Synthesis, spectroscopic and cyclic voltammetry studies of copper(II) complexes with open chain, cyclic and a new macrocyclic thiosemicarbazones

New copper complexes have been prepared from benzilbisthiosemicarbazone ((LH6)-H-1) and from the cyclic 6-methoxi-1,6-diphenyl-4-thio-3,4,5,6-tetrahydro-2,3,5-triazine ((LH2)-H-2). The complexes were characterized by mass spectrometry, IR, electronic and electron paramagnetic resonance spectra. Complexes from (LH6)-H-1 (1-5) present 1:1 stoichiometry and show different characteristics with a variable grade of deprotonation in the ligand, depending on the salt used (chloride, nitrate or sulfate) and the presence of acid in the medium. A macrocyclic Schiff base, 3,4,9,10-tetraphenyl-1,2,5,6,8,11-hexaazacyclododeca-7,12-dithione-3,4,9,10-tetraene ((LH2)-H-3), containing thiosemicarbazone moieties is readily prepared and characterized for the first time, with fairly good yield, from the mesocycle ((LH2)-H-2) in methanol with copper chloride as template. Near quantitative synthesis of the precursor, (LH2)-H-2, which is a potential chemotherapeutic agent against cancer, has been achieved by reacting benzil and thiosemicarbazide in the absence of metal salt and using a high dilution technique. Macrocyclic complexes 6 and 7 containing thiosemicarbazone moieties were obtained from (LH2)-H-2 and copper nitrate and sulfate. Direct reaction between the copper salt and the macrocyclic thiosemicarbazone ((LH2)-H-3) gave similar complexes but with a lower grade of purity. Macrocyclic complexes 6 and 7 present metal-ligand ratios of 1:2 and 1:1 and the ligand is in a deprotonated form. The redox behaviour was explored by cyclic voltammetry. (LH6)-H-1 complexes show Cu(II)/Cu(I) couples and quasireversible waves associated with the Cu(III)/Cu(II) process. The reduction/oxidation potential depends on the structure and conformation of the central atom in the coordination compounds. (C) 2000 Elsevier Science Ltd All rights reserved.