Extended X-Ray Absorption Fine Structure Studies in Some Aqueous Copper(II) Solutions

With a laboratory EXAFS apparatus consisting of a usual X-ray generater, an LiF crystal, and a position sensitive X-ray detector with a self-scanning photodiode array, EXAFS spectra were obtained for aqueous [Cu(NH3)4]SO4, [Cu(en)2]Cl2 (en=ethylenediamine), and CuSO4 solutions. By reference to similar spectra of the corresponding crystals, the solution spectra were analyzed by the curve-fitting method. The values obtained for the distances between the metal and its first-shell atoms in the ammine and sulfate solutions are 2.03 (±0.02) and 1.98 (±0.03) Å, in accordance with those derived from the X-ray diffraction experiments. The Cu–N distance of [Cu(en)2]2+ in solution is 2.02 or 2.04 (±0.02) Å. These values obtained for the solutions are very close to those of corresponding solid complexes.