X-RAY-ABSORPTION STUDIES OF METAL-COMPLEXES IN AQUEOUS-SOLUTION AT ELEVATED-TEMPERATURES

Experimental methods for performing X-ray absorption spectroscopy (XAS ) on metal complexes in dilute aqueous solutions at temperatures up to 573 K are presented, The solutions are contained in silica tubes for study by X-rays of energies greater than 16 keV, For experiments using X-rays of energies in the range 6.5-16 keV, we have developed a titan ium cell with Kapton windows, These cells can be heated in an aluminiu m oven up to 573 K, Using these methods we have studied the tetrahedra l: octahedral equilibrium for cobalt(II) in aqueous chloride solutions , Na2MoO4 . 2H(2)O in aqueous solution and cadmium(II) in aqueous chlo ride solutions. For cobalt(II) in chloride concentrations between 5 an d 7 m we have found evidence that [CoCl4](2-) is not the only importan t tetrahedral species, In molybdate(VI) solutions, [MoO4](2-) is the p redominant species over the temperature range 298-573 K. Cadmium(II) i n aqueous chloride solutions shows two major cadmium complexes [Cd(OH2 )(6)](2+) and [CdCl4](2-). Bond distances for the principal species in these solutions are presented and are found to be in general agreemen t with those obtained from X-ray crystallographic studies on related s olids.