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 GdAl; x = 2.5, Ln = Eu, abbreviated as EuAl; HIN = isonicotinic acid) have been meticulously designed and obtained by hydrothermal reaction at low pH. The crystallographic study revealed that both GdAl and EuAl 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 GdAl 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.