Synthesis, structure and properties of Sr3In11--optimizing the chemical bonding of hypoelectronic SrIn4

The new binary phase Sr3In11was obtained from high-temperature reactions of the elements in welded Ta tubes. Its structure was established by single-crystal X-ray diffraction. The title compound crystallizes in the orthorhombic space group Immm (No. 71) with cell parameters of a=4.9328(6), b=11.240(1) and c=16.829 (3) A. The crystal structure of Sr3In11, isomorphous with the La3Al11 structure, features two types of tunnels along the a-axis that are formed by indium pentagons and hexagons. Its structural relationships with BaIn4 and SrIn4 phases are examined. Extended-Hueckel band structure calculations indicate that the new metallic binary phase has all bonding states optimized in contrast to the hypoelectronic SrIn4