Interactions of aromatic rings in the crystal structures of hybrid polyoxometalates and Ru clusters

Abstract

This work reports analysis of the π–π interactions between {(arene)Ru}²⁺ and related fragments {Cp*M}²⁺ (Cp* = C₅(CH₃)₅⁻; M = Rh, Ir) grafted on polyoxometalates (POMs). Ru clusters bearing {(arene)Ru}²⁺ groups are also included in the analysis. Considering the π–π interactions as structural vectors results in coordination networks of different types including dimers, chains or even 3D frameworks. The later structural organization suggests the use of such compounds as πOF materials. Quantum chemical calculations together with QTAIM analysis reveal that these π–π interactions are attractive and weak (estimated strength for each individual C⋯C contact does not exceed 1 kcal mol⁻¹). In the case of layered Na₄[{Cp*Ir}₂Nb₆O₁₉]·22H₂O, bond critical points (3, −1) for C⋯C contacts responsible for π–π interactions are not found at all, thus defining this as a kind of graphite type structure.