Pseudo-oxocarbon complexes — crystal structure of a copper(II) complex with 2,4-bis(dicyanomethylene)cyclobutane-1,3-dione

The reaction of copper(II) ions with the 2,4-bis(dicyanomethylene)cyclobutane-1,3-dione dianion (2,4-dcmsq2−), a pseudo-oxocarbon derived from squaric acid in which two carbonyl oxygen atoms have been substituted by dicyanomethylene groups C(CN)2, leads to many complexes according to the preparative scheme. The complex [Cu(2,4-dcmsq)(H2O)4]n has been synthesized and characterized by single-crystal X-ray diffraction. The structure consists of a chain of copper atoms bridged by the ligand with short CuN bonds. Spectroscopic and structural characterizations of the product are compared with those of the previously described [Cu(2,4-dcmsq)(H2O)4·2H2O]n.