DOE OSTI2020
NaCaMgCr(SiO3)4 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.65 Å. In the second Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.38–2.67 Å. There are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.26–2.78 Å. In the second Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.26–2.70 Å. There are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 2.03–2.55 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 pentagonal pyramids that share corners with two equivalent SiO4 tetrahedra and edges with two equivalent SiO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 1.99–2.41 Å. There are two inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with two SiO4 tetrahedra, an edgeedge with one CrO6 octahedra, and edges with two SiO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 1.99–2.09 Å. In the second Cr3+ site, Cr3+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with two equivalent SiO4 tetrahedra, edges with two equivalent CrO6 octahedra, and edges with two equivalent SiO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 2.02–2.09 Å. There are six inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one MgO6 pentagonal pyramid and corners with two SiO4 tetrahedra. There is two shorter (1.63 Å) and two longer (1.70 Å) Si–O bond length. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one CrO6 octahedra and corners with two SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 67°. There are a spread of Si–O bond distances ranging from 1.60–1.70 Å. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two SiO4 tetrahedra and an edgeedge with one MgO6 pentagonal pyramid. There are a spread of Si–O bond distances ranging from 1.62–1.71 Å. In the fourth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one CrO6 octahedra, corners with two SiO4 tetrahedra, and an edgeedge with one CrO6 octahedra. The corner-sharing octahedral tilt angles are 66°. There are a spread of Si–O bond distances ranging from 1.63–1.69 Å. In the fifth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two SiO4 tetrahedra and an edgeedge with one CrO6 octahedra. There are a spread of Si–O bond distances ranging from 1.65–1.69 Å. In the sixth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one CrO6 octahedra, corners with two SiO4 tetrahedra, and an edgeedge with one CrO6 octahedra. The corner-sharing octahedral tilt angles are 68°. There are a spread of Si–O bond distances ranging from 1.63–1.69 Å. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two Si4+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+, one Mg2+, and one Si4+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+, two Mg2+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+, one Mg2+, one Cr3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Mg2+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two Si4+ atoms. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two Si4+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Mg2+, and one Si4+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+, two Mg2+, and one Si4+ atom. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+ and two Si4+ atoms. In the eleventh O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Cr3+, and one Si4+ atom. In the twelfth O2- site, O2- is bonded to one Na1+, two Cr3+, and one Si4+ atom to form a mixture of distorted edge and corner-sharing ONaCr2Si trigonal pyramids. In the thirteenth O2- site, O2- is bonded to one Na1+, one Mg2+, one Cr3+, and one Si4+ atom to form a mixture of distorted edge and corner-sharing ONaMgCrSi trigonal pyramids. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Cr3+, and one Si4+ atom. In the fifteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+ and two Si4+ atoms. In the sixteenth O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+ and two Si4+ atoms. In the seventeenth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Cr3+, and one Si4+ atom. In the eighteenth O2- site, O2- is bonded to one Na1+, two Cr3+, and one Si4+ atom to form a mixture of distorted edge and corner-sharing ONaCr2Si trigonal pyramids.