Eringathodi Suresh

Versatile synthetic protocols and characterization of a functionally (–OH; –CONH–) decorated mixed-ligand Cd( ii )-based 2D MOF (ADES-7) and its application for CO ₂ capture and reversible adsorptive removal of cationic dyes have been investigated.

Two isostructural MOFs {[Cd(BDC)(L)] ⋅ CH₃OH}_n (1) and {[Cd(NH₂‐BDC)(L)] ⋅ CH₃OH}_n (1‐NH₂) involving Cd metal center and different dicarboxylate ligands (1,4‐benzenedicarboxylate (BDC) in 1 and 2‐amino‐1,4‐benzenedicarboxylate (NH₂‐BDC) in 1‐NH₂) and a common amide functionalized N‐donor ligand ((E)‐N′‐(pyridin‐3‐ylmethylene)nicotinohydrazide (L)) has been synthesized in bulk by diverse routes with phase‐purity. The MOFs were characterized by spectroscopic methods such as FT‐IR, elemental, TGA analysis, PXRD, and SXRD analysis. Amide functionality of L in 1 and both amide/‐NH₂ functional groups attached to the ligands in 1‐NH₂ of the interpenetrated isostructural 3D framework has been found to be catalytically active basic site towards multiple organic transformations. Both 1 and 1‐NH₂ showed good catalytic activity towards both CO₂‐epoxide cycloaddition and Biginelli reaction. A comparative study of the catalytic activity of 1 and 1‐NH₂ for cycloaddition and Biginelli reaction revealed that the amine‐functionalized framework 1‐NH₂ showed better catalytic performance than 1 due to the existence of additional amino site. Presence of accessible functionally decorated Lewis basic ‐NH₂ and amide sites on BDC and N‐donor ligands of 1‐NH₂ synergistically activate the substrate making this framework interesting and efficient heterogeneous base catalyst. Excellent product yield under moderate conditions with reusability is the highlight in both catalytic reactions.

AlCl ₃ ‐Catalyzed oxidative cyclization of thiosemicarbazones / triazolothiones with propargylic alcohols is achieved to afford a diverse set of triazolothiazines in good yields. Triazolothiazines were synthesized in a shorter duration at room temperature under an open‐air environment with atom economical approach.

A series of non-heme μ-oxo-bridged dinuclear iron(III) complexes of the type [Fe₂(μ-O)(L1–L6)₂Cl₂]Cl₂ 1–6 have been isolated and their catalytic activity towards oxidative transformation of alkanes into alcohols has been studied using m-choloroperbenzoic acid (m-CPBA) as an oxidant. All the complexes were characterized by CHN, electrochemical, and UV-visible spectroscopic techniques. The molecular structures of 2 and 5 have been determined successfully by single crystal X-ray diffraction analysis and both possesses octahedral coordination geometry and each iron atom is coordinated by four nitrogen atoms of the 4N ligand and a bridging oxygen. The sixth position of each octahedron is coordinated by a chloride ion. The (μ-oxo)diiron(III) core is linear in 2 (Fe–O–Fe, 180.0°), whereas it is non-linear (Fe–O–Fe, 161°) in 5. All the diiron(III) complexes show quasi-reversible one electron transfer in the cyclic voltammagram and catalyze the hydroxylation of alkanes like cyclohexane, adamantane with m-CPBA as an oxidant. In acetonitrile solution, adding excess m-CPBA to the diiron(III) complex 2 without chloride ions leads to intramolecular hydroxylation reaction of the oxidant. Interestingly, 2 catalyzes alkane hydroxylation in the presence of chloride ions, but intramolecular hydroxylation in the absence of chloride ions. The observed selectivity for cyclohexane (A/K, 5–7) and adamantane (3°/2°, 9–18) suggests the involvement of high-valent iron–oxo species rather than freely diffusing radicals in the catalytic reaction. Moreover, 4 oxidizes (A/K, 7) cyclohexane very efficiently up to 513 TON while 5 oxidizes adamantane with good selectivity (3°/2°, 18) using m-CPBA as an oxidant. The electronic effects of ligand donors dictate the efficiency and selectivity of catalytic hydroxylation of alkanes.

The development of high-efficiency and durable bifunctional electrocatalysts is an important and challenging topic in the area of energy storage/conversion. Herein, we prepared metallic cobalt nanoparticle decorated N-doped graphitic sheets (Co@NGr) by adopting facile pyrolysis of a mixed ligand cobalt-based MOF (CoMOF-2) as a sacrificial template displaying good OER and HER activity. The catalytic material harvested at three different pyrolytic temperatures was characterized by various analytical methods such as PXRD, SEM, TEM, Raman, and XPS analyses. The catalytic activity of the obtained hybrid composite materials towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was studied. Co@NGr-900 was found to be an efficient bifunctional electrocatalyst and 10 mA cm⁻² current density was afforded at an overpotential of 390 mV for OER and 340 mV for HER respectively. This study provides insight for the development of cost-effective nonprecious element-based electrocatalysts for water splitting which has relevance in energy storage and conversion. Catalytic performance is governed by the synergistic compositional effect of metallic cobalt/nitrogen-doping in the graphitic carbon increasing the electrical conductivity/active sites of the composite material.

Functional neutral metal–organic frameworks (MOFs) {[M(5OH-IP)(L)]}_n [M = Zn(II) for ADES-4; Cd(II) for ADES-5; 5OH-IP = 5-hydroxyisophthalate; L = (E)-N′-(pyridin-3-ylmethylene)nicotinohydrazide) have been synthesized by a diffusion/conventional reflux/mechanochemical method and characterized by various analytical techniques. Crystals were harvested by a diffusion method, and single-crystal X-ray diffraction (SXRD) analysis revealed that an adjacent [M₂(COO)₂]_n ladder chain generates isostructural two-dimensional network motifs by doubly pillaring via L. The bulk-phase purity of ADES-4 and ADES-5 synthesized by a versatile synthetic approach has been recognized by the decent match of powder X-ray diffraction patterns with the simulated one. Both ADES-4 and ADES-5 showed selective adsorption of cationic dyes methylene blue (MB), methyl violet (MV), and rhodamine B (RhB) over anionic dye methyl orange (MO) from water with good uptake and rapid adsorption. Utilization of ADES-4 as a chromatographic column filler for adsorptive removal of individual cationic dyes as well as a mixture of dyes has been demonstrated from the aqueous phase. Interestingly, ADES-4 is reusable with good stability, and it showed a dye desorption phenomenon in methanol. The probable mechanism of cationic dye removal based on insight from structural information and plausible supramolecular interactions has also been explored. Both MOFs also showed efficient catalytic transformation of fructose and glucose into the high-value chemical intermediate 5-hydroxymethylfurfural of industrial significance.

Catalytic synthesis of vicinal diols via ring-opening hydrolysis of spiro-epoxyoxindoles.

An atom-economical and efficient route for the direct amidation and amination of aryl C–H bonds using our synthesized recyclable heterogeneous Cu-MnO catalyst is reported here. The direct C–H amidation was carried out using a simple amide without any preactivated coupling partner, and simple air was used as the sole oxidant. The reaction proceeds very smoothly with a broad range of substrates containing numerous functional groups in very good to excellent yields. Direct C–H aminations with a secondary amine were carried out under base-, ligand-, and external oxidant-free conditions in very good to excellent yields in very mild conditions. Both the amidation and amination can be scaled up on a gram scale with similar yields. The major advantage is that our catalyst is recyclable and reused several times without any significant loss of reactivity.