Synthesis and spectroscopy of nickel(II) complexes with 5-methyl-3-formylpyrazole N(4)-methyl-N(4)-cyclohexyl thiosemicarbazone (HMPz4MCy):: X-ray crystal structure of [Ni(HMPz4MCy)2]Cl2 • 2.5H2O

The coordination behaviour of a new pyrazolyl thiosemicarbazone, HMPz4MCy, synthesized and characterized (elemental analyses, mass spectrum, i.r. and H-1-n.m.r) for the first time, is reported via solid state isolation of Ni-II complexes, [Ni(HMPz4MCy)(2)]X-2.nH(2)O (X = Cl, Br, NO3, ClO4 and BF4; n = 2-3). The complex species were spectroscopically and structurally characterized. I.r. data for the free ligand and its Ni-II complexes indicate that the ligand, HMPz4MCy, exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen (tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a distorted octahedral environment for the six-coordinate Ni-II species. X-ray crystallography of a representative species, [Ni(HMPz4MCy)(2)]Cl-2.2.5H(2)O (P2(1)/c, monoclinic) has shown unambiguously that the crystallographic asymmetric unit consists of a [Ni(HMPz4MCy)(2)](2+) cation and two Cl- anions with the solvent of crystallization consisting of two H2O molecules with full occupancy and a third H2O molecule with half occupancy. The two NNS ligands orthogonally coordinate to the central nickel(II) ion with two azomethine nitrogen atoms in trans and the pyrazolyl nitrogen and the thione sulphur atoms in cis-positions. The crystal structure is stabilized by an extensive network of hydrogen bonds and is also additionally stabilized by C-H...S contacts restricting free rotation about the N-C single bonds.