Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Re–Cu, Ir–Cu, and Pt–Cu clusters

Abstract

The extended x-ray absorption fine structure (EXAFS) associated with the LIII absorption edges of rhenium, iridium, and platinum, and the K absorption edge of copper, has been used to study the structures of silica supported Re–Cu, Ir–Cu, and Pt-Cu, bimetallic clusters. The atomic ratio of copper to the other metal was approximately one in all cases. The systems were chosen to investigate the effect of varying miscibility of the components on the structural features of the bimetallic clusters. At one extreme, platinum and copper are totally miscible in the bulk. At the other extreme, rhenium and copper are completely immiscible. Iridium and copper are only slightly miscible in the bulk. In the bimetallic clusters, atoms of rhenium, iridium, or platinum are all coordinated to copper atoms about as extensively as they are to atoms of their own kind. This result is particularly interesting for the Re–Cu and Ir–Cu clusters, in view of the limited miscibility of either iridium or rhenium with copper in the bulk. The surprisingly good coordination of iridium and rhenium to copper is attributed to a very high state of dispersion of these metal clusters.