Ba4UCr2S9 crystallizes in the trigonal P321 space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(5) atoms. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to two equivalent S(3), two equivalent S(4), two equivalent S(5), and four equivalent S(2) atoms. In the third Ba site, Ba(3) is bonded in a 8-coordinate geometry to two equivalent S(3), two equivalent S(5), and four equivalent S(1) atoms. There are two inequivalent U sites. In the first U site, U(1) is bonded to three equivalent S(1) and three equivalent S(2) atoms to form distorted US6 pentagonal pyramids that share  a faceface with one Cr(1)S6 octahedra and  a faceface with one Cr(3)S6 octahedra. In the second U site, U(2) is bonded to six equivalent S(5) atoms to form distorted US6 pentagonal pyramids that share faces with two equivalent Cr(2)S6 octahedra. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to three equivalent S(1) and three equivalent S(3) atoms to form CrS6 octahedra that share  a faceface with one Cr(3)S6 octahedra and  a faceface with one U(1)S6 pentagonal pyramid. In the second Cr site, Cr(2) is bonded to three equivalent S(4) and three equivalent S(5) atoms to form CrS6 octahedra that share  a faceface with one Cr(2)S6 octahedra and  a faceface with one U(2)S6 pentagonal pyramid. In the third Cr site, Cr(3) is bonded to three equivalent S(2) and three equivalent S(3) atoms to form CrS6 octahedra that share  a faceface with one Cr(1)S6 octahedra and  a faceface with one U(1)S6 pentagonal pyramid. There are five inequivalent S sites. In the first S site, S(5) is bonded to one Ba(2), one Ba(3), two equivalent Ba(1), one U(2), and one Cr(2) atom to form distorted SBa4UCr octahedra that share  a cornercorner with one S(4)Ba4Cr2 octahedra, corners with three equivalent S(5)Ba4UCr octahedra, corners with four equivalent S(1)Ba4UCr octahedra, corners with five equivalent S(3)Ba4Cr2 octahedra,  an edgeedge with one S(5)Ba4UCr octahedra, edges with two equivalent S(1)Ba4UCr octahedra,  a faceface with one S(3)Ba4Cr2 octahedra, faces with two equivalent S(4)Ba4Cr2 octahedra, and faces with two equivalent S(5)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 5-70°. In the second S site, S(1) is bonded to two equivalent Ba(1), two equivalent Ba(3), one U(1), and one Cr(1) atom to form distorted SBa4UCr octahedra that share corners with two equivalent S(4)Ba4Cr2 octahedra, corners with three equivalent S(3)Ba4Cr2 octahedra, corners with three equivalent S(1)Ba4UCr octahedra, corners with four equivalent S(5)Ba4UCr octahedra,  an edgeedge with one S(3)Ba4Cr2 octahedra, edges with two equivalent S(5)Ba4UCr octahedra, faces with two equivalent S(3)Ba4Cr2 octahedra, and faces with three equivalent S(1)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 2-70°. In the third S site, S(2) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one U(1), and one Cr(3) atom. In the fourth S site, S(3) is bonded to one Ba(2), one Ba(3), two equivalent Ba(1), one Cr(1), and one Cr(3) atom to form SBa4Cr2 octahedra that share corners with two equivalent S(3)Ba4Cr2 octahedra, corners with two equivalent S(4)Ba4Cr2 octahedra, corners with three equivalent S(1)Ba4UCr octahedra, corners with five equivalent S(5)Ba4UCr octahedra,  an edgeedge with one S(4)Ba4Cr2 octahedra,  an edgeedge with one S(1)Ba4UCr octahedra,  a faceface with one S(5)Ba4UCr octahedra, faces with two equivalent S(3)Ba4Cr2 octahedra, and faces with two equivalent S(1)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 2-63°. In the fifth S site, S(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Cr(2) atoms to form distorted SBa4Cr2 octahedra that share corners with two equivalent S(5)Ba4UCr octahedra, corners with four equivalent S(3)Ba4Cr2 octahedra, corners with four equivalent S(1)Ba4UCr octahedra, edges with two equivalent S(3)Ba4Cr2 octahedra, faces with two equivalent S(4)Ba4Cr2 octahedra, and faces with four equivalent S(5)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 5-56°.
Ba4UCr2S9 crystallizes in the trigonal P321 space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(5) atoms. The Ba(1)-S(4) bond length is 3.16 Å. There is one shorter (3.20 Å) and one longer (3.40 Å) Ba(1)-S(1) bond length. There is one shorter (3.12 Å) and one longer (3.55 Å) Ba(1)-S(2) bond length. There is one shorter (3.24 Å) and one longer (3.26 Å) Ba(1)-S(3) bond length. There is one shorter (3.32 Å) and one longer (3.48 Å) Ba(1)-S(5) bond length. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to two equivalent S(3), two equivalent S(4), two equivalent S(5), and four equivalent S(2) atoms. Both Ba(2)-S(3) bond lengths are 3.21 Å. Both Ba(2)-S(4) bond lengths are 3.34 Å. Both Ba(2)-S(5) bond lengths are 3.54 Å. There are two shorter (3.42 Å) and two longer (3.84 Å) Ba(2)-S(2) bond lengths. In the third Ba site, Ba(3) is bonded in a 8-coordinate geometry to two equivalent S(3), two equivalent S(5), and four equivalent S(1) atoms. Both Ba(3)-S(3) bond lengths are 3.14 Å. Both Ba(3)-S(5) bond lengths are 3.15 Å. There are two shorter (3.32 Å) and two longer (3.34 Å) Ba(3)-S(1) bond lengths. There are two inequivalent U sites. In the first U site, U(1) is bonded to three equivalent S(1) and three equivalent S(2) atoms to form distorted US6 pentagonal pyramids that share  a faceface with one Cr(1)S6 octahedra and  a faceface with one Cr(3)S6 octahedra. All U(1)-S(1) bond lengths are 2.72 Å. All U(1)-S(2) bond lengths are 2.67 Å. In the second U site, U(2) is bonded to six equivalent S(5) atoms to form distorted US6 pentagonal pyramids that share faces with two equivalent Cr(2)S6 octahedra. All U(2)-S(5) bond lengths are 2.69 Å. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to three equivalent S(1) and three equivalent S(3) atoms to form CrS6 octahedra that share  a faceface with one Cr(3)S6 octahedra and  a faceface with one U(1)S6 pentagonal pyramid. All Cr(1)-S(1) bond lengths are 2.46 Å. All Cr(1)-S(3) bond lengths are 2.46 Å. In the second Cr site, Cr(2) is bonded to three equivalent S(4) and three equivalent S(5) atoms to form CrS6 octahedra that share  a faceface with one Cr(2)S6 octahedra and  a faceface with one U(2)S6 pentagonal pyramid. All Cr(2)-S(4) bond lengths are 2.41 Å. All Cr(2)-S(5) bond lengths are 2.45 Å. In the third Cr site, Cr(3) is bonded to three equivalent S(2) and three equivalent S(3) atoms to form CrS6 octahedra that share  a faceface with one Cr(1)S6 octahedra and  a faceface with one U(1)S6 pentagonal pyramid. All Cr(3)-S(2) bond lengths are 2.42 Å. All Cr(3)-S(3) bond lengths are 2.46 Å. There are five inequivalent S sites. In the first S site, S(5) is bonded to one Ba(2), one Ba(3), two equivalent Ba(1), one U(2), and one Cr(2) atom to form distorted SBa4UCr octahedra that share  a cornercorner with one S(4)Ba4Cr2 octahedra, corners with three equivalent S(5)Ba4UCr octahedra, corners with four equivalent S(1)Ba4UCr octahedra, corners with five equivalent S(3)Ba4Cr2 octahedra,  an edgeedge with one S(5)Ba4UCr octahedra, edges with two equivalent S(1)Ba4UCr octahedra,  a faceface with one S(3)Ba4Cr2 octahedra, faces with two equivalent S(4)Ba4Cr2 octahedra, and faces with two equivalent S(5)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 5-70°. In the second S site, S(1) is bonded to two equivalent Ba(1), two equivalent Ba(3), one U(1), and one Cr(1) atom to form distorted SBa4UCr octahedra that share corners with two equivalent S(4)Ba4Cr2 octahedra, corners with three equivalent S(3)Ba4Cr2 octahedra, corners with three equivalent S(1)Ba4UCr octahedra, corners with four equivalent S(5)Ba4UCr octahedra,  an edgeedge with one S(3)Ba4Cr2 octahedra, edges with two equivalent S(5)Ba4UCr octahedra, faces with two equivalent S(3)Ba4Cr2 octahedra, and faces with three equivalent S(1)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 2-70°. In the third S site, S(2) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one U(1), and one Cr(3) atom. In the fourth S site, S(3) is bonded to one Ba(2), one Ba(3), two equivalent Ba(1), one Cr(1), and one Cr(3) atom to form SBa4Cr2 octahedra that share corners with two equivalent S(3)Ba4Cr2 octahedra, corners with two equivalent S(4)Ba4Cr2 octahedra, corners with three equivalent S(1)Ba4UCr octahedra, corners with five equivalent S(5)Ba4UCr octahedra,  an edgeedge with one S(4)Ba4Cr2 octahedra,  an edgeedge with one S(1)Ba4UCr octahedra,  a faceface with one S(5)Ba4UCr octahedra, faces with two equivalent S(3)Ba4Cr2 octahedra, and faces with two equivalent S(1)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 2-63°. In the fifth S site, S(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Cr(2) atoms to form distorted SBa4Cr2 octahedra that share corners with two equivalent S(5)Ba4UCr octahedra, corners with four equivalent S(3)Ba4Cr2 octahedra, corners with four equivalent S(1)Ba4UCr octahedra, edges with two equivalent S(3)Ba4Cr2 octahedra, faces with two equivalent S(4)Ba4Cr2 octahedra, and faces with four equivalent S(5)Ba4UCr octahedra. The corner-sharing octahedral tilt angles range from 5-56°.