MgMo3Se4 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Se(1), one Se(3), one Se(4), one Se(5), and one Se(8) atom. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Mo(6), one Se(2), one Se(3), one Se(4), one Se(5), one Se(6), and one Se(8) atom. There are six inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to one Se(1), one Se(3), one Se(4), and two equivalent Se(2) atoms to form distorted MoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  an edgeedge with one Mo(2)MoSe5 square pyramid,  an edgeedge with one Mo(3)MoSe5 square pyramid,  an edgeedge with one Mo(4)MoSe5 square pyramid,  an edgeedge with one Mo(5)MoSe5 square pyramid, and  an edgeedge with one Mo(1)Se5 square pyramid. In the second Mo site, Mo(2) is bonded to one Mo(6), one Se(1), one Se(2), one Se(6), and two equivalent Se(5) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(2)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(3)MoSe5 square pyramid, and  a faceface with one Mo(4)MoSe5 square pyramid. In the third Mo site, Mo(3) is bonded to one Mo(6), one Se(2), one Se(3), one Se(5), and two equivalent Se(7) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(3)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(2)MoSe5 square pyramid, and  a faceface with one Mo(5)MoSe5 square pyramid. In the fourth Mo site, Mo(4) is bonded to one Mo(6), one Se(4), one Se(6), one Se(8), and two equivalent Se(1) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(4)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(2)MoSe5 square pyramid, and  a faceface with one Mo(5)MoSe5 square pyramid. In the fifth Mo site, Mo(5) is bonded to one Mo(6), one Se(3), one Se(7), one Se(8), and two equivalent Se(4) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(5)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(3)MoSe5 square pyramid, and  a faceface with one Mo(4)MoSe5 square pyramid. In the sixth Mo site, Mo(6) is bonded in a 10-coordinate geometry to one Mg(2), one Mo(2), one Mo(3), one Mo(4), one Mo(5), one Se(5), one Se(6), one Se(7), and two equivalent Se(8) atoms. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mo(1), one Mo(2), and two equivalent Mo(4) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Mg(2), one Mo(2), one Mo(3), and two equivalent Mo(1) atoms. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), one Mo(1), one Mo(3), and one Mo(5) atom. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(2), one Mo(1), one Mo(4), and two equivalent Mo(5) atoms. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(2), one Mo(3), one Mo(6), and two equivalent Mo(2) atoms. In the sixth Se site, Se(6) is bonded in a 4-coordinate geometry to one Mg(2), one Mo(2), one Mo(4), and one Mo(6) atom. In the seventh Se site, Se(7) is bonded in a rectangular see-saw-like geometry to one Mo(5), one Mo(6), and two equivalent Mo(3) atoms. In the eighth Se site, Se(8) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(2), one Mo(4), one Mo(5), and two equivalent Mo(6) atoms.
MgMo3Se4 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Se(1), one Se(3), one Se(4), one Se(5), and one Se(8) atom. The Mg(1)-Se(1) bond length is 2.63 Å. The Mg(1)-Se(3) bond length is 2.60 Å. The Mg(1)-Se(4) bond length is 2.61 Å. The Mg(1)-Se(5) bond length is 2.62 Å. The Mg(1)-Se(8) bond length is 3.26 Å. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Mo(6), one Se(2), one Se(3), one Se(4), one Se(5), one Se(6), and one Se(8) atom. The Mg(2)-Mo(6) bond length is 3.12 Å. The Mg(2)-Se(2) bond length is 2.59 Å. The Mg(2)-Se(3) bond length is 3.15 Å. The Mg(2)-Se(4) bond length is 2.77 Å. The Mg(2)-Se(5) bond length is 2.96 Å. The Mg(2)-Se(6) bond length is 2.66 Å. The Mg(2)-Se(8) bond length is 2.61 Å. There are six inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to one Se(1), one Se(3), one Se(4), and two equivalent Se(2) atoms to form distorted MoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  an edgeedge with one Mo(2)MoSe5 square pyramid,  an edgeedge with one Mo(3)MoSe5 square pyramid,  an edgeedge with one Mo(4)MoSe5 square pyramid,  an edgeedge with one Mo(5)MoSe5 square pyramid, and  an edgeedge with one Mo(1)Se5 square pyramid. The Mo(1)-Se(1) bond length is 2.60 Å. The Mo(1)-Se(3) bond length is 2.61 Å. The Mo(1)-Se(4) bond length is 2.67 Å. There is one shorter (2.62 Å) and one longer (2.73 Å) Mo(1)-Se(2) bond length. In the second Mo site, Mo(2) is bonded to one Mo(6), one Se(1), one Se(2), one Se(6), and two equivalent Se(5) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(2)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(3)MoSe5 square pyramid, and  a faceface with one Mo(4)MoSe5 square pyramid. The Mo(2)-Mo(6) bond length is 2.71 Å. The Mo(2)-Se(1) bond length is 2.65 Å. The Mo(2)-Se(2) bond length is 2.63 Å. The Mo(2)-Se(6) bond length is 2.59 Å. There is one shorter (2.63 Å) and one longer (2.88 Å) Mo(2)-Se(5) bond length. In the third Mo site, Mo(3) is bonded to one Mo(6), one Se(2), one Se(3), one Se(5), and two equivalent Se(7) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(3)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(2)MoSe5 square pyramid, and  a faceface with one Mo(5)MoSe5 square pyramid. The Mo(3)-Mo(6) bond length is 2.67 Å. The Mo(3)-Se(2) bond length is 2.58 Å. The Mo(3)-Se(3) bond length is 2.62 Å. The Mo(3)-Se(5) bond length is 2.68 Å. There is one shorter (2.62 Å) and one longer (2.76 Å) Mo(3)-Se(7) bond length. In the fourth Mo site, Mo(4) is bonded to one Mo(6), one Se(4), one Se(6), one Se(8), and two equivalent Se(1) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(5)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(4)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(2)MoSe5 square pyramid, and  a faceface with one Mo(5)MoSe5 square pyramid. The Mo(4)-Mo(6) bond length is 2.67 Å. The Mo(4)-Se(4) bond length is 2.70 Å. The Mo(4)-Se(6) bond length is 2.58 Å. The Mo(4)-Se(8) bond length is 2.60 Å. There is one shorter (2.64 Å) and one longer (2.75 Å) Mo(4)-Se(1) bond length. In the fifth Mo site, Mo(5) is bonded to one Mo(6), one Se(3), one Se(7), one Se(8), and two equivalent Se(4) atoms to form distorted MoMoSe5 square pyramids that share  a cornercorner with one Mo(2)MoSe5 square pyramid,  a cornercorner with one Mo(3)MoSe5 square pyramid,  a cornercorner with one Mo(4)MoSe5 square pyramid,  a cornercorner with one Mo(1)Se5 square pyramid,  an edgeedge with one Mo(5)MoSe5 square pyramid,  an edgeedge with one Mo(1)Se5 square pyramid,  a faceface with one Mo(3)MoSe5 square pyramid, and  a faceface with one Mo(4)MoSe5 square pyramid. The Mo(5)-Mo(6) bond length is 2.67 Å. The Mo(5)-Se(3) bond length is 2.68 Å. The Mo(5)-Se(7) bond length is 2.59 Å. The Mo(5)-Se(8) bond length is 2.66 Å. There is one shorter (2.64 Å) and one longer (2.86 Å) Mo(5)-Se(4) bond length. In the sixth Mo site, Mo(6) is bonded in a 10-coordinate geometry to one Mg(2), one Mo(2), one Mo(3), one Mo(4), one Mo(5), one Se(5), one Se(6), one Se(7), and two equivalent Se(8) atoms. The Mo(6)-Se(5) bond length is 2.63 Å. The Mo(6)-Se(6) bond length is 2.65 Å. The Mo(6)-Se(7) bond length is 2.59 Å. There is one shorter (2.65 Å) and one longer (2.77 Å) Mo(6)-Se(8) bond length. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mo(1), one Mo(2), and two equivalent Mo(4) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Mg(2), one Mo(2), one Mo(3), and two equivalent Mo(1) atoms. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), one Mo(1), one Mo(3), and one Mo(5) atom. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(2), one Mo(1), one Mo(4), and two equivalent Mo(5) atoms. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(2), one Mo(3), one Mo(6), and two equivalent Mo(2) atoms. In the sixth Se site, Se(6) is bonded in a 4-coordinate geometry to one Mg(2), one Mo(2), one Mo(4), and one Mo(6) atom. In the seventh Se site, Se(7) is bonded in a rectangular see-saw-like geometry to one Mo(5), one Mo(6), and two equivalent Mo(3) atoms. In the eighth Se site, Se(8) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(2), one Mo(4), one Mo(5), and two equivalent Mo(6) atoms.