BaCo2P2H2O9 crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(5), four equivalent O(3), and four equivalent O(4) atoms. Co(1) is bonded to one O(1), one O(3), one O(4), one O(5), and two equivalent O(2) atoms to form distorted CoO6 octahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-67°. P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Co(1)O6 octahedra and  an edgeedge with one Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-59°. H(1) is bonded in a single-bond geometry to one O(1) atom. There are five inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to two equivalent Co(1) and two equivalent H(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Co(1) and one P(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Co(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to two equivalent Ba(1), one Co(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ba(1), one Co(1), and one P(1) atom.
BaCo2P2H2O9 crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(5), four equivalent O(3), and four equivalent O(4) atoms. Both Ba(1)-O(5) bond lengths are 2.87 Å. There are two shorter (2.80 Å) and two longer (3.32 Å) Ba(1)-O(3) bond lengths. There are two shorter (2.79 Å) and two longer (3.14 Å) Ba(1)-O(4) bond lengths. Co(1) is bonded to one O(1), one O(3), one O(4), one O(5), and two equivalent O(2) atoms to form distorted CoO6 octahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-67°. The Co(1)-O(1) bond length is 2.36 Å. The Co(1)-O(3) bond length is 2.05 Å. The Co(1)-O(4) bond length is 2.25 Å. The Co(1)-O(5) bond length is 2.07 Å. There is one shorter (2.05 Å) and one longer (2.18 Å) Co(1)-O(2) bond length. P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Co(1)O6 octahedra and  an edgeedge with one Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-59°. The P(1)-O(2) bond length is 1.58 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.55 Å. H(1) is bonded in a single-bond geometry to one O(1) atom. The H(1)-O(1) bond length is 0.98 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to two equivalent Co(1) and two equivalent H(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Co(1) and one P(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Co(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to two equivalent Ba(1), one Co(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ba(1), one Co(1), and one P(1) atom.