The (Dioximate)Ni/I System: Ligand Oxidation and Binding Modes of Triiodide Species.

Reinvestigation of (-benzoquinonedioximate)Ni/I systems demonstrated that the reaction itself and also the crystallization conditions dramatically affect the identity of generated species. Crystallization (CHCl, 20-25 °C) of the nickel(II) dioximate complex [Ni(bqoxH)] (bqoxH = -benzoquinonedioxime) with I in the 1:(1-10) molar ratios of the reactants led to several (-benzoquinonedioximate)Ni derivatives and/or iodine adducts [Ni(I)(bqoxH)(bqoxH)]·/I, [Ni(I)(bqoxH)(bqoxH)]·[Ni(bqoxH)], and [Ni(I)(bqox)(bqoxH)]·I; the latter one, featuring the anion-radical bqox ligand, is derived from the formal (-2H/1)-oxidation of bqoxH. In these three adducts, various types of noncovalent interactions were identified experimentally and their existence was supported theoretically. The [Ni(I)(bqox)(bqoxH)]·I adduct exhibits simultaneous semicoordination and coordination patterns of the triiodide ligand; this is the first recognition of the semicoordination of any polyiodide ligand to a metal center. The semicoordination noncovalent contact Ni···I (3.7011(10) Å) is substantially longer that the Ni-I coordination bond (2.8476(9) Å), and the difference in energies between these two types of linkages is 8-12 kcal/mol.