Stabilization of a Novel Zeolite-like Opened Sn Framework by Bi Heteroatom in the Zint Phase Na13Sn26Bi

The new ternary Zintl phase, Na13Sn26Bi, was synthesized by combination of the elements and, its crystal structure refined from single crystal X-ray diffraction data. Its crystallizes in a triclinic cell, space group P-1 (No. 2, Z = 1) with a = 9.0942(1) Å (alpha = 112.008(1)°), b = 11.2637(2) Å ( beta= 99.793(1)°), c = 13.2573(2) Å (gamma = 101.455(1)°) and V = 1188.46(3) Å3. According to the Zintl Klemm concept, its structure consists of the covalently bonded [Sn26]10– polyanions that are directly interconnected to form a new 3D zeolite-like opened framework and they interact with anionic Bi3– located in its largest channel, through electron-rich three-centre four-electron (3c-4e) bonds. There are three types of channels of different size, on which the two are occupied by either Na cations in the pentagonal shape channels or Na and Bi atoms in the largest clover-like shape channels. DFT first principles electronic band structure calculations were conducted on the idealized fully ordered model Na13Sn26Bi to understand the chemical bonding and the structure directing factors. It confirms that the title compound is charge balanced with optimized chemical bonding as predicted by implementing the Zintl-Klemm concept and assuming electron-rich 3c-4e bonding between Sn and Bi.