Cu3AsS4 crystallizes in the monoclinic Pm space group. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(2), and two equivalent S(4) atoms to form distorted CuS4 trigonal pyramids that share corners with four equivalent Cu(2)S4 tetrahedra, corners with two equivalent Cu(1)S4 trigonal pyramids, corners with four equivalent Cu(3)S4 trigonal pyramids, and  an edgeedge with one As(1)S4 tetrahedra. In the second Cu site, Cu(2) is bonded to one S(3), one S(4), and two equivalent S(1) atoms to form CuS4 tetrahedra that share corners with two equivalent Cu(2)S4 tetrahedra, corners with four equivalent As(1)S4 tetrahedra, corners with four equivalent Cu(1)S4 trigonal pyramids, and  an edgeedge with one Cu(3)S4 trigonal pyramid. In the third Cu site, Cu(3) is bonded to one S(3), one S(4), and two equivalent S(2) atoms to form CuS4 trigonal pyramids that share corners with four equivalent As(1)S4 tetrahedra, corners with two equivalent Cu(3)S4 trigonal pyramids, corners with four equivalent Cu(1)S4 trigonal pyramids, and  an edgeedge with one Cu(2)S4 tetrahedra. As(1) is bonded to one S(1), one S(2), and two equivalent S(3) atoms to form AsS4 tetrahedra that share corners with two equivalent As(1)S4 tetrahedra, corners with four equivalent Cu(2)S4 tetrahedra, corners with four equivalent Cu(3)S4 trigonal pyramids, and  an edgeedge with one Cu(1)S4 trigonal pyramid. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Cu(1), two equivalent Cu(2), and one As(1) atom to form SCu3As trigonal pyramids that share corners with four equivalent S(3)Cu2As2 tetrahedra, corners with two equivalent S(1)Cu3As trigonal pyramids, corners with four equivalent S(4)Cu4 trigonal pyramids, and  an edgeedge with one S(2)Cu3As tetrahedra. In the second S site, S(2) is bonded to one Cu(1), two equivalent Cu(3), and one As(1) atom to form SCu3As tetrahedra that share corners with two equivalent S(2)Cu3As tetrahedra, corners with four equivalent S(3)Cu2As2 tetrahedra, corners with four equivalent S(4)Cu4 trigonal pyramids, and  an edgeedge with one S(1)Cu3As trigonal pyramid. In the third S site, S(3) is bonded to one Cu(2), one Cu(3), and two equivalent As(1) atoms to form distorted SCu2As2 tetrahedra that share corners with two equivalent S(3)Cu2As2 tetrahedra, corners with four equivalent S(2)Cu3As tetrahedra, corners with four equivalent S(1)Cu3As trigonal pyramids, and  an edgeedge with one S(4)Cu4 trigonal pyramid. In the fourth S site, S(4) is bonded to one Cu(2), one Cu(3), and two equivalent Cu(1) atoms to form SCu4 trigonal pyramids that share corners with four equivalent S(2)Cu3As tetrahedra, corners with two equivalent S(4)Cu4 trigonal pyramids, corners with four equivalent S(1)Cu3As trigonal pyramids, and  an edgeedge with one S(3)Cu2As2 tetrahedra.
Cu3AsS4 crystallizes in the monoclinic Pm space group. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(2), and two equivalent S(4) atoms to form distorted CuS4 trigonal pyramids that share corners with four equivalent Cu(2)S4 tetrahedra, corners with two equivalent Cu(1)S4 trigonal pyramids, corners with four equivalent Cu(3)S4 trigonal pyramids, and  an edgeedge with one As(1)S4 tetrahedra. The Cu(1)-S(1) bond length is 2.46 Å. The Cu(1)-S(2) bond length is 2.36 Å. Both Cu(1)-S(4) bond lengths are 2.27 Å. In the second Cu site, Cu(2) is bonded to one S(3), one S(4), and two equivalent S(1) atoms to form CuS4 tetrahedra that share corners with two equivalent Cu(2)S4 tetrahedra, corners with four equivalent As(1)S4 tetrahedra, corners with four equivalent Cu(1)S4 trigonal pyramids, and  an edgeedge with one Cu(3)S4 trigonal pyramid. The Cu(2)-S(3) bond length is 2.34 Å. The Cu(2)-S(4) bond length is 2.30 Å. Both Cu(2)-S(1) bond lengths are 2.34 Å. In the third Cu site, Cu(3) is bonded to one S(3), one S(4), and two equivalent S(2) atoms to form CuS4 trigonal pyramids that share corners with four equivalent As(1)S4 tetrahedra, corners with two equivalent Cu(3)S4 trigonal pyramids, corners with four equivalent Cu(1)S4 trigonal pyramids, and  an edgeedge with one Cu(2)S4 tetrahedra. The Cu(3)-S(3) bond length is 2.80 Å. The Cu(3)-S(4) bond length is 2.24 Å. Both Cu(3)-S(2) bond lengths are 2.29 Å. As(1) is bonded to one S(1), one S(2), and two equivalent S(3) atoms to form AsS4 tetrahedra that share corners with two equivalent As(1)S4 tetrahedra, corners with four equivalent Cu(2)S4 tetrahedra, corners with four equivalent Cu(3)S4 trigonal pyramids, and  an edgeedge with one Cu(1)S4 trigonal pyramid. The As(1)-S(1) bond length is 2.30 Å. The As(1)-S(2) bond length is 2.30 Å. Both As(1)-S(3) bond lengths are 2.35 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Cu(1), two equivalent Cu(2), and one As(1) atom to form SCu3As trigonal pyramids that share corners with four equivalent S(3)Cu2As2 tetrahedra, corners with two equivalent S(1)Cu3As trigonal pyramids, corners with four equivalent S(4)Cu4 trigonal pyramids, and  an edgeedge with one S(2)Cu3As tetrahedra. In the second S site, S(2) is bonded to one Cu(1), two equivalent Cu(3), and one As(1) atom to form SCu3As tetrahedra that share corners with two equivalent S(2)Cu3As tetrahedra, corners with four equivalent S(3)Cu2As2 tetrahedra, corners with four equivalent S(4)Cu4 trigonal pyramids, and  an edgeedge with one S(1)Cu3As trigonal pyramid. In the third S site, S(3) is bonded to one Cu(2), one Cu(3), and two equivalent As(1) atoms to form distorted SCu2As2 tetrahedra that share corners with two equivalent S(3)Cu2As2 tetrahedra, corners with four equivalent S(2)Cu3As tetrahedra, corners with four equivalent S(1)Cu3As trigonal pyramids, and  an edgeedge with one S(4)Cu4 trigonal pyramid. In the fourth S site, S(4) is bonded to one Cu(2), one Cu(3), and two equivalent Cu(1) atoms to form SCu4 trigonal pyramids that share corners with four equivalent S(2)Cu3As tetrahedra, corners with two equivalent S(4)Cu4 trigonal pyramids, corners with four equivalent S(1)Cu3As trigonal pyramids, and  an edgeedge with one S(3)Cu2As2 tetrahedra.