is rea
dily transformed in its corresponding 3(2-) and 3(4-) anions upon oxidation
and reduction, respectively. Systematic observation of apparently exceptio
nal electron counts and redox propensity by the above Ni-centered icosahedr
al clusters validate the previous attribution of these properties to the pr
esence of interstitial nickel atoms and concomitant stabilization imparted
by the peripheral antimony heteroatoms. (C) 2000 Elsevier Science S.A. All
rights reserved.