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CoAs is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Co3+ is bonded to six equivalent As3- atoms to form a mixture of face, edge, and corner-sharing CoAs6 octahedra. The corner-sharing octahedral tilt angles are 50°. All Co–As bond lengths are 2.41 Å. As3- is bonded in a 6-coordinate geometry to six equivalent Co3+ atoms.
Co2As crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are six inequivalent Co+1.50+ sites. In the first Co+1.50+ site, Co+1.50+ is bonded in a 5-coordinate geometry to five As3- atoms. There are one shorter (2.27 Å) and four longer (2.51 Å) Co–As bond lengths. In the second Co+1.50+ site, Co+1.50+ is bonded to five As3- atoms to form distorted CoAs5 square pyramids that share corners with six CoAs5 square pyramids, corners with six CoAs4 tetrahedra, edges with two equivalent CoAs5 square pyramids, and edges with eight CoAs4 tetrahedra. There are one shorter (2.42 Å) and four longer (2.62 Å) Co–As bond lengths. In the third Co+1.50+ site, Co+1.50+ is bonded to five As3- atoms to form distorted CoAs5 square pyramids that share corners with eight CoAs5 square pyramids, corners with eight CoAs4 tetrahedra, edges with five equivalent CoAs5 square pyramids, and edges with five CoAs4 tetrahedra. There are a spread of Co–As bond distances ranging from 2.39–2.58 Å. In the fourth Co+1.50+ site, Co+1.50+ is bonded to four As3- atoms to form CoAs4 tetrahedra that share corners with four CoAs5 square pyramids, corners with twelve CoAs4 tetrahedra, edges with four equivalent CoAs5 square pyramids, and edges with two equivalent CoAs4 tetrahedra. There are two shorter (2.24 Å) and two longer (2.35 Å) Co–As bond lengths. In the fifth Co+1.50+ site, Co+1.50+ is bonded to four As3- atoms to form CoAs4 tetrahedra that share corners with six equivalent CoAs5 square pyramids, corners with four CoAs4 tetrahedra, edges with four CoAs5 square pyramids, and edges with four equivalent CoAs4 tetrahedra. There are two shorter (2.33 Å) and two longer (2.36 Å) Co–As bond lengths. In the sixth Co+1.50+ site, Co+1.50+ is bonded to four As3- atoms to form CoAs4 tetrahedra that share corners with six CoAs5 square pyramids, corners with seven CoAs4 tetrahedra, edges with five CoAs5 square pyramids, and edges with two equivalent CoAs4 tetrahedra. There are a spread of Co–As bond distances ranging from 2.25–2.36 Å. There are four inequivalent As3- sites. In the first As3- site, As3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms. In the second As3- site, As3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms. In the third As3- site, As3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms. In the fourth As3- site, As3- is bonded in a 9-coordinate geometry to nine Co+1.50+ atoms.
Co2As crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. there are two inequivalent Co+1.50+ sites. In the first Co+1.50+ site, Co+1.50+ is bonded in a 6-coordinate geometry to six equivalent As3- atoms. All Co–As bond lengths are 2.65 Å. In the second Co+1.50+ site, Co+1.50+ is bonded in a trigonal planar geometry to three equivalent As3- atoms. All Co–As bond lengths are 2.26 Å. As3- is bonded in a 3-coordinate geometry to nine Co+1.50+ atoms.
CoAs2 is Marcasite-like structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Co4+ is bonded to six As2- atoms to form a mixture of edge and corner-sharing CoAs6 octahedra. The corner-sharing octahedra tilt angles range from 51–58°. There are a spread of Co–As bond distances ranging from 2.32–2.42 Å. There are two inequivalent As2- sites. In the first As2- site, As2- is bonded in a 4-coordinate geometry to three equivalent Co4+ and one As2- atom. The As–As bond length is 2.51 Å. In the second As2- site, As2- is bonded in a 4-coordinate geometry to three equivalent Co4+ and one As2- atom.
CoAs3 is Skutterudite structured and crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Co1+ is bonded to six equivalent As+0.33- atoms to form corner-sharing CoAs6 octahedra. The corner-sharing octahedral tilt angles are 56°. All Co–As bond lengths are 2.35 Å. As+0.33- is bonded in a distorted bent 120 degrees geometry to two equivalent Co1+ and two equivalent As+0.33- atoms. There are one shorter (2.51 Å) and one longer (2.63 Å) As–As bond lengths.
CoAs is Modderite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Co3+ is bonded to six equivalent As3- atoms to form a mixture of distorted face, edge, and corner-sharing CoAs6 octahedra. The corner-sharing octahedra tilt angles range from 47–59°. There are a spread of Co–As bond distances ranging from 2.31–2.51 Å. As3- is bonded in a 6-coordinate geometry to six equivalent Co3+ atoms.
CoAs2 is zeta iron carbide structured and crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. Co4+ is bonded to six equivalent As2- atoms to form a mixture of edge and corner-sharing CoAs6 octahedra. The corner-sharing octahedral tilt angles are 54°. There are two shorter (2.36 Å) and four longer (2.37 Å) Co–As bond lengths. As2- is bonded in a 4-coordinate geometry to three equivalent Co4+ and one As2- atom. The As–As bond length is 2.52 Å.