BaGe4O9 crystallizes in the trigonal P321 space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. There are four inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to six equivalent O(4) atoms to form corner-sharing GeO6 octahedra. In the second Ge site, Ge(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form corner-sharing GeO6 octahedra. In the third Ge site, Ge(3) is bonded to two equivalent O(4) and two equivalent O(5) atoms to form GeO4 tetrahedra that share corners with two equivalent Ge(1)O6 octahedra and corners with two equivalent Ge(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 60°. In the fourth Ge site, Ge(4) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(2)O6 octahedra,  a cornercorner with one Ge(3)O4 tetrahedra, and  a cornercorner with one Ge(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-59°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(3), and one Ge(4) atom. In the second O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent Ba(1) and two equivalent Ge(4) atoms. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ge(2), and one Ge(4) atom. In the fourth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(2), and one Ge(4) atom. In the fifth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(1), and one Ge(3) atom.
BaGe4O9 crystallizes in the trigonal P321 space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Both Ba(1)-O(1) bond lengths are 3.22 Å. Both Ba(1)-O(2) bond lengths are 2.74 Å. Both Ba(1)-O(3) bond lengths are 3.03 Å. Both Ba(1)-O(4) bond lengths are 2.79 Å. Both Ba(1)-O(5) bond lengths are 2.93 Å. There are four inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to six equivalent O(4) atoms to form corner-sharing GeO6 octahedra. All Ge(1)-O(4) bond lengths are 1.90 Å. In the second Ge site, Ge(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form corner-sharing GeO6 octahedra. All Ge(2)-O(2) bond lengths are 1.87 Å. All Ge(2)-O(3) bond lengths are 1.88 Å. In the third Ge site, Ge(3) is bonded to two equivalent O(4) and two equivalent O(5) atoms to form GeO4 tetrahedra that share corners with two equivalent Ge(1)O6 octahedra and corners with two equivalent Ge(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 60°. Both Ge(3)-O(4) bond lengths are 1.76 Å. Both Ge(3)-O(5) bond lengths are 1.79 Å. In the fourth Ge site, Ge(4) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(2)O6 octahedra,  a cornercorner with one Ge(3)O4 tetrahedra, and  a cornercorner with one Ge(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-59°. The Ge(4)-O(1) bond length is 1.77 Å. The Ge(4)-O(2) bond length is 1.74 Å. The Ge(4)-O(3) bond length is 1.75 Å. The Ge(4)-O(5) bond length is 1.78 Å. There are five inequivalent O sites. In the first O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(3), and one Ge(4) atom. In the second O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent Ba(1) and two equivalent Ge(4) atoms. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ge(2), and one Ge(4) atom. In the fourth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(2), and one Ge(4) atom. In the fifth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(1), and one Ge(3) atom.