X-Ray Structure, Electrochemical and Electronic Spectroscopic Examination of Cobaloximatic Acid: Hydro-trans-diiodobis(ethanedioximato(1-)-N,N′)cobaltate(III). Extended Intermolecular O-H-O Bridging in the Solid

The structure of the cobaloximatic acid, hydro-trans-diiodobis(ethanedioximato(1-)-N,N′)cobaltate(III), has been determined by X-ray diffraction. Crystal data: C₄H₇CoI₂N₄O₄, M_r = 487.87; monoclinic space group P2₁/a (C_2h⁵ ); a = 10.795(7), b = 9.003(7), c = 11.881(6) Å; β = 97.29(6)°; V = 1145.35 ų; Z = 4; d_c = 2.83 Mg m^-3. R_w (R) = 3.6 (3.9)% for 3064 observed independent reflections and 148 parameters. The coordination geometry around Co^III is a distorted (4 + 2) octahedron of four chelating equatorial N atoms and two apical iodides. The compound is most adequately formulated as a monovalent strong acid: H(Co(GH)₂I₂) (GH- = ethanedioximate or glyoximate). The H atoms of the oxime groups are involved in the usual intramolecular, as well as in much stronger intermolecular O-H-O bridgings (O ••• O_intramol = 2.613-2.631, O ••• O_intramol = 2.454 A). The “acidic” H atom of each molecule participates in the intermolecular bridging which extends throughout the structure, and propagates nearly parallel to the [101] crystallographic direction. The redox properties of the present compound were examined by cyclic voltammetry in acetonitrile solution at room temperature. Redox waves attributed to the reduction of Co^III and to the oxidation of I^- were observed, along with a wave which may be linked to the reduction of the “acidic” proton