An unprecedented anionic Ln-MOF with a cage-within-cage motif: Spontaneous reduction and immobilization of ion-exchanged Pd(II) to Pd-NPs in the framework

An unprecedented microporous anionic Ln-MOF, [Me₂NH₂]₂₄[Tb₁₂(TATB)₁₆(HCOO)₁₂]·12DMF·48H₂O (1) (H₃TATB = 4,4′,4′′-s-triazine-2,4,6-tribenzoic acid), which is a rare cage-within-cage structure through interpenetration rather than covalent bonding, has been synthesized. Compound 1 contains a 3D net which is constructed using a large and a small Ln-carboxylate cage alternately arranged by sharing faces with each other. Interpenetration of two identical 3D nets occurs in such a way that each small cage of one net is encapsulated within the large cage of the other and vice versa, generating an overall 3D double-walled cage framework. Such interpenetration creates a unique structure of double-shelled hollow space to accommodate Pd nanoparticles (Pd-NPs), which could effectively prevent Pd-NPs from aggregation and leaching. Moreover, the ion-exchanged Pd(ii) embedded in the framework can be readily reduced at room temperature with no requirement of any chemical or thermal treatments, affording Pd-NPs with uniform size and even distribution. As a result, the as-prepared Pd-NPs@1 exhibits excellent activity and cycling stability for the hydrogenation of styrene and its derivatives.