Al2Ge2O7 crystallizes in the monoclinic C2/c space group. Al(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form AlO5 trigonal bipyramids that share corners with five equivalent Ge(1)O4 tetrahedra and edges with two equivalent Al(1)O5 trigonal bipyramids. Ge(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form GeO4 tetrahedra that share  a cornercorner with one Ge(1)O4 tetrahedra and corners with five equivalent Al(1)O5 trigonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Ge(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Ge(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to two equivalent Ge(1) atoms. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(1) and one Ge(1) atom.
Al2Ge2O7 crystallizes in the monoclinic C2/c space group. Al(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form AlO5 trigonal bipyramids that share corners with five equivalent Ge(1)O4 tetrahedra and edges with two equivalent Al(1)O5 trigonal bipyramids. The Al(1)-O(4) bond length is 1.74 Å. There is one shorter (1.82 Å) and one longer (1.91 Å) Al(1)-O(1) bond length. There is one shorter (1.82 Å) and one longer (1.91 Å) Al(1)-O(2) bond length. Ge(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form GeO4 tetrahedra that share  a cornercorner with one Ge(1)O4 tetrahedra and corners with five equivalent Al(1)O5 trigonal bipyramids. The Ge(1)-O(1) bond length is 1.78 Å. The Ge(1)-O(2) bond length is 1.77 Å. The Ge(1)-O(3) bond length is 1.75 Å. The Ge(1)-O(4) bond length is 1.71 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Ge(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Al(1) and one Ge(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to two equivalent Ge(1) atoms. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(1) and one Ge(1) atom.