BaGe4O9 crystallizes in the trigonal P3 space group. Ba(1) is bonded in a 10-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(8), one O(9), and two equivalent O(7) atoms. There are six inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to three equivalent O(1) and three equivalent O(6) atoms to form corner-sharing GeO6 octahedra. In the second Ge site, Ge(2) is bonded to three equivalent O(5) and three equivalent O(8) atoms to form corner-sharing GeO6 octahedra. In the third Ge site, Ge(3) is bonded to three equivalent O(2) and three equivalent O(9) atoms to form corner-sharing GeO6 octahedra. In the fourth Ge site, Ge(4) is bonded to one O(1), one O(3), one O(6), and one O(7) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(1)O6 octahedra,  a cornercorner with one Ge(5)O4 tetrahedra, and  a cornercorner with one Ge(6)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-60°. In the fifth Ge site, Ge(5) is bonded to one O(2), one O(3), one O(4), and one O(9) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(3)O6 octahedra,  a cornercorner with one Ge(4)O4 tetrahedra, and  a cornercorner with one Ge(6)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-61°. In the sixth Ge site, Ge(6) is bonded to one O(4), one O(5), one O(7), and one O(8) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(2)O6 octahedra,  a cornercorner with one Ge(4)O4 tetrahedra, and  a cornercorner with one Ge(5)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-60°. There are nine inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to two equivalent Ba(1), one Ge(4), and one Ge(6) atom. In the second O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(2), and one Ge(6) atom. In the third O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(3), and one Ge(5) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ge(1), and one Ge(4) atom. In the fifth O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(3), and one Ge(5) atom. In the sixth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(4), and one Ge(5) atom. In the seventh O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(5), and one Ge(6) atom. In the eighth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ge(2), and one Ge(6) atom. In the ninth O site, O(6) is bonded in a bent 120 degrees geometry to one Ba(1), one Ge(1), and one Ge(4) atom.
BaGe4O9 crystallizes in the trigonal P3 space group. Ba(1) is bonded in a 10-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(8), one O(9), and two equivalent O(7) atoms. The Ba(1)-O(1) bond length is 2.77 Å. The Ba(1)-O(2) bond length is 2.81 Å. The Ba(1)-O(3) bond length is 2.96 Å. The Ba(1)-O(4) bond length is 2.94 Å. The Ba(1)-O(5) bond length is 2.77 Å. The Ba(1)-O(6) bond length is 3.10 Å. The Ba(1)-O(8) bond length is 3.08 Å. The Ba(1)-O(9) bond length is 2.83 Å. There is one shorter (3.25 Å) and one longer (3.28 Å) Ba(1)-O(7) bond length. There are six inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to three equivalent O(1) and three equivalent O(6) atoms to form corner-sharing GeO6 octahedra. All Ge(1)-O(1) bond lengths are 1.90 Å. All Ge(1)-O(6) bond lengths are 1.90 Å. In the second Ge site, Ge(2) is bonded to three equivalent O(5) and three equivalent O(8) atoms to form corner-sharing GeO6 octahedra. All Ge(2)-O(5) bond lengths are 1.90 Å. All Ge(2)-O(8) bond lengths are 1.91 Å. In the third Ge site, Ge(3) is bonded to three equivalent O(2) and three equivalent O(9) atoms to form corner-sharing GeO6 octahedra. All Ge(3)-O(2) bond lengths are 1.93 Å. All Ge(3)-O(9) bond lengths are 1.94 Å. In the fourth Ge site, Ge(4) is bonded to one O(1), one O(3), one O(6), and one O(7) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(1)O6 octahedra,  a cornercorner with one Ge(5)O4 tetrahedra, and  a cornercorner with one Ge(6)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-60°. The Ge(4)-O(1) bond length is 1.76 Å. The Ge(4)-O(3) bond length is 1.80 Å. The Ge(4)-O(6) bond length is 1.77 Å. The Ge(4)-O(7) bond length is 1.80 Å. In the fifth Ge site, Ge(5) is bonded to one O(2), one O(3), one O(4), and one O(9) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(3)O6 octahedra,  a cornercorner with one Ge(4)O4 tetrahedra, and  a cornercorner with one Ge(6)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 59-61°. The Ge(5)-O(2) bond length is 1.77 Å. The Ge(5)-O(3) bond length is 1.81 Å. The Ge(5)-O(4) bond length is 1.81 Å. The Ge(5)-O(9) bond length is 1.77 Å. In the sixth Ge site, Ge(6) is bonded to one O(4), one O(5), one O(7), and one O(8) atom to form GeO4 tetrahedra that share corners with two equivalent Ge(2)O6 octahedra,  a cornercorner with one Ge(4)O4 tetrahedra, and  a cornercorner with one Ge(5)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-60°. The Ge(6)-O(4) bond length is 1.81 Å. The Ge(6)-O(5) bond length is 1.76 Å. The Ge(6)-O(7) bond length is 1.79 Å. The Ge(6)-O(8) bond length is 1.77 Å. There are nine inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to two equivalent Ba(1), one Ge(4), and one Ge(6) atom. In the second O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(2), and one Ge(6) atom. In the third O site, O(9) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(3), and one Ge(5) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ge(1), and one Ge(4) atom. In the fifth O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(3), and one Ge(5) atom. In the sixth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(4), and one Ge(5) atom. In the seventh O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ge(5), and one Ge(6) atom. In the eighth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ge(2), and one Ge(6) atom. In the ninth O site, O(6) is bonded in a bent 120 degrees geometry to one Ba(1), one Ge(1), and one Ge(4) atom.