Self-Assembly of Lanthanide–Aluminum Cluster-Organic Frameworks with Magnetocaloric Effect and Luminescence

The self-assembly of the lanthanide metal–organic frameworks presents a formidable challenge but profound significance. Compared with the metal–organic frameworks based on 4f–3d ions, the chemistry of 4f–3p metal–organic frameworks has not been fully explored so far. In this study, two lanthanide–aluminum-based clusters [Ln₆Al(IN)₁₀(μ₃–OH)₅(μ₃-O)₃(H₂O)₈]·xH₂O (x = 2, Ln = Gd, abbreviated as Gd₆Al; x = 2.5, Ln = Eu, abbreviated as Eu₆Al; HIN = isonicotinic acid) have been meticulously designed and obtained by hydrothermal reaction at low pH. The crystallographic study revealed that both Gd₆Al and Eu₆Al clusters exhibit an unprecedented sandwiched metal–organic framework holding a highly ordered honeycomb network. To our knowledge, it is the first case of Ln–Al-based cluster-organic frameworks. Furthermore, magnetic investigation of Gd₆Al manifests a decent magnetic entropy change of −ΔS_m^max = 28.8 J kg^–1 K^–1 at 2 K for ΔH = 7.0 T. Significantly, the introduction of Al^III ions into the lanthanide metal–organic frameworks displays excellent solid-state luminescent capability with a lifetime of 371.6 μs and quantum yield of 6.64%. The construction and investigation of these two Ln–Al clusters represent great progress in the 4f–3p metal–organic framework.