Na2Ca(AsO3)4 crystallizes in the tetragonal P4/nbm space group. Na(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NaO6 octahedra that share corners with eight equivalent As(1)O4 tetrahedra. Ca(1) is bonded in a 8-coordinate geometry to eight equivalent O(2) atoms. As(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form AsO4 tetrahedra that share corners with four equivalent Na(1)O6 octahedra and corners with two equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-72°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Na(1) and two equivalent As(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one Ca(1), and one As(1) atom.
Na2Ca(AsO3)4 crystallizes in the tetragonal P4/nbm space group. Na(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NaO6 octahedra that share corners with eight equivalent As(1)O4 tetrahedra. Both Na(1)-O(1) bond lengths are 2.65 Å. All Na(1)-O(2) bond lengths are 2.32 Å. Ca(1) is bonded in a 8-coordinate geometry to eight equivalent O(2) atoms. All Ca(1)-O(2) bond lengths are 2.49 Å. As(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form AsO4 tetrahedra that share corners with four equivalent Na(1)O6 octahedra and corners with two equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-72°. Both As(1)-O(1) bond lengths are 1.81 Å. Both As(1)-O(2) bond lengths are 1.67 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Na(1) and two equivalent As(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one Ca(1), and one As(1) atom.