Synthesis, crystal structures and properties of six new mixed ligand cobalt(II) 4-nitrobenzoates

The synthesis, spectral characteristics, thermal properties and single crystal structures of [Co(N-meim)(2)(4-nba)(2)] (N-meim = N-methylimidazole; 4-nba = 4-nitrobenzoate) (1), [Co(2-meim)(2)(4-nba)(2)] (2-meim = 2-methylimidazole) (2), [Co(pyr)(3)(4-nba)(2)] (pyr = pyrazole) (3), [Co(H2O)(2)(form)(2)(4-nba)(2)]center dot form (form = formamide) (4), [Co(H2O) (aceta)(2)(4-nba)(2)] (aceta = acetamide) (5) and [Co(H2O)(3)(N-mepyr)(4-nba)](4-nba) (N-mepyr = N-methylpyrazole) (6) are reported. The central Co(II) exhibits tetrahedral geometry in 1 and 2, trigonal bipyramidal geometry in 3 and octahedral geometry in 4-6. In the anhydrous compounds 1-3 as well as the diaqua compound 4, the monoaqua compound 5 and the triaqua compound 6, the neutral N-donor co-ligands or the O-donor amides function as terminal ligands. The aromatic 4-nba ligand exhibits monodentate binding mode in 1-4 and monodentate and bidentate binding in 5, while 6 contains an uncoordinated 4-nba in addition to a bidentate 4-nba ligand. A single C-H center dot center dot center dot O interaction links molecules of 1 into an infinite chain while the N-H center dot center dot center dot O bonds in 2 result in a two-dimensional network. Compounds 4 and 5 exhibit three varieties of H-bonding. Thermal decomposition of 1-6 results in the formation of a spinel oxide. A comparative study of thirty-one structurally characterized cobalt-4-nitrobenzoates is described.