Dr. Lawrence F. Dahl of the Department of Chemistry, University of Wisconsin at Madison, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division to continue his studies on high-nuclearity metal carbonyl clusters. The main thrust of this project is the synthesis, X-ray structural characterization, and structure-bonding analysis of new high-nuclearity (10 or more metal atoms) homo- and hetero-metallic carbonyl clusters. The synthesis of a series of palladium-carbonyl-phosphine clusters will be optimized and extended to include clusters with different phosphine ligands. This series, including a cluster with 59 Pd atoms, will be studied by proton NMR to determine if hydrido-like H atoms are present. New Pd-Ni clusters will be synthesized in sufficient amounts to permit physical/chemical characterization. These clusters will be reacted with phosphine ligands to determine the ligand effect on metal segregation since previous clusters of this type have shown a surprising degree of metal order. A novel carbonyl-phosphine-hydrido cluster with 28 Pd and 12 Pt atoms will be further studied by NMR and hydrogen-deuterium exchange, and synthetically extended by incorporation of additional Pt and Ni atoms. The preparation of a series of Ni-Pd(or Pt)-Rh(or Ir) carbonyl-hydrido clusters with unprecedented metal frameworks will be attempted. The challenging characterization of these unusual clusters will be accomplished by the combination of X-ray crystallography (CCD area detector), electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry, X-ray fluorescence, magnetic susceptibility, and NMR measurements. Theoretical studies on several clusters including a 18-atom Ni-Au cluster will be carried out using density functional methods that include relativistic effects in order to determine the nature of the Ni-Au bonds and to compare the results to those of previous calculations using the Fenske-Hall MO model. Finally, synthetic methods will be improved and optimized to prepare larger amounts of recently discovered 38-metal Au-Pd-Ni and 35-metal Cu-Ni clusters for physical-chemical studies. This project will add fundamental knowledge about bonds between metal atoms, especially ones between different metal types. The large discreet metal clusters also can serve as models for metal particles and surfaces and contribute fundamentally to our understanding of surface science, metal-particle physics, and heterogeneous catalysis. The multi-metal palladium clusters have potential technological importance in the design of new materials with useful catalytic, electronic, magnetic, optical, and hydrogen storage/isotope separation properties. This work also advances state-of-the-art methods of chemical analysis by applying these techniques to extraordinarily demanding problems.