BIS(DIMETHYLVIOLURATO)(PHENANTHROLINE)COBALT(II), A LOW-SPIN OCTAHEDRAL COBALT(II) COMPLEX - CRYSTAL-STRUCTURE OF [CO(DMVI)2PHEN].2CHCL3

The complexes of formula [Co(dmvi)2phen].2solv (dmvi, C6H6N3O4, dimethylviolurate anion; phen, C12H8N2, 1,10-phenanthroline; and solv = H2O, CHCl3) have been synthesized, and the structure of chloroform solvate has been determined by X-ray crystallographic methods. Crystal data: monoclinic system, space group C2/c, a = 17.394(2) angstrom, b = 10.229(1) angstrom, c = 21.714(3), beta = 117.4(1)-degrees, Z = 4. Data up to theta = 25-degrees (Mo Ka radiation) were collected at room temperature on a CAD-4 diffractometer. The structure was solved by Patterson methods and refined by least-squares methods to conventional agreement indices R = R(w) = 0.044 with 1979 observed reflections [I greater-than-or-equal-to 3sigma(I)]. The structure consists of [Co(dmvi)2(phen)] neutral unities and chloroform molecules linked by van der Waals interactions. The metal ion exhibits a trans-N4O2 distorted-octahedral surrounding. The phenanthroline ligand occupies two equatorial positions in the coordination sphere of the metal ion (Co-N bond length, 1.97 angstrom). Dimethylviolurate ligands are coordinated to the metal ion through the oxime nitrogen atom (equatorial distance 1.89 angstrom) and one of the carbonyl oxygen atoms (axial distance 2.17 angstrom). Magnetic measurements, with mu(eff) = 2.0 in the 80-300 K range, and EPR spectra, with g(perpendicular-to) = 2.23 and g(parallel-to) = 2.02, prove that this octahedral Co(II) complex has a low-spin electron configuration at room temperature. Its electrochemical behavior was also investigated. Formation equilibria in aqueous solution of the mixed complexes in the Co(II)-dimethylviolurate-phenanthroline system have been studied and the stability constants determined.