Materials Data on KAlCr2(HO4)2 by Materials Project
KCr2Al(HO4)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. K1+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of K–O bond distances ranging from 2.81–3.16 Å. Cr5+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with two equivalent AlH2O4 octahedra. The corner-sharing octahedral tilt angles are 40°. There is two shorter (1.62 Å) and two longer (1.72 Å) Cr–O bond length. Al3+ is bonded to two equivalent H1+ and four equivalent O2- atoms to form AlH2O4 octahedra that share corners with four equivalent CrO4 tetrahedra. Both Al–H bond lengths are 1.98 Å. All Al–O bond lengths are 1.83 Å. H1+ is bonded in a single-bond geometry to one Al3+ atom. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one K1+ and one Cr5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to two equivalent K1+ and one Cr5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+, one Cr5+, and one Al3+ atom.