Cr3(PO4)4 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(10), one O(12), one O(14), one O(15), one O(6), and one O(8) atom to form CrO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra, and  an edgeedge with one Cr(2)O5 trigonal bipyramid. In the second Cr site, Cr(2) is bonded to one O(10), one O(13), one O(14), one O(16), and one O(4) atom to form CrO5 trigonal bipyramids that share  a cornercorner with one Cr(3)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra,  an edgeedge with one Cr(1)O6 octahedra, and  an edgeedge with one P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. In the third Cr site, Cr(3) is bonded to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form CrO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and  a cornercorner with one Cr(2)O5 trigonal bipyramid. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(5), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(1)O6 octahedra and corners with two equivalent Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 36-50°. In the second P site, P(2) is bonded to one O(1), one O(12), one O(15), and one O(16) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(3)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, and  a cornercorner with one Cr(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 23-44°. In the third P site, P(3) is bonded to one O(10), one O(11), one O(4), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(1)O6 octahedra, corners with two equivalent Cr(3)O6 octahedra, and  an edgeedge with one Cr(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 34-53°. In the fourth P site, P(4) is bonded to one O(13), one O(14), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(3)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, and corners with two equivalent Cr(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 38-54°. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Cr(3) and one P(2) atom. In the second O site, O(2) is bonded in a single-bond geometry to one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cr(3) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Cr(2), one Cr(3), and one P(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(4) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(4) atom. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to one Cr(1) and one P(1) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Cr(3) and one P(3) atom. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Cr(1), one Cr(2), and one P(3) atom. In the eleventh O site, O(11) is bonded in a single-bond geometry to one P(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(4) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Cr(1), one Cr(2), and one P(4) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the sixteenth O site, O(16) is bonded in a bent 120 degrees geometry to one Cr(2) and one P(2) atom.
Cr3(PO4)4 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(10), one O(12), one O(14), one O(15), one O(6), and one O(8) atom to form CrO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra, and  an edgeedge with one Cr(2)O5 trigonal bipyramid. The Cr(1)-O(10) bond length is 2.02 Å. The Cr(1)-O(12) bond length is 1.98 Å. The Cr(1)-O(14) bond length is 2.24 Å. The Cr(1)-O(15) bond length is 1.92 Å. The Cr(1)-O(6) bond length is 1.99 Å. The Cr(1)-O(8) bond length is 1.92 Å. In the second Cr site, Cr(2) is bonded to one O(10), one O(13), one O(14), one O(16), and one O(4) atom to form CrO5 trigonal bipyramids that share  a cornercorner with one Cr(3)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra,  an edgeedge with one Cr(1)O6 octahedra, and  an edgeedge with one P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. The Cr(2)-O(10) bond length is 2.01 Å. The Cr(2)-O(13) bond length is 1.85 Å. The Cr(2)-O(14) bond length is 1.90 Å. The Cr(2)-O(16) bond length is 1.78 Å. The Cr(2)-O(4) bond length is 1.95 Å. In the third Cr site, Cr(3) is bonded to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form CrO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and  a cornercorner with one Cr(2)O5 trigonal bipyramid. The Cr(3)-O(1) bond length is 1.98 Å. The Cr(3)-O(3) bond length is 1.95 Å. The Cr(3)-O(4) bond length is 2.25 Å. The Cr(3)-O(5) bond length is 1.94 Å. The Cr(3)-O(7) bond length is 1.98 Å. The Cr(3)-O(9) bond length is 2.02 Å. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(5), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(1)O6 octahedra and corners with two equivalent Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 36-50°. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.54 Å. The P(1)-O(8) bond length is 1.56 Å. In the second P site, P(2) is bonded to one O(1), one O(12), one O(15), and one O(16) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(3)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, and  a cornercorner with one Cr(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 23-44°. The P(2)-O(1) bond length is 1.52 Å. The P(2)-O(12) bond length is 1.53 Å. The P(2)-O(15) bond length is 1.52 Å. The P(2)-O(16) bond length is 1.62 Å. In the third P site, P(3) is bonded to one O(10), one O(11), one O(4), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(1)O6 octahedra, corners with two equivalent Cr(3)O6 octahedra, and  an edgeedge with one Cr(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 34-53°. The P(3)-O(10) bond length is 1.60 Å. The P(3)-O(11) bond length is 1.50 Å. The P(3)-O(4) bond length is 1.65 Å. The P(3)-O(9) bond length is 1.53 Å. In the fourth P site, P(4) is bonded to one O(13), one O(14), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Cr(3)O6 octahedra, corners with two equivalent Cr(1)O6 octahedra, and corners with two equivalent Cr(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 38-54°. The P(4)-O(13) bond length is 1.55 Å. The P(4)-O(14) bond length is 1.63 Å. The P(4)-O(6) bond length is 1.52 Å. The P(4)-O(7) bond length is 1.52 Å. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Cr(3) and one P(2) atom. In the second O site, O(2) is bonded in a single-bond geometry to one P(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cr(3) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Cr(2), one Cr(3), and one P(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(4) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(4) atom. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to one Cr(1) and one P(1) atom. In the ninth O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Cr(3) and one P(3) atom. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Cr(1), one Cr(2), and one P(3) atom. In the eleventh O site, O(11) is bonded in a single-bond geometry to one P(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(4) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Cr(1), one Cr(2), and one P(4) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the sixteenth O site, O(16) is bonded in a bent 120 degrees geometry to one Cr(2) and one P(2) atom.