K3NaHf2(SiO4)3 crystallizes in the trigonal R-3c space group. K(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. Na(1) 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 24-34°. There are two inequivalent O sites. In the first O site, O(2) is bonded in a 5-coordinate geometry to two equivalent K(1), one Na(1), one Hf(1), and one Si(1) atom. In the second O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Hf(1), and one Si(1) atom.
K3NaHf2(SiO4)3 crystallizes in the trigonal R-3c space group. K(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. There are two shorter (2.80 Å) and two longer (2.92 Å) K(1)-O(1) bond lengths. There are two shorter (2.62 Å) and two longer (2.76 Å) K(1)-O(2) bond lengths. Na(1) is bonded in a distorted hexagonal planar geometry to six equivalent O(2) atoms. All Na(1)-O(2) bond lengths are 2.61 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 2.06 Å. All Hf(1)-O(2) bond lengths are 2.14 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 24-34°. Both Si(1)-O(1) bond lengths are 1.65 Å. Both Si(1)-O(2) bond lengths are 1.65 Å. There are two inequivalent O sites. In the first O site, O(2) is bonded in a 5-coordinate geometry to two equivalent K(1), one Na(1), one Hf(1), and one Si(1) atom. In the second O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Hf(1), and one Si(1) atom.