Laboratory Stopped-Flow XAFS Apparatus. Structure Determination of the Short-Lived Peroxochromium Intermediate Formed during Reduction Process of Chromate(VI) Ion by Hydrogen Peroxide

In order to determ ine the structure param eters o f the reaction interm ediate form ed during the reduction process of chrom ate(V I) ion by hydrogen peroxide, a laboratory stopped-flow X-ray absorption fine structure (X A F S ) apparatus, which was constructed by a rotating an­ ode X-ray generator, an energy scanning spectrom eter, a stopped-flow assem bly, and X-ray detectors, was newly developed. U sing the apparatus, the Cr K-edge X A F S spectrum of the reaction interm ediate was m easured. O ne oxo group, tw o peroxo groups, and one water m olecule are coordinated to the Cr(VI) center in the interm ediate, C r 0 ( 0 2)2(H 20 ) , with C r -O bond lengths of 157, 168, and 193 pm, respectively. The geom etry around the Cr(VI) center is probably 6-coordinate pentagonal pyramidal.