Spectroscopic and electrochemical properties of nickel(II), iron(III) and cobalt(II) complexes with benzilbisthiosemicarbazone - importance of working conditions and the metal salt used in the final complex

Reactions of benzilbisthiosemicarbazone (LH6) with nickel, cobalt and iron chloride and nitrate give different complexes depending on the salts used a nd the working conditions. Reactions from nickel chloride give three comple xes, 1, 2 and 3 when the solvent or the pH is modified. Complex 1 is obtain ed in ethanol under reflux, and in methanol, independently of temperature a nd also with basic medium. Complex 2 is formed by working in ethanol at roo m temperature. The ligand acts as a dianion in both complexes. In the prese nce of hydrochloric acid, the new isolated complex 3 presents the neutral f orm of the ligand. Reaction from nitrate yields only complex 1. Reactions w ith iron chloride give two new complexes with different formulae and grade of deprotonation in the ligand. For complex 4, obtained at room temperature , LH6 acts as an anion with a ligand-iron ratio of 2:1 and in its neutral f orm with a 1:1 ratio in complex 5, working under reflux. Reactions with iro n nitrate yield complex 6, with the ligand in an intermediate situation, as anion but a nitrate remains. Complexes 7 and 8, with a 1:1 cobalt-ligand m olar ratio are isolated from reactions with cobalt nitrate; both contain ni trate and ethanol or water to complete the co-ordination sphere. Attempts t o get a macrocyclic thiosemicarbazone from reaction of benzil and LH6 in th e presence of nickel or iron salt gave the complexes obtained, in absence o f the dicarbonyl molecule. Electrochemical behaviour of complexes studied b y cyclic voltammetry show metal-centred reduction processes for all of them . The reduction/oxidation potential values depend on the structures of comp lexes. Nickel complexes exhibit waves corresponding to Ni(III)-Ni(II) proce ss. Electrochemical response of iron complexes depends on the presence of c hloride ions. (C) 2000 Elsevier Science Ltd. All rights reserved.