Cr2Se3 crystallizes in the triclinic P-1 space group. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one Se(3), one Se(4), two equivalent Se(1), and two equivalent Se(6) atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 50-52°. In the second Cr site, Cr(2) is bonded to one Se(3), one Se(4), one Se(5), one Se(6), and two equivalent Se(2) atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. In the third Cr site, Cr(3) is bonded to one Se(1), one Se(2), one Se(3), one Se(4), and two equivalent Se(5) atoms to form a mixture of edge and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-52°. In the fourth Cr site, Cr(4) is bonded to one Se(1), one Se(2), one Se(4), one Se(5), and two equivalent Se(6) atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Cr(3), one Cr(4), and two equivalent Cr(1) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Cr(3), one Cr(4), and two equivalent Cr(2) atoms. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Cr(1), one Cr(2), and one Cr(3) atom. In the fourth Se site, Se(4) is bonded in a rectangular see-saw-like geometry to one Cr(1), one Cr(2), one Cr(3), and one Cr(4) atom. In the fifth Se site, Se(5) is bonded to one Cr(2), one Cr(4), and two equivalent Cr(3) atoms to form SeCr4 trigonal pyramids that share  a cornercorner with one Se(6)Cr5 trigonal bipyramid,  an edgeedge with one Se(6)Cr5 trigonal bipyramid, and  an edgeedge with one Se(5)Cr4 trigonal pyramid. In the sixth Se site, Se(6) is bonded to one Cr(2), two equivalent Cr(1), and two equivalent Cr(4) atoms to form distorted SeCr5 trigonal bipyramids that share  a cornercorner with one Se(5)Cr4 trigonal pyramid, edges with two equivalent Se(6)Cr5 trigonal bipyramids, and  an edgeedge with one Se(5)Cr4 trigonal pyramid.
Cr2Se3 crystallizes in the triclinic P-1 space group. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one Se(3), one Se(4), two equivalent Se(1), and two equivalent Se(6) atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 50-52°. The Cr(1)-Se(3) bond length is 2.45 Å. The Cr(1)-Se(4) bond length is 2.61 Å. There is one shorter (2.49 Å) and one longer (2.52 Å) Cr(1)-Se(1) bond length. There is one shorter (2.58 Å) and one longer (2.61 Å) Cr(1)-Se(6) bond length. In the second Cr site, Cr(2) is bonded to one Se(3), one Se(4), one Se(5), one Se(6), and two equivalent Se(2) atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Cr(2)-Se(3) bond length is 2.47 Å. The Cr(2)-Se(4) bond length is 2.54 Å. The Cr(2)-Se(5) bond length is 2.58 Å. The Cr(2)-Se(6) bond length is 2.61 Å. There is one shorter (2.51 Å) and one longer (2.53 Å) Cr(2)-Se(2) bond length. In the third Cr site, Cr(3) is bonded to one Se(1), one Se(2), one Se(3), one Se(4), and two equivalent Se(5) atoms to form a mixture of edge and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-52°. The Cr(3)-Se(1) bond length is 2.52 Å. The Cr(3)-Se(2) bond length is 2.53 Å. The Cr(3)-Se(3) bond length is 2.47 Å. The Cr(3)-Se(4) bond length is 2.54 Å. There is one shorter (2.56 Å) and one longer (2.59 Å) Cr(3)-Se(5) bond length. In the fourth Cr site, Cr(4) is bonded to one Se(1), one Se(2), one Se(4), one Se(5), and two equivalent Se(6) atoms to form a mixture of edge, face, and corner-sharing CrSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. The Cr(4)-Se(1) bond length is 2.57 Å. The Cr(4)-Se(2) bond length is 2.54 Å. The Cr(4)-Se(4) bond length is 2.51 Å. The Cr(4)-Se(5) bond length is 2.52 Å. There is one shorter (2.59 Å) and one longer (2.60 Å) Cr(4)-Se(6) bond length. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Cr(3), one Cr(4), and two equivalent Cr(1) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Cr(3), one Cr(4), and two equivalent Cr(2) atoms. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Cr(1), one Cr(2), and one Cr(3) atom. In the fourth Se site, Se(4) is bonded in a rectangular see-saw-like geometry to one Cr(1), one Cr(2), one Cr(3), and one Cr(4) atom. In the fifth Se site, Se(5) is bonded to one Cr(2), one Cr(4), and two equivalent Cr(3) atoms to form SeCr4 trigonal pyramids that share  a cornercorner with one Se(6)Cr5 trigonal bipyramid,  an edgeedge with one Se(6)Cr5 trigonal bipyramid, and  an edgeedge with one Se(5)Cr4 trigonal pyramid. In the sixth Se site, Se(6) is bonded to one Cr(2), two equivalent Cr(1), and two equivalent Cr(4) atoms to form distorted SeCr5 trigonal bipyramids that share  a cornercorner with one Se(5)Cr4 trigonal pyramid, edges with two equivalent Se(6)Cr5 trigonal bipyramids, and  an edgeedge with one Se(5)Cr4 trigonal pyramid.