MgTm4Sm4O12 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(3), one O(5), and one O(7) atom. There are four inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(1), one O(10), one O(12), one O(3), one O(5), and one O(8) atom to form distorted corner-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. In the second Tm site, Tm(2) is bonded to one O(1), one O(11), one O(12), one O(2), one O(4), and one O(9) atom to form corner-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 30-53°. In the third Tm site, Tm(3) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(5), one O(6), one O(7), and one O(8) atom. In the fourth Tm site, Tm(4) is bonded to one O(11), one O(2), one O(4), one O(6), one O(7), and one O(9) atom to form corner-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 30-49°. There are four inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 6-coordinate geometry to one O(10), one O(11), one O(12), one O(4), one O(5), and one O(6) atom. In the second Sm site, Sm(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(7), one O(8), and one O(9) atom. In the third Sm site, Sm(3) is bonded in a 6-coordinate geometry to one O(10), one O(11), one O(12), one O(4), one O(6), and one O(9) atom. In the fourth Sm site, Sm(4) is bonded in a 6-coordinate geometry to one O(1), one O(11), one O(2), one O(7), one O(8), and one O(9) atom. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Tm(1), one Tm(2), one Sm(2), and one Sm(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Tm(2), one Tm(4), one Sm(2), and one Sm(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Tm(1), one Tm(3), and one Sm(2) atom. In the fourth O site, O(4) is bonded to one Tm(2), one Tm(4), one Sm(1), and one Sm(3) atom to form distorted OSm2Tm2 trigonal pyramids that share corners with two equivalent O(10)Sm2Tm2 tetrahedra, corners with three equivalent O(9)Sm3Tm2 trigonal bipyramids, corners with three equivalent O(12)Sm2Tm2 trigonal pyramids, and edges with two equivalent O(11)Sm3Tm2 trigonal bipyramids. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), one Tm(1), one Tm(3), one Sm(1), and one Sm(2) atom. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Tm(3), one Tm(4), one Sm(1), and one Sm(3) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Mg(1), one Tm(3), one Tm(4), one Sm(2), and one Sm(4) atom. In the eighth O site, O(8) is bonded to one Tm(1), one Tm(3), one Sm(2), and one Sm(4) atom to form distorted OSm2Tm2 trigonal pyramids that share corners with two equivalent O(10)Sm2Tm2 tetrahedra,  a cornercorner with one O(11)Sm3Tm2 trigonal bipyramid,  a cornercorner with one O(12)Sm2Tm2 trigonal pyramid, and  an edgeedge with one O(9)Sm3Tm2 trigonal bipyramid. In the ninth O site, O(9) is bonded to one Tm(2), one Tm(4), one Sm(2), one Sm(3), and one Sm(4) atom to form distorted OSm3Tm2 trigonal bipyramids that share  a cornercorner with one O(10)Sm2Tm2 tetrahedra, corners with three equivalent O(4)Sm2Tm2 trigonal pyramids, edges with two equivalent O(11)Sm3Tm2 trigonal bipyramids,  an edgeedge with one O(12)Sm2Tm2 trigonal pyramid, and  an edgeedge with one O(8)Sm2Tm2 trigonal pyramid. In the tenth O site, O(10) is bonded to one Tm(1), one Tm(3), one Sm(1), and one Sm(3) atom to form OSm2Tm2 tetrahedra that share  a cornercorner with one O(9)Sm3Tm2 trigonal bipyramid,  a cornercorner with one O(12)Sm2Tm2 trigonal pyramid, corners with two equivalent O(4)Sm2Tm2 trigonal pyramids, corners with two equivalent O(8)Sm2Tm2 trigonal pyramids,  an edgeedge with one O(11)Sm3Tm2 trigonal bipyramid, and  an edgeedge with one O(12)Sm2Tm2 trigonal pyramid. In the eleventh O site, O(11) is bonded to one Tm(2), one Tm(4), one Sm(1), one Sm(3), and one Sm(4) atom to form distorted OSm3Tm2 trigonal bipyramids that share  a cornercorner with one O(12)Sm2Tm2 trigonal pyramid,  a cornercorner with one O(8)Sm2Tm2 trigonal pyramid,  an edgeedge with one O(10)Sm2Tm2 tetrahedra, edges with two equivalent O(9)Sm3Tm2 trigonal bipyramids,  an edgeedge with one O(12)Sm2Tm2 trigonal pyramid, and edges with two equivalent O(4)Sm2Tm2 trigonal pyramids. In the twelfth O site, O(12) is bonded to one Tm(1), one Tm(2), one Sm(1), and one Sm(3) atom to form distorted OSm2Tm2 trigonal pyramids that share  a cornercorner with one O(10)Sm2Tm2 tetrahedra,  a cornercorner with one O(11)Sm3Tm2 trigonal bipyramid,  a cornercorner with one O(8)Sm2Tm2 trigonal pyramid, corners with three equivalent O(4)Sm2Tm2 trigonal pyramids,  an edgeedge with one O(10)Sm2Tm2 tetrahedra,  an edgeedge with one O(11)Sm3Tm2 trigonal bipyramid, and  an edgeedge with one O(9)Sm3Tm2 trigonal bipyramid.
MgTm4Sm4O12 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(3), one O(5), and one O(7) atom. The Mg(1)-O(1) bond length is 2.08 Å. The Mg(1)-O(3) bond length is 2.01 Å. The Mg(1)-O(5) bond length is 2.01 Å. The Mg(1)-O(7) bond length is 2.09 Å. There are four inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(1), one O(10), one O(12), one O(3), one O(5), and one O(8) atom to form distorted corner-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Tm(1)-O(1) bond length is 2.50 Å. The Tm(1)-O(10) bond length is 2.30 Å. The Tm(1)-O(12) bond length is 2.28 Å. The Tm(1)-O(3) bond length is 2.21 Å. The Tm(1)-O(5) bond length is 2.44 Å. The Tm(1)-O(8) bond length is 2.18 Å. In the second Tm site, Tm(2) is bonded to one O(1), one O(11), one O(12), one O(2), one O(4), and one O(9) atom to form corner-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 30-53°. The Tm(2)-O(1) bond length is 2.22 Å. The Tm(2)-O(11) bond length is 2.26 Å. The Tm(2)-O(12) bond length is 2.50 Å. The Tm(2)-O(2) bond length is 2.22 Å. The Tm(2)-O(4) bond length is 2.17 Å. The Tm(2)-O(9) bond length is 2.40 Å. In the third Tm site, Tm(3) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(5), one O(6), one O(7), and one O(8) atom. The Tm(3)-O(10) bond length is 2.21 Å. The Tm(3)-O(3) bond length is 2.35 Å. The Tm(3)-O(5) bond length is 2.34 Å. The Tm(3)-O(6) bond length is 2.18 Å. The Tm(3)-O(7) bond length is 2.49 Å. The Tm(3)-O(8) bond length is 2.28 Å. In the fourth Tm site, Tm(4) is bonded to one O(11), one O(2), one O(4), one O(6), one O(7), and one O(9) atom to form corner-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 30-49°. The Tm(4)-O(11) bond length is 2.41 Å. The Tm(4)-O(2) bond length is 2.18 Å. The Tm(4)-O(4) bond length is 2.19 Å. The Tm(4)-O(6) bond length is 2.16 Å. The Tm(4)-O(7) bond length is 2.45 Å. The Tm(4)-O(9) bond length is 2.32 Å. There are four inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 6-coordinate geometry to one O(10), one O(11), one O(12), one O(4), one O(5), and one O(6) atom. The Sm(1)-O(10) bond length is 2.41 Å. The Sm(1)-O(11) bond length is 2.56 Å. The Sm(1)-O(12) bond length is 2.30 Å. The Sm(1)-O(4) bond length is 2.56 Å. The Sm(1)-O(5) bond length is 2.36 Å. The Sm(1)-O(6) bond length is 2.64 Å. In the second Sm site, Sm(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(7), one O(8), and one O(9) atom. The Sm(2)-O(1) bond length is 2.56 Å. The Sm(2)-O(2) bond length is 2.82 Å. The Sm(2)-O(3) bond length is 2.26 Å. The Sm(2)-O(5) bond length is 3.02 Å. The Sm(2)-O(7) bond length is 2.37 Å. The Sm(2)-O(8) bond length is 2.28 Å. The Sm(2)-O(9) bond length is 2.36 Å. In the third Sm site, Sm(3) is bonded in a 6-coordinate geometry to one O(10), one O(11), one O(12), one O(4), one O(6), and one O(9) atom. The Sm(3)-O(10) bond length is 2.27 Å. The Sm(3)-O(11) bond length is 2.51 Å. The Sm(3)-O(12) bond length is 2.43 Å. The Sm(3)-O(4) bond length is 2.35 Å. The Sm(3)-O(6) bond length is 2.33 Å. The Sm(3)-O(9) bond length is 2.55 Å. In the fourth Sm site, Sm(4) is bonded in a 6-coordinate geometry to one O(1), one O(11), one O(2), one O(7), one O(8), and one O(9) atom. The Sm(4)-O(1) bond length is 2.60 Å. The Sm(4)-O(11) bond length is 2.44 Å. The Sm(4)-O(2) bond length is 2.38 Å. The Sm(4)-O(7) bond length is 2.29 Å. The Sm(4)-O(8) bond length is 2.52 Å. The Sm(4)-O(9) bond length is 2.47 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Tm(1), one Tm(2), one Sm(2), and one Sm(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Tm(2), one Tm(4), one Sm(2), and one Sm(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Tm(1), one Tm(3), and one Sm(2) atom. In the fourth O site, O(4) is bonded to one Tm(2), one Tm(4), one Sm(1), and one Sm(3) atom to form distorted OSm2Tm2 trigonal pyramids that share corners with two equivalent O(10)Sm2Tm2 tetrahedra, corners with three equivalent O(9)Sm3Tm2 trigonal bipyramids, corners with three equivalent O(12)Sm2Tm2 trigonal pyramids, and edges with two equivalent O(11)Sm3Tm2 trigonal bipyramids. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), one Tm(1), one Tm(3), one Sm(1), and one Sm(2) atom. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Tm(3), one Tm(4), one Sm(1), and one Sm(3) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Mg(1), one Tm(3), one Tm(4), one Sm(2), and one Sm(4) atom. In the eighth O site, O(8) is bonded to one Tm(1), one Tm(3), one Sm(2), and one Sm(4) atom to form distorted OSm2Tm2 trigonal pyramids that share corners with two equivalent O(10)Sm2Tm2 tetrahedra,  a cornercorner with one O(11)Sm3Tm2 trigonal bipyramid,  a cornercorner with one O(12)Sm2Tm2 trigonal pyramid, and  an edgeedge with one O(9)Sm3Tm2 trigonal bipyramid. In the ninth O site, O(9) is bonded to one Tm(2), one Tm(4), one Sm(2), one Sm(3), and one Sm(4) atom to form distorted OSm3Tm2 trigonal bipyramids that share  a cornercorner with one O(10)Sm2Tm2 tetrahedra, corners with three equivalent O(4)Sm2Tm2 trigonal pyramids, edges with two equivalent O(11)Sm3Tm2 trigonal bipyramids,  an edgeedge with one O(12)Sm2Tm2 trigonal pyramid, and  an edgeedge with one O(8)Sm2Tm2 trigonal pyramid. In the tenth O site, O(10) is bonded to one Tm(1), one Tm(3), one Sm(1), and one Sm(3) atom to form OSm2Tm2 tetrahedra that share  a cornercorner with one O(9)Sm3Tm2 trigonal bipyramid,  a cornercorner with one O(12)Sm2Tm2 trigonal pyramid, corners with two equivalent O(4)Sm2Tm2 trigonal pyramids, corners with two equivalent O(8)Sm2Tm2 trigonal pyramids,  an edgeedge with one O(11)Sm3Tm2 trigonal bipyramid, and  an edgeedge with one O(12)Sm2Tm2 trigonal pyramid. In the eleventh O site, O(11) is bonded to one Tm(2), one Tm(4), one Sm(1), one Sm(3), and one Sm(4) atom to form distorted OSm3Tm2 trigonal bipyramids that share  a cornercorner with one O(12)Sm2Tm2 trigonal pyramid,  a cornercorner with one O(8)Sm2Tm2 trigonal pyramid,  an edgeedge with one O(10)Sm2Tm2 tetrahedra, edges with two equivalent O(9)Sm3Tm2 trigonal bipyramids,  an edgeedge with one O(12)Sm2Tm2 trigonal pyramid, and edges with two equivalent O(4)Sm2Tm2 trigonal pyramids. In the twelfth O site, O(12) is bonded to one Tm(1), one Tm(2), one Sm(1), and one Sm(3) atom to form distorted OSm2Tm2 trigonal pyramids that share  a cornercorner with one O(10)Sm2Tm2 tetrahedra,  a cornercorner with one O(11)Sm3Tm2 trigonal bipyramid,  a cornercorner with one O(8)Sm2Tm2 trigonal pyramid, corners with three equivalent O(4)Sm2Tm2 trigonal pyramids,  an edgeedge with one O(10)Sm2Tm2 tetrahedra,  an edgeedge with one O(11)Sm3Tm2 trigonal bipyramid, and  an edgeedge with one O(9)Sm3Tm2 trigonal bipyramid.