Synthesis, structure, and bonding of open-shell Sr3In5: An unusual electron deficiency in an indium network, beyond the Zintl boundary

The new title compound has been synthesized and characterized by physical p roperty measurements and electronic structure calculations. The results rat ify the highly uncommon deficiency of one electron that has been long specu lated for its Ca3Ga5-type structure on the basis of the simple Zintl electr on counting formalism. In the Sr3In5 structure (Cmcm), 4- and 2-bonded indi um atoms in a 4:1 ratio form a three-dimensional classical network that enc apsulates strontium atoms in its narrow channels. The electrical conductivi ty of the compound shows typical metallic behavior. The detailed electronic structure analysis suggests that the electron hole is mainly localized on a nonbonding p-orbital on the 2-bonded indium atoms, and that these orbital s, stacked in a a-type way along (a) over right arrow (4.97 Angstrom), inte ract only weakly with each other to form highly one-dimensional bands.