FeAs(Se) crystallizes in the monoclinic P2_1/c space group. Fe(1) is bonded to three equivalent As(1) and three equivalent Se(1) atoms to form FeAs3Se3 octahedra that share corners with eight equivalent Fe(1)As3Se3 octahedra, corners with three equivalent As(1)Fe3Se tetrahedra, corners with three equivalent Se(1)Fe3As tetrahedra, and edges with two equivalent Fe(1)As3Se3 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. As(1) is bonded to three equivalent Fe(1) and one Se(1) atom to form distorted AsFe3Se tetrahedra that share corners with three equivalent Fe(1)As3Se3 octahedra, corners with four equivalent As(1)Fe3Se tetrahedra, corners with nine equivalent Se(1)Fe3As tetrahedra, and  an edgeedge with one As(1)Fe3Se tetrahedra. The corner-sharing octahedral tilt angles range from 68-74°. Se(1) is bonded to three equivalent Fe(1) and one As(1) atom to form distorted SeFe3As tetrahedra that share corners with three equivalent Fe(1)As3Se3 octahedra, corners with four equivalent Se(1)Fe3As tetrahedra, corners with nine equivalent As(1)Fe3Se tetrahedra, and  an edgeedge with one Se(1)Fe3As tetrahedra. The corner-sharing octahedral tilt angles range from 76-79°.
FeAs(Se) crystallizes in the monoclinic P2_1/c space group. Fe(1) is bonded to three equivalent As(1) and three equivalent Se(1) atoms to form FeAs3Se3 octahedra that share corners with eight equivalent Fe(1)As3Se3 octahedra, corners with three equivalent As(1)Fe3Se tetrahedra, corners with three equivalent Se(1)Fe3As tetrahedra, and edges with two equivalent Fe(1)As3Se3 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. There are a spread of Fe(1)-As(1) bond distances ranging from 2.39-2.41 Å. There are a spread of Fe(1)-Se(1) bond distances ranging from 2.30-2.33 Å. As(1) is bonded to three equivalent Fe(1) and one Se(1) atom to form distorted AsFe3Se tetrahedra that share corners with three equivalent Fe(1)As3Se3 octahedra, corners with four equivalent As(1)Fe3Se tetrahedra, corners with nine equivalent Se(1)Fe3As tetrahedra, and  an edgeedge with one As(1)Fe3Se tetrahedra. The corner-sharing octahedral tilt angles range from 68-74°. The As(1)-Se(1) bond length is 2.52 Å. Se(1) is bonded to three equivalent Fe(1) and one As(1) atom to form distorted SeFe3As tetrahedra that share corners with three equivalent Fe(1)As3Se3 octahedra, corners with four equivalent Se(1)Fe3As tetrahedra, corners with nine equivalent As(1)Fe3Se tetrahedra, and  an edgeedge with one Se(1)Fe3As tetrahedra. The corner-sharing octahedral tilt angles range from 76-79°.