Si(Ni3Se)2 crystallizes in the tetragonal I4mm space group. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to four equivalent Ni(2), four equivalent Ni(3), and four equivalent Si(1) atoms to form NiSi4Ni8 cuboctahedra that share corners with four equivalent Ni(1)Si4Ni8 cuboctahedra, faces with four equivalent Ni(1)Si4Ni8 cuboctahedra, and faces with four equivalent Si(1)Ni12 cuboctahedra. In the second Ni site, Ni(2) is bonded in a distorted water-like geometry to two equivalent Ni(1), two equivalent Si(1), and two equivalent Se(1) atoms. In the third Ni site, Ni(3) is bonded in a 2-coordinate geometry to two equivalent Ni(1), two equivalent Si(1), and two equivalent Se(2) atoms. In the fourth Ni site, Ni(4) is bonded to one Se(1) and four equivalent Se(2) atoms to form a mixture of distorted corner and edge-sharing NiSe5 square pyramids. Si(1) is bonded to four equivalent Ni(1), four equivalent Ni(2), and four equivalent Ni(3) atoms to form SiNi12 cuboctahedra that share corners with four equivalent Si(1)Ni12 cuboctahedra, faces with four equivalent Ni(1)Si4Ni8 cuboctahedra, and faces with four equivalent Si(1)Ni12 cuboctahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Ni(4) and four equivalent Ni(2) atoms. In the second Se site, Se(2) is bonded in a 8-coordinate geometry to four equivalent Ni(3) and four equivalent Ni(4) atoms.
Si(Ni3Se)2 crystallizes in the tetragonal I4mm space group. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to four equivalent Ni(2), four equivalent Ni(3), and four equivalent Si(1) atoms to form NiSi4Ni8 cuboctahedra that share corners with four equivalent Ni(1)Si4Ni8 cuboctahedra, faces with four equivalent Ni(1)Si4Ni8 cuboctahedra, and faces with four equivalent Si(1)Ni12 cuboctahedra. All Ni(1)-Ni(2) bond lengths are 2.47 Å. All Ni(1)-Ni(3) bond lengths are 2.46 Å. All Ni(1)-Si(1) bond lengths are 2.53 Å. In the second Ni site, Ni(2) is bonded in a distorted water-like geometry to two equivalent Ni(1), two equivalent Si(1), and two equivalent Se(1) atoms. Both Ni(2)-Si(1) bond lengths are 2.48 Å. Both Ni(2)-Se(1) bond lengths are 2.33 Å. In the third Ni site, Ni(3) is bonded in a 2-coordinate geometry to two equivalent Ni(1), two equivalent Si(1), and two equivalent Se(2) atoms. Both Ni(3)-Si(1) bond lengths are 2.45 Å. Both Ni(3)-Se(2) bond lengths are 2.44 Å. In the fourth Ni site, Ni(4) is bonded to one Se(1) and four equivalent Se(2) atoms to form a mixture of distorted corner and edge-sharing NiSe5 square pyramids. The Ni(4)-Se(1) bond length is 2.30 Å. All Ni(4)-Se(2) bond lengths are 2.55 Å. Si(1) is bonded to four equivalent Ni(1), four equivalent Ni(2), and four equivalent Ni(3) atoms to form SiNi12 cuboctahedra that share corners with four equivalent Si(1)Ni12 cuboctahedra, faces with four equivalent Ni(1)Si4Ni8 cuboctahedra, and faces with four equivalent Si(1)Ni12 cuboctahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Ni(4) and four equivalent Ni(2) atoms. In the second Se site, Se(2) is bonded in a 8-coordinate geometry to four equivalent Ni(3) and four equivalent Ni(4) atoms.