A polyrotaxane-like metal–organic framework exhibiting luminescent sensing of Eu3+ cations and proton conductivity

Abstract

A novel microporous metal–organic framework (MOF), namely {[Cd₂L₃(DMF)(NO₃)]·2DMF·3H₂O}_n (1), where L = 1,3-bis(4-carboxyphenyl)imidazolium chloride, was prepared via a hydrothermal process. The structure of 1 shows the first example of 6-fold polyrotaxane-like interpenetration combined with interdigitation which extends the structure into a three-dimensional framework and exhibits reversible and irreversible guest-dependent structural conversion; because of the 1D channels running along the b axis, 1 can serve as a host to encapsulate and sensitize Eu³⁺ cations in water. Moreover, the framework also exhibits a proton conductivity of over 10⁻⁵ S cm⁻¹ at 298 K and 98% relative humidity because the methylene hydrogens of the imidazolium moiety are highly acidic and aligned inside the channels enhancing the proton conductivity.