K2Ni3Se4 crystallizes in the orthorhombic Fddd space group. K(1) is bonded in a 14-coordinate geometry to two equivalent Ni(1), four equivalent Ni(2), and eight equivalent Se(1) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a square co-planar geometry to four equivalent K(1) and four equivalent Se(1) atoms. In the second Ni site, Ni(2) is bonded in a square co-planar geometry to four equivalent K(1) and four equivalent Se(1) atoms. Se(1) is bonded in a 7-coordinate geometry to four equivalent K(1), one Ni(1), and two equivalent Ni(2) atoms.
K2Ni3Se4 crystallizes in the orthorhombic Fddd space group. K(1) is bonded in a 14-coordinate geometry to two equivalent Ni(1), four equivalent Ni(2), and eight equivalent Se(1) atoms. Both K(1)-Ni(1) bond lengths are 3.65 Å. There are two shorter (3.66 Å) and two longer (3.67 Å) K(1)-Ni(2) bond lengths. There are a spread of K(1)-Se(1) bond distances ranging from 3.53-3.56 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a square co-planar geometry to four equivalent K(1) and four equivalent Se(1) atoms. All Ni(1)-Se(1) bond lengths are 2.35 Å. In the second Ni site, Ni(2) is bonded in a square co-planar geometry to four equivalent K(1) and four equivalent Se(1) atoms. There are two shorter (2.34 Å) and two longer (2.35 Å) Ni(2)-Se(1) bond lengths. Se(1) is bonded in a 7-coordinate geometry to four equivalent K(1), one Ni(1), and two equivalent Ni(2) atoms.