MgU2(SiO9)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a linear geometry to two equivalent O(4) and four equivalent O(6) atoms. U(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), and four equivalent O(5) atoms. Si(1) is bonded in a tetrahedral geometry to one O(3), one O(4), and two equivalent O(5) atoms. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one U(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one U(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one U(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one Mg(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent U(1) and one Si(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Mg(1) and one O(7) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to two equivalent O(6) atoms.
MgU2(SiO9)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a linear geometry to two equivalent O(4) and four equivalent O(6) atoms. Both Mg(1)-O(4) bond lengths are 1.83 Å. All Mg(1)-O(6) bond lengths are 2.73 Å. U(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), and four equivalent O(5) atoms. The U(1)-O(1) bond length is 1.82 Å. The U(1)-O(2) bond length is 1.82 Å. The U(1)-O(3) bond length is 2.17 Å. There are two shorter (2.27 Å) and two longer (2.54 Å) U(1)-O(5) bond lengths. Si(1) is bonded in a tetrahedral geometry to one O(3), one O(4), and two equivalent O(5) atoms. The Si(1)-O(3) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.59 Å. Both Si(1)-O(5) bond lengths are 1.66 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one U(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one U(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one U(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one Mg(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent U(1) and one Si(1) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Mg(1) and one O(7) atom. The O(6)-O(7) bond length is 1.29 Å. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to two equivalent O(6) atoms.