Exploratory Synthesis: The Fascinating and Diverse Chemistry of Polar Intermetallic Phases†This article is based on J. D. Corbett’s address upon receipt of the 2008 American Chemical Society’s F. Albert Cotton Award in Synthetic Inorganic Chemistry sponsored by the F. Albert Cotton Endowment Fund.

Abstract

Exploratory synthetic adventures regarding the inorganic chemistry of polar intermetallic phases have proven to be especially productive of novel compositions, new and unprecedented structures, and unusual bonding regimes. Reactions of diverse elements with widely different electronegativities allow the definition of two opposed classes of products: polycationic or polyanionic clusters or networks of metals paired with the corresponding monatomic anions or cations. These can be usefully viewed as intermetallic "salts", redox products of simpler neutral intermetallic systems but with widely different factors governing their stabilities. Thus, combinations of rare-earth metals alone or with late transition metals form a novel variety of polymetal network structures with relatively isolated telluride (or halide) spacer anions. Similarly, extensions of traditional Zintl phases of the alkali or alkaline-earth metals from the later p elements to the earlier triels, Ga-Tl especially, yield many new and elegant polyanionic structures. The substitution or addition of still earlier p or late d metal components produces still electron-poorer and more condensed polar intermetallic phases with increasingly delocalized bonding, higher coordination numbers, and more unusual structures and bonding. These discoveries have also led to new approaches: electronic tuning via band calculations to generate new families of quasicrystals and their crystalline approximants with their characteristic structural regimes and regularities. Gold as a substituent generates particularly novel bonding in arrays of mixed metals or polygold anionic networks.

Ionic vs. van der Waals layered materials: identification and comparison of elastic anisotropy

“…Sc 6 PdTe 2 , CaBe 2 Ge 2 ). 64,65 Perhaps less appreciated are the layered structures with electronegative spacers. Examples such as ClCa 2 N and I 3 La 5 Si 5 have halogen spacers and polycationic slabs.…”

Revisiting the Zintl‒Klemm Concept for ALn2Ag3Te5-Type Alkaline-Metal (A) Lanthanide (Ln) Silver Tellurides

“…In fact, examining the electronic structures of (active-metal) transition-metal tellurides (active-metal = group I and III elements) revealed that the bonding nature in these tellurides is dominated by strong transition-metal−tellurium interactions beside minor transition-metal−transition-metal or tellurium−tellurium interactions. Because the transition-metal−tellurium interactions in these tellurides exhibited attributes of strong mixed-metal bonds, it was concluded that these tellurides should be assigned to the groups of polar intermetallics [19,20] rather than the Zintl phases.…”

Revealing the Nature of Chemical Bonding in an ALn2Ag3Te5-Type Alkaline-Metal (A) Lanthanide (Ln) Silver Telluride

“…Yet, certain concepts, e.g., those stated by Hume-Rothery [6][7][8] or Zintl and Klemm [9][10][11], help to understand the distributions of valence-electrons in some intermetallics. On the other hand, more recent research [1,12] on polar intermetallic compounds revealed the existence of polyanionic or polycationic units ("clusters") which are combined with monoatomic counterions, but are electron-poorer relative to Zintl phases.…”