Materials Data on MgCr2O7 by Materials Project
MgCr2O7 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. Mg2+ is bonded to five O2- atoms to form MgO5 trigonal bipyramids that share corners with five CrO4 tetrahedra and corners with two equivalent MgO5 trigonal bipyramids. There are a spread of Mg–O bond distances ranging from 2.02–2.36 Å. There are two inequivalent Cr6+ sites. In the first Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share a cornercorner with one CrO4 tetrahedra and corners with three equivalent MgO5 trigonal bipyramids. There are a spread of Cr–O bond distances ranging from 1.59–1.76 Å. In the second Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share a cornercorner with one CrO4 tetrahedra and corners with two equivalent MgO5 trigonal bipyramids. There are a spread of Cr–O bond distances ranging from 1.59–1.81 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Mg2+ and one Cr6+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Mg2+ and one Cr6+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Mg2+ and one Cr6+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mg2+ and one Cr6+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to two Cr6+ atoms. In the seventh O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom.