Metal cluster topology 19. Beyond the auride ion: triangulated gold networks and ethane-like structural units in binary and ternary alkali metal gold intermetallics

Abstract

The range of known structurally characterized alkali metal gold intermetallics now extends far beyond the simple ‘auride’ derivatives CsAu and RbAu containing the discrete auride ion, Au −, isoelectronic with Hg o. The structurally characterized binary alkali metal gold intermetallics M 2Au 3 (M = K, Rb), Rb 3Au 7 and MAu 5 (M = K, Rb) contain infinite triangulated anionic gold subnetworks which can be constructed from linear sp-hybridized gold atoms linked to each other through multicenter bonding within Au 4 tetrahedra (for RFb 3Au 7), Au 4 butterflies (for M 2Au 3) or Au 5 trigonal bipyramids (for MAu 5). The infinite anionic gold subnetworks in other alkali metal gold intermetallics provide examples of two-coordinate gold in Na 2Au; four-coordinate gold in AeAu 2 (Ae = Ca, Sr), Na 2LiAu 3 and NaAuGe; and six-coordinate gold in MAu 2 (M = Na, K) and NaAuIn 2. More complicated gold structures are found in other sodium-gold-indium ternary intermetallics including in-centered Au 12 and empty Au 6 octahedra in Na 2Au 6In 5 as well as squashed Au 6In pentagonal bipyramids in Na 8Au 11In 6. Many ternary gold intermetallics (E = Ge, In) also contain ethane-like E 2Au 6 units with unbridged EE bonds (e.g., K 4Au 2Ge 2, NuAuGe, and NaAuIn 2) or diborane-like E 2Au 6 units with EE bonds bridged by two gold atoms (e.g., Na 2Au 6In 5).