EXAFS study of binuclear hydroxo-bridged copper(II) complexes

Abstract

Extended X-ray absorption fine structure (EXAFS) measurements have been recorded at the K-edge of copper in binuclear monohydroxo-bridged copper(II) complexes [(bpy)2Cu–OH–Cu(bpy)2](ClO4)3 (1) and [(phen)2Cu–OH–Cu(phen)2](C1O4)3 (2) and dihydroxo-bridged copper(II) complexes [Cu2(μ–OH)2(bipy)2]SO4 · 5H2O (3) and [Cu2(μ–OH)2(phen)2]SO4 · 5H2O (4) (where bpy and phen are 2,2′-bipyridine and 1,10-phenanthroline, respectively) using the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The EXAFS data have been analyzed using the software, Athena and Artemis. Theoretical models have been generated for 1 and 3 using available crystallographic data and then fitted to their experimental EXAFS data to obtain the structural parameters, which include bond-lengths, coordination numbers, and thermal disorders. The results obtained have been found to be comparable with their crystallographic results. As the crystallographic data for 2 and 4 are not available in the literature, we have determined their structural parameters by fitting their experimental EXAFS data with the same theoretical models which were generated for their corresponding analogous complexes 1 and 3, respectively. The structural parameters thus determined have been reported. Also, on the basis of the analysis of the EXAFS data, these four complexes have been shown to be binuclear, i.e. they contain two metals. Further, the values of the chemical shifts suggest that copper is in +2 oxidation state in these complexes.