Synthesis, crystal structure and thermochromism of benzimidazolium tetrachlorocuprate:: (C7H7N2)2[CuCl4]

The synthesis and crystal structure of thermochromic, yellow benzimidazolium tetrachlorocuprate(II), (C7H7N2)(2)CuCl4 (1), have been reported. The compoundcrystallizes in the C2/c space group and contains discrete tetrahedral CUCl42- species. It absorbs one molecule of water from humid atmosphere at room temperature to produce a hydrated green form, (C7H7N2)(2)CuCl4.H2O, which upon heating loses the water molecule in two steps to form the anhydrous yellow compound 1. The role of the water molecule on the solid state, yellowreversible arrowgreen thermochromic transformation is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.