Synthetic, spectroscopic, and X-ray crystallographic studies on binuclear copper(II) complexes with a tridentate NNS-bonding 2-formylpyridine thiosemicarbazone ligand. The characterization of both neutral and deprotonated co-ordinated ligand structures

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Abstract
The preparation of the complexes [(CuLX)2](HL = 2-formylpyridine thiosemicarbazone) from the interaction of HL with the appropriate copper salt (X = CH3COO, Cl, NO3, or ClO4) or by reaction of an HL–KX mixture with copper(II) acetate monohydrate (X = Br or I) is described. Dissolution of [{CuL(CH3COO)}2] in H2SO4 or HCl yields the protonated ligand complexes [{Cu(HL)(SO4)}2] and [{Cu(HL)Cl2}2]·2H2O respectively. The complexes have been characterized by a variety of spectroscopic techniques and the crystal and molecular structures of [{CuL(CH3COO)}2] and [{Cu(HL)(SO4)}2] determined by single-crystal X-ray diffraction techniques from diffractometer data. Crystals of [{CuL(CH3COO)}2] are triclinic, space group P, with a= 8.827(3), b= 8.813(3), c= 8.997(3)Å, α= 117.49(2), β= 110.96(3), γ= 91.65(3)°, and Z= 1. Crystals of [{Cu(HL)(SO4)}2] are monoclinic, space group C2/c, with a= 14.751(3), b= 9.138(2), c= 17.468(4)Å, β= 104.91(2)°, and Z= 4. After full-matrix least-squares refinement the final R value was 0.027 for both complexes (2 216 and 2 206 observed reflections were used respectively). Both complexes consist of discrete centrosymmetric dimers, the monomeric units being bridged by two acetato or sulphato ligands. The copper atoms have a distorted square-pyramidal co-ordination geometry with three donor atoms (NNS) coming from L or HL to form a tricyclic ligating system. The fourth donor atom (oxygen) comes from the bridging CH3COO– or SO4 2– ion. The fifth co-ordination position is occupied by a less strongly bound oxygen from the second bridging anion.