The early transition metals, especially Zr, Hf, Hb and Ta, exhibit a metal-rich chemistry that is often surprising in its structural and physical aspects. Unfamiliarity with this chemistry is illustrated by the discovery of several new binary compounds in the Ta-S, Ta-Se, Ta-Te, and Hf-Te systems within the past few years. Some striking differences observed between the metal-rich chalcogenides of Zr and Hf or between Nb and Ta challenge basic presumptions about the similarity of these congeneric pairs. The factors controlling the structural anisotropy of a new class of tetragonal layered compounds that includes Ta 2Se, Ta 2− x Nb x S, Hf 3Te 2, and ZrZTe (Z Si, Ge, Sn) are discussed. Strongly early-late transition intermetallic bonding leads to the formation of an expanding class of compounds that includes Ta 9M 2S 6 (M Fe, Co, Ni), Ta 11M 2Se 8 (M Fe, Co, Ni), Ta 8NiSe 8 and the newly discovered hafnium tellurides, Hf 8MTe 6 (M Mn, Fe, Co, Ni, Ru) and Hf 5MTe 3 (M Fe, Co). Our efforts to dismantle solid-state Zr-halide cluster compounds is described. Ambient temperature molten salts help us achieve the controlled excision of [(Zr 6Z)CL 18] n− from solid state precursors; we describe the applications of electronic and NMR spectroscopies in characterizing clusters in solution. Finally, we discuss bonding in metal-rich systems, with particular emphasis on localized bonding descriptions for metalmetal bonds in extended metal-linked networks. Such localized descriptions increase our understanding of otherwise anomalous properties and illuminate the artificiality of separate “metallic” and “covalent” bonding concepts.
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Open Access
Jan 1, 1998
Pierre Bonhôte + 5
