Ta2Co4O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Co(2)O6 octahedra, corners with six equivalent Co(1)O6 octahedra, edges with three equivalent Co(2)O6 octahedra, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to six equivalent O(2) atoms to form CoO6 octahedra that share corners with three equivalent Co(2)O6 octahedra, corners with six equivalent Ta(1)O6 octahedra, edges with three equivalent Co(1)O6 octahedra, and  a faceface with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the second Co site, Co(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted CoO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, edges with three equivalent Ta(1)O6 octahedra, and  a faceface with one Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-65°. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ta(1) and two equivalent Co(2) atoms to form distorted OTa2Co2 trigonal pyramids that share corners with four equivalent O(1)Ta2Co2 trigonal pyramids, corners with eight equivalent O(2)TaCo3 trigonal pyramids, edges with two equivalent O(1)Ta2Co2 trigonal pyramids, and edges with two equivalent O(2)TaCo3 trigonal pyramids. In the second O site, O(2) is bonded to one Ta(1), one Co(2), and two equivalent Co(1) atoms to form distorted OTaCo3 trigonal pyramids that share corners with four equivalent O(1)Ta2Co2 trigonal pyramids, corners with eight equivalent O(2)TaCo3 trigonal pyramids,  an edgeedge with one O(1)Ta2Co2 trigonal pyramid, and edges with three equivalent O(2)TaCo3 trigonal pyramids.
Ta2Co4O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Co(2)O6 octahedra, corners with six equivalent Co(1)O6 octahedra, edges with three equivalent Co(2)O6 octahedra, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. All Ta(1)-O(1) bond lengths are 2.14 Å. All Ta(1)-O(2) bond lengths are 1.92 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to six equivalent O(2) atoms to form CoO6 octahedra that share corners with three equivalent Co(2)O6 octahedra, corners with six equivalent Ta(1)O6 octahedra, edges with three equivalent Co(1)O6 octahedra, and  a faceface with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. There are three shorter (2.08 Å) and three longer (2.18 Å) Co(1)-O(2) bond lengths. In the second Co site, Co(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted CoO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, edges with three equivalent Ta(1)O6 octahedra, and  a faceface with one Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-65°. All Co(2)-O(1) bond lengths are 2.04 Å. All Co(2)-O(2) bond lengths are 2.26 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ta(1) and two equivalent Co(2) atoms to form distorted OTa2Co2 trigonal pyramids that share corners with four equivalent O(1)Ta2Co2 trigonal pyramids, corners with eight equivalent O(2)TaCo3 trigonal pyramids, edges with two equivalent O(1)Ta2Co2 trigonal pyramids, and edges with two equivalent O(2)TaCo3 trigonal pyramids. In the second O site, O(2) is bonded to one Ta(1), one Co(2), and two equivalent Co(1) atoms to form distorted OTaCo3 trigonal pyramids that share corners with four equivalent O(1)Ta2Co2 trigonal pyramids, corners with eight equivalent O(2)TaCo3 trigonal pyramids,  an edgeedge with one O(1)Ta2Co2 trigonal pyramid, and edges with three equivalent O(2)TaCo3 trigonal pyramids.