A bridge-bond isomerism. X-Ray crystal structure, spectral and magnetic properties of two dinuclear isomeric complexes [Cu(bipyo)Cl2](bipyo = 2,2′-bipyridine N,N′-dioxide)

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Abstract
Copper(II) chloride reacts with 2,2′-bipyridine N,N′-dioxide (bipyo), in methanolic solution, in a manner depending on the reaction conditions (temperature, ligand : metal ion ratio, concentration, etc.) to form different products. Two of them, a green and a yellow-orange isomer of [Cu2(bipyo)2Cl4], have been characterized by elemental microanalysis, electronic, IR and ESR spectra and magnetic susceptibility measurements. The crystal and molecular structures of both isomers have been determined from X-ray diffractometer data by the heavy-atom method and refined by full-matrix least-squares. The structures of the green and yellow-orange isomers, respectively, have been refined to R= 0.054 (for 1366 reflections) and 0.063 (for 1283 reflections): green isomer, triclinic, space group P, a= 8.664(2), b= 8.732(2), c= 9.099(3)Å, α= 95.62(2), β= 107.04(2), γ= 114.05(2)°, and Z= 1; yellow-orange isomer, monoclinic, space group P21/c, a= 7.912(2), b= 9.878(2), c= 15.086(3)Å, β= 99.86(2)° and Z= 2. Both crystal structures comprise centrosymmetric dimeric [Cu2(bipyo)2Cl4] molecules. The copper(II) atoms of the green isomer are bridged by two chlorine atoms, those of the orange-yellow isomer by the oxygen atoms of two bipyo ligands.