RbFeCu(PO4)2 crystallizes in the monoclinic P2_1/c space group. Rb(1) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(4), one O(6), one O(7), two equivalent O(2), and two equivalent O(5) atoms. Fe(1) is bonded to one O(2), one O(3), one O(4), one O(6), one O(7), and one O(8) atom to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and corners with two equivalent Cu(1)O5 trigonal bipyramids. Cu(1) is bonded to one O(5), one O(7), one O(8), and two equivalent O(1) atoms to form distorted CuO5 trigonal bipyramids that share corners with two equivalent Fe(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra,  an edgeedge with one P(2)O4 tetrahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 51-61°. There are two inequivalent P sites. In the first P site, 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 three equivalent Fe(1)O6 octahedra and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 36-38°. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 38-43°. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Fe(1), and one P(1) atom. In the second O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(1), one Cu(1), and one P(2) atom. In the third O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Fe(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a 3-coordinate geometry to one Rb(1), one Fe(1), one Cu(1), and one P(2) atom. In the fifth O site, O(8) is bonded in a 3-coordinate geometry to one Fe(1), one Cu(1), and one P(2) atom. In the sixth O site, O(1) is bonded in a 3-coordinate geometry to one Rb(1), two equivalent Cu(1), and one P(1) atom. In the seventh O site, O(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(1), one Fe(1), and one P(1) atom. In the eighth O site, O(3) is bonded in a 2-coordinate geometry to one Rb(1), one Fe(1), and one P(1) atom.
RbFeCu(PO4)2 crystallizes in the monoclinic P2_1/c space group. Rb(1) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(4), one O(6), one O(7), two equivalent O(2), and two equivalent O(5) atoms. The Rb(1)-O(1) bond length is 3.16 Å. The Rb(1)-O(3) bond length is 2.94 Å. The Rb(1)-O(4) bond length is 3.07 Å. The Rb(1)-O(6) bond length is 3.19 Å. The Rb(1)-O(7) bond length is 3.15 Å. There is one shorter (3.03 Å) and one longer (3.13 Å) Rb(1)-O(2) bond length. There is one shorter (2.99 Å) and one longer (3.01 Å) Rb(1)-O(5) bond length. Fe(1) is bonded to one O(2), one O(3), one O(4), one O(6), one O(7), and one O(8) atom to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and corners with two equivalent Cu(1)O5 trigonal bipyramids. The Fe(1)-O(2) bond length is 1.99 Å. The Fe(1)-O(3) bond length is 1.97 Å. The Fe(1)-O(4) bond length is 1.95 Å. The Fe(1)-O(6) bond length is 2.01 Å. The Fe(1)-O(7) bond length is 2.25 Å. The Fe(1)-O(8) bond length is 2.13 Å. Cu(1) is bonded to one O(5), one O(7), one O(8), and two equivalent O(1) atoms to form distorted CuO5 trigonal bipyramids that share corners with two equivalent Fe(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra,  an edgeedge with one P(2)O4 tetrahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 51-61°. The Cu(1)-O(5) bond length is 1.96 Å. The Cu(1)-O(7) bond length is 2.02 Å. The Cu(1)-O(8) bond length is 2.05 Å. There is one shorter (1.94 Å) and one longer (2.27 Å) Cu(1)-O(1) bond length. There are two inequivalent P sites. In the first P site, 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 three equivalent Fe(1)O6 octahedra and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 36-38°. The P(1)-O(1) bond length is 1.57 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 38-43°. The P(2)-O(5) bond length is 1.53 Å. The P(2)-O(6) bond length is 1.53 Å. The P(2)-O(7) bond length is 1.59 Å. The P(2)-O(8) bond length is 1.59 Å. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Fe(1), and one P(1) atom. In the second O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(1), one Cu(1), and one P(2) atom. In the third O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Fe(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a 3-coordinate geometry to one Rb(1), one Fe(1), one Cu(1), and one P(2) atom. In the fifth O site, O(8) is bonded in a 3-coordinate geometry to one Fe(1), one Cu(1), and one P(2) atom. In the sixth O site, O(1) is bonded in a 3-coordinate geometry to one Rb(1), two equivalent Cu(1), and one P(1) atom. In the seventh O site, O(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(1), one Fe(1), and one P(1) atom. In the eighth O site, O(3) is bonded in a 2-coordinate geometry to one Rb(1), one Fe(1), and one P(1) atom.