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

Abstract

The crystal structures of two copper(II) complexes of croconate violet (3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate=L 2−) have been determined by X-ray methods. Complex 1 consists of mononuclear [CuL 2(H 2O) 2] 2− ions, potassium cations and two crystallisation water molecules. Complex 2 consists of mononuclear [CuL 3] 4− ions, (NBu 4) + 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.