EXAFS ATOMIC DISTRIBUTIONS IN MODEL CLUSTERS OF PD AND PT

High-nuclear clusters of known X-ray structures: Pd-10(CO)(12)L(6) (1) , Pd-16(CO)(13)L(9) (2), Pd-23(CO)(22)L(10) (3), Pd-23(CO)(20)L(8) (4) , Pd-38(CO)(28)L(12) (5), and Pt-4(CO)(5)L(4) (6) (L = phosphine), wer e studied by synchrotron EXAFS. spectrometry [K(Pd) and L(III)(Pt) edg es] to model the supported M(n) clusters in catalysts. Atomic radial d istributions from EXAFS and X-ray data are in agreement; however, the systematic shortening in Pd-Pd distances of the first Pd sphere (2.75- 2.80; X-ray 2.78-2.82 Angstrom) was observed. FCC(1), (3) and BCC(4) c lusters display more pronounced EXAFS patterns than the distorted 'amo rphous' (2) and (5). Cluster cores of(1) and (6) do not change noticea bly in o-xylene solutions.