利用水热合成法, 以柔性的乙二胺四乙酸(H₄EDTA)为配体、 氧化镨以及氯化镉为金属源合成了一种镨-镉异金属-有机配合物[Pr₂Cd₃(EDTA)₃(H₂O)₁₁]·14H₂O (1)。 通过X射线单晶衍射确定化合物1的结构, 该化合物属单斜晶系的 C2空间群, a=16.154(3) Å, b=14.863(3) Å, c=14.875(3) Å, β=115.855(3)°, V=3214.2(9) ų, Z=2, 化合物1的结构中存在纳米尺寸大小的“心形”Pr₆Cd₆O₁₂轮簇。 其中Cd²⁺的配位数为7, 采取单帽三棱柱的配位构型, 而Pr³⁺采取十配位双帽四方反棱柱的构型。 EDTA^4-配体的四个羧基全部去质子化, 与一个Cd²⁺和两个Pr³⁺配位, 其中4个羧基氧原子和2个氮原子都与Cd²⁺配位, 两个羧基分别桥连1个Pr³⁺。 Pr³⁺和Cd²⁺通过μ₂-O氧原子交替连接形成Pr₆Cd₆O₁₂轮簇, 每个Pr₆Cd₆O₁₂轮簇与附近的6个Pr₆Cd₆O₁₂轮簇共边连接, 从而形成一个二维(6, 3)层状结构。 二维层再通过…AAA…类型的堆积方式形成三维超分子结构。 游离水分子填充在二维层空隙中, 与羧基以及配位水分子之间形成比较强的O—H…O氢键, 这些氢键有利于结构的稳定。 通过热重分析、 稳态荧光光谱、 热微扰二维红外相关光谱(2D-IR COS)、 固体紫外-可见漫反射光谱等手段进一步对化合物1的谱学性能进行表征。 在红外光谱上, 由于存在大量的氢键, 化合物的红外光谱在3 680~2 640 cm^-1波数范围内出现宽而强的吸收谱带。 同时配体H₄EDTA中的羧基脱去了质子氢, 并且与金属离子发生配位, 因此化合物1中羧基的C=O双键的伸缩振动吸收峰与未配位配体中的C=O双键的伸缩振动吸收峰相比, 向低波数移动, 在1 527 cm^-1波数处出现吸收峰。 固体荧光测试显示在325 nm的紫外光照射下, 配合物1能发出强的360 nm左右的荧光, 主要是由能量在Cd²⁺和EDTA^4-之间发生明显的LMCT跃迁转移引起的, 因此化合物1可作为一类潜在的发光材料。 热微扰下的二维红外光谱显示, 由于水分子与羧基及水分子之间存在氢键, 使得O—H的伸缩振动吸收峰对热的微扰响应比较敏感。 紫外-可见光谱测试显示化合物1在位于216 nm处出现很强的紫外吸收峰, 归属于化合物1中EDTA^4-配体的中 n→ σ^*跃迁及π→π^*, 位于444, 468和484 nm的弱吸收峰, 归属为Pr³⁺的 f— f跃迁。

A 2D Pr-Cd heterometal-organic compound, [Pr₂Cd₃(EDTA)₃(H₂O)₁₁]·(H₂O)₁₄(1) (H₄EDTA=ethylene diamine tetraacetic acid) has been successfully prepared by the H₄EDTA ligand, Pr₆O₁₁ and CdCl₂·2.5H₂O. The structure of 1 was determined by X-ray single-crystal diffraction. Compound 1 crystallizes in the monoclinic space group C2, a=16.154(3) Å, b=14.863(3)Å, c=14.875(3)Å, β=115.855(3)°, V=3 214.2(9)ų, Z=2. There are nanosized heart-like Pr₆Cd₆O₁₂ wheel-clusters in the structure. The coordination geometries for the two seven-coordinated Cd²⁺ ions are both close to that of a monocapped trigonal prism. The Pr³⁺ ion is ten-coordinate and described as seriously distorted dicapped square antiprism. The completely deprotonated EDTA^4- ligand link one Cd²⁺ and two Pr³⁺ ions. Four carboxylate O and two N atoms of the EDTA^4- ligand are all coordinated to the Cd²⁺ cation and the remaining carboxylate groups connect one Pr³⁺ ion, respectively. The Pr³⁺ and Cd²⁺ cations are bridged by₂-O alternatively to form a Pr₆Cd₆O₁₂ wheel-clusters. Each Pr₆Cd₆O₁₂ is linked to six surrounding wheels by sharing Pr³⁺, forming a highly ordered layered network. The 2D layers are further packed in …AAA… stacking mode and the free water molecules are suspended between the layers. There are strong O—H…O hydrogen-bond interactions between water molecules and carboxylate groups, and the O…O distance ranges from 2.666 to 3.050 Å. The hydrogen-bond interactions play an important role in stabling the structure. At the same time, PXRD, TG/DSC, IR and 2D IR correlation spectroscopy, solid Luminescent spectrum and UV-Visible absorption spectrum are studied. Because there are strong O—H…O hydrogen bonds, the IR spectrum of compound 1 shows broad bands around 3 680~2 640 cm^-1. The four carboxylic acid groups of EDTA^4- ligand are completely deprotonated, The C=O stretching vibrations peak of carboxylate groups of compound 1 shift lower wavenumber compared to H₄EDTA ligand. Compound 1 shows emission peak at 360 nm that can be assigned to LMCT transition of between Cd²⁺and EDTA^4- when it is excited at 325 nm. Compound 1 is a potential luminescent material. 2D IR correlation spectrum of 1 indicates that the stretching vibrations of O—H are sensitive with the thermal perturbation because of strong hydrogen-bond interactions between water molecules and carboxylate groups. The UV-Visible absorption spectrum of compound 1 shows the absorption bands of n→ σ^* and π→π^* transitions of EDTA^4- ligand and f→ f transition of Pr³⁺.