二维镨-镉异核金属配合物的水热合成、晶体结构及谱学性能研究

The Hydrothermal Synthesis, Crystal Structure and Spectral Properties of a 2D Pr-Cd Heterometal Complex

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)A,b=14.863(3)A,c=14.875(3)A,β=115.855(3)°,V=3214.2(9)A^3,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Cd^2+的配位数为7,采取单帽三棱柱的配位构型,而Pr^3+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Cd^2+和两个Pr^3+配位,其中4个羧基氧原子和2个氮原子都与Cd^2+配位,两个羧基分别桥连1个Pr^3+。Pr^3+和Cd^2+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-IRCOS)、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3680~2640cm^-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CO双键的伸缩振动吸收峰与未配位配体中的CO双键的伸缩振动吸收峰相比,向低波数移动,在1527cm^-1波数处出现吸收峰。固体荧光测试显示在325nm的紫外光照射下,配合物1能发出强的360nm左右的荧光,主要是由能量在Cd^2+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216nm处出现很强的紫外吸收峰,归属于化合物1中EDTA4-配体的中n→σ^*跃迁及π→π^*,位于444,468和484nm的弱吸收峰,归属为Pr^3+的f—f跃迁。

A 2D Pr-Cd heterometal-organic compound,[Pr2Cd3(EDTA)3(H 2O)11]·(H2O)14(1)(H4EDTA=ethylene diamine tetraacetic acid)has been successfully prepared by the H4EDTA ligand,Pr 6O 11 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)A,b=14.863(3)A,c=14.875(3)A,β=115.855(3)°,V=3 214.2(9)A^3,Z=2.There are nanosized heart-like Pr 6Cd 6O 12 wheel-clusters in the structure.The coordination geometries for the two seven-coordinated Cd^2+ions are both close to that of a monocapped trigonal prism.The Pr^3+ion is ten-coordinate and described as seriously distorted dicapped square antiprism.The completely deprotonated EDTA^4-ligand link one Cd^2+and two Pr^3+ions.Four carboxylate O and two N atoms of the EDTA^4-ligand are all coordinated to the Cd^2+cation and the remaining carboxylate groups connect one Pr^3+ion,respectively.The Pr^3+and Cd^2+cations are bridged by 2-O alternatively to form a Pr 6Cd 6O 12 wheel-clusters.Each Pr 6Cd 6O 12 is linked to six surrounding wheels by sharing Pr^3+,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.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 H 4EDTA ligand.Compound 1 shows emission peak at 360 nm that can be assigned to LMCT transition of between Cd^2+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^*andπ→π^*transitions of EDTA 4-ligand and f→f transition of Pr^3+.