HfTa3C4 is Caswellsilverite-like structured and crystallizes in the trigonal P-3m1 space group. Hf(1) is bonded to six equivalent C(1) atoms to form HfC6 octahedra that share corners with twelve equivalent Ta(2)C6 octahedra, edges with six equivalent Hf(1)C6 octahedra, and faces with two equivalent Ta(2)C6 octahedra. The corner-sharing octahedral tilt angles are 47°. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to six equivalent C(2) atoms to form a mixture of face, corner, and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 47°. In the second Ta site, Ta(2) is bonded to three equivalent C(1) and three equivalent C(2) atoms to form TaC6 octahedra that share corners with six equivalent Hf(1)C6 octahedra, corners with six equivalent Ta(1)C6 octahedra, edges with six equivalent Ta(2)C6 octahedra,  a faceface with one Hf(1)C6 octahedra, and  a faceface with one Ta(1)C6 octahedra. The corner-sharing octahedral tilt angles are 47°. There are two inequivalent C sites. In the first C site, C(1) is bonded to three equivalent Hf(1) and three equivalent Ta(2) atoms to form distorted CHf3Ta3 pentagonal pyramids that share corners with three equivalent C(1)Hf3Ta3 pentagonal pyramids, corners with three equivalent C(2)Ta6 pentagonal pyramids, edges with three equivalent C(2)Ta6 pentagonal pyramids, and edges with nine equivalent C(1)Hf3Ta3 pentagonal pyramids. In the second C site, C(2) is bonded to three equivalent Ta(1) and three equivalent Ta(2) atoms to form distorted CTa6 pentagonal pyramids that share corners with three equivalent C(1)Hf3Ta3 pentagonal pyramids, corners with three equivalent C(2)Ta6 pentagonal pyramids, edges with three equivalent C(1)Hf3Ta3 pentagonal pyramids, and edges with nine equivalent C(2)Ta6 pentagonal pyramids.
HfTa3C4 is Caswellsilverite-like structured and crystallizes in the trigonal P-3m1 space group. Hf(1) is bonded to six equivalent C(1) atoms to form HfC6 octahedra that share corners with twelve equivalent Ta(2)C6 octahedra, edges with six equivalent Hf(1)C6 octahedra, and faces with two equivalent Ta(2)C6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Hf(1)-C(1) bond lengths are 2.36 Å. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to six equivalent C(2) atoms to form a mixture of face, corner, and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Ta(1)-C(2) bond lengths are 2.29 Å. In the second Ta site, Ta(2) is bonded to three equivalent C(1) and three equivalent C(2) atoms to form TaC6 octahedra that share corners with six equivalent Hf(1)C6 octahedra, corners with six equivalent Ta(1)C6 octahedra, edges with six equivalent Ta(2)C6 octahedra,  a faceface with one Hf(1)C6 octahedra, and  a faceface with one Ta(1)C6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Ta(2)-C(1) bond lengths are 2.27 Å. All Ta(2)-C(2) bond lengths are 2.31 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded to three equivalent Hf(1) and three equivalent Ta(2) atoms to form distorted CHf3Ta3 pentagonal pyramids that share corners with three equivalent C(1)Hf3Ta3 pentagonal pyramids, corners with three equivalent C(2)Ta6 pentagonal pyramids, edges with three equivalent C(2)Ta6 pentagonal pyramids, and edges with nine equivalent C(1)Hf3Ta3 pentagonal pyramids. In the second C site, C(2) is bonded to three equivalent Ta(1) and three equivalent Ta(2) atoms to form distorted CTa6 pentagonal pyramids that share corners with three equivalent C(1)Hf3Ta3 pentagonal pyramids, corners with three equivalent C(2)Ta6 pentagonal pyramids, edges with three equivalent C(1)Hf3Ta3 pentagonal pyramids, and edges with nine equivalent C(2)Ta6 pentagonal pyramids.