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John D. Corbett
Inorganic Solid-State Chemistry
A veritable gold mine of remarkable stoichiometries, unprecedented structures, strong metal-metal bonding, and potential new materials is to be found through synthetic explorations of, for example, highly reduced metal halides, chalcogenides and polar intermetallic phases. The metal-metal-bonded halide examples we have discovered among the early transition metals Sc, Y, La, Zr, Nb especially&SHY;range from isolated six-metal-atom clusters and oligomers through infinite chains of condensed clusters to double-metal-sheets that behave as two-dimensional metals. Many contain essential interstitial atoms, and a diverse and systematic structural chemistry can often be "forced" by that selection. An example is shown below for the metal portion of Scl9(Ru4)Br28. Iodide clusters seem to be especially versatile, the interstitial list including Be-N, Al-P, Cr-Cu, Ru-Pd and Re-Au!
Chemistry of and in intermetallic phases is a new and developing area of solid state chemistry. An unprecedented array of new structures and bonding is found among polar intermetallic phases. These include families like Zr5Sn3Ni, Ca5Sb3Cl, and La5Ge3Sb in which up to 18 elements may serve in the role of the third-listed interstitial. H, C, N, O are found to have major stabilizing effects in many compounds. Remarkable Zintl (valence) phases have also been discovered with isolated clusters like Tl13 11- , the tin
networks in K8Sn25 (shown), and indium buckyballs in an onion-like structure (below).
Innovative and successful syntheses are naturally the first steps to significant solid state discoveries. Unconventional synthetic techniques include the use of welded tantalum or niobium containers, high temperature reactions (600-1400 °C), fluxes, and chemical transport processes. Specialized powder and single crystal X-ray diffraction are important tools in revealing both composition and structure of new materials. Magnetic susceptibility and electrical conductivity measurements, photoelectron and NMR spectroscopy, electron microscopy, and theoretical (extended-Hückel) MO and band calculations are also used to illuminate and to understand the properties and bonding in these new types of solids.
Corbett Research Group November 2009