Ta11Co2Se8 crystallizes in the orthorhombic Pnnm space group. There are six inequivalent Ta sites. In the first Ta site, Ta(1) is bonded in a 5-coordinate geometry to two equivalent Co(1), one Se(3), and two equivalent Se(1) atoms. In the second Ta site, Ta(2) is bonded in a 4-coordinate geometry to one Co(1), two equivalent Se(2), and two equivalent Se(4) atoms. In the third Ta site, Ta(3) is bonded in a 5-coordinate geometry to two equivalent Co(1), one Se(4), and two equivalent Se(1) atoms. In the fourth Ta site, Ta(4) is bonded in a 5-coordinate geometry to one Co(1), one Se(2), one Se(4), and two equivalent Se(3) atoms. In the fifth Ta site, Ta(5) is bonded in a 5-coordinate geometry to two equivalent Co(1), one Se(2), and two equivalent Se(4) atoms. In the sixth Ta site, Ta(6) is bonded in a distorted square co-planar geometry to two equivalent Co(1) and two equivalent Se(1) atoms. Co(1) is bonded in a 9-coordinate geometry to one Ta(2), one Ta(4), one Ta(6), two equivalent Ta(1), two equivalent Ta(3), and two equivalent Ta(5) atoms. There are four inequivalent Se sites. In the first Se site, Se(3) is bonded in a 3-coordinate geometry to one Ta(1) and two equivalent Ta(4) atoms. In the second Se site, Se(4) is bonded to one Ta(3), one Ta(4), two equivalent Ta(2), and two equivalent Ta(5) atoms to form distorted edge-sharing SeTa6 pentagonal pyramids. In the third Se site, Se(1) is bonded in a 5-coordinate geometry to one Ta(6), two equivalent Ta(1), and two equivalent Ta(3) atoms. In the fourth Se site, Se(2) is bonded in a 4-coordinate geometry to one Ta(4), one Ta(5), and two equivalent Ta(2) atoms.
Ta11Co2Se8 crystallizes in the orthorhombic Pnnm space group. There are six inequivalent Ta sites. In the first Ta site, Ta(1) is bonded in a 5-coordinate geometry to two equivalent Co(1), one Se(3), and two equivalent Se(1) atoms. Both Ta(1)-Co(1) bond lengths are 2.50 Å. The Ta(1)-Se(3) bond length is 2.56 Å. Both Ta(1)-Se(1) bond lengths are 2.75 Å. In the second Ta site, Ta(2) is bonded in a 4-coordinate geometry to one Co(1), two equivalent Se(2), and two equivalent Se(4) atoms. The Ta(2)-Co(1) bond length is 2.87 Å. Both Ta(2)-Se(2) bond lengths are 2.64 Å. Both Ta(2)-Se(4) bond lengths are 2.68 Å. In the third Ta site, Ta(3) is bonded in a 5-coordinate geometry to two equivalent Co(1), one Se(4), and two equivalent Se(1) atoms. Both Ta(3)-Co(1) bond lengths are 2.56 Å. The Ta(3)-Se(4) bond length is 2.71 Å. Both Ta(3)-Se(1) bond lengths are 2.73 Å. In the fourth Ta site, Ta(4) is bonded in a 5-coordinate geometry to one Co(1), one Se(2), one Se(4), and two equivalent Se(3) atoms. The Ta(4)-Co(1) bond length is 2.86 Å. The Ta(4)-Se(2) bond length is 2.67 Å. The Ta(4)-Se(4) bond length is 2.78 Å. Both Ta(4)-Se(3) bond lengths are 2.62 Å. In the fifth Ta site, Ta(5) is bonded in a 5-coordinate geometry to two equivalent Co(1), one Se(2), and two equivalent Se(4) atoms. Both Ta(5)-Co(1) bond lengths are 2.48 Å. The Ta(5)-Se(2) bond length is 2.62 Å. Both Ta(5)-Se(4) bond lengths are 2.76 Å. In the sixth Ta site, Ta(6) is bonded in a distorted square co-planar geometry to two equivalent Co(1) and two equivalent Se(1) atoms. Both Ta(6)-Co(1) bond lengths are 2.77 Å. Both Ta(6)-Se(1) bond lengths are 2.71 Å. Co(1) is bonded in a 9-coordinate geometry to one Ta(2), one Ta(4), one Ta(6), two equivalent Ta(1), two equivalent Ta(3), and two equivalent Ta(5) atoms. There are four inequivalent Se sites. In the first Se site, Se(3) is bonded in a 3-coordinate geometry to one Ta(1) and two equivalent Ta(4) atoms. In the second Se site, Se(4) is bonded to one Ta(3), one Ta(4), two equivalent Ta(2), and two equivalent Ta(5) atoms to form distorted edge-sharing SeTa6 pentagonal pyramids. In the third Se site, Se(1) is bonded in a 5-coordinate geometry to one Ta(6), two equivalent Ta(1), and two equivalent Ta(3) atoms. In the fourth Se site, Se(2) is bonded in a 4-coordinate geometry to one Ta(4), one Ta(5), and two equivalent Ta(2) atoms.