Conductivity in metal-organic frameworks
Metal–organic frameworks (MOFs), are a class of crystalline materials whose crystal structure is made up from metal-containing clusters connected by multidentate organic linkers1,2. MOFs are attracting considerable attention due to the possible rational design of crystal structures of coordination frameworks with versatile metal ions and organic ligands. In principle, MOFs topologies along with intermolecular distances between various building blocks can be controlled using the fundamentals of reticular chemistry. This offers a great potential for tailoring MOFs properties for a wide scope of high-tech applications (high-capacity adsorbents, membranes, thin film devices, catalysis, biomedical imaging, etc.). MOFs have traditionally been used for gas storage and separation, and much less attention has been devoted to their electronic properties3. This has changed in the past decade and MOFS with high electrical conductivity, charge carrier mobility and charge storage capacity became an emerging area of research. The physico-chemistry of inorganic (molecular) and organic (coordination polymers) conductivity are well understood by condensed matter researchers; however, this area is diverse and full of complexity. Thus, combination of both will represent a new paradigm. Considering MOFS, conductivity can come from the metal, i.e. inorganic part ( metal chain, quantum dot), ligand, or incorporating in the pore. In addition, when we are speaking about electronic conductivity, it should be mentioned that electrons do not have an absolute monopoly on electrical conduction in solids. In literature still possible to meet a great uncertainty as to whether typical measurements allow researcher to conclude that conduction in a given m is due predominately to ions or to electrons. Many researchers have assumed that some of the MOFS can be treated as wide band gap semiconductors but other scientists have believed that most of known conductive structures conduct by the movement of ions. It is of great interest to find the methodology to design new MOF with good charge transport or improve known system, in terms of conductive properties. Two main approaches reported so far. One is the “through-space” approach, which relies on π-stacking interactions between electroactive moieties. tetrathiafulvalene (TTF)-based MOF with high charge mobility. 3c The second approach relies on a “through-bond” formalism, where both symmetry and energy overlap between the covalently bonded components must exist to promote good charge transport. Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation that two main approaches can be
employed to construct new MOFs with good charge transport
1. C. Janiak, Dalton Trans., 2003, 2781–2804.
2. A. K. Cheetham, C. N. R. Rao and R. K. Feller, Chem. Commun., 2006, 4780. 3. A. K. Cheetham and C. N. R. Rao, Science, 2007, 318, 58–59.
Band gap modification of MIL-125
Christopher H. Hendon, Davide Tiana, Marc Fontecave, Clément Sanchez, Loïc D’arras, Capucine Sassoye §, Laurence Rozes, Caroline Mellot-Draznieks, and Aron Walsh. Engineering the Optical Response of the Titanium-MIL-125 Metal−Organic Framework through Ligand Functionalization J. Am. Chem. Soc., 2013, 135 (30), pp 10942–10945
According to the Silva and oth.1 the general structural requirements for MOFs to act as semiconductors are the irradiation with photons of energy larger than their bandgap and ability to generate either the electron or the whole (charge careers) which can easily migrate through the whole particle, i.e. photoinduced charge separation. Direct detection of electrons and holes or their trapping constitute firm, for example, by using absorption and emission spectroscopies, proof of MOF’s semiconductor nature. Therefore, material can potentially be...
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