MgHo8(Ge2O7)4 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to one O(15), two equivalent O(3), and two equivalent O(8) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Ge(4)O4 tetrahedra and edges with two equivalent Ge(2)O4 trigonal pyramids. There are four inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to one O(11), one O(12), one O(13), one O(14), one O(7), and two equivalent O(4) atoms to form distorted HoO7 pentagonal bipyramids that share corners with two equivalent Ge(1)O4 tetrahedra, corners with two equivalent Ge(3)O4 tetrahedra,  a cornercorner with one Ge(2)O4 trigonal pyramid,  an edgeedge with one Ho(1)O7 pentagonal bipyramid, edges with three equivalent Ho(2)O7 pentagonal bipyramids, and  an edgeedge with one Ge(3)O4 tetrahedra. In the second Ho site, Ho(2) is bonded to one O(1), one O(11), one O(12), one O(13), one O(4), one O(6), and one O(7) atom to form distorted HoO7 pentagonal bipyramids that share  a cornercorner with one Ge(1)O4 tetrahedra, corners with three equivalent Ge(3)O4 tetrahedra,  a cornercorner with one Ge(2)O4 trigonal pyramid, edges with three equivalent Ho(1)O7 pentagonal bipyramids, and  an edgeedge with one Ge(1)O4 tetrahedra. In the third Ho site, Ho(3) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(6), one O(8), and two equivalent O(5) atoms. In the fourth Ho site, Ho(4) is bonded in a 7-coordinate geometry to one O(13), one O(14), one O(2), one O(3), one O(5), one O(6), and one O(8) atom. There are four inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to one O(1), one O(10), one O(13), and one O(7) atom to form GeO4 tetrahedra that share  a cornercorner with one Ho(2)O7 pentagonal bipyramid, corners with two equivalent Ho(1)O7 pentagonal bipyramids,  a cornercorner with one Ge(1)O4 tetrahedra, and  an edgeedge with one Ho(2)O7 pentagonal bipyramid. In the second Ge site, Ge(2) is bonded to one O(14), one O(15), one O(6), and one O(8) atom to form distorted GeO4 trigonal pyramids that share  a cornercorner with one Ho(1)O7 pentagonal bipyramid,  a cornercorner with one Ho(2)O7 pentagonal bipyramid,  a cornercorner with one Ge(2)O4 trigonal pyramid, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. In the third Ge site, Ge(3) is bonded to one O(11), one O(12), one O(4), and one O(9) atom to form GeO4 tetrahedra that share corners with two equivalent Ho(1)O7 pentagonal bipyramids, corners with three equivalent Ho(2)O7 pentagonal bipyramids,  a cornercorner with one Ge(4)O4 tetrahedra, and  an edgeedge with one Ho(1)O7 pentagonal bipyramid. In the fourth Ge site, Ge(4) is bonded to one O(2), one O(3), one O(5), and one O(9) atom to form GeO4 tetrahedra that share  a cornercorner with one Ge(3)O4 tetrahedra and  a cornercorner with one Mg(1)O5 trigonal bipyramid. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ho(2), one Ho(3), and one Ge(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ho(3), one Ho(4), and one Ge(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Ho(3), one Ho(4), and one Ge(4) atom. In the fourth O site, O(4) is bonded to one Ho(2), two equivalent Ho(1), and one Ge(3) atom to form a mixture of distorted corner and edge-sharing OHo3Ge trigonal pyramids. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ho(4), two equivalent Ho(3), and one Ge(4) atom. In the sixth O site, O(6) is bonded to one Ho(2), one Ho(3), one Ho(4), and one Ge(2) atom to form OHo3Ge tetrahedra that share  a cornercorner with one O(8)Ho2MgGe trigonal pyramid,  a cornercorner with one O(4)Ho3Ge trigonal pyramid,  an edgeedge with one O(8)Ho2MgGe trigonal pyramid, and  an edgeedge with one O(13)Ho3Ge trigonal pyramid. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Ho(1), one Ho(2), and one Ge(1) atom. In the eighth O site, O(8) is bonded to one Mg(1), one Ho(3), one Ho(4), and one Ge(2) atom to form distorted OHo2MgGe trigonal pyramids that share  a cornercorner with one O(6)Ho3Ge tetrahedra,  a cornercorner with one O(8)Ho2MgGe trigonal pyramid,  a cornercorner with one O(13)Ho3Ge trigonal pyramid, and  an edgeedge with one O(6)Ho3Ge tetrahedra. In the ninth O site, O(9) is bonded in a distorted bent 150 degrees geometry to one Ge(3) and one Ge(4) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to two equivalent Ge(1) atoms. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ho(1), one Ho(2), and one Ge(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ho(1), one Ho(2), and one Ge(3) atom. In the thirteenth O site, O(13) is bonded to one Ho(1), one Ho(2), one Ho(4), and one Ge(1) atom to form distorted OHo3Ge trigonal pyramids that share  a cornercorner with one O(8)Ho2MgGe trigonal pyramid, corners with three equivalent O(4)Ho3Ge trigonal pyramids, and  an edgeedge with one O(6)Ho3Ge tetrahedra. In the fourteenth O site, O(14) is bonded in a trigonal planar geometry to one Ho(1), one Ho(4), and one Ge(2) atom. In the fifteenth O site, O(15) is bonded in a T-shaped geometry to one Mg(1) and two equivalent Ge(2) atoms.
MgHo8(Ge2O7)4 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to one O(15), two equivalent O(3), and two equivalent O(8) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Ge(4)O4 tetrahedra and edges with two equivalent Ge(2)O4 trigonal pyramids. The Mg(1)-O(15) bond length is 1.95 Å. Both Mg(1)-O(3) bond lengths are 2.37 Å. Both Mg(1)-O(8) bond lengths are 1.91 Å. There are four inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to one O(11), one O(12), one O(13), one O(14), one O(7), and two equivalent O(4) atoms to form distorted HoO7 pentagonal bipyramids that share corners with two equivalent Ge(1)O4 tetrahedra, corners with two equivalent Ge(3)O4 tetrahedra,  a cornercorner with one Ge(2)O4 trigonal pyramid,  an edgeedge with one Ho(1)O7 pentagonal bipyramid, edges with three equivalent Ho(2)O7 pentagonal bipyramids, and  an edgeedge with one Ge(3)O4 tetrahedra. The Ho(1)-O(11) bond length is 2.35 Å. The Ho(1)-O(12) bond length is 2.26 Å. The Ho(1)-O(13) bond length is 2.29 Å. The Ho(1)-O(14) bond length is 2.19 Å. The Ho(1)-O(7) bond length is 2.23 Å. There is one shorter (2.41 Å) and one longer (2.55 Å) Ho(1)-O(4) bond length. In the second Ho site, Ho(2) is bonded to one O(1), one O(11), one O(12), one O(13), one O(4), one O(6), and one O(7) atom to form distorted HoO7 pentagonal bipyramids that share  a cornercorner with one Ge(1)O4 tetrahedra, corners with three equivalent Ge(3)O4 tetrahedra,  a cornercorner with one Ge(2)O4 trigonal pyramid, edges with three equivalent Ho(1)O7 pentagonal bipyramids, and  an edgeedge with one Ge(1)O4 tetrahedra. The Ho(2)-O(1) bond length is 2.33 Å. The Ho(2)-O(11) bond length is 2.19 Å. The Ho(2)-O(12) bond length is 2.32 Å. The Ho(2)-O(13) bond length is 2.54 Å. The Ho(2)-O(4) bond length is 2.29 Å. The Ho(2)-O(6) bond length is 2.28 Å. The Ho(2)-O(7) bond length is 2.37 Å. In the third Ho site, Ho(3) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(6), one O(8), and two equivalent O(5) atoms. The Ho(3)-O(1) bond length is 2.18 Å. The Ho(3)-O(2) bond length is 2.42 Å. The Ho(3)-O(3) bond length is 2.50 Å. The Ho(3)-O(6) bond length is 2.23 Å. The Ho(3)-O(8) bond length is 2.36 Å. There is one shorter (2.42 Å) and one longer (2.96 Å) Ho(3)-O(5) bond length. In the fourth Ho site, Ho(4) is bonded in a 7-coordinate geometry to one O(13), one O(14), one O(2), one O(3), one O(5), one O(6), and one O(8) atom. The Ho(4)-O(13) bond length is 2.42 Å. The Ho(4)-O(14) bond length is 2.27 Å. The Ho(4)-O(2) bond length is 2.23 Å. The Ho(4)-O(3) bond length is 2.44 Å. The Ho(4)-O(5) bond length is 2.31 Å. The Ho(4)-O(6) bond length is 2.44 Å. The Ho(4)-O(8) bond length is 2.38 Å. There are four inequivalent Ge sites. In the first Ge site, Ge(1) is bonded to one O(1), one O(10), one O(13), and one O(7) atom to form GeO4 tetrahedra that share  a cornercorner with one Ho(2)O7 pentagonal bipyramid, corners with two equivalent Ho(1)O7 pentagonal bipyramids,  a cornercorner with one Ge(1)O4 tetrahedra, and  an edgeedge with one Ho(2)O7 pentagonal bipyramid. The Ge(1)-O(1) bond length is 1.76 Å. The Ge(1)-O(10) bond length is 1.79 Å. The Ge(1)-O(13) bond length is 1.79 Å. The Ge(1)-O(7) bond length is 1.75 Å. In the second Ge site, Ge(2) is bonded to one O(14), one O(15), one O(6), and one O(8) atom to form distorted GeO4 trigonal pyramids that share  a cornercorner with one Ho(1)O7 pentagonal bipyramid,  a cornercorner with one Ho(2)O7 pentagonal bipyramid,  a cornercorner with one Ge(2)O4 trigonal pyramid, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The Ge(2)-O(14) bond length is 1.80 Å. The Ge(2)-O(15) bond length is 2.03 Å. The Ge(2)-O(6) bond length is 1.91 Å. The Ge(2)-O(8) bond length is 1.98 Å. In the third Ge site, Ge(3) is bonded to one O(11), one O(12), one O(4), and one O(9) atom to form GeO4 tetrahedra that share corners with two equivalent Ho(1)O7 pentagonal bipyramids, corners with three equivalent Ho(2)O7 pentagonal bipyramids,  a cornercorner with one Ge(4)O4 tetrahedra, and  an edgeedge with one Ho(1)O7 pentagonal bipyramid. The Ge(3)-O(11) bond length is 1.75 Å. The Ge(3)-O(12) bond length is 1.75 Å. The Ge(3)-O(4) bond length is 1.80 Å. The Ge(3)-O(9) bond length is 1.81 Å. In the fourth Ge site, Ge(4) is bonded to one O(2), one O(3), one O(5), and one O(9) atom to form GeO4 tetrahedra that share  a cornercorner with one Ge(3)O4 tetrahedra and  a cornercorner with one Mg(1)O5 trigonal bipyramid. The Ge(4)-O(2) bond length is 1.78 Å. The Ge(4)-O(3) bond length is 1.80 Å. The Ge(4)-O(5) bond length is 1.81 Å. The Ge(4)-O(9) bond length is 1.82 Å. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ho(2), one Ho(3), and one Ge(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ho(3), one Ho(4), and one Ge(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Ho(3), one Ho(4), and one Ge(4) atom. In the fourth O site, O(4) is bonded to one Ho(2), two equivalent Ho(1), and one Ge(3) atom to form a mixture of distorted corner and edge-sharing OHo3Ge trigonal pyramids. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ho(4), two equivalent Ho(3), and one Ge(4) atom. In the sixth O site, O(6) is bonded to one Ho(2), one Ho(3), one Ho(4), and one Ge(2) atom to form OHo3Ge tetrahedra that share  a cornercorner with one O(8)Ho2MgGe trigonal pyramid,  a cornercorner with one O(4)Ho3Ge trigonal pyramid,  an edgeedge with one O(8)Ho2MgGe trigonal pyramid, and  an edgeedge with one O(13)Ho3Ge trigonal pyramid. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Ho(1), one Ho(2), and one Ge(1) atom. In the eighth O site, O(8) is bonded to one Mg(1), one Ho(3), one Ho(4), and one Ge(2) atom to form distorted OHo2MgGe trigonal pyramids that share  a cornercorner with one O(6)Ho3Ge tetrahedra,  a cornercorner with one O(8)Ho2MgGe trigonal pyramid,  a cornercorner with one O(13)Ho3Ge trigonal pyramid, and  an edgeedge with one O(6)Ho3Ge tetrahedra. In the ninth O site, O(9) is bonded in a distorted bent 150 degrees geometry to one Ge(3) and one Ge(4) atom. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to two equivalent Ge(1) atoms. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ho(1), one Ho(2), and one Ge(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ho(1), one Ho(2), and one Ge(3) atom. In the thirteenth O site, O(13) is bonded to one Ho(1), one Ho(2), one Ho(4), and one Ge(1) atom to form distorted OHo3Ge trigonal pyramids that share  a cornercorner with one O(8)Ho2MgGe trigonal pyramid, corners with three equivalent O(4)Ho3Ge trigonal pyramids, and  an edgeedge with one O(6)Ho3Ge tetrahedra. In the fourteenth O site, O(14) is bonded in a trigonal planar geometry to one Ho(1), one Ho(4), and one Ge(2) atom. In the fifteenth O site, O(15) is bonded in a T-shaped geometry to one Mg(1) and two equivalent Ge(2) atoms.