SYNTHESIS, CHARACTERIZATION, AND BONDING OF INDIUM CLUSTER PHASES - NA15IN27.4, A NETWORK OF IN16 AND IN11 CLUSTERS - NA2IN WITH ISOLATED INDIUM TETRAHEDRA

The remaining phases in the Na-In system have been identified and characterized. The indium-richest is Na15In27.4, with a structure containing novel closo-In16 clusters interconnected to two kinds of nido-In11 units and isolated, 4-bonded atoms (Cmcm, Z = 8, a = 16.108(4) Å, b = 35.279(8) Å, c = 15.931(3) Å, R/Rw = 0.041/0.044 at the indium-rich limit Na15In27.54). Fractional occupancy of two atoms in cluster chain positions were found, one as a function of a narrow nonstoichiometry. The structure is related to that recently established for Na7In11.8. Resistivity and magnetic properties are consistent with a small (0.5-3.2%) excess of electrons relative to the calculated bonding requirements. The sodium-richest phase is the stable, diamagnetic, and weakly metallic Na2In, isostructural with Na2Tl (C2221, Z = 16, a = 13.855(1) Å, b = 8.836(1) Å, c = 11.762(1) Å, R/Rw = 0.030/0.034). A corrected phase diagram is given. © 1993 Academic Press, Inc.