N, N′-Substituted thioureas and their metal complexes: Syntheses, structures and electronic properties

Abstract

The synthesis of six N,N′-substituted thiourea ligands (L1a-L3b) was achieved in two steps. A corresponding extensive series of Cu(i), Cu(ii), Ni(ii) and Zn(ii) complexes (1-24) with varying formulations were synthesised from these ligands by the reaction of a 1 : 1 or a 1 : 2 mixture of Cu(ii), Ni(ii) and Zn(ii) perchlorate or chloride salts. Complexes 1-24 have been comprehensively characterised by mass spectrometry, elemental analysis, UV-vis., IR, and 1H and 13C{1H} NMR spectroscopies where applicable. The X-ray crystal structures were obtained for eight examples: [(L1a)2Cu]ClO4 (1), [(L1c)2Zn](ClO4)2 (4), [(L2a)2Cu]ClO4 (6), [(L2c)2Ni](ClO4)2 (7), [(L1b)2Cu](ClO4) (15), [(L1b)CuCl] (16), [(L4)2CuCl2] (19) and [(L3b)CuClO4] (21). These studies reveal that L1c and L2c represent ligands that have undergone cleavage during reaction with the metal salt; L4 represents an intramolecular rearrangement (via a Hugershoff reaction) of L2b; and in most cases Cu(ii) is reduced to Cu(i) during the ligand reaction. The X-ray crystal structures also reveal that 1, 4, 6, 15 and 16 are monometallic species in the solid state; that Cu(i) in 1, 6, 15 and 16 and Zn(ii) in 4 are arranged in a distorted tetrahedral geometry; that Cu(i) in 21 adopts a trigonal planar geometry; and that in 7 and 19 the Ni(ii) and Cu(ii) centres, respectively, possess square planar geometry. Preliminary studies on the biological activity (using the Malaria Sybr Green I Fluorescence assay) of the thiourea containing complexes suggests that the d10 complexes, and increased ligand stoichiometries, may afford higher potency.