HfReSi2 crystallizes in the orthorhombic Pbam space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 7-coordinate geometry to two equivalent Re(2), four equivalent Re(1), two equivalent Si(2), two equivalent Si(5), and three equivalent Si(1) atoms. In the second Hf site, Hf(2) is bonded in a 12-coordinate geometry to one Re(2), three equivalent Re(1), one Si(1), one Si(3), two equivalent Si(2), two equivalent Si(4), and two equivalent Si(5) atoms. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to two equivalent Hf(1), three equivalent Hf(2), one Re(2), one Si(1), one Si(2), one Si(3), one Si(4), and two equivalent Si(5) atoms to form distorted ReHf5ReSi6 cuboctahedra that share corners with three equivalent Re(2)Hf4Re2Si6 cuboctahedra, corners with five equivalent Re(1)Hf5ReSi6 cuboctahedra,  an edgeedge with one Re(2)Hf4Re2Si6 cuboctahedra, edges with two equivalent Re(1)Hf5ReSi6 cuboctahedra, faces with two equivalent Re(2)Hf4Re2Si6 cuboctahedra, and faces with three equivalent Re(1)Hf5ReSi6 cuboctahedra. In the second Re site, Re(2) is bonded to two equivalent Hf(1), two equivalent Hf(2), two equivalent Re(1), two equivalent Si(1), two equivalent Si(3), and two equivalent Si(5) atoms to form ReHf4Re2Si6 cuboctahedra that share corners with six equivalent Re(1)Hf5ReSi6 cuboctahedra,  an edgeedge with one Re(2)Hf4Re2Si6 cuboctahedra, edges with two equivalent Re(1)Hf5ReSi6 cuboctahedra,  a faceface with one Re(2)Hf4Re2Si6 cuboctahedra, and faces with four equivalent Re(1)Hf5ReSi6 cuboctahedra. There are five inequivalent Si sites. In the first Si site, Si(3) is bonded in a 6-coordinate geometry to two equivalent Hf(2), two equivalent Re(1), and two equivalent Re(2) atoms. In the second Si site, Si(4) is bonded in a 7-coordinate geometry to four equivalent Hf(2), two equivalent Re(1), and one Si(4) atom. In the third Si site, Si(5) is bonded in a 7-coordinate geometry to one Hf(1), two equivalent Hf(2), one Re(2), two equivalent Re(1), and one Si(5) atom. In the fourth Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Hf(2), three equivalent Hf(1), two equivalent Re(1), and two equivalent Re(2) atoms. In the fifth Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Hf(1), four equivalent Hf(2), two equivalent Re(1), and one Si(2) atom.
HfReSi2 crystallizes in the orthorhombic Pbam space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 7-coordinate geometry to two equivalent Re(2), four equivalent Re(1), two equivalent Si(2), two equivalent Si(5), and three equivalent Si(1) atoms. Both Hf(1)-Re(2) bond lengths are 3.10 Å. There are two shorter (3.08 Å) and two longer (3.20 Å) Hf(1)-Re(1) bond lengths. There is one shorter (2.80 Å) and one longer (2.81 Å) Hf(1)-Si(2) bond length. Both Hf(1)-Si(5) bond lengths are 2.86 Å. There are a spread of Hf(1)-Si(1) bond distances ranging from 2.85-2.88 Å. In the second Hf site, Hf(2) is bonded in a 12-coordinate geometry to one Re(2), three equivalent Re(1), one Si(1), one Si(3), two equivalent Si(2), two equivalent Si(4), and two equivalent Si(5) atoms. The Hf(2)-Re(2) bond length is 3.03 Å. There are a spread of Hf(2)-Re(1) bond distances ranging from 3.01-3.08 Å. The Hf(2)-Si(1) bond length is 2.73 Å. The Hf(2)-Si(3) bond length is 2.79 Å. There is one shorter (2.85 Å) and one longer (2.89 Å) Hf(2)-Si(2) bond length. There is one shorter (2.90 Å) and one longer (2.91 Å) Hf(2)-Si(4) bond length. There is one shorter (2.86 Å) and one longer (2.87 Å) Hf(2)-Si(5) bond length. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to two equivalent Hf(1), three equivalent Hf(2), one Re(2), one Si(1), one Si(2), one Si(3), one Si(4), and two equivalent Si(5) atoms to form distorted ReHf5ReSi6 cuboctahedra that share corners with three equivalent Re(2)Hf4Re2Si6 cuboctahedra, corners with five equivalent Re(1)Hf5ReSi6 cuboctahedra,  an edgeedge with one Re(2)Hf4Re2Si6 cuboctahedra, edges with two equivalent Re(1)Hf5ReSi6 cuboctahedra, faces with two equivalent Re(2)Hf4Re2Si6 cuboctahedra, and faces with three equivalent Re(1)Hf5ReSi6 cuboctahedra. The Re(1)-Re(2) bond length is 2.76 Å. The Re(1)-Si(1) bond length is 2.62 Å. The Re(1)-Si(2) bond length is 2.42 Å. The Re(1)-Si(3) bond length is 2.66 Å. The Re(1)-Si(4) bond length is 2.42 Å. There is one shorter (2.50 Å) and one longer (2.59 Å) Re(1)-Si(5) bond length. In the second Re site, Re(2) is bonded to two equivalent Hf(1), two equivalent Hf(2), two equivalent Re(1), two equivalent Si(1), two equivalent Si(3), and two equivalent Si(5) atoms to form ReHf4Re2Si6 cuboctahedra that share corners with six equivalent Re(1)Hf5ReSi6 cuboctahedra,  an edgeedge with one Re(2)Hf4Re2Si6 cuboctahedra, edges with two equivalent Re(1)Hf5ReSi6 cuboctahedra,  a faceface with one Re(2)Hf4Re2Si6 cuboctahedra, and faces with four equivalent Re(1)Hf5ReSi6 cuboctahedra. Both Re(2)-Si(1) bond lengths are 2.54 Å. Both Re(2)-Si(3) bond lengths are 2.55 Å. Both Re(2)-Si(5) bond lengths are 2.54 Å. There are five inequivalent Si sites. In the first Si site, Si(3) is bonded in a 6-coordinate geometry to two equivalent Hf(2), two equivalent Re(1), and two equivalent Re(2) atoms. In the second Si site, Si(4) is bonded in a 7-coordinate geometry to four equivalent Hf(2), two equivalent Re(1), and one Si(4) atom. The Si(4)-Si(4) bond length is 2.40 Å. In the third Si site, Si(5) is bonded in a 7-coordinate geometry to one Hf(1), two equivalent Hf(2), one Re(2), two equivalent Re(1), and one Si(5) atom. The Si(5)-Si(5) bond length is 2.36 Å. In the fourth Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Hf(2), three equivalent Hf(1), two equivalent Re(1), and two equivalent Re(2) atoms. In the fifth Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Hf(1), four equivalent Hf(2), two equivalent Re(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.38 Å.