Arijit Halder

Eye-Catching Dual-Fluorescent Dynamic Metal-Organic Framework Senses Traces of Water: Experimental Findings and Theoretical Correlation.

A guest-dependent dynamic fivefold interpenetrated 3D porous metal-organic framework (MOF) of ZnII ions has been synthesized that exhibits selective carbon dioxide adsorption. Furthermore, the MOF shows excellent luminescence behavior, which is supported by a systematic study on the guest-responsive multicolor emission of a suspension of the MOF. The dual-emission behavior arises from the excited-state intramolecular proton transfer (ESIPT), and the compound also shows remarkable potential to detect traces of water in various organic solvents. The experimental observations were also painstakingly authenticated by using time-dependent density-functional-theory (DFT) calculations.

Hydrogen Uptake by an Inclined Polycatenated Dynamic Metal-Organic Framework Based Material

A 2D + 2D → 3D inclined polycatenated dynamic metal-organic framework of {[Cu(4-bpe)(2-ntp)(H2O)2]·2H2O}n [1, where 2-ntp2- = 2-nitroterephthalate and 4-bpe = 1,2-bis-(4-pyridyl)ethane] has been synthesized and characterized. The variable-temperature powder X-ray diffraction study indicates the dynamic nature of the inclined polycatenated framework, and the dehydrated framework with exposed metal centers exhibits excellent type I H2 adsorption of 1.94 wt % at 77 K and 1 bar of pressure.

Dynamic metal–organic frameworks: syntheses, characterizations, sorption studies and their hydrolytic inter-conversion

Two metal–organic frameworks of Cd(II) from 3,4-pyridinedicarboxylate (3,4-pyrdc) and 1,2-bis(4-pyridyl)ethane (bpe) ligands, {[Cd(3,4-pyrdc)(bpe)(CH3OH)]·(H2O)}n (1) and {[Cd(3,4-pyrdc)(bpe)0.5(H2O)]·(H2O)}n (2) have been synthesized by changing the reaction medium. Compound 1 exhibited a 2D structure while compound 2 showed a 3D structure, which have both been revealed by single crystal X-ray studies. Both of the compounds showed interesting solvent mediated reversible structural transformations which have been established by exhaustive X-ray powder diffraction studies, elemental analysis, IR spectroscopy and thermogravimetric analysis. The desolvated form of the 2D framework (1) undergoes an irreversible structural transformation to form the 3D framework (2) upon soaking with water. The 2D to 3D transformation occurs through precise bond rotation and bond breaking which has been established by a GC–MS study. Sorption experiments with different gases and volatiles were performed for both the metal–organic frameworks and clearly indicated the differences in their inherent flexibility and transformability.

Structure and properties of dynamic metal–organic frameworks: a brief accounts of crystalline-to-crystalline and crystalline-to-amorphous transformations

In the last decade, dynamic metal–organic frameworks (MOFs) have been under the intense scrutiny of chemical researchers for their potential applications in many interesting fields. Due to the flexibility in the structure, this class of materials can recognize or respond towards a signal by changing their structural architecture as well as their physiochemical properties. Therefore dynamic MOFs can be considered as “smart materials” for their use in many future technologies. All the transformations of a dynamic MOF occur through solid-state structural changes, hence these dynamicity driven materials sometimes have unique structures that cannot be derived by conventional synthetic methods. So far, a mammoth study has been performed about the synthetic procedures and applications of dynamic metal–organic frameworks. The stimuli response, which is the most important parameter in the dynamism of such structures, has also been elaborately discussed. Most of the previous review works in this area have covered the structure-stimuli-application flowchart, but in this highlight we discuss the point-to-point structural changes with an aim to understand the dynamicity pathway process of MOFs. Some associated changes in their properties, precisely, after and before structural changes, are also covered.

Multifunctional mixed ligand metal organic frameworks: X-ray structure, adsorption, luminescence and electrical conductivity with theoretical correlation

Two new mixed ligand metal–organic frameworks of Zn(II) with disodium 5-hydroxyisophthalate and 4,4′-azobispyridine (azbpy) ligands, {[Zn(azbpy)(HO-1,3-bdc)(H2O)]·(azbpy)}n (1) and {[Zn(azbpy)0.5(HO-1,3-bdc)(C2H5OH)]·(H2O)}n (2) have been synthesized by changing the reaction medium (methanol to ethanol) and structurally characterized by elemental analysis, IR, PXRD, TG and single crystal X-ray diffraction. Compound 1 exhibits a 2D sheet network structure with free azbpy ligands in its void space, and is stabilized by π–π and C–H⋯π interactions, whereas 2 has a 2D layered architecture with lattice water molecules in its void space. Compound 2 has a flexible structure and shows gated adsorption (gas and solvent) behavior, while framework 1 is nonporous. These two MOFs exhibit remarkable electrical conductivity values at room temperature and their comparison is discussed carefully. Theoretical calculations suggest that both the compounds are p-type semiconductors and correlate the structure–property relationship. Schottky barrier diode electronic devices have been fabricated by using these two semiconductor materials with aluminium (Al) and indium tin oxide (ITO) in sandwich configuration, ITO/MOF-1 or 2/Al, and both the devices exhibit sound rectification behavior. The photoluminescent properties of both the compounds in the solid state are also investigated in detail.

CCDC 1831429: Experimental Crystal Structure Determination

Related Article: Saheli Ghosh, Goutam Pahari, Dilip K. Maity, Arijit Halder, Debajyoti Ghoshal|2018|Chem. Sel.|3|8980|doi:10.1002/slct.201801720

CCDC 1831427: Experimental Crystal Structure Determination

Related Article: Saheli Ghosh, Goutam Pahari, Dilip K. Maity, Arijit Halder, Debajyoti Ghoshal|2018|Chem. Sel.|3|8980|doi:10.1002/slct.201801720

CCDC 1831426: Experimental Crystal Structure Determination

Related Article: Saheli Ghosh, Goutam Pahari, Dilip K. Maity, Arijit Halder, Debajyoti Ghoshal|2018|Chem. Sel.|3|8980|doi:10.1002/slct.201801720

Dynamic Zn-MOF: sensing, dual emission, ESIPT and selective CO2 sorption

After a long journey in the path of conventional organic and inorganic chemistry, a lane of materials with tunable functionality have been opened as a variety of hybrid materials like metal–organic frameworks (MOFs), with crystalline structure correlated with their physicochemical properties. Eventually, such compounds has drawn a significant attention and their structural features have extensively been investigated due to their appealing prospects with different functionalities namely, gas storage/separation, catalysis, conductivity, magnetism, drug delivery and many more. Recently, MOF have emerged to the field of sensing and several MOFs have also been employed as sensor materials and imaging agents. A wide class of materials have been so far utilised for the sensing applications, however, ideally, chemo-sensors should be a robust material, unaltered irrespective of the molecular environment with high sensitivity to the concerned analytes even in its very low concentration. In this frame of reference, dynamic MOFs are a good choice for the designing of sensors, as the dynamic nature makes them more promising for detection of the incoming analyte molecule as the dynamism is a manifesto of external stimuli, sometimes by the accommodation of guest molecules in their flexible pores through host-guest interactions. Whereas the conventional rigid MOFs fail to do so as the external stimuli have a little effect on them. Thus, this guest dependent dynamic MOFs are under the closest attention of the relevant vigilante for the preparation of the next generation functional materials having controlled sensing application. Nowadays, instantaneous, reliable and selective detection of water traces has become a significant issue not only for the chemical industry but also to prepare water free bio-alcohol based fuel as the minute of water can hinder the use of such alternative energy recourses. Up to the date, mainly organic sensors have been used for detecting the water traces, but they not up to the mark when the aqua impurity is very low in concentration. Now this limitation can be overcome by the use of dynamic MOFs where water is the stimuli for the dynamism. In this regard, we are presenting a Zn(II) based dynamic MOF synthesised using 2,5-dihydroxyterephthalic acid (H2-DHT). The DHT has already there with its efficiency as a handy linker for the construction of porous MOFs[1] and can show excited-state intramolecular proton transfer (ESIPT) phenomenon. Our system is a five-fold interpenetrated 3D porous MOF, {[Zn(4-bpdh)(DHT)].(MeOH)(H2O)}n of Zn(II) with a neutral N,N′-donor organic ligand (4-bpdh), and shows interesting guest-dependent reversible structural dynamism. [2] Upon desolvation, relative squeezing of the pores occurs which only be opened selectively upon carbon dioxide adsorption. Moreover, the excited state intra-molecular proton transfer chromophore promotes spectacular guest-responsive multicolour dual emission in water and DMF. Interestingly, this guest free MOF detects water at a very low concentration in various organic solvent through luminescent turn on and then dual emission way. The overall observation points out that discussed Zn-MOF has the alluring prospect in chemical industries as a luminescent water sensor. [1] Bloch, E. D. et. al. (2012). Science, 335, 1606-1610. [2] Bhattachary, B. et. al. (2016). Chem. Eur. J., 22, 14998-15005.