Synthesis and crystal structure of a new Zintl phase Sr5In2Bi6

A new Zintl phase, Sr5In2Bi6, has been synthesized by solid-state reactions of the corresponding elements in a stoichiometric ratio in welded niobium tube at 750 °C. Its structure was established by single-crystal X-ray diffraction. Sr5In2Bi6 crystallizes in the orthorhombic space group Pbam (No. 55) with cell parameters of a = 24.4500(3), b = 7.8800(8), c = 4.7400(5) Å and V = 913.2(2) Å3. It belongs to the Ca5Al2Bi6 structure type and its structure features one-dimensional anionic double chains of [In2Bi6]10− with the Sr2+ ions as spacers. Within the double anionic chain, the In atom is four-bonded by four Bi atoms in a tetrahedral geometry, and these InBi4 tetrahedra are interconnected into a 1D chain via corner-sharing, each pair of such chains are further condensed into a double chain via Bi–Bi bonds. Results of extended Hückel band structure calculations indicate that Sr5In2Bi6 is a semiconductor with a band gap of ∼1.5 eV. Sr5In2Bi6 is diamagnetic based on magnetic property measurements.