Ca3Ni3(AsO4)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(4), one O(5), one O(7), one O(8), and two equivalent O(3) atoms. In the second Ca site, Ca(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(8) atoms to form CaO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra, and edges with two equivalent Ni(1)O5 trigonal bipyramids. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(4), one O(7), and one O(8) atom to form NiO5 trigonal bipyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and  an edgeedge with one Ca(2)O6 octahedra. In the second Ni site, Ni(2) is bonded in a square co-planar geometry to two equivalent O(5) and two equivalent O(7) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AsO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra and corners with three equivalent Ni(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 47-64°. In the second As site, As(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one Ca(2)O6 octahedra and corners with two equivalent Ni(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 54°. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to one Ca(1), one Ni(1), one Ni(2), and one As(2) atom. In the second O site, O(8) is bonded to one Ca(1), one Ca(2), one Ni(1), and one As(1) atom to form distorted corner-sharing OCa2NiAs tetrahedra. In the third O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one Ni(1), and one As(1) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(2), one Ni(1), and one As(2) atom. In the fifth O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one As(2) atom. In the sixth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ni(1), and one As(1) atom. In the seventh O site, O(5) is bonded in a trigonal planar geometry to one Ca(1), one Ni(2), and one As(2) atom. In the eighth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(2) and one As(1) atom.
Ca3Ni3(AsO4)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(4), one O(5), one O(7), one O(8), and two equivalent O(3) atoms. The Ca(1)-O(1) bond length is 2.37 Å. The Ca(1)-O(4) bond length is 2.54 Å. The Ca(1)-O(5) bond length is 2.41 Å. The Ca(1)-O(7) bond length is 2.66 Å. The Ca(1)-O(8) bond length is 2.76 Å. There is one shorter (2.32 Å) and one longer (2.78 Å) Ca(1)-O(3) bond length. In the second Ca site, Ca(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(8) atoms to form CaO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra, and edges with two equivalent Ni(1)O5 trigonal bipyramids. Both Ca(2)-O(2) bond lengths are 2.31 Å. Both Ca(2)-O(6) bond lengths are 2.32 Å. Both Ca(2)-O(8) bond lengths are 2.49 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(4), one O(7), and one O(8) atom to form NiO5 trigonal bipyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and  an edgeedge with one Ca(2)O6 octahedra. The Ni(1)-O(1) bond length is 2.00 Å. The Ni(1)-O(2) bond length is 2.04 Å. The Ni(1)-O(4) bond length is 2.03 Å. The Ni(1)-O(7) bond length is 2.14 Å. The Ni(1)-O(8) bond length is 2.09 Å. In the second Ni site, Ni(2) is bonded in a square co-planar geometry to two equivalent O(5) and two equivalent O(7) atoms. Both Ni(2)-O(5) bond lengths are 1.98 Å. Both Ni(2)-O(7) bond lengths are 1.99 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AsO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra and corners with three equivalent Ni(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 47-64°. The As(1)-O(1) bond length is 1.74 Å. The As(1)-O(4) bond length is 1.73 Å. The As(1)-O(6) bond length is 1.69 Å. The As(1)-O(8) bond length is 1.75 Å. In the second As site, As(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one Ca(2)O6 octahedra and corners with two equivalent Ni(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 54°. The As(2)-O(2) bond length is 1.71 Å. The As(2)-O(3) bond length is 1.69 Å. The As(2)-O(5) bond length is 1.74 Å. The As(2)-O(7) bond length is 1.76 Å. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to one Ca(1), one Ni(1), one Ni(2), and one As(2) atom. In the second O site, O(8) is bonded to one Ca(1), one Ca(2), one Ni(1), and one As(1) atom to form distorted corner-sharing OCa2NiAs tetrahedra. In the third O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one Ni(1), and one As(1) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(2), one Ni(1), and one As(2) atom. In the fifth O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one As(2) atom. In the sixth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ni(1), and one As(1) atom. In the seventh O site, O(5) is bonded in a trigonal planar geometry to one Ca(1), one Ni(2), and one As(2) atom. In the eighth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(2) and one As(1) atom.