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CeSi crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ce4+ is bonded in a 7-coordinate geometry to seven equivalent Si4- atoms. There are a spread of Ce–Si bond distances ranging from 3.03–3.20 Å. Si4- is bonded in a 9-coordinate geometry to seven equivalent Ce4+ and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.48 Å.
CeSI crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Ce3+ is bonded in a 7-coordinate geometry to four equivalent S2- and three equivalent I1- atoms. There are three shorter (2.83 Å) and one longer (2.84 Å) Ce–S bond lengths. There are a spread of Ce–I bond distances ranging from 3.27–3.47 Å. S2- is bonded to four equivalent Ce3+ atoms to form a mixture of distorted edge and corner-sharing SCe4 tetrahedra. I1- is bonded in a 3-coordinate geometry to three equivalent Ce3+ atoms.
Reported here is a revised crystal structure of β–ZrSi (TlI/CrB structure type), correcting the atomic position and bond distances. The Si–Si bond length has been modified substantially from 2.723(6) Å to 2.4411(8) Å. The β-ZrSi single crystals were grown from an arc-melted button, and were characterized using single crystal X-ray diffraction. A survey of the TlI/CrB structure type shows that changes to the nomenclature would be useful, separating it into four chemically distinct subtypes: TlI, CrB, CaSi, and ThCo. β–ZrSi is an example of the CaSi subtype. α-ZrSi crystallizes in the related FeB structure type, which is also divided here into the subtypes FeB, CeSi, and YNi. The effect of electron count on the relative phase stabilities of the CaSi and CeSi subtypes is rationalized with the aid of the Zintl concept and electronic structure calculations in the Linear Muffin-Tin Orbital (LMTO) basis.