HfMnSi2 crystallizes in the orthorhombic Pbam space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 8-coordinate geometry to one Si(4), one Si(5), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(3) atoms. In the second Hf site, Hf(2) is bonded to two equivalent Si(1), two equivalent Si(2), and three equivalent Si(4) atoms to form distorted HfSi7 pentagonal bipyramids that share corners with two equivalent Mn(2)Si6 cuboctahedra, corners with two equivalent Hf(2)Si7 pentagonal bipyramids, edges with three equivalent Hf(2)Si7 pentagonal bipyramids, and faces with two equivalent Mn(2)Si6 cuboctahedra. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded in a 6-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(5), and two equivalent Si(1) atoms. In the second Mn site, Mn(2) is bonded to two equivalent Si(1), two equivalent Si(4), and two equivalent Si(5) atoms to form distorted MnSi6 cuboctahedra that share corners with two equivalent Hf(2)Si7 pentagonal bipyramids, edges with two equivalent Mn(2)Si6 cuboctahedra, and faces with two equivalent Hf(2)Si7 pentagonal bipyramids. There are five inequivalent Si sites. In the first Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Hf(2), four equivalent Hf(1), two equivalent Mn(1), and one Si(2) atom. In the second Si site, Si(3) is bonded in a 2-coordinate geometry to four equivalent Hf(1) and two equivalent Mn(1) atoms. In the third Si site, Si(4) is bonded in a 9-coordinate geometry to two equivalent Hf(1), three equivalent Hf(2), two equivalent Mn(1), and two equivalent Mn(2) atoms. In the fourth Si site, Si(5) is bonded in a 6-coordinate geometry to two equivalent Hf(1), two equivalent Mn(1), and two equivalent Mn(2) atoms. In the fifth Si site, Si(1) is bonded in a 7-coordinate geometry to one Hf(2), two equivalent Hf(1), one Mn(2), two equivalent Mn(1), and one Si(1) atom.
HfMnSi2 crystallizes in the orthorhombic Pbam space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 8-coordinate geometry to one Si(4), one Si(5), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(3) atoms. The Hf(1)-Si(4) bond length is 2.69 Å. The Hf(1)-Si(5) bond length is 2.85 Å. There is one shorter (2.76 Å) and one longer (2.79 Å) Hf(1)-Si(1) bond length. There is one shorter (2.78 Å) and one longer (2.79 Å) Hf(1)-Si(2) bond length. There is one shorter (2.85 Å) and one longer (2.86 Å) Hf(1)-Si(3) bond length. In the second Hf site, Hf(2) is bonded to two equivalent Si(1), two equivalent Si(2), and three equivalent Si(4) atoms to form distorted HfSi7 pentagonal bipyramids that share corners with two equivalent Mn(2)Si6 cuboctahedra, corners with two equivalent Hf(2)Si7 pentagonal bipyramids, edges with three equivalent Hf(2)Si7 pentagonal bipyramids, and faces with two equivalent Mn(2)Si6 cuboctahedra. Both Hf(2)-Si(1) bond lengths are 2.74 Å. There is one shorter (2.70 Å) and one longer (2.71 Å) Hf(2)-Si(2) bond length. There are a spread of Hf(2)-Si(4) bond distances ranging from 2.71-2.83 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded in a 6-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(5), and two equivalent Si(1) atoms. The Mn(1)-Si(2) bond length is 2.37 Å. The Mn(1)-Si(3) bond length is 2.36 Å. The Mn(1)-Si(4) bond length is 2.43 Å. The Mn(1)-Si(5) bond length is 2.41 Å. Both Mn(1)-Si(1) bond lengths are 2.46 Å. In the second Mn site, Mn(2) is bonded to two equivalent Si(1), two equivalent Si(4), and two equivalent Si(5) atoms to form distorted MnSi6 cuboctahedra that share corners with two equivalent Hf(2)Si7 pentagonal bipyramids, edges with two equivalent Mn(2)Si6 cuboctahedra, and faces with two equivalent Hf(2)Si7 pentagonal bipyramids. Both Mn(2)-Si(1) bond lengths are 2.46 Å. Both Mn(2)-Si(4) bond lengths are 2.48 Å. Both Mn(2)-Si(5) bond lengths are 2.48 Å. There are five inequivalent Si sites. In the first Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Hf(2), four equivalent Hf(1), two equivalent Mn(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.42 Å. In the second Si site, Si(3) is bonded in a 2-coordinate geometry to four equivalent Hf(1) and two equivalent Mn(1) atoms. In the third Si site, Si(4) is bonded in a 9-coordinate geometry to two equivalent Hf(1), three equivalent Hf(2), two equivalent Mn(1), and two equivalent Mn(2) atoms. In the fourth Si site, Si(5) is bonded in a 6-coordinate geometry to two equivalent Hf(1), two equivalent Mn(1), and two equivalent Mn(2) atoms. In the fifth Si site, Si(1) is bonded in a 7-coordinate geometry to one Hf(2), two equivalent Hf(1), one Mn(2), two equivalent Mn(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.36 Å.