Na4Hf2(SiO4)3 crystallizes in the trigonal R-3c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. In the second Na site, Na(2) is bonded in a distorted hexagonal planar geometry to six equivalent O(2) atoms. Hf(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form HfO6 octahedra that share corners with six equivalent Si(1)O4 tetrahedra. Si(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Hf(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 29-34°. There are two inequivalent O sites. In the first O site, O(2) is bonded to one Na(2), two equivalent Na(1), one Hf(1), and one Si(1) atom to form a mixture of distorted edge, corner, and face-sharing ONa3HfSi trigonal bipyramids. In the second O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Na(1), one Hf(1), and one Si(1) atom.
Na4Hf2(SiO4)3 crystallizes in the trigonal R-3c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. There are two shorter (2.79 Å) and two longer (2.94 Å) Na(1)-O(1) bond lengths. There are two shorter (2.51 Å) and two longer (2.59 Å) Na(1)-O(2) bond lengths. In the second Na site, Na(2) is bonded in a distorted hexagonal planar geometry to six equivalent O(2) atoms. All Na(2)-O(2) bond lengths are 2.65 Å. Hf(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form HfO6 octahedra that share corners with six equivalent Si(1)O4 tetrahedra. All Hf(1)-O(1) bond lengths are 2.04 Å. All Hf(1)-O(2) bond lengths are 2.12 Å. Si(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Hf(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 29-34°. Both Si(1)-O(1) bond lengths are 1.64 Å. Both Si(1)-O(2) bond lengths are 1.64 Å. There are two inequivalent O sites. In the first O site, O(2) is bonded to one Na(2), two equivalent Na(1), one Hf(1), and one Si(1) atom to form a mixture of distorted edge, corner, and face-sharing ONa3HfSi trigonal bipyramids. In the second O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Na(1), one Hf(1), and one Si(1) atom.