Mn4Nb2O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted NbO6 octahedra that share corners with six equivalent Mn(2)O6 octahedra and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(2) atoms. In the second Mn site, Mn(2) is bonded to six equivalent O(2) atoms to form MnO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra and edges with three equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Nb(1) and two equivalent Mn(1) atoms to form distorted OMn2Nb2 trigonal pyramids that share corners with four equivalent O(1)Mn2Nb2 trigonal pyramids, corners with eight equivalent O(2)Mn3Nb trigonal pyramids, edges with two equivalent O(1)Mn2Nb2 trigonal pyramids, and edges with two equivalent O(2)Mn3Nb trigonal pyramids. In the second O site, O(2) is bonded to one Nb(1), one Mn(1), and two equivalent Mn(2) atoms to form distorted OMn3Nb trigonal pyramids that share corners with four equivalent O(1)Mn2Nb2 trigonal pyramids, corners with eight equivalent O(2)Mn3Nb trigonal pyramids,  an edgeedge with one O(1)Mn2Nb2 trigonal pyramid, and edges with three equivalent O(2)Mn3Nb trigonal pyramids.
Mn4Nb2O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted NbO6 octahedra that share corners with six equivalent Mn(2)O6 octahedra and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. All Nb(1)-O(1) bond lengths are 2.16 Å. All Nb(1)-O(2) bond lengths are 1.93 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(2) atoms. All Mn(1)-O(1) bond lengths are 2.06 Å. All Mn(1)-O(2) bond lengths are 2.33 Å. In the second Mn site, Mn(2) is bonded to six equivalent O(2) atoms to form MnO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra and edges with three equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are three shorter (2.12 Å) and three longer (2.22 Å) Mn(2)-O(2) bond lengths. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Nb(1) and two equivalent Mn(1) atoms to form distorted OMn2Nb2 trigonal pyramids that share corners with four equivalent O(1)Mn2Nb2 trigonal pyramids, corners with eight equivalent O(2)Mn3Nb trigonal pyramids, edges with two equivalent O(1)Mn2Nb2 trigonal pyramids, and edges with two equivalent O(2)Mn3Nb trigonal pyramids. In the second O site, O(2) is bonded to one Nb(1), one Mn(1), and two equivalent Mn(2) atoms to form distorted OMn3Nb trigonal pyramids that share corners with four equivalent O(1)Mn2Nb2 trigonal pyramids, corners with eight equivalent O(2)Mn3Nb trigonal pyramids,  an edgeedge with one O(1)Mn2Nb2 trigonal pyramid, and edges with three equivalent O(2)Mn3Nb trigonal pyramids.