Isomorphic substitution in molecular crystals and geometry of hypervalent tellurium: comments inspired by a case study of RMeTeI₂ and [RMe₂Te]⁺I⁻ (R = Ph, Fc)

The crystal structures of PhMeTeI₂ (1), FcMeTeI₂ (2) and [FcMe₂Te]⁺I⁻ (3), which are the products of iodomethylation of R₂Te₂ (R = Ph, ferrocenyl (Fc)) by MeI, are reported. Analysis of secondary interactions and packing patterns in 1–3 revealed Te⋯πPh chalcogen bonding in 1, unusual structural parallels between 2 and 3, and unprecedented isomorphic substitution in the crystals of 3 with an admixture of Te–I ionized molecules 2 [FcMeTeI⁺]I⁻. In summary, we are discussing the 3c-4e bonding model as a general, seamless scheme for the geometry and electronic structure of hypervalent tellurium atom coordination in both the isolated molecules and crystals, which overcomes the confusing division between the molecular and supramolecular geometry.