The remaining phases in the (\mathrm{Na}-\mathrm{In}) system have been identified and characterized. The indium-richest is (\mathrm{Na}{15} \mathbf{l n}{27.4}), with a structure containing novel closo. (\mathrm{In}{16}) clusters interconnected to two kinds of nido(\mathrm{In}{11}) units and isolated, 4-bonded atoms ( (\mathrm{Cmcm}, Z=8, a=16.108) (4) (\AA, b=35.279) (8) (\AA, c=15.931) (3) (\AA, R / R_{\mathrm{w}}=0.041 / 0.044) al the indium-rich limit (N a_{15}\left(n_{27.54}\right.) ). 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 (\mathrm{Na}{7} \mathrm{ln}{11.8}). 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 (\mathrm{Nat}{2} \mathrm{In}), isostructural with (\mathrm{Na}{i_{2}} \mathrm{TI}) (\left(c .222_{1}, Z=16, a=13.855\right.) (1) (\AA, b=8.836) (1) (\left.\dot{A}, c=11.762(1) \dot{A}, R / R_{\mathrm{w}}=0.030 / 0.034\right)). A correcled plase diagram is given. on 19y? Aetedenic Press, Inc.