Ca2Hf7O16 crystallizes in the trigonal R-3 space group. There are six inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. In the second Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. In the third Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. In the fourth Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. In the fifth Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. In the sixth Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. There are nine inequivalent Hf sites. In the first Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the second Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the third Hf site, Hf(2) is bonded to six equivalent O(2) atoms to form corner-sharing HfO6 octahedra. In the fourth Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the fifth Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the sixth Hf site, Hf(2) is bonded to six equivalent O(2) atoms to form corner-sharing HfO6 octahedra. In the seventh Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the eighth Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the ninth Hf site, Hf(2) is bonded to six equivalent O(2) atoms to form corner-sharing HfO6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to four Hf(1,1) atoms to form OHf4 tetrahedra that share corners with two equivalent O(3)CaHf3 tetrahedra, corners with two equivalent O(4)CaHf3 tetrahedra, corners with six equivalent O(1)Hf4 tetrahedra, corners with four equivalent O(2)Ca2Hf2 trigonal pyramids,  an edgeedge with one O(3)CaHf3 tetrahedra,  an edgeedge with one O(4)CaHf3 tetrahedra, and edges with three equivalent O(1)Hf4 tetrahedra. In the second O site, O(2) is bonded to two Ca(1,1); one Hf(1); and one Hf(2) atom to form distorted OCa2Hf2 trigonal pyramids that share  a cornercorner with one O(3)CaHf3 tetrahedra,  a cornercorner with one O(4)CaHf3 tetrahedra, corners with four equivalent O(1)Hf4 tetrahedra, corners with nine equivalent O(2)Ca2Hf2 trigonal pyramids,  an edgeedge with one O(3)CaHf3 tetrahedra,  an edgeedge with one O(4)CaHf3 tetrahedra, and edges with three equivalent O(2)Ca2Hf2 trigonal pyramids. In the third O site, O(3) is bonded to one Ca(1) and three equivalent Hf(1) atoms to form distorted OCaHf3 tetrahedra that share corners with four equivalent O(4)CaHf3 tetrahedra, corners with six equivalent O(1)Hf4 tetrahedra, corners with three equivalent O(2)Ca2Hf2 trigonal pyramids, edges with three equivalent O(1)Hf4 tetrahedra, and edges with three equivalent O(2)Ca2Hf2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Ca(1) and three equivalent Hf(1) atoms to form OCaHf3 tetrahedra that share corners with four equivalent O(3)CaHf3 tetrahedra, corners with six equivalent O(1)Hf4 tetrahedra, corners with three equivalent O(2)Ca2Hf2 trigonal pyramids, edges with three equivalent O(1)Hf4 tetrahedra, and edges with three equivalent O(2)Ca2Hf2 trigonal pyramids.
Ca2Hf7O16 crystallizes in the trigonal R-3 space group. There are six inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.52 Å. The Ca(1)-O(4) bond length is 2.45 Å. There are three shorter (2.48 Å) and three longer (2.54 Å) Ca(1)-O(2) bond lengths. In the second Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.52 Å. The Ca(1)-O(4) bond length is 2.45 Å. There are three shorter (2.48 Å) and three longer (2.54 Å) Ca(1)-O(2) bond lengths. In the third Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.52 Å. The Ca(1)-O(4) bond length is 2.45 Å. There are three shorter (2.48 Å) and three longer (2.54 Å) Ca(1)-O(2) bond lengths. In the fourth Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.52 Å. The Ca(1)-O(4) bond length is 2.45 Å. There are three shorter (2.48 Å) and three longer (2.54 Å) Ca(1)-O(2) bond lengths. In the fifth Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.52 Å. The Ca(1)-O(4) bond length is 2.45 Å. There are three shorter (2.48 Å) and three longer (2.54 Å) Ca(1)-O(2) bond lengths. In the sixth Ca site, Ca(1) is bonded in a body-centered cubic geometry to one O(3), one O(4), and six equivalent O(2) atoms. The Ca(1)-O(3) bond length is 2.52 Å. The Ca(1)-O(4) bond length is 2.45 Å. There are three shorter (2.48 Å) and three longer (2.54 Å) Ca(1)-O(2) bond lengths. There are nine inequivalent Hf sites. In the first Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The Hf(1)-O(2) bond length is 2.01 Å. The Hf(1)-O(3) bond length is 2.04 Å. The Hf(1)-O(4) bond length is 2.07 Å. There are a spread of Hf(1)-O(1) bond distances ranging from 2.13-2.27 Å. In the second Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The Hf(1)-O(2) bond length is 2.01 Å. The Hf(1)-O(3) bond length is 2.04 Å. The Hf(1)-O(4) bond length is 2.07 Å. There are a spread of Hf(1)-O(1) bond distances ranging from 2.13-2.27 Å. In the third Hf site, Hf(2) is bonded to six equivalent O(2) atoms to form corner-sharing HfO6 octahedra. All Hf(2)-O(2) bond lengths are 2.08 Å. In the fourth Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The Hf(1)-O(2) bond length is 2.01 Å. The Hf(1)-O(3) bond length is 2.04 Å. The Hf(1)-O(4) bond length is 2.07 Å. There are a spread of Hf(1)-O(1) bond distances ranging from 2.13-2.27 Å. In the fifth Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The Hf(1)-O(2) bond length is 2.01 Å. The Hf(1)-O(3) bond length is 2.04 Å. The Hf(1)-O(4) bond length is 2.07 Å. There are a spread of Hf(1)-O(1) bond distances ranging from 2.13-2.27 Å. In the sixth Hf site, Hf(2) is bonded to six equivalent O(2) atoms to form corner-sharing HfO6 octahedra. All Hf(2)-O(2) bond lengths are 2.08 Å. In the seventh Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The Hf(1)-O(2) bond length is 2.01 Å. The Hf(1)-O(3) bond length is 2.04 Å. The Hf(1)-O(4) bond length is 2.07 Å. There are a spread of Hf(1)-O(1) bond distances ranging from 2.13-2.27 Å. In the eighth Hf site, Hf(1) is bonded to one O(2), one O(3), one O(4), and four equivalent O(1) atoms to form distorted HfO7 pentagonal bipyramids that share  a cornercorner with one Hf(2)O6 octahedra; corners with two equivalent Hf(1)O7 pentagonal bipyramids; and edges with seven Hf(1,1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The Hf(1)-O(2) bond length is 2.01 Å. The Hf(1)-O(3) bond length is 2.04 Å. The Hf(1)-O(4) bond length is 2.07 Å. There are a spread of Hf(1)-O(1) bond distances ranging from 2.13-2.27 Å. In the ninth Hf site, Hf(2) is bonded to six equivalent O(2) atoms to form corner-sharing HfO6 octahedra. All Hf(2)-O(2) bond lengths are 2.08 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to four Hf(1,1) atoms to form OHf4 tetrahedra that share corners with two equivalent O(3)CaHf3 tetrahedra, corners with two equivalent O(4)CaHf3 tetrahedra, corners with six equivalent O(1)Hf4 tetrahedra, corners with four equivalent O(2)Ca2Hf2 trigonal pyramids,  an edgeedge with one O(3)CaHf3 tetrahedra,  an edgeedge with one O(4)CaHf3 tetrahedra, and edges with three equivalent O(1)Hf4 tetrahedra. In the second O site, O(2) is bonded to two Ca(1,1); one Hf(1); and one Hf(2) atom to form distorted OCa2Hf2 trigonal pyramids that share  a cornercorner with one O(3)CaHf3 tetrahedra,  a cornercorner with one O(4)CaHf3 tetrahedra, corners with four equivalent O(1)Hf4 tetrahedra, corners with nine equivalent O(2)Ca2Hf2 trigonal pyramids,  an edgeedge with one O(3)CaHf3 tetrahedra,  an edgeedge with one O(4)CaHf3 tetrahedra, and edges with three equivalent O(2)Ca2Hf2 trigonal pyramids. In the third O site, O(3) is bonded to one Ca(1) and three equivalent Hf(1) atoms to form distorted OCaHf3 tetrahedra that share corners with four equivalent O(4)CaHf3 tetrahedra, corners with six equivalent O(1)Hf4 tetrahedra, corners with three equivalent O(2)Ca2Hf2 trigonal pyramids, edges with three equivalent O(1)Hf4 tetrahedra, and edges with three equivalent O(2)Ca2Hf2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Ca(1) and three equivalent Hf(1) atoms to form OCaHf3 tetrahedra that share corners with four equivalent O(3)CaHf3 tetrahedra, corners with six equivalent O(1)Hf4 tetrahedra, corners with three equivalent O(2)Ca2Hf2 trigonal pyramids, edges with three equivalent O(1)Hf4 tetrahedra, and edges with three equivalent O(2)Ca2Hf2 trigonal pyramids.