THERMOCHROMISM IN COPPER(II) COMPLEXES - STRUCTURES OF THE RED AND BLUE-VIOLET FORMS OF BIS(N,N-DIETHYLETHYLENEDIAMINE)COPPER(II) PERCHLORATE AND THE NONTHERMOCHROMIC VIOLET BIS(N-ETHYLETHYLENEDIAMINE)COPPER(II) PERCHLORATE

The crystal and molecular structures of the title compounds have been determined by three-dimensional X-ray diffraction data by using an automatic four-circle diffractometer. The red low-temperature form of the thermochromic compound, studied at 25 °C, is triclinic, [formula omitted] and γ=63.34 (8)°, and the blue-violet high-temperature form studied at 60 °C is monoclinic, 12, Z=4, a=13.34 (1) υ, b=8.414 (5) υ, c=9.978 (5) υ, and β=97.43 (5)υ. The violet nonthermochromic compound, studied at 25 °C, is triclinic, [formula omitted] and γ=63.34 (8)υ. The copper atom has a square-planar coordination geometry in both forms of the thermochromic compound but a tetragonally elongated octahedral coordination in the bis(N-ethylethylenediamine) copper (II) complex with weakly coordinated perchlorate oxygen atoms at the axial positions. The thermochromic behavior in bis (N,N-diethylethylene-diamine)copper(II) perchlorate is thus not caused by a change in the axial coordination of copper (II) but is rather an effect of a change in the in-plane field strength. Although there is no significant difference in the Cu-N distance, the conformation of the ligands is different in the red and blue-violet forms of the thermochromic compound. In the high-temperature form a thermally induced inversion of the conformation of the copper-ethylenediamine rings seems to be the cause of large atomic movements perpendicular to the ring system. The ring inversion also results in large atomic motions of the ethyl side chains. This interpretation is supported by a proton magnetic resonance study, which indicates an averaging of the local magnetic fields by atomic motion. In the three compounds investigated the Cu-N bond distances increase significantly with increasing substitution on the amino group. A comparison with previously reported distances shows the weak axial interactions to have only a negligible influence on the Cu-N4 in-plane bond lengths. © 1979, American Chemical Society. All rights reserved.