NiSi is Modderite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ni4+ is bonded to six equivalent Si4- atoms to form a mixture of distorted corner, edge, and face-sharing NiSi6 pentagonal pyramids. There are a spread of Ni–Si bond distances ranging from 2.28–2.40 Å. Si4- is bonded in a 8-coordinate geometry to six equivalent Ni4+ and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.66 Å.