Bikash Garai

A mechanochemically synthesized covalent organic framework as a proton-conducting solid electrolyte

Mechanochemistry has become an increasingly important synthetic tool for a waste-free environment. However, the poor quality of the so-derived materials in terms of their crystallinity and porosity has been their major drawback for any practical applications. In this report, we have for the first time successfully leveraged such characteristics to show that the mechanochemically synthesized bipyridine based covalent organic framework (COF) outperforms its conventional solvothermal counterpart as an efficient solid-state electrolyte in PEM fuel cells. Marking the first such attempt in COFs, a Membrane Electrode Assembly (MEA) fabricated using the mechanochemically synthesized COF was observed to inhibit the fuel crossover and build up a stable Open Circuit Voltage (OCV = 0.93 V at 50 °C), thereby establishing itself as an effective solid electrolyte material (with a proton conductivity of 1.4 × 10−2 S cm−1), while the solvothermally synthesized COF proved ineffective under similar conditions.

Hydrolytic Conversion of a Metal–Organic Polyhedron into a Metal–Organic Framework†

Twist and release: The metal-organic polyhedron 1 synthesized from 5-(prop-2-ynyloxy)isophthalic acid and Cu(NO3 )2 ⋅ 3 H2 O has a hydrophobic outer surface and a hydrophilic inner core. In an aqueous medium, the resulting polarity gradient led to the transformation of 1 into the 2D metal-organic framework 2. This unique phenomenon enabled the gradual release of entrapped drug molecules.

Pore surface engineering in porous, chemically stable covalent organic frameworks for water adsorption

Herein, we have explored the possibility of a class of covalent organic frameworks (COFs) as water adsorbing materials. We have selected, synthesized 12 chemically stable functionalized Schiff base COFs and thoroughly studied their water uptake behaviour. Further, a deep understanding was developed with these COFs towards the effects of condensation pressure of water and hydrophilic/hydrophobic groups present in the COF pores on water absorption capacity and ultimately, their recyclability. Among all reported COFs, TpPa-1 shows the highest water uptake of 30 wt% (368 cm3 g−1; 17 mmol g−1) at P/P0 = 0.3, which is also comparable with the recently reported carbon materials and few well known MOFs. This study also reveals that the overall water uptake of COFs can be tuned systematically based on chemical functionality and pore size in a wider window of relative pressures.

Employing carboxylic acids in aryne multicomponent coupling triggered by aziridines/azetidines

The transition-metal-free aryne multicomponent coupling (MCC) involving carboxylic acids initiated by aziridines/azetidines has been reported. The use of aziridines as nucleophiles afforded N-aryl β-amino alcohol derivatives and the application of azetidines as nucleophilic triggers furnished N-aryl γ-amino alcohol derivatives in moderate to good yields. These reactions proceed under mild conditions and result in the formation of a new carbon–nitrogen bond and a new carbon–oxygen bond. The utility of carboxylic acids in aryne MCCs has been demonstrated, and the synthetic potential of phenols as acid surrogates in the present aryne MCCs has been realized.

Electrocatalytic water oxidation by a molecular cobalt complex through a high valent cobalt oxo intermediate

Biuret-modified tetraamidomacrocyclic cobalt complex [CoIII-bTAML]- is shown to catalyze electrochemical water oxidation at basic pH leading to the formation of O2. Electrochemical and spectroscopic studies indicate a high valent cobalt oxo intermediate isoelectronic to CoV(O) as the active oxidant. The kinetic isotope effect of 8.63 indicates an atom proton transfer mechanism.

Electrochemical formation of FeV(O) and mechanism of its reaction with water during O-O bond formation.

A detailed electrochemical investigation of a series of iron complexes (biuret-modified tetraamido iron macrocycles FeIII -bTAML), including the first electrochemical generation of FeV (O), and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium are reported. Spectroelectrochemical and mass spectral studies indicated FeV (O) as the active oxidant, formed due to two redox transitions, which were assigned as FeIV (O)/FeIII (OH2 ) and FeV (O)/FeIV (O). The spectral properties of both of these high-valent iron oxo species perfectly match those of their chemically synthesised versions, which were thoroughly characterised by several spectroscopic techniques. The O-O bond-formation step occurs by nucleophilic attack of H2 O on FeV (O). A kinetic isotope effect of 3.2 indicates an atom-proton transfer (APT) mechanism. The reaction of chemically synthesised FeV (O) in CH3 CN and water was directly probed by electrochemistry and was found to be first-order in water. The pKa value of the buffer base plays a critical role in the rate-determining step by increasing the reaction rate several-fold. The electronic effect on redox potential, WO rates, and onset overpotential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework. Changing the substituents from OMe to NO2 resulted in an eightfold increase in reaction rate, while the overpotential increased threefold.

Functionalization and Isoreticulation in a Series of Metal–Organic Frameworks Derived from Pyridinecarboxylates

The partially fluorinated metal-organic frameworks (F-MOFs) have been constructed from 3-fluoro-4-pyridinecarboxylic acid and trans-3-fluoro-4-pyridineacrylic acid linkers using Mn(2+), Co(2+), and Cd(2+) metals via the solvothermal method, which show isostructural isomerism with their nonfluorinated counterparts synthesized using 4-pyridinecarboxylic acid and trans-4-pyridineacrylic acid, respectively. The simultaneous effect of partial fluorination and isoreticulation on structure and H2 adsorption has been studied systematically in isostructural nonfluorinated and partially fluorinated MOFs, which shows that the increment in the hydrogen uptake properties in F-MOFs is not a universal phenomenon but is rather system-specific and changes from one system to another.

Self-Exfoliated Metal-Organic Nanosheets through Hydrolytic Unfolding of Metal-Organic Polyhedra

Few-layers thick metal-organic nanosheets have been synthesized using water-assisted solid-state transformation through a combined top-down and bottom-up approach. The metal-organic polyhedra (MOPs) convert into metal-organic frameworks (MOFs) which subsequently self-exfoliate into few-layered metal-organic nanosheets. These MOP crystals experience a hydrophobicity gradient with the inner surface during contact with water because of the existence of hydrophobic spikes on their outer surface. When the amount of water available for interaction is higher, the resultant layers are not stacked to form bulk materials; instead few-layered nanosheets with high uniformity were obtained in high yield. The phenomenon has resulted high yield production of uniformly distributed layered metal-organic nanosheets from three different MOPs, showing its general adaptability.

Unprecedented ferrocene–quinoline conjugates: facile proton conduction via 1D helical water chains and a selective chemosensor for Zn(II) ions in water

Two novel ferrocene–quinoline derivatives 3 (C22H19O2N3Fe) and 4 (C34H28O4N6Fe) have been synthesized and structurally characterized. Compound 3 exhibits good proton conductivity through 1D helical water chains. In addition, both compounds 3 and 4 selectively detect Zn2+ ions in water with a detection limit of 2 ppb through multiple channels.

Photochromic metal–organic frameworks for inkless and erasable printing

Inkless and erasable printing is the key solution towards a more sustainable paper industry, in terms of reducing paper wastages and the associated environmental hazards from waste paper processing. However, only a few cases have been reported in the literature where inkless printing has been tested in some practical systems. In an attempt to address this solution, we used photochromic metal–organic frameworks (MOFs) and tested their capability as inkless and erasable printing media. The printing was performed using sunlight as the light source on MOF-coated papers. The resulting printing had good resolution and stability, and was capable of being read both by the human eye and smart electronic devices; furthermore, the paper could be reused for several cycles without any significant loss in intensity. Interestingly, different coloured printing with a similar efficiency was achieved by varying the structure of the MOF.