Chalcogen bonds provide supramolecular association of beta-octamolybdate and chalconium cations†

Abstract

The interactions of triple σ-(Q^IV)-hole donating chalconium cations ([Q(bPh)R]⁺, when Q = S, Se, and Te) with nucleophilic beta-octamolybdate ([β-Mo₈O₂₆]⁴⁻) result in supramolecular association. The main focus of such assembly is on σ-(Q^IV)-hole recognition by the molybdate in cations with a biphenyl aromatic fragment. This leads to a remarkable diversity of the association patterns producing: (i) neutral 4 : 1 {[Q(bPh)R]₄[β-Mo₈O₂₆]} complexes with cations stacked by π–π interactions; (ii) (Bu₄N)⁺, [Q(bPh)R]⁺ and [β-Mo₈O₂₆]⁴⁻ complexes of 2 : 2 : 1 stoichiometry with π–π interactions; (iii) (Bu₄N)⁺, [Q(bPh)R]⁺ and [β-Mo₈O₂₆]⁴⁻ complexes of a 2 : 2 : 1 stoichiometry without π–π interactions; and (iv) {[Q(bPh)R]₂}₂[β-Mo₈O₂₆] salts with π–π stacked cations but lacking any (Q^IV)⋯O interactions. Moreover, interactions in the system can drive the reorganization of [β-Mo₈O₂₆]⁴⁻ into [α-Mo₈O₂₆]⁴⁻. The halogen-bonded (Q^IV)⋯O {(Q(bPh)R)_x[β-Mo₈O₂₆]⁴⁻} (x = 2 and 4) assemblies, π–π stacked cationic dimers {(Q(bPh)R)₂}²⁺ and complicated associates based on both types of interactions have been the subjects of crystallographic and computational studies.