ZnCr2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form CrO6 octahedra that share corners with three equivalent Zn(1)O6 pentagonal pyramids, edges with two equivalent Cr(1)O6 octahedra, edges with four equivalent Cr(2)O6 octahedra, and  an edgeedge with one Zn(1)O6 pentagonal pyramid. 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 CrO6 octahedra that share edges with two equivalent Cr(2)O6 octahedra, edges with four equivalent Cr(1)O6 octahedra, and edges with two equivalent Zn(1)O6 pentagonal pyramids. There are two inequivalent Zn sites. In the first Zn site, Zn(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form distorted ZnO6 pentagonal pyramids that share corners with six equivalent Cr(1)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with four equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 5-18°. In the second Zn site, Zn(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Cr(1), two equivalent Cr(2), and one Zn(1) atom. In the second O site, O(2) is bonded to one Cr(1), two equivalent Cr(2), and one Zn(2) atom to form OZnCr3 trigonal pyramids that share corners with four equivalent O(3)Zn2Cr3 trigonal bipyramids, corners with three equivalent O(2)ZnCr3 trigonal pyramids, and edges with four equivalent O(3)Zn2Cr3 trigonal bipyramids. In the third O site, O(3) is bonded to one Cr(2), two equivalent Cr(1), one Zn(1), and one Zn(2) atom to form OZn2Cr3 trigonal bipyramids that share corners with five equivalent O(3)Zn2Cr3 trigonal bipyramids, corners with two equivalent O(2)ZnCr3 trigonal pyramids, edges with four equivalent O(3)Zn2Cr3 trigonal bipyramids, and edges with two equivalent O(2)ZnCr3 trigonal pyramids.
ZnCr2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form CrO6 octahedra that share corners with three equivalent Zn(1)O6 pentagonal pyramids, edges with two equivalent Cr(1)O6 octahedra, edges with four equivalent Cr(2)O6 octahedra, and  an edgeedge with one Zn(1)O6 pentagonal pyramid. The Cr(1)-O(1) bond length is 2.01 Å. The Cr(1)-O(2) bond length is 1.99 Å. There are two shorter (2.00 Å) and two longer (2.09 Å) Cr(1)-O(3) 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 CrO6 octahedra that share edges with two equivalent Cr(2)O6 octahedra, edges with four equivalent Cr(1)O6 octahedra, and edges with two equivalent Zn(1)O6 pentagonal pyramids. Both Cr(2)-O(1) bond lengths are 1.98 Å. Both Cr(2)-O(2) bond lengths are 2.04 Å. Both Cr(2)-O(3) bond lengths are 2.04 Å. There are two inequivalent Zn sites. In the first Zn site, Zn(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form distorted ZnO6 pentagonal pyramids that share corners with six equivalent Cr(1)O6 octahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with four equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 5-18°. Both Zn(1)-O(1) bond lengths are 2.05 Å. All Zn(1)-O(3) bond lengths are 2.32 Å. In the second Zn site, Zn(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. Both Zn(2)-O(2) bond lengths are 2.08 Å. All Zn(2)-O(3) bond lengths are 2.32 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Cr(1), two equivalent Cr(2), and one Zn(1) atom. In the second O site, O(2) is bonded to one Cr(1), two equivalent Cr(2), and one Zn(2) atom to form OZnCr3 trigonal pyramids that share corners with four equivalent O(3)Zn2Cr3 trigonal bipyramids, corners with three equivalent O(2)ZnCr3 trigonal pyramids, and edges with four equivalent O(3)Zn2Cr3 trigonal bipyramids. In the third O site, O(3) is bonded to one Cr(2), two equivalent Cr(1), one Zn(1), and one Zn(2) atom to form OZn2Cr3 trigonal bipyramids that share corners with five equivalent O(3)Zn2Cr3 trigonal bipyramids, corners with two equivalent O(2)ZnCr3 trigonal pyramids, edges with four equivalent O(3)Zn2Cr3 trigonal bipyramids, and edges with two equivalent O(2)ZnCr3 trigonal pyramids.