Syntheses, crystal structures and solid state thermochromism of copper(II) complexes of trans-1,2-diaminocyclohexane

Abstract

The complexes CuL 2X 2 · nH 2O (L = trans-1,2-diaminocyclohexane; n = 2 when X is Cl and n = 0 when X is NO 3) have been synthesized. The complexes [CuL 2(H 2O) 2]Cl 2 ( 1) and [CuL 2(NO 3) 2] ( 2) have been characterized by single crystal structural analyses and their thermochromism was studied in the solid state. Single crystal X-ray structure analysis of 1 and 2 shows that in both complexes copper ion possesses distorted (4+2) octahedral geometry with N 4O 2 chromophore. Complex 1 shows time-dependent reversible discontinuous thermochromism whereas, 2 shows reversible continuous thermochromism in the solid state. The discontinuous thermochromism in 1, is due to the different ligand field strength between H 2O and Cl, and is associated with deaquation-anation reaction. The IR and electronic spectra of 2 vary with temperature, indicating reversible continuous thermochromism arising from axial interaction between semi-coordinated nitrate ions and CuN 4 plane.