Formation of Spherical Giant Molecules and Dynamic Behaviour of Supramolecular Assemblies Based on Pn-Ligand Complexes

We report herein on our concept of using En-ligand complexes (E = P, As) as linking units for the creation of novel supramolecular ensembles. The reaction of these complexes with Group 11 metal salts of coordinating anions leads to the formation of insoluble oligomers, 1D and 2D polymers as well as soluble spherical nanoscaled clusters. In contrast, the reaction of En-ligand complexes with Group 11 metal salts of weakly coordinating anions yields soluble oligomers and polymers, which display monomer-oligomer equilibria in solution

Structural Analysis of Silica-Supported Molybdena Based on X-ray Spectroscopy: Quantum Theory and Experiment

Oxygen core excitations in different molecular molybdena silica models are evaluated using density-functional theory (DFT). These results can be compared with in situ X-ray absorption fine structure (NEXAFS) measurements near the O K-edge of molybdena model catalysts supported on SBA-15 silica, used for exploratory catalytic activity studies. The comparison allows an analysis of structural details of the molybdena species. The silica support is found to contribute to the NEXAFS spectrum in an energy range well above that of the molybdena units, allowing a clear separation between the corresponding contributions. Different types of oxygen species, O(1) in terminal MdO bonds, O(2) in interphase Mo—O—Si bridges and in Mo—O—Mo linkages, as well as O(2) in terminal Mo—O—H groups can be distinguished in the theoretical spectra of the molybdena species with molybdenum in tetrahedral (dioxo species), pentahedral (monooxo species), and octahedral coordination. The experimental NEXAFS spectra exhibit a pronounced double-peak structure in the O 1s to Mo 4dO 2p excitation range of 529 536 eV. Comparison with the present theoretical data gives clear indications that dioxo molybdena species with tetrahedral MoO4 units can explain the experimental spectrum. This does not fully exclude species with other Mo coordination, like pentahedral. However, the latter are believed to exist in the present samples in much smaller amounts. The experimental NEXAFS spectrum for the supported molybdena species differs substantially from that for MoO3 bulk material with octahedral MoO6 units where the observed asymmetric peak structure is also reproduced by the calculations