Y4BBr6 crystallizes in the monoclinic C2/c space group. There are four inequivalent Y sites. In the first Y site, Y(1) is bonded to two equivalent B(1), one Br(1), one Br(4), one Br(5), and one Br(6) atom to form YB2Br4 octahedra that share  a cornercorner with one Y(3)B2Br4 octahedra,  a cornercorner with one Y(2)BBr5 octahedra,  an edgeedge with one Y(1)B2Br4 octahedra, edges with two equivalent Y(2)BBr5 octahedra, edges with two equivalent Y(4)BBr5 octahedra, and edges with three equivalent Y(3)B2Br4 octahedra. The corner-sharing octahedral tilt angles are 7°. In the second Y site, Y(2) is bonded to one B(1), one Br(1), one Br(5), one Br(6), and two equivalent Br(3) atoms to form YBBr5 octahedra that share  a cornercorner with one Y(1)B2Br4 octahedra,  a cornercorner with one Y(3)B2Br4 octahedra,  a cornercorner with one Y(4)BBr5 octahedra,  an edgeedge with one Y(2)BBr5 octahedra,  an edgeedge with one Y(4)BBr5 octahedra, edges with two equivalent Y(1)B2Br4 octahedra, and edges with two equivalent Y(3)B2Br4 octahedra. The corner-sharing octahedral tilt angles range from 5-13°. In the third Y site, Y(3) is bonded to two equivalent B(1), one Br(2), one Br(6), and two equivalent Br(5) atoms to form YB2Br4 octahedra that share  a cornercorner with one Y(1)B2Br4 octahedra,  a cornercorner with one Y(2)BBr5 octahedra, corners with two equivalent Y(4)BBr5 octahedra,  an edgeedge with one Y(4)BBr5 octahedra, edges with two equivalent Y(3)B2Br4 octahedra, edges with two equivalent Y(2)BBr5 octahedra, and edges with three equivalent Y(1)B2Br4 octahedra. The corner-sharing octahedral tilt angles range from 4-13°. In the fourth Y site, Y(4) is bonded to one B(1), one Br(3), two equivalent Br(2), and two equivalent Br(4) atoms to form YBBr5 octahedra that share  a cornercorner with one Y(2)BBr5 octahedra, corners with two equivalent Y(3)B2Br4 octahedra,  an edgeedge with one Y(3)B2Br4 octahedra,  an edgeedge with one Y(2)BBr5 octahedra, edges with two equivalent Y(1)B2Br4 octahedra, and edges with two equivalent Y(4)BBr5 octahedra. The corner-sharing octahedral tilt angles range from 4-5°. B(1) is bonded to one Y(2), one Y(4), two equivalent Y(1), and two equivalent Y(3) atoms to form edge-sharing BY6 octahedra. There are six inequivalent Br sites. In the first Br site, Br(1) is bonded in an L-shaped geometry to one Y(1) and one Y(2) atom. In the second Br site, Br(2) is bonded in a T-shaped geometry to one Y(3) and two equivalent Y(4) atoms. In the third Br site, Br(3) is bonded in a T-shaped geometry to one Y(4) and two equivalent Y(2) atoms. In the fourth Br site, Br(4) is bonded in a distorted T-shaped geometry to one Y(1) and two equivalent Y(4) atoms. In the fifth Br site, Br(5) is bonded in a rectangular see-saw-like geometry to one Y(1), one Y(2), and two equivalent Y(3) atoms. In the sixth Br site, Br(6) is bonded in a distorted T-shaped geometry to one Y(1), one Y(2), and one Y(3) atom.
Y4BBr6 crystallizes in the monoclinic C2/c space group. There are four inequivalent Y sites. In the first Y site, Y(1) is bonded to two equivalent B(1), one Br(1), one Br(4), one Br(5), and one Br(6) atom to form YB2Br4 octahedra that share  a cornercorner with one Y(3)B2Br4 octahedra,  a cornercorner with one Y(2)BBr5 octahedra,  an edgeedge with one Y(1)B2Br4 octahedra, edges with two equivalent Y(2)BBr5 octahedra, edges with two equivalent Y(4)BBr5 octahedra, and edges with three equivalent Y(3)B2Br4 octahedra. The corner-sharing octahedral tilt angles are 7°. There is one shorter (2.64 Å) and one longer (2.68 Å) Y(1)-B(1) bond length. The Y(1)-Br(1) bond length is 2.89 Å. The Y(1)-Br(4) bond length is 2.93 Å. The Y(1)-Br(5) bond length is 2.95 Å. The Y(1)-Br(6) bond length is 2.99 Å. In the second Y site, Y(2) is bonded to one B(1), one Br(1), one Br(5), one Br(6), and two equivalent Br(3) atoms to form YBBr5 octahedra that share  a cornercorner with one Y(1)B2Br4 octahedra,  a cornercorner with one Y(3)B2Br4 octahedra,  a cornercorner with one Y(4)BBr5 octahedra,  an edgeedge with one Y(2)BBr5 octahedra,  an edgeedge with one Y(4)BBr5 octahedra, edges with two equivalent Y(1)B2Br4 octahedra, and edges with two equivalent Y(3)B2Br4 octahedra. The corner-sharing octahedral tilt angles range from 5-13°. The Y(2)-B(1) bond length is 2.51 Å. The Y(2)-Br(1) bond length is 2.75 Å. The Y(2)-Br(5) bond length is 2.97 Å. The Y(2)-Br(6) bond length is 2.84 Å. There is one shorter (2.87 Å) and one longer (3.06 Å) Y(2)-Br(3) bond length. In the third Y site, Y(3) is bonded to two equivalent B(1), one Br(2), one Br(6), and two equivalent Br(5) atoms to form YB2Br4 octahedra that share  a cornercorner with one Y(1)B2Br4 octahedra,  a cornercorner with one Y(2)BBr5 octahedra, corners with two equivalent Y(4)BBr5 octahedra,  an edgeedge with one Y(4)BBr5 octahedra, edges with two equivalent Y(3)B2Br4 octahedra, edges with two equivalent Y(2)BBr5 octahedra, and edges with three equivalent Y(1)B2Br4 octahedra. The corner-sharing octahedral tilt angles range from 4-13°. There is one shorter (2.60 Å) and one longer (2.66 Å) Y(3)-B(1) bond length. The Y(3)-Br(2) bond length is 3.00 Å. The Y(3)-Br(6) bond length is 2.88 Å. There is one shorter (2.94 Å) and one longer (3.06 Å) Y(3)-Br(5) bond length. In the fourth Y site, Y(4) is bonded to one B(1), one Br(3), two equivalent Br(2), and two equivalent Br(4) atoms to form YBBr5 octahedra that share  a cornercorner with one Y(2)BBr5 octahedra, corners with two equivalent Y(3)B2Br4 octahedra,  an edgeedge with one Y(3)B2Br4 octahedra,  an edgeedge with one Y(2)BBr5 octahedra, edges with two equivalent Y(1)B2Br4 octahedra, and edges with two equivalent Y(4)BBr5 octahedra. The corner-sharing octahedral tilt angles range from 4-5°. The Y(4)-B(1) bond length is 2.51 Å. The Y(4)-Br(3) bond length is 2.88 Å. There is one shorter (2.83 Å) and one longer (3.05 Å) Y(4)-Br(2) bond length. There is one shorter (2.86 Å) and one longer (2.87 Å) Y(4)-Br(4) bond length. B(1) is bonded to one Y(2), one Y(4), two equivalent Y(1), and two equivalent Y(3) atoms to form edge-sharing BY6 octahedra. There are six inequivalent Br sites. In the first Br site, Br(1) is bonded in an L-shaped geometry to one Y(1) and one Y(2) atom. In the second Br site, Br(2) is bonded in a T-shaped geometry to one Y(3) and two equivalent Y(4) atoms. In the third Br site, Br(3) is bonded in a T-shaped geometry to one Y(4) and two equivalent Y(2) atoms. In the fourth Br site, Br(4) is bonded in a distorted T-shaped geometry to one Y(1) and two equivalent Y(4) atoms. In the fifth Br site, Br(5) is bonded in a rectangular see-saw-like geometry to one Y(1), one Y(2), and two equivalent Y(3) atoms. In the sixth Br site, Br(6) is bonded in a distorted T-shaped geometry to one Y(1), one Y(2), and one Y(3) atom.