Hexa- and hepta-coordinate cobalt(II) complexes bearing bis(2-pyridylmethyl)ether.

Hexa- and hepta-coordinate cobalt(II) complexes bearing bis(2-pyridylmethyl)ether (bpme) as a tridentate supporting ligand were synthesized and structurally characterized by single crystal X-ray diffraction (SCXRD). The reactions of the penta-coordinate dichloridocobalt(II) complex, [CoIICl2(bpme)], with a molar equivalent of AgX (X = NO3 and CH3CO2) afforded hexa-coordinate octahedral complexes, fac-[CoIICl(L)(bpme)] (L = nitrato-κ2O1,O2; [1] and acetato-κ2O1,O2; [2]), whereas those with two molar equivalents of AgNO3 resulted in the isolation of the hepta-coordinate pentagonal bipyramidal complex, [CoII(nitrato-κ2O1,O2)2(bpme)] ([3]). When 2,2'-bipyridine (bpy) was reacted with [CoIICl2(bpme)], one bpy-coordinated octahedral complex, mer-[CoIICl(bpy)(bpme)]+ ([4]+), was formed. Furthermore, it has been suggested that the reactions with a molar equivalent of AgClO4 in acetonitrile could afford octahedral complexes with meridional geometry, concomitant with [CoIICl2(bpme)] and mer-[CoII(bpme)2]2+: a perchlorato-coordinated monomer, mer-[CoII(NCCH3)(OH2)(OClO3)(bpme)]ClO4 ([5]ClO4), and a doubly chlorido-bridged dimer, mer-[{CoII(NCCH3)(bpme)}2(μ-Cl)2](ClO4)2 ([6](ClO4)2), both of which were identified only by SCXRD analysis. The electronic structures of the mononuclear complexes [1]-[3], all having the Co(II) centre (S = 3/2) at 296-298 K, are discussed comprehensively with respect to electrochemical, spectroscopic, and theoretical investigations.