Abstract

We describe the insertion and physical entrapment of cis-SnCl₄(OH₂)₂ completely inside the annulus of the cyclic methylene-linked glycoluril heptamer known as cucurbit[7]uril (Q7). This is the first endoannular metal halide–cucurbituril complex, [cis-SnCl₄(OH₂)₂]@Q7, contained in crystalline {[cis-SnCl₄(OH₂)₂]@Q7}₂·(H₃O⁺)₆[SnCl₆²⁻]₃(H₂O)₂₃. The crystals are formed by reaction of Q7 and SnCl₄ in hydrochloric acid. The cis-SnCl₄(OH₂)₂ complex is contained completely within Q7, and is stabilised by the formation of excellent internal hydrogen bonds between coordinated water and carbonyl oxygen. The two crystallographically independent Q7 molecules in the crystal are incompletely occupied (75%, 50%), probably due to the premature crystallisation of the insoluble crystals. The crystal packing is analysed in some detail in order to understand the low solubility and to enable formation of more soluble forms of [cis-SnCl₄(OH₂)₂]@Q7 which will allow development of its new coordination chemistry. Some results of computational modelling of the dynamics of ingress of the chlorotin complexes into Q7 are reported.