3:00 pm in Howey Lecture Room 5 (pre-reception at 2:30 in Howey N201)
Robert Whetten
Georgia Institute of Technology
"Molecular Metallurgy: Principles & Promise"
Recently, an increasing number of molecular metallic-cluster compounds have emerged with precise composition and structure, e.g. Au102T44 & Al50Cp12. In each case, a compact shell of ligands encapsulates the metallic core, in the form of stable metal-adatom complexes. Hence the term protected metallic clusters. Their molecular nature has far-reaching consequences: High purity facilitates chemical modification; established composition & structure stimulate benchmark electronic-structure analysis; precise replication leads to completely ordered solid-state molecular crystals, as contrasted to metal-colloid crystals. Structure-bonding analysis led to a unifying Superatom Complex Model, in which a crucial role is assumed by the count of free electrons. These fill a universal aufbau scheme, which identifies the frontier orbitals, while also behaving as a quantized ‘plasma’, accounting thereby for the signature properties: 1. Chemical: Molecular capacitance (governing e-transfer reactions); 2. Physical: Polarizability, NIR-optical response, & excitation transfer. 3. Solid-state (collective): Emergence of efficient transport & broken-symmetry ground states. The establishment of a Southeast-US based Center for Molecular Metallurgy could facilitate the fulfillment of the promise of a rapidly growing range of metallic, alloy, and intermetallic molecules identified and characterized; solid-state structural and transport measurements performed thereupon; as well as theoretical analysis and prediction. A timely opportunity is presented, under (3.) above: the search for high-Tc superconductivity in molecular-metallic crystals. Motivating examples include superconductivity in molecular Ga84-cluster crystals — interpreted analogously to alkali-doped fulleride solids (the highest-Tc molecular crystals) — and evidence of high Tc in selected ligand-free Nb-compound and Al clusters.
