DOE OSTI2019
Ca2Ga2Si(HO4)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two SiO4 tetrahedra, corners with four GaO4 tetrahedra, and edges with three CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.31–2.55 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two SiO4 tetrahedra, corners with four GaO4 tetrahedra, and edges with three CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.31–2.67 Å. In the third Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two SiO4 tetrahedra, corners with four GaO4 tetrahedra, and edges with three CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.31–2.53 Å. In the fourth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two SiO4 tetrahedra, corners with four GaO4 tetrahedra, and edges with three CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.30–2.59 Å. There are four inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to four O2- atoms to form GaO4 tetrahedra that share corners with four CaO6 octahedra, corners with two GaO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 63–73°. There are a spread of Ga–O bond distances ranging from 1.82–1.91 Å. In the second Ga3+ site, Ga3+ is bonded to four O2- atoms to form GaO4 tetrahedra that share corners with four CaO6 octahedra, corners with two GaO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 62–72°. There are a spread of Ga–O bond distances ranging from 1.83–1.90 Å. In the third Ga3+ site, Ga3+ is bonded to four O2- atoms to form GaO4 tetrahedra that share corners with four CaO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three GaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–65°. There are a spread of Ga–O bond distances ranging from 1.84–1.90 Å. In the fourth Ga3+ site, Ga3+ is bonded to four O2- atoms to form GaO4 tetrahedra that share corners with four CaO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three GaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–64°. There are a spread of Ga–O bond distances ranging from 1.84–1.89 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four CaO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three GaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 62–69°. There are a spread of Si–O bond distances ranging from 1.64–1.69 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four CaO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three GaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 62–67°. There are a spread of Si–O bond distances ranging from 1.64–1.70 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to three Ca2+ and one H1+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and two Si4+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Ga3+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Ga3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Ga3+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Ga3+, and one Si4+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to three Ca2+ and one H1+ atom. In the eighth O2- site, O2- is bonded in a trigonal planar geometry to one Ca2+ and two Ga3+ atoms. In the ninth O2- site, O2- is bonded in a distorted single-bond geometry to three Ca2+ and one H1+ atom. In the tenth O2- site, O2- is bonded in a trigonal planar geometry to one Ca2+ and two Ga3+ atoms. In the eleventh O2- site, O2- is bonded in a trigonal planar geometry to one Ca2+ and two Ga3+ atoms. In the twelfth O2- site, O2- is bonded in a trigonal planar geometry to one Ca2+ and two Ga3+ atoms. In the thirteenth O2- site, O2- is bonded in a trigonal planar geometry to one Ca2+ and two Ga3+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Ga3+, and one Si4+ atom. In the fifteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Ga3+, and one Si4+ atom. In the sixteenth O2- site, O2- is bonded in a distorted single-bond geometry to three Ca2+ and one H1+ atom.