Physical properties of metal-organic frameworks

金属有机骨架的物理性质

• 批准号: 394332735
• 负责人: Privatdozent Dr. Eiken Haussühl
• 金额: --
• 依托单位: Professur für Kristallographie und Mineralogie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/394332735?language=en
• 关键词: Physical; properties; metal; organic; frameworks

Metal-organic frameworks (MOFs) essentially consist of metal ions, which are two- or three-dimensionally connected via organic bridging molecules. By variation of the inorganic and organic units numerous combinations and hence a large variety of MOF materials with very different physical properties, can be synthesized. MOFs were investigated manifold due to their extreme large porosity in respect to gas storage, their photoluminescence, and their magnetic and electric properties such as ferroelectrics.The electric properties are closely linked to the elastic properties via the electro-mechanic coupling. However, only for single ferroelectric MOFs a part of their elastic properties was investigated so far. The aim of the project is to investigate the elastic properties of selected MOFs of metal formates and tartrates with the help of conventional ultrasound methods and in particular with the resonant ultrasound spectroscopy (RUS) technique as a function of temperature in order to grasp the main features of the elastic and thermoelastic behaviour of this group of MOFs for the first time. As the elastic properties reflect the three-dimensional bonding system of the crystal structure, ultrasound techniques like RUS show a highly sensitive probe for the detection of structural instabilities and phase transitions. For this purpose single crystals with several millimeters in size are required, which will be synthesized and grown in further experiments. Up to now most of MOFs which were known from literature were grown only in small crystals of a few millimeters and less.The results are supposed to give information on (1) to what extent ferroelectric MOFs show clear changes of the elastic behavior at the transition from the paraelectric to the ferroelectric phase, (2) whether magneto-elastic coupling, like it was found in [(CH3)2NH2][Co(HCOO)3], also exists in isotypic and structurally related MOFs, and (3) how this influences the elastic properties of multiferroic MOFs. Further, it will be determined whether some of the here to be examined ferroic MOFs show not only ferroelectric but also ferroelastic behaviour. Especially, the question is to be answered with respect to the group of tartrates, whether by substitution MOFs can be made, which exhibit similar ferroelectric and ferroelastic phase transitions to [(NH4)Li(C4H4O6)] H2O. Another aspect deals with the determination of the influence of the size of the organic bridging molecules and their hydrogen bonds on the elastic and thermoelastic behaviour of MOFs, and with the question, whether the anisotropy of the thermoelastic behaviour is influenced by the main directions/orientation of the hydrogen bonds.

金属-有机框架（mof）本质上是由金属离子组成的，它们通过有机桥接分子进行二维或三维连接。通过无机和有机单元的变化，可以合成具有不同物理性质的多种MOF材料。由于mof的储气性能、光致发光性能以及铁电性等磁性和电学性能，人们对其进行了广泛的研究。电学性能通过机电耦合与弹性性能密切相关。然而，目前只研究了单个铁电mof的部分弹性特性。该项目的目的是在常规超声方法的帮助下，特别是在共振超声光谱（RUS）技术的帮助下，研究选定的金属甲酸盐和酒石酸盐mof的弹性特性，以作为温度的函数，以便首次掌握这组mof的弹性和热弹性行为的主要特征。由于晶体结构的弹性性质反映了晶体结构的三维键合系统，因此像RUS这样的超声技术对于结构不稳定性和相变的检测具有很高的灵敏度。为此，需要几毫米大小的单晶，这些单晶将在进一步的实验中合成和生长。到目前为止，从文献中已知的mof大多只生长在几毫米或更小的晶体中。这些结果应该提供以下信息：(1)铁电mof在从准电相到铁电相转变时弹性行为的明显变化程度；(2)磁弹性耦合是否也存在于同型和结构相关的mof中，就像在[(CH3)2NH2][Co(HCOO)3]中发现的那样，以及(3)这如何影响多铁mof的弹性性能。此外，还将确定某些待检测的铁mof是否不仅具有铁电性，而且具有铁弹性。特别是对于酒石酸盐族，是否可以通过取代制得具有与[(NH4)Li(C4H4O6)] H2O相似的铁电和铁弹性相变的MOFs，这个问题有待回答。另一个方面涉及确定有机桥接分子及其氢键的大小对mof的弹性和热弹性行为的影响，以及热弹性行为的各向异性是否受到氢键的主要方向/取向的影响。