LaRu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. La3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All La–Si bond lengths are 3.31 Å. Ru+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of distorted edge and corner-sharing RuSi4 tetrahedra. All Ru–Si bond lengths are 2.40 Å. Si4- is bonded in a 4-coordinate geometry to four equivalent La3+ and four equivalent Ru+2.50+ atoms.