6533b85afe1ef96bd12b9569

RESEARCH PRODUCT

Study of the interaction between [Cu(bipy)]2+ and oxalate in dimethyl sulfoxide. Crystal structure of [Cu2(bipy)2(H2O)2ox]SO4·[Cu(bipy)ox]

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Abstract A study of complex formation between [Cu(bipy)]2+ and ox2− (bipy and ox2− being 2,2′-bipyridyl and the dianion of oxalic acid), has been carried out by potentiometry in dimethyl sulfoxide solution. The constants of the equilibria and are log β110 = 11.165(1) and log β210 = 13.185(5) at 25 °C and 0.1 mol dm−3 tetra-n- butylammonium perchlorate. The high values of these constants are consistent with the symmetrical bidentate and bis-bidentate modes of oxalate in [Cu(bipy)ox] and [Cu2(bipy)2ox]2+ units, respectively, as shown by X-ray diffraction studies. Well-formed single crystals of [Cu2(bipy)2(H2O)2ox]SO4· [Cu(bipy)ox] were grown from aqueous solutions and characterized by X-ray diffraction. The system is monoclinic, space group C2/c, with a = 22.706(5), b = 10.485(3), c = 16.172(4) A, β = 92.63(3)°, V = 3846(3) A3, Z = 4, Dx = 1.670 g cm−3, μ(Mo Kα) = 18.38 cm−1, F(000) = 1956 and T = 298 K. A total of 3214 reflections was collected over the range 2⩽θ⩽25°; of these, 1099 (independent and with I⩾2.5σ(I) were used in the structural analysis. The final R and Rw residuals were 0.067 and 0.070, respectively. The structure is made up of cationic centrosymmetric [Cu2(bipy)2ox]2+ dinuclear units, neutral axiosymmetric [Cu(bipy)ox] mononuclear entities and SO42− as a counterion. Each copper atom of the dinuclear unit shows a square-pyramidal environment with the two nitrogen atoms of 2,2′-bipyridyl and two oxygen atoms of oxalato bridge building the basal plane and an oxygen atom of a water molecule filling the apical position. The copper atom of the mononuclear unit is bound to two oxygen atoms of oxalate and two nitrogen atoms of 2,2′-bipyridyl forming a four-fold surrounding slightly deviating from planarity. In these complexes, copper coordination is 4 + 1 + 1 (dinuclear unit) or 4 + 2 (mononuclear unit) because of the weak binding of the sulfate group in a bis-monodentate fashion linking alternately dinuclear and mononuclear entities. This is a rare case where the two copper(II) complexes bound to the same ligands, that have been observed in solution, are found in the same compound in the solid state.