InAlSe3 crystallizes in the hexagonal P6_1 space group. In(1) is bonded to one Se(2), two equivalent Se(1), and two equivalent Se(3) atoms to form InSe5 trigonal bipyramids that share corners with four equivalent Al(1)Se4 tetrahedra,  an edgeedge with one Al(1)Se4 tetrahedra, and edges with two equivalent In(1)Se5 trigonal bipyramids. Al(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form AlSe4 tetrahedra that share corners with two equivalent Al(1)Se4 tetrahedra, corners with four equivalent In(1)Se5 trigonal bipyramids, and  an edgeedge with one In(1)Se5 trigonal bipyramid. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted T-shaped geometry to two equivalent In(1) and one Al(1) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one In(1) and two equivalent Al(1) atoms. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to two equivalent In(1) and one Al(1) atom.
InAlSe3 crystallizes in the hexagonal P6_1 space group. In(1) is bonded to one Se(2), two equivalent Se(1), and two equivalent Se(3) atoms to form InSe5 trigonal bipyramids that share corners with four equivalent Al(1)Se4 tetrahedra,  an edgeedge with one Al(1)Se4 tetrahedra, and edges with two equivalent In(1)Se5 trigonal bipyramids. The In(1)-Se(2) bond length is 2.68 Å. There is one shorter (2.62 Å) and one longer (2.86 Å) In(1)-Se(1) bond length. There is one shorter (2.63 Å) and one longer (2.84 Å) In(1)-Se(3) bond length. Al(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form AlSe4 tetrahedra that share corners with two equivalent Al(1)Se4 tetrahedra, corners with four equivalent In(1)Se5 trigonal bipyramids, and  an edgeedge with one In(1)Se5 trigonal bipyramid. The Al(1)-Se(1) bond length is 2.38 Å. The Al(1)-Se(3) bond length is 2.37 Å. There is one shorter (2.41 Å) and one longer (2.43 Å) Al(1)-Se(2) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted T-shaped geometry to two equivalent In(1) and one Al(1) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one In(1) and two equivalent Al(1) atoms. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to two equivalent In(1) and one Al(1) atom.