Hexanuclear Niobium Cluster Alcoholates - First Representatives with Isopropanolato Ligands

Four new compounds were synthesized which belong to the so far very small group of hexanuclear niobium cluster alcoholates. These are [Mg(HOCH3)(6)](3)[Nb6Cl12(OCH3)(6)](2) center dot 6CH(3)OH (1), (Ph4P)(2)[Nb-6(OC2H5)(12)Cl-6] (2), (Ph4P)(2)[Nb-6(OC3H7)(4)(Cl8Cl6a)-Cl-i-Cl-i] (3) and (NC5H6)(2)[Nb-6(OC3H7)(12)Cl-6] (4). The last two compounds represent the first examples with isopropanolato ligands on the inner coordination sites of the octahedral metal atom cores. The X-ray structures of 1-3 have been determined. All cluster units with alcoholato ligands on the inner sites carry 14 cluster-based electrons (CBEs), as do all other so far known cluster alcoholates. The cluster unit in Compound 1, which carries chloride ligands on the inner coordination sites, is a 15 CBE unit. The cluster anion in 3 has four inner ligand sites occupied by isopropanolate anions, which are arranged trans to each other and define a common plane. Because of the smaller size of the alcoholato O donor atom compared to halogenido ligands matrix effects are not much or not at all present in the cluster anions of 2 and 3 (and 4) and thereby the Nb-Nb distances are much smaller than found in cluster units with halogenido ligands.