Synthesis,characterization, and bonding of indium clusters. Rb2In3, a zintl phase with layers of closo-indium octahedra

The Rb-In system contains only RbIn₄ (BaAl₄ type) and Rb₂In₃ in the 0–80 at.% In region. The structure of Rb₂In₃ consists of rubidium ions between layers of closo-In₆ clusters joined into sheets through exo bonds at four coplanar vertices (I4/mmm, a=6.8735 (4) Å, c=15.899 (1) Å, R(F)/R_w=3.2/3.5%). The phase is isostructural with Cs₂In₃ when a probable error in the earlier space group assignment is corrected. Rb₂In₃ is a poor conductor (P> 10³ μohm · cm) with a temperature-independent magnetic susceptibility of (0 ± 4) x 10^?6 emu/mol after core and orbital corrections. The corresponding Zintl phase (closed shell configuration) predicted on the basis of conventional electron counting for the cluster network is supported by extended-Hückel MO calculations. The structures of Rb₄In₆ and In₄Rb show a close, inverse relationship in the same space group.