Reversible switching of copper(ΙΙ) complexes using a hemilabile N,N′-Bis(β-carbamoylethyl)trans-1,2-diaminocyclohexane ligand

The reaction of CuCl2·2H2O with one equivalent hemilabile diaminodiamide ligand N,N′-bis(β-carbamoylethyl)trans-1,2-diaminocyclohexane (1) gave a blue compound [Cu(C12H24N4O2)Cl]Cl·H2O (2). With more than one equivalent ligands, 2 was transformed to a purple species [Cu(C12H22N4O2)]·3H2O (3) by the Cu―O to Cu―N bond rearrangement at two amide sites of the complex. Compounds 2 and 3 are structurally switchable in response to the Cu(II)/1 ratios in an aqueous solution. Structures of 2 and 3 were characterized by single-crystal X-ray diffraction analysis. Structural data for 2 indicated that the copper atom adopts a five-coordinated N2O2Cl environment and gives a square-pyramidal geometry. The structure of 3 showed that the copper atom adopts a four-coordinated N4 environment, giving a distorted square-planar geometry. The color change could be described as a pH dependent isomerization of the ligand. The results presented could be useful in the design of new Cu(II)-based switching materials.