The S ⋅⋅⋅ Hal and Se ⋅⋅⋅ Hal chalcogen bonding in a series of thiourea, selenourea and their derivatives

Highlights: • Previously unknown selenourea iodide and 1,1-dimethylselenourea triiodide crystal structures were obtained and characterized. • Extensive study on the complexation of thiourea, selenourea and their derivatives with halogens has been carried out. • Thioureas' molecules form dimers via the S⋯S bond in the case of lighter halogens and monomers in the case of iodine atoms. • Selenoureas undergo trimerization via the Se⋯Se bond in the presence of Cl and Br and dimerization in the case of I atoms. • A heavier halogen atom (iodine) reveals higher tendency to break the Ch···Ch bonds and to form strong Ch···Hal bonds instead. The chalcogen bonding (ChB) in a series of thiourea, selenourea and their derivatives has been investigated in the present paper. Thus, selenourea and dimethylselenourea undergo dimerization and trimerization processes in the presence of various halogen species (1–5). Selenourea and dimethylselenourea form trimers 3–4 in the presence of lighter halogens (chlorine and bromine) through Se⋯Se chalcogen bonding. When moving to heavier halogen (iodine), the dimers 1–2 are formed. Thiourea and its derivatives also tend to make very strong S⋯S bonds and form dimers in the case of lighter halogens chlorine and bromine (compounds 6–7). However, the monomers separated by the iodine species are formed upon interaction with iodine via very strong S⋯I bonding (compounds 9–12). Furthermore, among all the crystal structures of 1–12, only iodine cations I⁺ in 10 and 12 act as electron density acceptors, while in the remaining compounds 1–9 and 11 halogen species act as electron density donors.