Conductive Metal-Organic Frameworks (CMOF)

Metal-organic frameworks (MOFs) are compounds consisting of metal ions and organic molecules to form various low-dimensional nanostructures. Since their discovery only a decade ago, MOFs have enjoyed extensive exploration in synthesis and applications in gas storage/separation/purification, chromatography and catalysis. MOFs exhibiting extremely high surface areas are highly advantageous as they outperform other nanoporous materials such as zeolite, porous silica, activated carbon and carbon nanotubes with regard to structural variety and chemical functionality. One of the challenges towards their applications is to make MOFs optimally conductive to be used as conductive porous elements in electronics. It was reported last year that naturally non-conductive MOFs turn metallic by doping with donor molecules. Now, comprehensive understanding of the conduction mechanism is urgently needed for implementations of MOFs into electronic devices. The project aims at understanding mechanisms for electrical conduction in doped MOFs and utilizing metallic and semiconducting MOFs as electronic components in prototypical sensing, solar cell, optoelectronic and spintronic devices that havent been realized so far. This will gain insight into how charge transfer and orbital hybridization between the MOF host and molecular guest lead to enhancements in electrical conduction of molecule- doped MOFs, and further to the emergence of advanced electronic, magnetic and magneto-transport properties due to quantum confinement of charge carriers. Our unique approach combines chemical doping with donor molecules or ions, and field effect doping in MOF-based devices in order to control doping levels. The key to the electrical conduction is electronic interaction at the molecular interfaces that will be exclusively accessed by mean of element-specific and resonance-enhanced spectroscopy techniques combined with cutting-edge characterization techniques including atomic-resolution electron microscopy, electrical transport and magnetization measurements. The principal investigator (PI) will conduct the project with experimental facilities and resources provided by the Atominstitut at TU Wien, national and international research partner institutions. PI is a leading academic in the field of nanoscience with his research focused on electronic, magnetic and optical properties on nanostructures such as carbon nanotubes, metal clusters and MOFs. His experience in leading an international project, knowledge in solid-state physics and skills in high-end spectroscopy and microscopy techniques, being complemented by the national and international collaborators expertise, will be elemental for the project which is highly demanding in terms of problem solving strategies in a cooperative manner on a state of the art level.

Metal-organic frameworks (MOFs) represent a new class of hybrid organic-inorganic supramolecular materials. The ordered low-dimensional nanoporous networks made of metal ions and organic molecules have extremely high surface areas, various pore sizes and chemical functionalities, and act as hosts for a variety of guest molecules. Since their discovery only a decade ago, a large number of MOFs had been synthesized and their applications in gas storage/separation/purification, chromatography and catalysis had been extensively studied, while much less had been studied regarding their physical properties and related applications. Electrically conductive MOFs reported recently represent the importance of MOFs and related compounds as electronic materials. A comprehensive understanding of the physical properties of MOFs is elemental for their applications in electronics. The project aimed to understand the physical properties of MOFs in depth and to pave the way for their applications as electronic materials. The first objective was to synthesize quality crystals or thin films of MOFs and related materials including coordination polymers and metal complexes. We have successfully synthesized large crystals or homogeneous thin films of various MOFs, such as HKUST-1 and M-MOF-74 (M=Mg, Mn, Co or Zn). Single crystals of spin-crossover iron-triazole coordination polymer [Fe(Htrz)2(trz)](BF4) synthesized were as long as 80 m, that is, to the best of our knowledge, the largest ever reported for this coordination polymer. Furthermore, as results of attempting to synthesize MOFs, single crystals of various new molecular structures (metal complexes, coordination polymers and other metal-organic hybrid materials) were discovered. Based on the large and quality crystals, the lattice structures were determined by single-crystal diffractometry, as well as extensive studies on electronic, optical and magnetic properties were carried out. Our findings in terms of physical properties include the crystal size dependence of the thermal spin crossover in [Fe(Htrz)2(trz)](BF4), the nature of charge transfer between the M-MOF-74 and various molecular dopants, photoluminescence of HKUST-1 in the visible range associated with crystallographic defects, and metamagnetism in one-dimensional trinuclear spin chains in a new cobalt coordination polymer. Some of the findings were utilized for electronic applications. We have fabricated resistive gas sensors and electrochromic devices using MOFs as active components. These will pave the way for applications of MOFs as electronic components and stimulate further research on the physics of MOFs and related materials.