Indirect evidences of desulfurization of a thiosemicarbazonecopper(II) system in aqueous basic medium

A basic aqueous solution of the [{Cu(L)(NO3)}2] compound (HL = C8H10N4S, pyridine-2-carbaldehyde 4N-methylthiosemicarbazone) at pH = 11 is acidified to pH = 5 by addition of diluted nitric acid yielding the [{Cu(L)}2(NO3)](OH) · 5H2O (1) complex. The structure of 1 contains a bidentate Cu–ON(O)O–Cu nitrato bridge. However, a 1:2 copper:thiosemicarbazone ratio in the image system leads to the attainment of the [{Cu(L)(H2O)}{Cu(L)(SO4)}] · 5H2O (2) compound. The monodentate sulfato group in 2 arises from the desulfurization of thiosemicarbazone ligands. In both cases, the crystal structures consist of dinuclear non-centrosymmetric entities where the thiosemicarbazone sulfur atoms act as bridges between copper(II) ions in distorted square-pyramidal environments.