CuNi2(PO4)2 crystallizes in the monoclinic P2_1/c space group. Ni(1) is bonded to one O(1), one O(2), one O(4), and two equivalent O(3) atoms to form NiO5 trigonal bipyramids that share corners with five equivalent P(1)O4 tetrahedra and  an edgeedge with one Ni(1)O5 trigonal bipyramid. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(4) atoms. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with five equivalent Ni(1)O5 trigonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ni(1), one Cu(1), and one P(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Ni(1), one Cu(1), and one P(1) atom.
CuNi2(PO4)2 crystallizes in the monoclinic P2_1/c space group. Ni(1) is bonded to one O(1), one O(2), one O(4), and two equivalent O(3) atoms to form NiO5 trigonal bipyramids that share corners with five equivalent P(1)O4 tetrahedra and  an edgeedge with one Ni(1)O5 trigonal bipyramid. The Ni(1)-O(1) bond length is 2.08 Å. The Ni(1)-O(2) bond length is 2.03 Å. The Ni(1)-O(4) bond length is 2.05 Å. Both Ni(1)-O(3) bond lengths are 2.05 Å. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(4) atoms. Both Cu(1)-O(1) bond lengths are 1.96 Å. Both Cu(1)-O(4) bond lengths are 2.04 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with five equivalent Ni(1)O5 trigonal bipyramids. The P(1)-O(1) bond length is 1.57 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.57 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ni(1), one Cu(1), and one P(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Ni(1), one Cu(1), and one P(1) atom.