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 P21/n (No.14), unit cell parameters a=13.6090(4), b=13.5900(2), c=14.5370(4) Å, β=116.394(1)°, Z=2 and Dcalc=2.07 g cm−3. The structure consists of centrosymmetric [Cu2(2IbzO)4(caf)2] units (2IbzO=2-iodobenzoate, caf=caffeine). These binuclear units are mutually held by van der Waals forces. Cu atoms are pentacoordinated by four carboxylic O atoms in the basal plane and one apical N atom from the caffeine molecule. CuO bond lengths are 1.961(3), 1.969(3), 1.969(2), 1.974(3) Å, and CuN bond length is 2.238(3) Å. The displacement of Cu atom from the basal plane is 0.2354(4) Å. The calculated Cu(II)N bond length by bond-valence sum model is 2.31 Å. The Cu…Cu distance is 2.7041(6) Å. The non-bonding character of Cu(II)…Cu(II) contact in 26 binuclear carboxylic complexes with CuO4N chromophores is proved.