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Ta2Co is Khatyrkite structured and crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Ta is bonded in a 4-coordinate geometry to four equivalent Co atoms. All Ta–Co bond lengths are 2.62 Å. Co is bonded in a 10-coordinate geometry to eight equivalent Ta and two equivalent Co atoms. Both Co–Co bond lengths are 2.49 Å.
Ta2Co crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are five inequivalent Ta sites. In the first Ta site, Ta is bonded to six Ta and six equivalent Co atoms to form TaTa6Co6 cuboctahedra that share corners with eighteen equivalent CoTa9Co3 cuboctahedra, edges with eighteen TaTa6Co6 cuboctahedra, faces with six equivalent CoTa9Co3 cuboctahedra, and faces with fourteen TaTa6Co6 cuboctahedra. All Ta–Ta bond lengths are 2.84 Å. All Ta–Co bond lengths are 2.87 Å. In the second Ta site, Ta is bonded to eight Ta and four equivalent Co atoms to form distorted TaTa8Co4 cuboctahedra that share corners with twelve TaTa8Co4 cuboctahedra, edges with eight equivalent CoTa9Co3 cuboctahedra, edges with sixteen TaTa6Co6 cuboctahedra, faces with eight equivalent CoTa9Co3 cuboctahedra, and faces with ten TaTa6Co6 cuboctahedra. There are four shorter (2.81 Å) and two longer (2.99 Å) Ta–Ta bond lengths. All Ta–Co bond lengths are 2.77 Å. In the third Ta site, Ta is bonded to eight Ta and four equivalent Co atoms to form distorted TaTa8Co4 cuboctahedra that share corners with twelve TaTa8Co4 cuboctahedra, edges with eight equivalent CoTa9Co3 cuboctahedra, edges with sixteen TaTa6Co6 cuboctahedra, faces with eight equivalent CoTa9Co3 cuboctahedra, and faces with ten TaTa6Co6 cuboctahedra. All Ta–Co bond lengths are 2.77 Å. In the fourth Ta site, Ta is bonded to eight Ta and four equivalent Co atoms to form distorted TaTa8Co4 cuboctahedra that share corners with twelve TaTa8Co4 cuboctahedra, edges with eight equivalent CoTa9Co3 cuboctahedra, edges with sixteen TaTa6Co6 cuboctahedra, faces with eight equivalent CoTa9Co3 cuboctahedra, and faces with ten TaTa6Co6 cuboctahedra. There are four shorter (2.81 Å) and two longer (2.99 Å) Ta–Ta bond lengths. All Ta–Co bond lengths are 2.77 Å. In the fifth Ta site, Ta is bonded to eight Ta and four equivalent Co atoms to form distorted TaTa8Co4 cuboctahedra that share corners with twelve TaTa8Co4 cuboctahedra, edges with eight equivalent CoTa9Co3 cuboctahedra, edges with sixteen TaTa6Co6 cuboctahedra, faces with eight equivalent CoTa9Co3 cuboctahedra, and faces with ten TaTa6Co6 cuboctahedra. There are two shorter (2.81 Å) and one longer (2.99 Å) Ta–Ta bond lengths. All Ta–Co bond lengths are 2.77 Å. Co is bonded to nine Ta and three equivalent Co atoms to form distorted CoTa9Co3 cuboctahedra that share corners with nine equivalent TaTa6Co6 cuboctahedra, corners with nine equivalent CoTa9Co3 cuboctahedra, edges with six equivalent CoTa9Co3 cuboctahedra, edges with twelve TaTa8Co4 cuboctahedra, faces with five equivalent CoTa9Co3 cuboctahedra, and faces with fifteen TaTa6Co6 cuboctahedra. All Co–Co bond lengths are 2.87 Å.
TaReCoSe4TaSe2ReSe2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one ReSe2 sheet oriented in the (0, 0, 1) direction; one TaReCoSe4 sheet oriented in the (0, 0, 1) direction; and one TaSe2 sheet oriented in the (0, 0, 1) direction. In the ReSe2 sheet, Re3+ is bonded to six Se2- atoms to form distorted edge-sharing ReSe6 pentagonal pyramids. All Re–Se bond lengths are 2.54 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Re3+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Re3+ atoms. In the TaReCoSe4 sheet, Ta4+ is bonded to six Se2- atoms to form distorted TaSe6 pentagonal pyramids that share corners with six equivalent CoSe6 octahedra, edges with six equivalent TaSe6 pentagonal pyramids, and a faceface with one CoSe6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are three shorter (2.61 Å) and three longer (2.63 Å) Ta–Se bond lengths. Re3+ is bonded to six Se2- atoms to form distorted ReSe6 pentagonal pyramids that share corners with six equivalent CoSe6 octahedra, edges with six equivalent ReSe6 pentagonal pyramids, and a faceface with one CoSe6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are three shorter (2.52 Å) and three longer (2.59 Å) Re–Se bond lengths. Co2+ is bonded to six Se2- atoms to form CoSe6 octahedra that share corners with six equivalent TaSe6 pentagonal pyramids, corners with six equivalent ReSe6 pentagonal pyramids, edges with six equivalent CoSe6 octahedra, a faceface with one TaSe6 pentagonal pyramid, and a faceface with one ReSe6 pentagonal pyramid. There are three shorter (2.37 Å) and three longer (2.49 Å) Co–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to three equivalent Re3+ and three equivalent Co2+ atoms. In the second Se2- site, Se2- is bonded to three equivalent Ta4+ and three equivalent Co2+ atoms to form distorted edge-sharing SeTa3Co3 pentagonal pyramids. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Ta4+ atoms. In the fourth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent Re3+ atoms. In the TaSe2 sheet, Ta4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing TaSe6 pentagonal pyramids. All Ta–Se bond lengths are 2.61 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Ta4+ atoms.