Desulfurization processes of thiosemicarbazonecopper(ii) derivatives in acidic and basic aqueous media

Abstract

This work provides structural evidence for different desulfurization processes in aqueous solutions of [CuL]⁺ derivatives (HL = pyridine-2-carbaldehyde thiosemicarbazone). Structural resolution has been achieved for the [{CuL(SH)}₂] (1), [CuLCl]₂[Cu(pic)₂] (pic⁻ = picolinato, pyridine-2-carboxilato) (2) and [Cu(HL)(NCS)](NO₃) (4) compounds, together with a derivative of 4 with formula [Cu(HL)(NCS)][Cu(HL)(NCS)_0.72(NO₃)_0.28](NO₃)₂ (5), whose HS⁻, pic⁻ and NCS⁻ ligands come from thiosemicarbazone breakage. The behaviour of the [CuL]⁺ species in basic aqueous solutions or water under reflux has been compared with that exhibited by iron(III), cobalt(III), zinc(II) and lead(II) derivatives of the same thiosemicarbazone ligand. [Cu(L′)]⁺ species (HL′ = pyridine-2-carbaldehyde N4-methylthiosemicarbazone) have also been analyzed by infrared spectroscopy or mass spectrometry under the same experimental conditions. In addition, preparative methods for a rational synthesis of the serendipitously obtained compounds are proposed. In this way, the crystal structure of [CuL(pic)]·3H₂O (3) has been elucidated too. The partial desulfurization of coordinated thiosemicarbazones could lead to a reinterpretation of their biological activity with consequences for the search for possible therapeutic uses.