Five sra Topological Ln(III)-MOFs Based on Novel Metal-Carboxylate/Cl Chain: Structure, Near-Infrared Luminescence and Magnetic Properties

Five isostructural three-dimensional (3D) lanthanide (Ln) frameworks [LnCl­(bpdc)­(DMF)] (Ln = La (1), Ce (2), Pr (3), Nd (4), and Sm (5), H2bpdc = 4,4′-biphenyl-dicarboxylic acid, DMF = N,N-dimethylformamide) have been solvothermally synthesized and characterized by TGA, IR, and X-ray single crystal diffraction. The frameworks contain unusual Ln-carboxylate/Cl chains, and which are extended by bpdc2‑ linkers to form 4-connected sra networks with 1D rhombic channels. The effect of lanthanide contraction induces the decreases of average Ln–O and Ln–Cl distances from La to Sm. 4 exhibits strong characteristic luminescence of Nd3+ ions in the near-infrared (NIR) region, resulting from the sensitization of bpdc2–. 3 displays weak NIR emission due to the inefficient sensitization of Pr3+ ions. The depopulation of the Stark levels and possible antiferromagnetic interactions within the Ln-carboxylate/Cl chains lead to the continuous decreases of χMT for 2–4 along the decreasing temperatures.五种同构的三维（3D）镧系（lanthanide, Ln）金属有机框架[LnCl(bpdc)(DMF)]（其中Ln代表La(1)、Ce(2)、Pr(3)、Nd(4)与Sm(5)，H₂bpdc为4,4'-联苯二甲酸，DMF为N,N-二甲基甲酰胺）经溶剂热法合成，并通过热重分析（TGA）、红外光谱（IR）及X射线单晶衍射完成表征。该类框架内含独特的镧系-羧酸盐/氯桥链，该链经由bpdc²⁻配体桥联延伸，最终构筑得到具有一维菱形孔道的四连接sra拓扑网络。镧系收缩效应使得从La到Sm的平均Ln-O与Ln-Cl键长逐渐缩短。化合物4在近红外（near-infrared, NIR）区域表现出Nd³+离子的特征强发光，该发光源于bpdc²⁻配体的敏化作用；化合物3因Pr³+离子的敏化效率不足，仅呈现微弱的近红外发射。镧系-羧酸盐/氯桥链内的斯塔克能级布居弛豫以及可能存在的反铁磁相互作用，导致化合物2-4的χMT值随温度降低持续减小。