NbCr3(PO4)6 crystallizes in the trigonal R3 space group. Nb(1) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form NbO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to three equivalent O(2) and three equivalent O(5) atoms to form CrO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. In the second Cr site, Cr(2) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form CrO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. In the third Cr site, Cr(3) is bonded to three equivalent O(7) and three equivalent O(8) atoms to form CrO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(4), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Cr(1)O6 octahedra,  a cornercorner with one Cr(2)O6 octahedra, and  a cornercorner with one Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-32°. In the second P site, P(2) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Cr(1)O6 octahedra,  a cornercorner with one Cr(2)O6 octahedra, and  a cornercorner with one Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-31°. There are eight inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(1) atom. In the second O site, O(3) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(1) atom. In the third O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the fourth O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the fifth O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(2) atom. In the sixth O site, O(7) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(2) atom. In the seventh O site, O(8) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(1) atom. In the eighth O site, O(1) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(2) atom.
NbCr3(PO4)6 crystallizes in the trigonal R3 space group. Nb(1) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form NbO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. All Nb(1)-O(4) bond lengths are 2.01 Å. All Nb(1)-O(6) bond lengths are 1.97 Å. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to three equivalent O(2) and three equivalent O(5) atoms to form CrO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. All Cr(1)-O(2) bond lengths are 1.96 Å. All Cr(1)-O(5) bond lengths are 1.94 Å. In the second Cr site, Cr(2) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form CrO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. All Cr(2)-O(1) bond lengths are 1.92 Å. All Cr(2)-O(3) bond lengths are 1.94 Å. In the third Cr site, Cr(3) is bonded to three equivalent O(7) and three equivalent O(8) atoms to form CrO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. All Cr(3)-O(7) bond lengths are 1.94 Å. All Cr(3)-O(8) bond lengths are 1.95 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(4), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Cr(1)O6 octahedra,  a cornercorner with one Cr(2)O6 octahedra, and  a cornercorner with one Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-32°. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.55 Å. The P(1)-O(8) bond length is 1.53 Å. In the second P site, P(2) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Cr(1)O6 octahedra,  a cornercorner with one Cr(2)O6 octahedra, and  a cornercorner with one Cr(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-31°. The P(2)-O(1) bond length is 1.53 Å. The P(2)-O(5) bond length is 1.53 Å. The P(2)-O(6) bond length is 1.56 Å. The P(2)-O(7) bond length is 1.53 Å. There are eight inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(1) atom. In the second O site, O(3) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(1) atom. In the third O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the fourth O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the fifth O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(2) atom. In the sixth O site, O(7) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(2) atom. In the seventh O site, O(8) is bonded in a bent 150 degrees geometry to one Cr(3) and one P(1) atom. In the eighth O site, O(1) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(2) atom.