Synthesis, characterization and coordinating properties of an NNS donor system, 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone (HMPzPyr), and it's cobalt(III), nickel(II) and copper(II) complexes

Abstract

The ligational behaviour of 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone has been demonstrated by isolation and characterisation of its complexes with cobalt(III), nickel(II) and copper(II) with different counterions. Magnetic and spectral features indicate [Co(MPzPyr) 2 ]X (X = Cl, Br, NO 3 , ClO 4 or BF 4 ) as the diamagnetic octahedral species with the ligand in the deprotonated thiol form, while [Ni(HMPzPyr) 2 ]X 2 (X = Cl, Br or NO 3 ) is proposed as octahedral complex with the ligand in the neutral thione form. However, at pH ∼6, nickel(II) salts afford octahedral bis-nickel(II) complex, Ni(MPzPyr) 2 , while copper(II) salts in acetonitrile medium give Cu(MPzPyr)X (X = Cl, Br or NO 3 ) with the deprotonated ligand. IR spectra indicate that the pyrazolyl ring nitrogen ( 2 N), the azomethine nitrogen and the sulphur atom are the points of attachment with the metal ion in all these complex species. The cyclovoltammetric study of copper(II) complexes reveals the quasi-reversible one-electron process (Cu II → Cu I ), where the EPR data confirm the presence of d x2―y2 ground state of these complexes.