Se–Cl Interactions in Selenite Chlorides: A Theoretical Study

The Se–Cl interactions in five selenite chlorides (α,β-Zn2(SeO3)Cl2 (sofiite and its polymorph), α,β-Cu5O2(SeO3)2Cl2 (georgbokiite and parageorgbokiite), and KCdCu7O2(SeO3)2Cl9 (burnsite)) have been investigated by means of the analysis of their theoretical electron density distributions. The analysis reveals the existence in the structures of two basic types of interactions: intermediate interactions with essential covalent contribution and closed-shell interactions. In Zn2(SeO3)Cl2 polymorphs and burnsite, all metal-oxide and metal-chloride interactions are of the first type, whereas in georgbokiite and parageorgbokiite, the Jahn–Teller distortion results in the elongation of some of the Cu–X bonds and their transition to the closed-shell type. All anion–anion interactions are of the closed-shell type. The energy of the closed-shell Se–Cl interactions can be estimated as 1.4–2.6 kcal.mol−1, which is comparable to weak hydrogen bonds. Despite their weakness, these interactions provide additional stabilization of structural architectures. The Se4+–Cl− configurations are localized inside framework channels or cavities, which can be therefore be viewed as regions of weak and soft interactions in the structure