Hf3(CuSi)4 crystallizes in the orthorhombic Immm space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 12-coordinate geometry to six equivalent Cu(1), two equivalent Si(2), and four equivalent Si(1) atoms. In the second Hf site, Hf(2) is bonded to eight equivalent Cu(1), two equivalent Si(2), and four equivalent Si(1) atoms to form distorted face-sharing HfCu8Si6 octahedra. Cu(1) is bonded in a 12-coordinate geometry to two equivalent Hf(2), three equivalent Hf(1), three equivalent Cu(1), one Si(1), and three equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Hf(2), four equivalent Hf(1), two equivalent Cu(1), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Hf(2), two equivalent Hf(1), and six equivalent Cu(1) atoms.
Hf3(CuSi)4 crystallizes in the orthorhombic Immm space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 12-coordinate geometry to six equivalent Cu(1), two equivalent Si(2), and four equivalent Si(1) atoms. There are four shorter (2.81 Å) and two longer (2.92 Å) Hf(1)-Cu(1) bond lengths. Both Hf(1)-Si(2) bond lengths are 2.84 Å. All Hf(1)-Si(1) bond lengths are 2.80 Å. In the second Hf site, Hf(2) is bonded to eight equivalent Cu(1), two equivalent Si(2), and four equivalent Si(1) atoms to form distorted face-sharing HfCu8Si6 octahedra. All Hf(2)-Cu(1) bond lengths are 3.18 Å. Both Hf(2)-Si(2) bond lengths are 2.79 Å. All Hf(2)-Si(1) bond lengths are 2.75 Å. Cu(1) is bonded in a 12-coordinate geometry to two equivalent Hf(2), three equivalent Hf(1), three equivalent Cu(1), one Si(1), and three equivalent Si(2) atoms. There is one shorter (2.44 Å) and two longer (2.92 Å) Cu(1)-Cu(1) bond lengths. The Cu(1)-Si(1) bond length is 2.32 Å. There are two shorter (2.37 Å) and one longer (2.44 Å) Cu(1)-Si(2) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Hf(2), four equivalent Hf(1), two equivalent Cu(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.43 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Hf(2), two equivalent Hf(1), and six equivalent Cu(1) atoms.