Synthesis, Structure, and Photoluminescence of Color-Tunable and White-Light-Emitting Lanthanide Metal–Organic Open Frameworks Composed of AlMo₆(OH)₆O₁₈^3– Polyanion and Nicotinate

A series of isostructural compounds Na­(HL)­(CH3COO)­Ln­(Al­(OH)6Mo6O18)­(H2O)6·10H2O [L = nicotinate; Ln = Eu (1), Tb (2)] and Na­(HL)­(CH3COO)­EumTbnLa1–m–n(AlMo6(OH)6O18)­(H2O)6·10H2O (3–8, L = nicotinate), wherein Anderson-type polyanions AlMo6(OH)6O183– as basic inorganic building blocks are connected by Eu­(CH3COO)­(HL)­(H2O)3]24+ and [Na2(H2O)8]2+ cations, resulting in formation of three-dimensional lanthanide metal–organic open frameworks, were synthesized successfully with AlCl3·6H2O, Na2MoO4·2H2O, nicotinic acid, and lanthanide nitrates as starting materials. The compounds were characterized by UV–vis, IR, elemental analysis, powder XRD, and TG–DTA measurements. The single-crystal structures of compounds 1 and 2 show that the two compounds display three-dimensional open frameworks with 1D channels along the b and c axes. Investigation of the energy transfer mechanism indicated that the organic nicotinate ligand can transfer energy efficiently to Tb3+ rather than Eu3+. The influence of the POM moiety on the fluorescence of the compounds is also studied. Compounds 1–8 exhibit tunable luminescence color, and emitting of white light was realized through adjusting the molar ratio of Eu:Tb:La within the compounds.以AlCl₃·6H₂O、Na₂MoO₄·2H₂O、烟酸（nicotinic acid）及稀土硝酸盐为起始原料，成功合成了一系列同构化合物：Na(HL)(CH₃COO)Ln(Al(OH)₆Mo₆O₁₈)(H₂O)₆·10H₂O [L = 烟酸根（nicotinate）；Ln = 铕(Eu，1)、铽(Tb，2)] 与Na(HL)(CH₃COO)EuₘTbₙLa₁–ₘ–ₙ(AlMo₆(OH)₆O₁₈)(H₂O)₆·10H₂O（3~8，L = 烟酸根）。其中，安德森型多阴离子（Anderson-type polyanions）AlMo₆(OH)₆O₁₈³⁻作为基础无机结构基元，通过[Eu(CH₃COO)(HL)(H₂O)₃]²⁺与[Na₂(H₂O)₈]²⁺阳离子桥连，最终构筑得到三维稀土金属-有机开放骨架。采用紫外-可见（UV–vis）光谱、红外（IR）光谱、元素分析、粉末X射线衍射（powder XRD）以及热重-差热（TG–DTA）分析对所合成的化合物进行了表征。化合物1和2的单晶结构表明，二者均呈现出沿b轴与c轴方向拥有一维通道的三维开放骨架结构。对能量转移机制的研究显示，有机烟酸根配体可将能量高效传递至Tb³⁺，而非Eu³⁺。同时探究了多金属氧酸盐（Polyoxometalate, POM）片段对化合物荧光性能的影响。该系列化合物1~8均可表现出可调谐的发光颜色，通过调控化合物内Eu:Tb:La的摩尔比，可实现白光发射。