Fe2Cu8P4O21 crystallizes in the monoclinic C2/m space group. Fe(1) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with two equivalent Cu(2)O5 trigonal bipyramids, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(7), one O(8), one O(9), and two equivalent O(6) atoms to form CuO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid, corners with two equivalent Cu(3)O5 trigonal bipyramids, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Cu(2)O5 trigonal bipyramids. In the second Cu site, Cu(2) is bonded to one O(7), one O(8), one O(9), and two equivalent O(3) atoms to form CuO5 trigonal bipyramids that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra,  a cornercorner with one Cu(2)O5 trigonal bipyramid, edges with two equivalent Cu(1)O5 trigonal bipyramids, and edges with two equivalent Cu(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°. In the third Cu site, Cu(3) is bonded to one O(1), one O(3), one O(4), one O(5), and one O(8) atom to form CuO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid,  an edgeedge with one Cu(2)O5 trigonal bipyramid, and edges with two equivalent Cu(3)O5 trigonal bipyramids. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Cu(2)O5 trigonal bipyramids, and corners with four equivalent Cu(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 49°. In the second P site, P(2) is bonded to one O(4), one O(5), and two equivalent O(6) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with four equivalent Cu(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 53°. There are nine inequivalent O sites. In the first O site, O(3) is bonded in a 3-coordinate geometry to one Cu(2), one Cu(3), and one P(1) atom. In the second O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Cu(3) and one P(2) atom. In the third O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Cu(3) and one P(2) atom. In the fourth O site, O(6) is bonded in a 3-coordinate geometry to one Fe(1), one Cu(1), and one P(2) atom. In the fifth O site, O(7) is bonded to two equivalent Fe(1), one Cu(1), and one Cu(2) atom to form OFe2Cu2 trigonal pyramids that share corners with two equivalent O(8)Cu4 trigonal pyramids and corners with two equivalent O(7)Fe2Cu2 trigonal pyramids. In the sixth O site, O(8) is bonded to one Cu(1), one Cu(2), and two equivalent Cu(3) atoms to form corner-sharing OCu4 trigonal pyramids. In the seventh O site, O(9) is bonded in a square co-planar geometry to two equivalent Cu(1) and two equivalent Cu(2) atoms. In the eighth O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Cu(3) and one P(1) atom. In the ninth O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Fe(1) and one P(1) atom.
Fe2Cu8P4O21 crystallizes in the monoclinic C2/m space group. Fe(1) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, corners with two equivalent Cu(2)O5 trigonal bipyramids, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. Both Fe(1)-O(2) bond lengths are 2.10 Å. Both Fe(1)-O(6) bond lengths are 2.03 Å. Both Fe(1)-O(7) bond lengths are 2.01 Å. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(7), one O(8), one O(9), and two equivalent O(6) atoms to form CuO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid, corners with two equivalent Cu(3)O5 trigonal bipyramids, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Cu(2)O5 trigonal bipyramids. The Cu(1)-O(7) bond length is 2.05 Å. The Cu(1)-O(8) bond length is 1.91 Å. The Cu(1)-O(9) bond length is 1.97 Å. Both Cu(1)-O(6) bond lengths are 2.16 Å. In the second Cu site, Cu(2) is bonded to one O(7), one O(8), one O(9), and two equivalent O(3) atoms to form CuO5 trigonal bipyramids that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra,  a cornercorner with one Cu(2)O5 trigonal bipyramid, edges with two equivalent Cu(1)O5 trigonal bipyramids, and edges with two equivalent Cu(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°. The Cu(2)-O(7) bond length is 1.95 Å. The Cu(2)-O(8) bond length is 1.97 Å. The Cu(2)-O(9) bond length is 2.05 Å. Both Cu(2)-O(3) bond lengths are 2.08 Å. In the third Cu site, Cu(3) is bonded to one O(1), one O(3), one O(4), one O(5), and one O(8) atom to form CuO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid,  an edgeedge with one Cu(2)O5 trigonal bipyramid, and edges with two equivalent Cu(3)O5 trigonal bipyramids. The Cu(3)-O(1) bond length is 2.02 Å. The Cu(3)-O(3) bond length is 2.16 Å. The Cu(3)-O(4) bond length is 2.10 Å. The Cu(3)-O(5) bond length is 2.01 Å. The Cu(3)-O(8) bond length is 1.96 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Cu(2)O5 trigonal bipyramids, and corners with four equivalent Cu(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 49°. The P(1)-O(1) bond length is 1.57 Å. The P(1)-O(2) bond length is 1.58 Å. Both P(1)-O(3) bond lengths are 1.54 Å. In the second P site, P(2) is bonded to one O(4), one O(5), and two equivalent O(6) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with four equivalent Cu(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 53°. The P(2)-O(4) bond length is 1.53 Å. The P(2)-O(5) bond length is 1.57 Å. Both P(2)-O(6) bond lengths are 1.55 Å. There are nine inequivalent O sites. In the first O site, O(3) is bonded in a 3-coordinate geometry to one Cu(2), one Cu(3), and one P(1) atom. In the second O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Cu(3) and one P(2) atom. In the third O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Cu(3) and one P(2) atom. In the fourth O site, O(6) is bonded in a 3-coordinate geometry to one Fe(1), one Cu(1), and one P(2) atom. In the fifth O site, O(7) is bonded to two equivalent Fe(1), one Cu(1), and one Cu(2) atom to form OFe2Cu2 trigonal pyramids that share corners with two equivalent O(8)Cu4 trigonal pyramids and corners with two equivalent O(7)Fe2Cu2 trigonal pyramids. In the sixth O site, O(8) is bonded to one Cu(1), one Cu(2), and two equivalent Cu(3) atoms to form corner-sharing OCu4 trigonal pyramids. In the seventh O site, O(9) is bonded in a square co-planar geometry to two equivalent Cu(1) and two equivalent Cu(2) atoms. In the eighth O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Cu(3) and one P(1) atom. In the ninth O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Fe(1) and one P(1) atom.