Synthesis, characterisation and coordination properties of 5-methyl-3-formylpyrazole 4 N-benzylthiosemicarbazone (HMPzNB) Cobalt(III), nickel(II) and copper(II) complexes with a NNS donor system

 Department of Chemistry, Panskura Banamali College, Midnapore-721 152, West Bengal, India
Department of Chemistry, University of Calcutta, 92, Acharya Prafulla Chandra Road,
Kolkata-700 009, India
Manuscript received 2 April 2006. revised 27 November 2006. accepted 27 November 2006

The title ligand, 5-methy1-3-formylpyrazole ⁴N-benzylthiosemicarbazone (abbreviated as HMPzNB) has been synthesised and physicochemically characterised by elemental analysis, IR, PMR and mass spectrum. The ligational behaviour of the pyrazole-derived thiosemicarbazone, HMPzNB, has been examined by isolation and characterisation of its complexes with Co^III , Ni^II and Cu^II with different counterions. Elemental analyses, magnetic and spectral features indicate [Co(MPzNB)₂]X (X = CI^-, Br^-, NO^-₃), CIO^-₄ or BF^-₄) as the diamagnetic octahedral species with the ligand in the deprotonated thiol form, while [Ni(HMPzNB)₂]X₂ (X = CI^-, Br^-, NO^-₃ or CIO^-4) is proposed as octahedral complex with the ligand in the neutral "thione" form. However, in the neutral condition (pH ~ 6) nickel(ll) salt affords octahedral bis-  ickel(ll) complex, Ni(MPzNB)₂, while copper(ll) salt gives [Cu(MPzNB)]X (X = CI^-, Br^-, NO^-₃ or CIO^-₄), with the deprotonated ligand. 5-Methyl-3-formylpyrazole ⁴N-benzylthiosemicarbazone possesses in its structure, the tertiary nitrogen atom (²N) of the pyrazole ring, the azomethine nitrogen and the sulphur atom as potential binding sites; thus the title ligand is expected to behave as a potential NNS tridentate during complex formation with a metal ion