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CrSe2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one CrSe2 sheet oriented in the (0, 0, 1) direction. Cr4+ is bonded to six equivalent Se2- atoms to form edge-sharing CrSe6 octahedra. All Cr–Se bond lengths are 2.50 Å. Se2- is bonded in a distorted T-shaped geometry to three equivalent Cr4+ atoms.
Mg(CrSe2)2 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Mg2+ is bonded to four equivalent Se2- atoms to form MgSe4 tetrahedra that share corners with twelve equivalent CrSe6 octahedra. The corner-sharing octahedral tilt angles are 59°. All Mg–Se bond lengths are 2.58 Å. Cr3+ is bonded to six equivalent Se2- atoms to form CrSe6 octahedra that share corners with six equivalent MgSe4 tetrahedra and edges with six equivalent CrSe6 octahedra. All Cr–Se bond lengths are 2.56 Å. Se2- is bonded to one Mg2+ and three equivalent Cr3+ atoms to form a mixture of distorted corner and edge-sharing SeMgCr3 trigonal pyramids.
CrSe2 is trigonal omega-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Cr4+ sites. In the first Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are three shorter (2.50 Å) and three longer (2.52 Å) Cr–Se bond lengths. In the second Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are a spread of Cr–Se bond distances ranging from 2.49–2.51 Å. In the third Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are a spread of Cr–Se bond distances ranging from 2.50–2.52 Å. In the fourth Cr4+ site, Cr4+ is bonded to six Se2- atoms to form edge-sharing CrSe6 octahedra. There are a spread of Cr–Se bond distances ranging from 2.50–2.52 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the third Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the fourth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the fifth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the sixth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the seventh Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms. In the eighth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three Cr4+ atoms.
Mn(CrSe2)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Cr3+ is bonded to six Se2- atoms to form CrSe6 octahedra that share corners with six equivalent MnSe6 octahedra, edges with six equivalent CrSe6 octahedra, and a faceface with one MnSe6 octahedra. The corner-sharing octahedra tilt angles range from 48–51°. There are a spread of Cr–Se bond distances ranging from 2.52–2.62 Å. Mn2+ is bonded to six Se2- atoms to form MnSe6 octahedra that share corners with twelve equivalent CrSe6 octahedra, edges with two equivalent MnSe6 octahedra, and faces with two equivalent CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 48–51°. There are two shorter (2.63 Å) and four longer (2.69 Å) Mn–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Cr3+ and two equivalent Mn2+ atoms to form a mixture of distorted corner and edge-sharing SeMn2Cr3 trigonal bipyramids. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to three equivalent Cr3+ and one Mn2+ atom.
ZnCr2Se4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Cr3+ is bonded to six equivalent Se2- atoms to form CrSe6 octahedra that share corners with six equivalent ZnSe4 tetrahedra and edges with six equivalent CrSe6 octahedra. All Cr–Se bond lengths are 2.54 Å. Zn2+ is bonded to four equivalent Se2- atoms to form ZnSe4 tetrahedra that share corners with twelve equivalent CrSe6 octahedra. The corner-sharing octahedral tilt angles are 58°. All Zn–Se bond lengths are 2.49 Å. Se2- is bonded to three equivalent Cr3+ and one Zn2+ atom to form a mixture of distorted edge and corner-sharing SeZnCr3 trigonal pyramids.
TiCr2Se4 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ti4+ is bonded to six Se2- atoms to form TiSe6 octahedra that share corners with twelve equivalent CrSe6 octahedra, edges with two equivalent TiSe6 octahedra, and faces with two equivalent CrSe6 octahedra. The corner-sharing octahedra tilt angles range from 49–51°. There are two shorter (2.58 Å) and four longer (2.63 Å) Ti–Se bond lengths. Cr2+ is bonded to six Se2- atoms to form CrSe6 octahedra that share corners with six equivalent TiSe6 octahedra, edges with six equivalent CrSe6 octahedra, and a faceface with one TiSe6 octahedra. The corner-sharing octahedra tilt angles range from 49–51°. There are a spread of Cr–Se bond distances ranging from 2.51–2.64 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two equivalent Ti4+ and three equivalent Cr2+ atoms to form a mixture of distorted edge and corner-sharing SeTi2Cr3 trigonal bipyramids. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to one Ti4+ and three equivalent Cr2+ atoms.