Supramolecular assemblies of [Mo3Se4Clx(H2O)9−x](4−x)+ with cucurbituril; complementarity control through the variation of x

From solutions of seleno bridged triangular cluster Mo3Se4(aq)4+ in HCl, crystalline adducts with cucurbituril (Cuc, C36H36N24O12) of different composition, depending on HCl concentration, were isolated. From 2 M HCl, a monosubstituted cationic cluster crystallizes as {[Mo3Se4Cl(H2O)8]2(C36H36N24O12)}Cl6·16H2O (1). Increase in HCl concentration to 6 M gives a pentasubstituted anionic species, (H3O)2[Mo3Se4Cl5(H2O)4]2(C36H36N24O12)·15H2O (2). The crystal structures of 1 and 2 were determined by X-ray crystallography. Each portal of Cuc in 1 is covered with cluster cations [Mo3Se4Cl(H2O)8]3+ like a ‘lid’ on a ‘barrel’. Six water molecules in the trans position to the core μ2-Se form complementary hydrogen bonds with oxygen atoms of Cuc (O⋯O, 2.713–3.067 Å). In 2 the complementarity is lost and the main structure building factor is short Se⋯Se interactions (Se⋯Se, 2.96–3.43 Å) between two adjacent anionic clusters. Stereochemistry of halide substitution in the triangular clusters M3Q4 is analyzed.