Phase stabilization through electronic tuning: Electron-poorer alkali-metal-indium compounds with unprecedented In/Li clusters

Three alkali-metal-indium compounds K34In92.30Li12.70 (I), K14Na20In91.82Li13.18 (II), and K14Na20I96.30 (III) (all R (3) over barm) have been synthesized and characterized by structural and physical property measurements and electronic structure calculations. Novel mixed In/Li anionic icosahedra and fused icosahedra form in I and II. All three contain In-28 as the first triply fused In icosahedra, which are further linked into (In-28)In(In-28) sandwich adducts in compounds I and II and (In-28)In-2(In-28) in III. Stabilization of these electron-poorer phases through electronic tuning occurs via two different structural (redox) perturbations, either by substitution of certain indium atoms in the clusters by electron-poorer lithium atoms or by the introduction of defects and disorder in the fused cluster (111). The preferential occurrence of either substitutions or defect formation in the clusters is consistent with extended Huckel band calculation results for both the ideal pure indium phase and the Li-substituted equivalent. Model (ideal) and experimental E-F values (based on stoichiometries) fall around a pseudogap in DOS. All three compounds are metallic according to both EHTB band calculations and measured resistivities. The cations (A = K, Na) in all the three structures generate A(136) clathrate-II type networks with remarkably specific and transferable cation dispositions around the two types of anionic cluster units.