Materials Data on Na(SrAs)4 by Materials Project

Abstract

Na(SrAs)4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Na1+ is bonded to five As+2.25- atoms to form NaAs5 square pyramids that share corners with six equivalent SrAs7 pentagonal bipyramids, corners with two equivalent NaAs5 square pyramids, and faces with four equivalent SrAs7 pentagonal bipyramids. There are a spread of Na–As bond distances ranging from 2.99–3.41 Å. There are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six As+2.25- atoms. There are a spread of Sr–As bond distances ranging from 3.07–3.29 Å. In the second Sr2+ site, Sr2+ is bonded to seven As+2.25- atoms to form distorted SrAs7 pentagonal bipyramids that share corners with six equivalent SrAs7 pentagonal bipyramids, corners with three equivalent NaAs5 square pyramids, edges with two equivalent SrAs7 pentagonal bipyramids, faces with three equivalent SrAs7 pentagonal bipyramids, and faces with two equivalent NaAs5 square pyramids. There are a spread of Sr–As bond distances ranging from 3.18–3.47 Å. There are three inequivalent As+2.25- sites. In the first As+2.25- site, As+2.25- is bonded in a 9-coordinate geometry to two equivalent Na1+, six Sr2+, and one As+2.25- atom. The As–As bond length is 2.54 Å. In the second As+2.25- site, As+2.25- is bonded in a 8-coordinate geometry to one Na1+, six Sr2+, and one As+2.25- atom. In the third As+2.25- site, As+2.25- is bonded in a 8-coordinate geometry to one Na1+ and seven Sr2+ atoms.