Synthesis and spectroscopic characterisation of copper(II) complexes with 5-methyl-1-(2'-pyridyl) pyrazole-3-carboxamide (MP_yP_zCA): X-ray crystal structure of [Cu(MP_yP_zCA)_2(H_2O)](ClO_4)_2

摘要

The coordination mode of the title ligand, MP_yP_zCA (synthesised for the first time and characterised by elemental analyses, mass, IR and PMR spectral parameters), is reported by solid state isolation and physicochemical identification of copper(II) complexes, Cu(MP_yP_zCA)_2X_2.H_2O (X = Cl/Br/NO_3/ClO_4). Magnetic and electronic spectral features classify the reported complexes as six coordinate distorted octahedral ones. IR spectra (4000-200 cm~(-1)) of MP_yP_zCA and its complexes indicate different denticity of the two ligand moities namely neutral bidentate function through pyrazolyl ~2N and pyridyl ~1'N of one ligand (A) and the neutral tridentate behaviour through pyrazolyl ~2N, pyrazolyl ~2N, pyridyl ~1'N and the amidic oxygen of the second ligand system (B). The sixth apical coordination site is occupied by a water molecule in the perchlorate complex (as evident by X-ray data) or by the counter ion, X (X = Cl/Br/NO_3). The electrochemical studies demonstrate easy oxidative nature of Cu(II) in the reported species. X-ray crystallographic studies of the perchlorate complex, [u(MP_yP_zCA)_2(H_2O)](ClO_4)_2, (Pna2_1, orthorhombic), has substantiated the conjecture that the geometry is distorted octahedral. The Cu-N (pyrazolyl) and Cu-N (pyridyl) bond lengths are 2.001(3) and 1.969(3) A and 2.020(4) and 2.206(4) A in the ligand systems, A and B, respectively; Cu-O (amidic oxygen) for ligand system B and Cu-O (water) bond lengths are 2.783(3) and 2.010(3) A, respectively. The crystal structure is highly stabilised through extensive hydrogen bonding.