DOE OSTI2020
Ca5Ga2Sb6 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to seven Sb+2.67- atoms to form distorted CaSb7 pentagonal bipyramids that share corners with nine CaSb6 octahedra, corners with four equivalent GaSb4 tetrahedra, edges with two equivalent CaSb6 octahedra, edges with two equivalent CaSb7 pentagonal bipyramids, edges with two equivalent GaSb4 tetrahedra, faces with two CaSb6 octahedra, and faces with three equivalent CaSb7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 31–47°. There are a spread of Ca–Sb bond distances ranging from 3.26–3.50 Å. In the second Ca2+ site, Ca2+ is bonded to six Sb+2.67- atoms to form CaSb6 octahedra that share corners with six equivalent CaSb6 octahedra, corners with four equivalent CaSb7 pentagonal bipyramids, corners with eight equivalent GaSb4 tetrahedra, edges with two equivalent CaSb6 octahedra, faces with two equivalent CaSb6 octahedra, and faces with two equivalent CaSb7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 32–52°. There are two shorter (3.19 Å) and four longer (3.20 Å) Ca–Sb bond lengths. In the third Ca2+ site, Ca2+ is bonded to six Sb+2.67- atoms to form CaSb6 octahedra that share corners with five CaSb6 octahedra, corners with seven equivalent CaSb7 pentagonal bipyramids, edges with two equivalent CaSb6 octahedra, edges with two equivalent CaSb7 pentagonal bipyramids, edges with four equivalent GaSb4 tetrahedra, a faceface with one CaSb6 octahedra, and a faceface with one CaSb7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 32–52°. There are a spread of Ca–Sb bond distances ranging from 3.18–3.25 Å. Ga3+ is bonded to four Sb+2.67- atoms to form GaSb4 tetrahedra that share corners with four equivalent CaSb6 octahedra, corners with four equivalent CaSb7 pentagonal bipyramids, corners with two equivalent GaSb4 tetrahedra, edges with four equivalent CaSb6 octahedra, and edges with two equivalent CaSb7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 45–62°. There are a spread of Ga–Sb bond distances ranging from 2.72–2.85 Å. There are three inequivalent Sb+2.67- sites. In the first Sb+2.67- site, Sb+2.67- is bonded in a 8-coordinate geometry to six Ca2+, one Ga3+, and one Sb+2.67- atom. The Sb–Sb bond length is 2.89 Å. In the second Sb+2.67- site, Sb+2.67- is bonded in a 6-coordinate geometry to four Ca2+ and two equivalent Ga3+ atoms. In the third Sb+2.67- site, Sb+2.67- is bonded to six Ca2+ and one Ga3+ atom to form a mixture of distorted face, edge, and corner-sharing SbCa6Ga pentagonal bipyramids.