The (Dioximate)Ni II /I 2 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.