Synthesis, structural and spectroscopic characterization of the thermochromic compounds A2CuCl4: [(Naphthyl ethylammonium)2CuCl4]

• DOI: 10.1016/j.poly.2015.02.036
• Publication Date: 2015-03-04T05:38:48Z
• Authors: Hemant M. Mande; Prasanna S. Ghalsasi; Arulsamy Navamoney
• Keywords: Thermochromism; Monoclinic crystal system

Abstract Two A2CuCl4 type (A = organic ammonium cation) compounds, namely bis-(R)-(+)-naphthyl-1-ethylammonium tetrachlorocuprate(II) (1) and bis-(R)-(+)-naphthyl-2-ethylammonium tetrachlorocuprate(II) (2) were synthesized. Compounds 1 and 2 crystallize in the monoclinic crystal system with the non-centrosymmetric space groups P21 and C2 respectively, with Z = 2. In both compounds the rigid regio-isomeric ligands surround the CuCl42− anion, forming an isolated distorted tetrahedral structure. Temperature dependent single crystal X-ray and FT-IR measurements show diverse ‘motifs’ in the NH⋯Cl interactions and concurrence with the structural phase transition in the DSC study. The observed structural transition is not due to a change in geometry around CuCl42−, normally seen in the literature, but is driven by ‘motifs’ conceived in the ligand itself. A polarizing microscopic study revealed that these reversible transitions are of a thermochromic nature.