Bond-valence approach to the copper-copper and copper-oxygen bonding in binuclear copper(II) complexes: Structure of tetrakis(2-fluoro-benzoato-O,O´)-bis(2-fluorobenzoate-O) dicopper(II)

Abstract

The crystal and molecular structure of tetrakis(2-fluorobenzoato-O,O´)-bis(2-fluorobenzoate-O) dicopper(II) - C42H26Cu2F60O12 - has been determined at room temperature. The blue-green crystals are monoclinic, space group P21/n (No.14), with unit cell parameters a=10.633(3) Å, b= 12.528(3) Å, c=14.729(3) Å, β = 91.62(4)°, Z= 2, Dm= 1.62 and Dx= 1.64 g/cm3. The final R value for independent reflections is equal to 0.045. The structure consists of two centrosymmetric units [Cu2(2FbzO)4(2HFbzO)2] (abbreviation 2FbzO stands for 2-fluorobenzoate, abbr. 2HFbzO for 2-fluorobezoic acid). These units are mutually held by Van der Waals forces. Within the binuclear unit the Cu atom is pentacoordinated by four carboxylic O atoms in the basal plane of tetragonal pyramid (Cu–O bond lengths being 1.962(3) Å, 1.963(2) Å, 1.958(2) Å and 1.996(2) Å and one apical O atom from HFbzO molecule, with Cu-O bond length 2.193(2) Å. The apical Cu(II)–O bond length predicted by bond valence method is 2.16 Å. The Cu...Cu distance is 2.6086(8) Å and the displacement of Cu atom from the basal plane is 0.1905(6) Å. Nonbonding character of Cu(II)...Cu(II) contact in 16 binuclear carboxylic complexes is proved.