METAL CLUSTER TOPOLOGY 19 - BEYOND THE AURIDE ION - TRIANGULATED GOLDNETWORKS AND ETHANE-LIKE STRUCTURAL UNITS IN BINARY AND TERNARY ALKALI-METAL GOLD INTERMETALLICS

The range of known structurally characterized alkali metal gold interm etallics now extends Ear beyond the simple 'auride' derivatives CsAu a nd RbAu containing the discrete auride ion, Au-, isoelectronic with Hg -O. The structurally characterized binary alkali metal gold intermetal lics M(2)AU(3) (M = K, Rb), Rb3Au7 and MAu5 (M = K, Rb) contain infini te triangulated anionic gold subnetworks which can be constructed from linear sp-hybridized gold atoms linked to each other through multicen ter bonding within Au, tetrahedra (for Rb3Au7), Au-4 butterflies (for M2Au3) or Au-5 trigonal bipyramids (for MAu5). The infinite anionic go ld subnetworks in other alkali metal gold intermetallics provide examp les of two-coordinate gold in Na2Au; four-coordinate gold in AeAu(2) ( Ae = Ca, Sr). Na2LiAu3 and NaAuGe; and six-coordinate gold in MAu2 (M = Na, K) and NaAuIn2. More complicated gold structures are found in ot her sodium-gold-indium ternary intermetallics including In-centered Au -12 and empty Au-6 octahedra in Na2Au6In5 as well as squashed Au6In pe ntagonal bipyramids in Na8Au11In6. Many ternary gold intermetallics (E = Ge, In) also contain ethane-like E2Au6 units with unbridged E-E bon ds (e.g., K4Au7Ge2, NaAuGe, and NaAuIn2) or diborane-like E2Au6 units with E-E bonds bridged by two gold atoms (e.g., Na2Au6In5). (C) 1998 E lsevier Science S.A. All rights reserved.