UMnSe3 crystallizes in the orthorhombic Cmcm space group. U(1) is bonded in a 9-coordinate geometry to three equivalent Se(1) and six equivalent Se(2) atoms. Mn(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form a mixture of edge and corner-sharing MnSe6 octahedra. The corner-sharing octahedral tilt angles are 41°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to three equivalent U(1) and two equivalent Mn(1) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to three equivalent U(1) and two equivalent Mn(1) atoms.
UMnSe3 crystallizes in the orthorhombic Cmcm space group. U(1) is bonded in a 9-coordinate geometry to three equivalent Se(1) and six equivalent Se(2) atoms. There are two shorter (2.96 Å) and one longer (3.25 Å) U(1)-Se(1) bond length. There are four shorter (2.90 Å) and two longer (3.08 Å) U(1)-Se(2) bond lengths. Mn(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form a mixture of edge and corner-sharing MnSe6 octahedra. The corner-sharing octahedral tilt angles are 41°. Both Mn(1)-Se(1) bond lengths are 2.44 Å. All Mn(1)-Se(2) bond lengths are 2.48 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to three equivalent U(1) and two equivalent Mn(1) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to three equivalent U(1) and two equivalent Mn(1) atoms.