八氰基镧系金属和过渡金属化合物的设计合成与性能研究

【作者】 周虎；

【导师】 刁国旺；

【作者基本信息】 扬州大学 ， 物理化学， 2013， 博士

【摘要】 功能材料的设计合成与研究已成为近年来人们关注的热点之一。八氰合金属盐构筑单元[M(CN)8]n-(M=Mo,W；n=3,4)由于具有灵活的配位方式和低的对称性等特点而被广泛研究,其与第二金属中心组装反应时可得到多种结构类型且性能优异的八氰基化合物。这些化合物结构中的[M(CN)8]n-构筑块根据其周围化学环境的变化可表现出十二面体、反四棱柱和双帽三棱柱等三种不同的几何构型。然而,八氰基化合物研究领域中还存在诸多问题：首先,由于镧系金属离子本身配位方式的灵活性和多变性,以及八氰基镧系金属化合物合成策略的缺失,导致了目前有关八氰基镧系金属化合物体系的研究报道较少,而且该体系的结构-磁性相关性研究尚处于探索阶段,亟待深入研究。其次,当前人们对八氰基过渡金属化合物的研究主要集中在结构和磁学性质方面,而有关该体系多孔性和吸附性质方面的研究报道极少。本论文在综述了八氰基体系国内外研究现状的基础上,针对该领域目前存在的问题,主要开展了两个方面的研究工作：八氰基镧系金属化合物和八氰基过渡金属化合物。本文以设计合成八氰基功能化合物为目标,采用缓慢扩散或溶液直接混合两种制备方法,将八氰合金属盐构筑单元[M(CN)8]n-(M=Mo, W; n=3,4)与系列镧系金属离子Ln3+(Ln=La-Tb)或过渡金属离子M’2+(M’=Mn,Co,Fe,Cd)组装反应,设计合成了15个八氰基化合物,其中包括8个八氰基镧系金属化合物和7个八氰基过渡金属化合物：Tb(H2O)4(pyrazine)0.5W(CN)8(1)La(H2O)4(pyrazine)0.5W(CN)8(2)Ce(H2O)4(pyrazine)0.5W(CN)8(3)Pr(H2O)4(pyrazine)0.5W(CN)8(4)Nd(H2O)4(pyrazine)0.5W(CN)8(5)Sm(H2O)4(pyrazine)0.5W(CN)8(6)Eu(H2O)4(pyrazine)0.5W(CN)8(7)Gd(H2O)4(pyrazine)0.5W(CN)8(8)[Mn(H2O)2]2Mo(CN)8·3H2O (9·7H2O)[Mn(H2O)2]2W(CN)8·3H2O (10·7H2O)[Mn(H2O)2]2Mo(CN)8·4H2O (11·8H2O)[Co(H2O)2]2Mo(CN)8·4H2O(12·8H20)[Fe(H2O)2]2Mo(CN)8·4H2O(13·8H2O)[Cd(H20)2]2Mo(CN)8·3.5H20(14·7.5H2O)[Cd(H2O)2]2W(CN)8·3.5H2O(15·7.5H2O)采用谱学、热分析、单晶X射线衍射、(变温)粉末X射线衍射、SQUID仪、蒸汽和气体吸附仪等现代物理化学测试手段对这些材料进行了系统表征与性质研究。对于三维八氰基镧系金属化合物,根据二维层化合物Ln(H2O)5W(CN)8(Ln=La-Tb)的结构特点和镧系金属离子的配位方式,有意选择含顺磁中心W(Ⅴ)的八氰合金属盐[W(CN)8]3-为构筑块,运用插层组装的构筑策略,将[W(CN)8]3-单元与系列镧系金属离子Ln3+(Ln=La-Tb)和二齿柱状含氮有机配体pyrazine在乙腈溶剂中组装反应,设计合成了8个同构的三维八氰基镧系金属化合物(1-8)。该合成策略为八氰基体系中首次利用二维层为构筑块来组装三维结构化合物的例子,同时化合物1-8也为首例八氰合钨(V)基镧系金属化合物。在对化合物1-8进行系统表征的基础上,深入探讨了这类晶体的形成机理,以及该类体系的结构与磁学性质之间的相互关系。研究结果表明,反应温度对化合物1-8晶体的形成至关重要。化合物1-8的磁性质主要依赖于结构中所含镧系金属离子的种类,以及骨架中由氰根相连的无机子网络的连接方式与维数。其中,化合物1,3,5,6和8为典型的软磁体。对于三维八氰基过渡金属化合物,以水作为反应溶剂,将八氰合金属盐构筑单元[M(CN)8]4-(M=Mo, W)与系列过渡金属离子M’2+(M=’ Mn, Co, Fe, Cd)组装反应,得到了7个三维八氰基过渡金属化合物：(9,10)·7H2O,(11-13)·8H2O和(14,15)·7.5H2O。这些化合物根据其结构和组成特点可分为三种类型,重点研究了这些化合物的多孔结构、热稳定性、对水分子的脱附／吸附过程及气体吸附性质。在此基础上,深入探讨了这三类化合物的骨架结构与多孔性及吸附性质之间的关联性。研究结果表明,这三类化合物的孔道形状及大小因结构中所含结晶水数目及过渡金属离子种类的不同而有所区别。其中,化合物(9,10)·7H2O结构中孔道内的四个结晶水和三个配位水分子全部脱除后仍保留牢固的多孔骨架,其脱水相9和10表现出典型的微孔特征,对水分子、氮气和氢气均具有较好的吸附性质。而化合物(11-13)·8H2O仅能脱除结构中的四个结晶水和两个配位水而变为部分脱水相(11-13)·2H2O。由于此时结构中孔道内仍有两个未被脱除的配位水分子,因此其孔尺寸和孔隙率相比脱水相9和10明显减小,几乎没有气体吸附性质。尽管化合物(14,15)·7.5H2O也可失去结构中的四个配位水和3.5个结晶水分子变为完全脱水相14和15,但由于结构中孔道尺寸较小,因此脱水相14和15并不具有明显的多孔性特征。此外,当这三类化合物脱附/吸附配位水分子时,结构中金属中心的配位环境均会发生改变,进而导致化合物结构的变化。同时,这三类化合物对配位水和结晶水分子的脱附/吸附均具有可逆性,但吸附过程的动力学略有差异。更重要的是,对化合物(9,10)·7H20,脱去结构中所有配位水和结晶水后的骨架中含有大量配位不饱和的Mn金属中心,而这些不饱和裸露位点的存在对于提高化合物三维骨架与客体分子之间的亲和力非常有利。更多还原

【Abstract】 In recent years, considerable efforts have been put into the design and elaboration of functional materials. Octacyanometallates [M(CN)8]n-(M=Mo, W; n=3,4) with flexible coordination modes and lower symmetries have been aggressively studied. The combination of the [M(CN)8]"" building blocks and the second metal centers has produced various dimensional molecular structures and the resulting materials have displayed interesting properties. The octacyanometallates units in these materials can adopt various geometries, e.g., dodecahedral, square antiprismatic or bicapped trigonal prismatic, depending on the external environments, such as the surrounding ligands. However, there are still some problems in this field. On one hand, the development of octacyano-and lanthanide-based assemblies has been somewhat hampered by the tendency of the lanthanide ions to adopt higher coordination numbers, their ability to easily adapt to given environments, and the absence of design strategies for4f-4d/5d networks. As far as we know, limited examples of octacyanometallate-based lanthanide compounds were documented to date. On the other hand, relatively few studies have focused on the porosities and adsorption/desorption properties, despite of the fact that a large number of [M(CN)8]n--based transition metal compounds have been characterized structurally and magnetically.The current research and development of octacyanometallate-based systems has been reviewed in this thesis, and both the [M(CN)8]n--based lanthanide or transition metal systems have been studied in detail, based on the present problems in this field. In order to construct functional [M(CN)8]n--based materials, fifteen three-dimensional (3D) compounds, including eight [W(CN)8]3--based lanthanide metal compounds and seven [M(CN)8]4--based transition metal compounds, have been synthesized through the slow diffusion or solution mixing methods, using the [M(CN)8]n-units as building blocks to react with series of lanthanide metal ions or transition metal ions. Tb(H2O)4(pyrazine)0.5W(CN)8(1) La(H2O)4(pyrazine)0.5W(CN)8(2) Ce(H2O)4(pyrazine)0.5W(CN)8(3) Pr(H2O)4(pyrazine)0.5W(CN)8(4) Nd(H2O)4(pyrazine)0.5W(CN)8(5) Sm(H2O)4(pyrazine)0.5W(CN)8(6) Eu(H2O)4(pyrazine)0.5W(CN)8(7) Gd(H2O)4(pyrazine)0.5W(CN)8(8)[Mn(H2O)2]2Mo(CN)8·3H2O (9·7H2O)[Mn(H2O)2]2W(CN)8·3H2O (10·7H2O)[Mn(H2O)2]2Mo(CN)8·4H2O (11·8H2O)[Co(H2O)2]2Mo(CN)8·4H2O (12·8H2O)[Fe(H2O)2]2Mo(CN)8·4H2O(13·8H2O)[Cd(H2O)2]2Mo(CN)8·3.5H2O(14·7.5H2O)[Cd(H2O)2]2W(CN)8·3.5H2O(15·7.5H2O)Then the resulting materials were characterized by spectroscopies, thermal analyses, single-crystal X-ray diffraction and (variable-temperature) powder X-ray diffraction, SQUID magnetometer, vapor and gas adsorption analyzers, and so on.For the3D octacyanometallate-based lanthanide metal compounds, the paramagnetic building block [W(CN)8]3-was employed to react with series of lanthanide metal ions Ln3+(Ln=La-Tb) and the pillar N-donor bidentate ligand pyrazine in the acetonitrile solution through the intercalation method, based on the structural features of2D layers Ln(H2O)5W(CN)8and the flexible coordination modes of lanthanide ions, isolating eight isostructural3D [W(CN)8]3"-based lanthanide compounds (1-8). These compounds mark the first structural patterns using neutral2D layers as building blocks and the first3D LnⅢ-WⅤ(CN)8compounds found in the octacyanometallate-based system. The possible formation mechanism and the relationship between structures and magnetic properties have been further investigated. The results showed that the diffusion temperature had played a crucial role for the formation of such3D system. Furthermore, the magnetic properties of these3D materials depend mainly on the lanthanides ions, together the structures and dimensionalities of inorganic cyanide subnetworks involved in frameworks. Importantly, compounds1,3,5,6and8were typical soft magnets.For the3D octacyanometallate-based transition metal compounds,[M(CN)8]4-(M=Mo, W) building blocks were employed to react with series of transition metal ions M’2+(M=Mn, Co, Fe, Cd) using water as the reaction solvent, resulting in the formation of seven3D [M(CN)8]4’-based transition metal compounds (9,10)·7H2O,(11-13)·8H2O and (14,15)·7.5H2O. The thermal stabilities, desorption/adsorption process of water molecules and gas adsorption properties have been studied. In addition, the relationship between structures and adsorption/desorption properties in such system has been further explored. The results showed that the porous features of these compounds were influenced obviously by the number of crystallized water molecules involved in pores and the difference of transition metal ions in frameworks. Among them, dehydrated compounds9and10exhibited typical porosities features and have moderate uptakes for water molecules, nitrogen and hydrogen gases, owing to the fact that all water molecules involved in pores can be removed without structural collapse. However, there are still two coordinated water molecules left in pores after partially dehydration for compounds (11-13)·8H2O, resulting in the small pore size, porosities and almost no uptake for hydrogen gas. There are still no gas uptake for fully dehydrated compounds14and15, although all water molecules can also been removed from pores in compounds (14,15)·7.5H2O, which can be attributed to the much small pore size for both materials. In addition, the coordination environment of metal centers for above seven compounds have changed with the desorption/adsorption of coordination water molecules, thus resulting in the change of porous frameworks. Interestingly, these materials can reversibly adsorb/desorb all crystallized and partial coordinated water molecules. More importantly, the high hydrogen enthalpy for dehydrated compounds9and10can be attributed to the presence of coordinatively-unsaturated Mn2+sites left exposed by the removal of coordinated water molecules in the structure.更多还原