Nb5Cu4Si4 crystallizes in the tetragonal I4/m space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a square co-planar geometry to four equivalent Si(1) atoms. In the second Nb site, Nb(2) is bonded in a 5-coordinate geometry to four equivalent Cu(1) and five equivalent Si(1) atoms. Cu(1) is bonded to four equivalent Nb(2), five equivalent Cu(1), and three equivalent Si(1) atoms to form a mixture of face, corner, and edge-sharing CuNb4Cu5Si3 cuboctahedra. Si(1) is bonded in a 9-coordinate geometry to one Nb(1), five equivalent Nb(2), and three equivalent Cu(1) atoms.
Nb5Cu4Si4 crystallizes in the tetragonal I4/m space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a square co-planar geometry to four equivalent Si(1) atoms. All Nb(1)-Si(1) bond lengths are 2.66 Å. In the second Nb site, Nb(2) is bonded in a 5-coordinate geometry to four equivalent Cu(1) and five equivalent Si(1) atoms. There are a spread of Nb(2)-Cu(1) bond distances ranging from 2.92-2.97 Å. There are a spread of Nb(2)-Si(1) bond distances ranging from 2.61-2.77 Å. Cu(1) is bonded to four equivalent Nb(2), five equivalent Cu(1), and three equivalent Si(1) atoms to form a mixture of face, corner, and edge-sharing CuNb4Cu5Si3 cuboctahedra. There are four shorter (2.61 Å) and one longer (2.68 Å) Cu(1)-Cu(1) bond length. There are two shorter (2.32 Å) and one longer (2.36 Å) Cu(1)-Si(1) bond length. Si(1) is bonded in a 9-coordinate geometry to one Nb(1), five equivalent Nb(2), and three equivalent Cu(1) atoms.