U2CoSe2S3 crystallizes in the monoclinic C2/c space group. U(1) is bonded in a 8-coordinate geometry to three equivalent Se(1), two equivalent S(1), and three equivalent S(2) atoms. Co(1) is bonded to four equivalent Se(1) and two equivalent S(2) atoms to form corner-sharing CoSe4S2 octahedra. The corner-sharing octahedral tilt angles are 39°. Se(1) is bonded to three equivalent U(1) and two equivalent Co(1) atoms to form distorted SeU3Co2 trigonal bipyramids that share corners with two equivalent Se(1)U3Co2 trigonal bipyramids, corners with four equivalent S(1)U4 trigonal pyramids, corners with seven equivalent S(2)U3Co trigonal pyramids, edges with five equivalent Se(1)U3Co2 trigonal bipyramids,  an edgeedge with one S(1)U4 trigonal pyramid, and edges with three equivalent S(2)U3Co trigonal pyramids. There are two inequivalent S sites. In the first S site, S(1) is bonded to four equivalent U(1) atoms to form SU4 trigonal pyramids that share corners with eight equivalent Se(1)U3Co2 trigonal bipyramids, corners with eight equivalent S(2)U3Co trigonal pyramids, edges with two equivalent Se(1)U3Co2 trigonal bipyramids, edges with two equivalent S(2)U3Co trigonal pyramids, and edges with two equivalent S(1)U4 trigonal pyramids. In the second S site, S(2) is bonded to three equivalent U(1) and one Co(1) atom to form distorted SU3Co trigonal pyramids that share corners with seven equivalent Se(1)U3Co2 trigonal bipyramids, corners with three equivalent S(2)U3Co trigonal pyramids, corners with four equivalent S(1)U4 trigonal pyramids, edges with three equivalent Se(1)U3Co2 trigonal bipyramids,  an edgeedge with one S(1)U4 trigonal pyramid, and edges with two equivalent S(2)U3Co trigonal pyramids.
U2CoSe2S3 crystallizes in the monoclinic C2/c space group. U(1) is bonded in a 8-coordinate geometry to three equivalent Se(1), two equivalent S(1), and three equivalent S(2) atoms. There is one shorter (2.95 Å) and two longer (2.96 Å) U(1)-Se(1) bond lengths. There is one shorter (2.75 Å) and one longer (2.77 Å) U(1)-S(1) bond length. There are a spread of U(1)-S(2) bond distances ranging from 2.65-2.92 Å. Co(1) is bonded to four equivalent Se(1) and two equivalent S(2) atoms to form corner-sharing CoSe4S2 octahedra. The corner-sharing octahedral tilt angles are 39°. There are two shorter (2.50 Å) and two longer (2.52 Å) Co(1)-Se(1) bond lengths. Both Co(1)-S(2) bond lengths are 2.48 Å. Se(1) is bonded to three equivalent U(1) and two equivalent Co(1) atoms to form distorted SeU3Co2 trigonal bipyramids that share corners with two equivalent Se(1)U3Co2 trigonal bipyramids, corners with four equivalent S(1)U4 trigonal pyramids, corners with seven equivalent S(2)U3Co trigonal pyramids, edges with five equivalent Se(1)U3Co2 trigonal bipyramids,  an edgeedge with one S(1)U4 trigonal pyramid, and edges with three equivalent S(2)U3Co trigonal pyramids. There are two inequivalent S sites. In the first S site, S(1) is bonded to four equivalent U(1) atoms to form SU4 trigonal pyramids that share corners with eight equivalent Se(1)U3Co2 trigonal bipyramids, corners with eight equivalent S(2)U3Co trigonal pyramids, edges with two equivalent Se(1)U3Co2 trigonal bipyramids, edges with two equivalent S(2)U3Co trigonal pyramids, and edges with two equivalent S(1)U4 trigonal pyramids. In the second S site, S(2) is bonded to three equivalent U(1) and one Co(1) atom to form distorted SU3Co trigonal pyramids that share corners with seven equivalent Se(1)U3Co2 trigonal bipyramids, corners with three equivalent S(2)U3Co trigonal pyramids, corners with four equivalent S(1)U4 trigonal pyramids, edges with three equivalent Se(1)U3Co2 trigonal bipyramids,  an edgeedge with one S(1)U4 trigonal pyramid, and edges with two equivalent S(2)U3Co trigonal pyramids.