Materials Data on Mg(AlSe2)2 by Materials Project
Mg(AlSe2)2 crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Mg(AlSe2)2 sheets oriented in the (0, 0, 1) direction. Mg2+ is bonded to six equivalent Se2- atoms to form MgSe6 octahedra that share corners with six equivalent AlSe4 tetrahedra and edges with six equivalent MgSe6 octahedra. All Mg–Se bond lengths are 2.68 Å. Al3+ is bonded to four Se2- atoms to form AlSe4 tetrahedra that share corners with three equivalent MgSe6 octahedra and corners with six equivalent AlSe4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. There are one shorter (2.31 Å) and three longer (2.51 Å) Al–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Mg2+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing SeMg3Al trigonal pyramids. In the second Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to three equivalent Al3+ atoms.