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 [Ni6(CO)12]2− dianion with SbCl3 in a 2.5:1 molar ratio leads to formation of the new [Ni15(μ12-Sb)(CO)24]2−, 12−, cluster with good selectivity. This has been conveniently separated from [Ni9(CO)18]2−, [Ni10(SbNi(CO)3)2(μ12-Ni)(CO)18]n−, 2n−, (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 Ni12(μ12-Sb) icosahedral moiety, capped by three Ni atoms on three adjacent triangular faces. The 12− 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 12− 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 2n− (n=3, 4), through the intermediate formation of the new [Ni10Sb2(μ12-Ni)(CO)18]n−, 3n−, (n=3, 4) species. Pure 33− has been obtained by degradation of 23− 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 33− trianion shows a chemical and electrochemical redox propensity comparable to that of the parent 23− compound and is readily transformed in its corresponding 32− and 34− 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.