Synthesis and spectroscopic characterization of new cobalt(III) complexes with 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex): X-ray crystallographic identification of HMPz3Hex and [Co(MPz3Hex)(2)]Br center dot H2O with

摘要

The coordinating properties of the title ligand, 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex), synthesized and characterized (elemental analysis, MS, IR, H-1 and C-13 NMR and X-ray crystallography) for the first time, are reported by solid-state isolation of cobalt(III) complexes, [Co(MPz3HeX)(2)]X . nH(2)O (X = Cl, Br, NO3, ClO4 or BF4; n = 1 to 2). The reported complex species have been spectroscopically characterized with X-ray structural identification of [Co(MPz3HeX)(2)]Br . H2O IR and NMR data (H-1 and C-13) for the free ligand and its Co-III complexes confirm that the ligand, HMPz3Hex, behaves as a uninegative anion with NNS tridentate function via the pyrazolyl tert-nitrogen, azomethine nitrogen and thiol sulfur. Electronic spectral data recommend a distorted octahedral environment for the six-coordinate Co-III species. X-ray crystallography of [Co(MPz3HeX)(2)]Br . H2O (C2/c, monoclinic), has shown. unambiguously that the crystallographic asymmetric unit consists of a [Co(MPz3HeX)(2)](+) cation and one Br- anion with one H2O molecule as solvent of crystallization. The two NNS ligands coordinate orthogonally to the central Co-III ion with mer-configuration. A critical scrutiny of the X-ray data of free HMPz3Hex (Pna2(1), orthorhombic) and [Co(MPz3HeX)(2)]Br . H2O indicates that an unusual rotation about the azomethine (C=N) double bond occurs during complexation with Co-III. A plausible reaction mechanism for the sameihas been proposed. Sulfur is involved in a C(7)-H(7)...S(1) intramolecular contact restricting the conformation of the ligand both in free and its complexed form. (C) 2003 Elsevier Ltd. All rights reserved.