Complexation of croconate violet with copper(II). Crystal structures, spectroscopic characterizations and redox studies

The crystal structures of two copper(II) complexes of croconate violet (3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate=L2−) have been determined by X-ray methods. Complex 1 consists of mononuclear [CuL2(H2O)2]2− ions, potassium cations and two crystallisation water molecules. Complex 2 consists of mononuclear [CuL3]4− ions, (NBu4)+ cations and one half crystallisation water molecule. In these two complexes, the ligand is coordinated in a chelating mode by two adjacent oxygen atoms. The electrochemical behaviour of these complexes is discussed and compared to that of the free croconate violet.