Bond-valence approach to the copper-copper and copper-nitrogen bonding in binuclear copper(II) complexes: Structure of tetrakis(2-iodobenzoato)bis(caffeine)dicopper(II) at 210 K

The crystal structure of tetrakis(2-iodobenzoato)bis(caffeine)dicopper(II) at 210 K is monoclinic, space group P2(1)/n (No.14), unit cell parameters a = 13.6090(4), b = 13.5900(2), c = 14.5370(4) Angstrom, beta = 116.394(1)de grees, Z = 2 and D-calc = 2.07 g cm(-3). The structure consists of centrosy mmetric [Cu-2(2IbzO),(caf)(2)] units (2IbzO = 2-iodobenzoate, caf = caffein e). These binuclear units are mutually held by van der Waals forces. Cu ato ms are pentacoordinated by four carboxylic O atoms in the basal plane and o ne apical N atom from the caffeine molecule. Cu-O bond lengths are 1.961(3) , 1.969(3), 1.969(2), 1.974(3) Angstrom, and Cu-N bond length is 2.238(3) A ngstrom. The displacement of Cu atom from the basal plane is 0.2354(4) Angs trom. The calculated Cu(II)-N bond length by bond-valence sum model is 2.31 Angstrom. The Cu...Cu distance is 2.7041(6) Angstrom. The non-bonding char acter of Cu(II)...Cu(II) contact in 26 binuclear carboxylic complexes with CuO4N chromophores is proved. (C) 2001 Elsevier Science B.V. All rights res erved.