Bonding analysis in inorganic transition-metal cubic clusters, 4 -: The distorted Pd9(μ:η5,η2-As2)4(PPh3)8 architecture

Extended Huckel and density functional calculations were carried out on the title compound 1. Results indicate that the bonding of the interstitial Pd-i atom with the D-2d distorted (Pd-s)(8)(As-2)(4) cubic host differs from that found in the related metal-centered cubic species M-9(mu(4)-E)(6)L-8. Species 1 can be described as an approximate square-planar 16-electron PdiL4 center bound through Pd-i-As rather than Pd-i-Pd-s contacts to a distorted cubic fragment composed of four 30-electron bimetallic Pd2L8 units. Although a substantial gap is computed between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for the observed electron count of 130 MVEs, calculations indicate that such an architecture should be observed for different electron counts close to that count. The incorporation of the central Pd atom does not seem to be essential to ensure the stability of the distorded Pd-8(As-2)(4)(PH3)(8) cluster. Such empty clusters, with formally four M-M bonds and eight planar 16-electron Pd, centers, should exist for electron counts close to 120 MVEs.