SYNTHESIS, CRYSTAL-STRUCTURE, AND PROPERTY OF NOVEL TETRANUCLEAR NICKEL(II) COMPLEX WITH MULTIDENTATE LIGAND 7-[(3,5-DICHLORO-2-PYRIDYL)AZO]-8-HYDROXYQUINOLINE-5-SULFONIC ACID

Reaction of nickel(II) perchlorate with the title ligand (Hpahqs) in aqueous solution followed by standing for about six months produces a complex having the formulation [Ni4(pahqs)4(H2O)4].20H2O. A single crystal X-ray analysis revealed that the complex contained the four nickel(II) and four ligand molecules and showed a novel structure of oxygen bridged tetranuclear nickel(II) complex. Crystal data: triclinic, space group P1BAR, a = 17.884(7), b = 22.071(8), c = 12.819(8) angstrom, alpha = 100.77(4)-degrees, beta = 92.55(4)-degrees, gamma = 71.46(4)-degrees, Z = 2. Except one N atom in each azo-group, all the other donor atoms in the ligand were fully used in coordination to nickel(II), forming either N,N,O-or N,O-chelate rings, simultaneously. The geometry around each of the four nickel(II) was distorted octahedron. The bond lengths of Ni-N(N atoms in N,N,O-terdentate moieties) were elongated compared with those of the corresponding complex, and the lengths of Ni-N(N atoms in quinoline rings) were kept almost similar values to those of the Ni(II)-8-hydroxyquinoline complex. The bond lengths of Ni-O were elongated compared with those of the nickel(II) complexes with either N,N,O- or N,O-chelate rings, resulting in the contraction of the angles of N-Ni-N or N-Ni-O. The angles of Ni-O-Ni around four nickel(II) sites were ca. 140-degrees. The antiferromagnetic exchange interaction was operating between the four nickel(II) via bridging oxygen atoms.