TmMnSi2 crystallizes in the orthorhombic Cmcm space group. Tm(1) is bonded in a 10-coordinate geometry to four equivalent Si(2) and six equivalent Si(1) atoms. Mn(1) is bonded in a 5-coordinate geometry to one Si(1) and four equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted single-bond geometry to six equivalent Tm(1), one Mn(1), and two equivalent Si(1) atoms. In the second Si site, Si(2) is bonded in a 4-coordinate geometry to four equivalent Tm(1) and four equivalent Mn(1) atoms.
TmMnSi2 crystallizes in the orthorhombic Cmcm space group. Tm(1) is bonded in a 10-coordinate geometry to four equivalent Si(2) and six equivalent Si(1) atoms. There are two shorter (3.04 Å) and two longer (3.13 Å) Tm(1)-Si(2) bond lengths. All Tm(1)-Si(1) bond lengths are 3.11 Å. Mn(1) is bonded in a 5-coordinate geometry to one Si(1) and four equivalent Si(2) atoms. The Mn(1)-Si(1) bond length is 2.28 Å. There are two shorter (2.30 Å) and two longer (2.31 Å) Mn(1)-Si(2) bond lengths. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted single-bond geometry to six equivalent Tm(1), one Mn(1), and two equivalent Si(1) atoms. Both Si(1)-Si(1) bond lengths are 2.49 Å. In the second Si site, Si(2) is bonded in a 4-coordinate geometry to four equivalent Tm(1) and four equivalent Mn(1) atoms.