Materials Data on NaAlCr2(HO4)2 by Materials Project
NaCr2Al(HO4)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Na1+ is bonded to eight O2- atoms to form distorted NaO8 hexagonal bipyramids that share corners with four equivalent CrO4 tetrahedra, edges with two equivalent AlH2O4 octahedra, and edges with two equivalent CrO4 tetrahedra. There are a spread of Na–O bond distances ranging from 2.56–2.80 Å. Cr5+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with two equivalent NaO8 hexagonal bipyramids, corners with two equivalent AlH2O4 octahedra, and an edgeedge with one NaO8 hexagonal bipyramid. The corner-sharing octahedra tilt angles range from 35–45°. There are a spread of Cr–O bond distances ranging from 1.62–1.73 Å. Al3+ is bonded to two equivalent H1+ and four O2- atoms to form AlH2O4 octahedra that share corners with four equivalent CrO4 tetrahedra and edges with two equivalent NaO8 hexagonal bipyramids. Both Al–H bond lengths are 2.00 Å. There is two shorter (1.82 Å) and two longer (1.83 Å) Al–O bond length. H1+ is bonded in a single-bond geometry to one Al3+ atom. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Na1+ and one Cr5+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Na1+, one Cr5+, and one Al3+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one Na1+ and one Cr5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Cr5+, and one Al3+ atom.