Stabilization of metal ensembles at room temperature. Palladium clusters in zeolites

Palladium clusters of low nuclearity have been prepared in the cavities of X zeolites via ion exchange with Pd(NH,),Cl,, oxidative dehydration, and subsequent reduction of the dry Pd(I1) zeolites with hydrogen at 295 and 425 K. Detailed EXAFS analysis of Pd K-edge data shows that the average first-shell Pd-Pd coordination number of the reduced system is only about N = 1.5 at a distance of 2.78 A. A long, relatively disordered coordination of the reduced Pd to framework oxygen and silicon indicates the stabilizing, templating function of the zeolite matrix. Geometric models based upon the EXAFS results show that intrazeolite Pdz, Pd,, and Pd4 clusters are formed by partial occupation of SI and SII positions of the sodalite subunits of the zeolite. This study presents evidence for the formation of molecular metal ensembles stabilized in an open-framework matrix to at least 425 K

Atomic XAFS as a probe of electron transfer within organometallic complexes: data analysis and theoretical calculations

The atomic XAFS (AXAFS) contributions in the Pt L2,3 X-ray absorption fine structure spectra (XAFS) of [PtCl(NCN)-Z] pincer complexes are shown to be a sensitive probe of changes in the electron density on the Pt atom induced by changes in a para-substituent on the neighboring benzene ring. Such electron density information is similar yet complementary to NMR data. These complexes provide a unique system for examining inductive effects on the AXAFS data, since the geometry around the Pt atom remains unchanged. An initial brief report on this work has been given previously. In this paper a more complete description of the AXAFS isolation technique and theoretical interpretation is given. The isolation of the AXAFS contributions from the XAFS spectrum is extensively described. The dependence of the AXAFS shape and intensity on the Pt atom electron density are shown and discussed in detail