Biguanidinium(2+) Hexachlorocuprate(II) dihydrate (C2H9N5)(2)[CuCl6] center dot 2H(2)O, a novel compound containing a separate [CuCl6](4-) anion: Synthesis and structure

The (BgH(2))(2)[CuCl6].2H(2)O compound, where BgH(2)(2+) is the biguanidini um(2+) cation, (C2H9N5)(2+), was synthesized and characterized by X-ray dif fraction analysis. The structure of the compound is ionic and built from th e [CuCl6](4-) anions, BgH(2)(2+) cations, and water molecules. The [CuCl6]( 4-) anion is shaped like a square bipyramid. The equatorial Cu-CI distances are equal to 2.2963(8) and 2.3395(8) Angstrom, and the axial Cu-CI distanc es are equal to 2.885(1) Angstrom. In the structure, the ions are arranged in layers joined together by hydrogen bonds. The EPR parameters change only slightly upon cooling to 77 K, suggesting that the nearest surrounding of the copper(II) ion is stable. The compound, from yellow at 293 K, turns to light green at 77 K.