ACO-Zeotype Iron Aluminum Phosphates with Variable Al/Fe Ratios Controlled by F− Ions

Three new iron aluminum phosphates |(C2H10N2)4|[Fe8 − xAlxFx(H2O)2 − x(PO4)8]·2H2O (χ = 1.64, 1.33, 0.80) with ACO-zeotype structures denoted as FeAPO-CJ66(a), FeAPO-CJ66(b), and FeAPO-CJ66(c), respectively, have been synthesized in the fluoride ion system. Their framework structures are made of double 4-ring (D4R) building units formed by the alternating connection of Fe(Al)O4F(O) trigonal bipyramids and PO4 tetrahedra, which possess 3D intersecting 8-ring channels running along the [001], [010], and [100] directions. Fluoride ions or water molecules reside in the center of D4Rs, and diprotonated ethylenediamine cations and water molecules are occluded in the free space of channels to stabilize the whole structure. Notably, the Al/Fe ratios in the frameworks can be effectively controlled from 1/3.9 to 1/5.0 to 1/9.0 by adjusting the amounts of phosphoric acid and hydrofluoric acid added to the initial reaction mixture. Mössbauer and magnetic measurements show that the Fe ions in the compounds are bivalent and undergo antiferromagnetic ordering at room temperature.本研究在氟离子体系中成功合成了三种新型磷酸铁铝材料，其化学式为(C₂H₁₀N₂)₄[Fe₈₋ₓAlₓFₓ(H₂O)₂₋ₓ(PO₄)₈]·2H₂O（χ分别为1.64、1.33、0.80），三者均具有ACO型沸石骨架结构，分别命名为FeAPO-CJ66(a)、FeAPO-CJ66(b)与FeAPO-CJ66(c)。该类材料的骨架结构由交替连接的Fe(Al)O₄F(O)三角双锥与PO₄四面体构成的双四元环（double 4-ring, D4R）结构基元组装而成，拥有沿[001]、[010]与[100]方向延伸的三维交叉8元环孔道。氟离子与水分子分别填充于D4R结构的中心，而双质子化乙二胺阳离子与水分子则被封装于孔道的自由空间中以维持整体骨架的稳定性。值得注意的是，通过调控初始反应体系中磷酸与氢氟酸的添加量，可有效调控骨架中的Al/Fe摩尔比，使其分别达到1/3.9、1/5.0与1/9.0。穆斯堡尔谱与磁学性能测试结果表明，该类材料中的铁离子均为二价态，且在室温下发生反铁磁有序转变。