Synthesis and characterization of new paramagnetic nickel carbonyl clusters containing antimony atoms: X-ray structure of [NEt3CH2Ph]2[Ni15(μ12-Sb)(CO)24] and [NEt4]3[Ni10Sb2(μ12-Ni)(CO)18]

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-), cluster 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 [NEt3CH2Ph]Cl and has been structurally characterized. The structure of 12- consists of a distorted Sb-centered Ni-12(mu(12)-Sb) icosahedral moiety, capped 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 species are stable only on the timescale of cyclic voltammetry. The 1(2-) dianion is readily degraded upon exposure to an atmosphere of carbon monoxide to 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 formation of the new [Ni10Sb2(mu(12)-Ni)(CO)(18)](n-), 3(n-), (n = 3, 4) species. Pure 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) and has been structurally characterized in its tetraethylammonium salt. The Ni-centered icosahedral 3(3-) trianion shows a chemical and electrochemical redox propensity comparable to that of the parent 2(3-) compound and is readily transformed in its corresponding 3(2-) and 3(4-) anions upon oxidation and reduction, respectively. Systematic observation of apparently exceptional electron counts and redox propensity by the above Ni-centered icosahedral clusters validate the previous attribution of these properties to the presence of interstitial nickel atoms and concomitant stabilization imparted by the peripheral antimony heteroatoms. (C) 2000 Elsevier Science S.A. All rights reserved.