NbCu3(PO4)4 crystallizes in the monoclinic Pm space group. Nb(1) is bonded to one O(1), one O(9), two equivalent O(11), and two equivalent O(5) atoms to form distorted NbO6 pentagonal pyramids that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(12), one O(4), two equivalent O(2), and two equivalent O(8) atoms to form distorted CuO6 octahedra that share  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(3)O4 tetrahedra. In the second Cu site, Cu(2) is bonded in a distorted see-saw-like geometry to one O(3), one O(7), and two equivalent O(5) atoms. In the third Cu site, Cu(3) is bonded in a 6-coordinate geometry to one O(10), one O(6), two equivalent O(2), and two equivalent O(8) atoms. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(10), and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Cu(1)O6 octahedra and  a cornercorner with one Nb(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 53°. In the second P site, P(2) is bonded to one O(6), one O(9), and two equivalent O(5) atoms to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 pentagonal pyramid and  an edgeedge with one Nb(1)O6 pentagonal pyramid. In the third P site, P(3) is bonded to one O(4), one O(7), and two equivalent O(8) atoms to form PO4 tetrahedra that share  a cornercorner with one Cu(1)O6 octahedra and  an edgeedge with one Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles are 47°. In the fourth P site, P(4) is bonded to one O(12), one O(3), and two equivalent O(11) atoms to form PO4 tetrahedra that share  a cornercorner with one Cu(1)O6 octahedra and corners with two equivalent Nb(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 47°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Cu(1), one Cu(3), and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Cu(2) and one P(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one P(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Nb(1), one Cu(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Cu(3) and one P(2) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Cu(2) and one P(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Cu(1), one Cu(3), and one P(3) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(2) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Cu(3) and one P(1) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Nb(1) and one P(4) atom. In the twelfth O site, O(12) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one P(4) atom.
NbCu3(PO4)4 crystallizes in the monoclinic Pm space group. Nb(1) is bonded to one O(1), one O(9), two equivalent O(11), and two equivalent O(5) atoms to form distorted NbO6 pentagonal pyramids that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(4)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The Nb(1)-O(1) bond length is 1.90 Å. The Nb(1)-O(9) bond length is 2.02 Å. Both Nb(1)-O(11) bond lengths are 2.00 Å. Both Nb(1)-O(5) bond lengths are 2.11 Å. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(12), one O(4), two equivalent O(2), and two equivalent O(8) atoms to form distorted CuO6 octahedra that share  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(3)O4 tetrahedra. The Cu(1)-O(12) bond length is 1.98 Å. The Cu(1)-O(4) bond length is 1.95 Å. Both Cu(1)-O(2) bond lengths are 2.05 Å. Both Cu(1)-O(8) bond lengths are 2.23 Å. In the second Cu site, Cu(2) is bonded in a distorted see-saw-like geometry to one O(3), one O(7), and two equivalent O(5) atoms. The Cu(2)-O(3) bond length is 1.90 Å. The Cu(2)-O(7) bond length is 1.88 Å. Both Cu(2)-O(5) bond lengths are 2.04 Å. In the third Cu site, Cu(3) is bonded in a 6-coordinate geometry to one O(10), one O(6), two equivalent O(2), and two equivalent O(8) atoms. The Cu(3)-O(10) bond length is 1.89 Å. The Cu(3)-O(6) bond length is 1.91 Å. Both Cu(3)-O(2) bond lengths are 2.49 Å. Both Cu(3)-O(8) bond lengths are 2.02 Å. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(10), and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Cu(1)O6 octahedra and  a cornercorner with one Nb(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 53°. The P(1)-O(1) bond length is 1.63 Å. The P(1)-O(10) bond length is 1.53 Å. Both P(1)-O(2) bond lengths are 1.53 Å. In the second P site, P(2) is bonded to one O(6), one O(9), and two equivalent O(5) atoms to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 pentagonal pyramid and  an edgeedge with one Nb(1)O6 pentagonal pyramid. The P(2)-O(6) bond length is 1.50 Å. The P(2)-O(9) bond length is 1.53 Å. Both P(2)-O(5) bond lengths are 1.59 Å. In the third P site, P(3) is bonded to one O(4), one O(7), and two equivalent O(8) atoms to form PO4 tetrahedra that share  a cornercorner with one Cu(1)O6 octahedra and  an edgeedge with one Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles are 47°. The P(3)-O(4) bond length is 1.53 Å. The P(3)-O(7) bond length is 1.55 Å. Both P(3)-O(8) bond lengths are 1.57 Å. In the fourth P site, P(4) is bonded to one O(12), one O(3), and two equivalent O(11) atoms to form PO4 tetrahedra that share  a cornercorner with one Cu(1)O6 octahedra and corners with two equivalent Nb(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 47°. The P(4)-O(12) bond length is 1.51 Å. The P(4)-O(3) bond length is 1.53 Å. Both P(4)-O(11) bond lengths are 1.60 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Cu(1), one Cu(3), and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Cu(2) and one P(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one P(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Nb(1), one Cu(2), and one P(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Cu(3) and one P(2) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Cu(2) and one P(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Cu(1), one Cu(3), and one P(3) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(2) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Cu(3) and one P(1) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Nb(1) and one P(4) atom. In the twelfth O site, O(12) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one P(4) atom.