SYNTHESIS AND CHARACTERIZATION OF SOME METAL(II) COMPLEXES OF QUINOLINIC ACID (H-2-QUIN) AND X-RAY CRYSTAL-STRUCTURES OF [NI(H-QUIN)2(H2O)2] AND [MN(H2O)6][MN(H-QUIN)3]2

Complexes of the types M(H-Quin)2 . 2H2O (M = Mn, Co, Ni and Zn) and M(H-2-Quin)(Quin) . 2H2O (M = Fe and Co), where H-2-Quin = quinolinic acid, have been prepared and characterized. The spectral results suggest that all these complexes contain distorted octahedral metal atoms. The crystal structures of the nickel(II) and manganese(II) complexes were determined by single-crystal X-ray diffraction methods. The nickel atom in centrosymmetric Ni(H-Quin)2 . 2H2O is octahedrally coordinated by two nitrogen atoms [Ni-N = 2.030(2) angstrom] and two oxygen atoms [Ni-O = 2.027(2) angstrom] belonging to the two H-Quin- anions and two trans-aqua molecules at Ni-O distances of 2.117(2) angstrom. The structure is consolidated by intra- and intermolecular O-H ... O hydrogen bonds. X-ray analysis of the Mn(H-Quin)2 .2H2O complex revealed that it should be formulated as [Mn(H2O)6][Mn(H-Quin)3]2. The octahedral [Mn(H-Quin)3]- and [Mn(H2O)6]2+ units lie on different three-fold axes and are connected together by O-H ... O hydrogen bonds between the aqua ligands and the non-coordinated oxygen of a carboxylato group or oxygen atoms of the carboxy group in position 3 in the pyridine ring.