FeSb(PO4)2 crystallizes in the triclinic P-1 space group. Fe(1) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form distorted FeO6 pentagonal pyramids that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. Sb(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 pentagonal pyramids. In the second P site, P(2) is bonded to one O(3), one O(4), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 pentagonal pyramid and  an edgeedge with one Fe(1)O6 pentagonal pyramid. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Sb(1) and one P(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Sb(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Fe(1), one Sb(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Fe(1), one Sb(1), and one P(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Fe(1), one Sb(1), and one P(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Fe(1), one Sb(1), and one P(2) atom.
FeSb(PO4)2 crystallizes in the triclinic P-1 space group. Fe(1) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form distorted FeO6 pentagonal pyramids that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The Fe(1)-O(1) bond length is 1.92 Å. The Fe(1)-O(3) bond length is 1.91 Å. The Fe(1)-O(5) bond length is 2.22 Å. The Fe(1)-O(6) bond length is 2.27 Å. The Fe(1)-O(7) bond length is 2.08 Å. The Fe(1)-O(8) bond length is 2.10 Å. Sb(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Sb(1)-O(2) bond length is 2.08 Å. The Sb(1)-O(4) bond length is 2.65 Å. The Sb(1)-O(5) bond length is 2.33 Å. The Sb(1)-O(6) bond length is 2.30 Å. The Sb(1)-O(7) bond length is 2.34 Å. The Sb(1)-O(8) bond length is 2.30 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 pentagonal pyramids. The P(1)-O(1) bond length is 1.53 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.58 Å. The P(1)-O(6) bond length is 1.58 Å. In the second P site, P(2) is bonded to one O(3), one O(4), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 pentagonal pyramid and  an edgeedge with one Fe(1)O6 pentagonal pyramid. The P(2)-O(3) bond length is 1.55 Å. The P(2)-O(4) bond length is 1.50 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(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Sb(1) and one P(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Sb(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Fe(1), one Sb(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Fe(1), one Sb(1), and one P(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Fe(1), one Sb(1), and one P(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Fe(1), one Sb(1), and one P(2) atom.