NaCr2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form edge-sharing CrO6 octahedra. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form edge-sharing CrO6 octahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Cr(2), and two equivalent Cr(1) atoms to form ONa2Cr3 trigonal bipyramids that share corners with five equivalent O(1)Na2Cr3 trigonal bipyramids, corners with two equivalent O(3)NaCr3 trigonal pyramids, edges with four equivalent O(1)Na2Cr3 trigonal bipyramids, and edges with two equivalent O(3)NaCr3 trigonal pyramids. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), one Cr(1), and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to one Na(1), one Cr(1), and two equivalent Cr(2) atoms to form distorted ONaCr3 trigonal pyramids that share corners with four equivalent O(1)Na2Cr3 trigonal bipyramids, corners with three equivalent O(3)NaCr3 trigonal pyramids, and edges with four equivalent O(1)Na2Cr3 trigonal bipyramids.
NaCr2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. Both Na(1)-O(3) bond lengths are 2.39 Å. All Na(1)-O(1) bond lengths are 2.52 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Both Na(2)-O(2) bond lengths are 2.44 Å. All Na(2)-O(1) bond lengths are 2.55 Å. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form edge-sharing CrO6 octahedra. The Cr(1)-O(2) bond length is 1.91 Å. The Cr(1)-O(3) bond length is 1.92 Å. There are two shorter (1.97 Å) and two longer (2.01 Å) Cr(1)-O(1) bond lengths. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form edge-sharing CrO6 octahedra. Both Cr(2)-O(1) bond lengths are 2.02 Å. Both Cr(2)-O(2) bond lengths are 2.00 Å. Both Cr(2)-O(3) bond lengths are 2.00 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Cr(2), and two equivalent Cr(1) atoms to form ONa2Cr3 trigonal bipyramids that share corners with five equivalent O(1)Na2Cr3 trigonal bipyramids, corners with two equivalent O(3)NaCr3 trigonal pyramids, edges with four equivalent O(1)Na2Cr3 trigonal bipyramids, and edges with two equivalent O(3)NaCr3 trigonal pyramids. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), one Cr(1), and two equivalent Cr(2) atoms. In the third O site, O(3) is bonded to one Na(1), one Cr(1), and two equivalent Cr(2) atoms to form distorted ONaCr3 trigonal pyramids that share corners with four equivalent O(1)Na2Cr3 trigonal bipyramids, corners with three equivalent O(3)NaCr3 trigonal pyramids, and edges with four equivalent O(1)Na2Cr3 trigonal bipyramids.