Ni3(AsO4)2 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent As(1)O4 tetrahedra and edges with four equivalent Ni(2)O6 octahedra. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent As(1)O4 tetrahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(2)O6 octahedra. As(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form AsO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and corners with six equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-56°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ni(2) and one As(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(1), two equivalent Ni(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), and one As(1) atom.
Ni3(AsO4)2 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent As(1)O4 tetrahedra and edges with four equivalent Ni(2)O6 octahedra. Both Ni(1)-O(2) bond lengths are 2.04 Å. All Ni(1)-O(3) bond lengths are 2.06 Å. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent As(1)O4 tetrahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(2)O6 octahedra. Both Ni(2)-O(1) bond lengths are 2.01 Å. Both Ni(2)-O(2) bond lengths are 2.11 Å. Both Ni(2)-O(3) bond lengths are 2.03 Å. As(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form AsO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and corners with six equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-56°. The As(1)-O(1) bond length is 1.70 Å. The As(1)-O(2) bond length is 1.76 Å. Both As(1)-O(3) bond lengths are 1.70 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ni(2) and one As(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(1), two equivalent Ni(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), and one As(1) atom.