Browsing by Author "Arindam Indra"

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Axial ligand-induced high electrocatalytic hydrogen evolution activity of molecular cobaloximes in homo- and heterogeneous medium
(Royal Society of Chemistry, 2024) Jitendra Kumar Yadav; Baghendra Singh; Anjali Mishra; Sarvesh Kumar Pal; Nanhai Singh; Prem Lama; Arindam Indra; Kamlesh Kumar
Three new molecular cobaloxime complexes with the general formula [ClCo(dpgH)2L] (1-3), where L1 = N-(4-pyridylmethyl)-1,8-naphthalimide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalimide, L3 = 4-piperidin-N-(4-pyridylmethyl)-1,8-naphthalimide, have been synthesized and characterized by UV-Vis, multinuclear NMR, FT-IR and PXRD spectroscopic techniques. The crystal structures of all complexes have also been reported. The electrocatalytic activity of complexes is investigated under two catalysis conditions: (i) homogeneous conditions in acetonitrile using acetic acid (AcOH) as a proton source and (ii) heterogeneous conditions upon immobilization onto the surface of activated carbon cloth (CC). Complex 3 exhibited high electrocatalytic HER activity under both homogeneous and heterogeneous conditions. It catalyses proton reduction to molecular hydrogen in acetonitrile solution at a lower overpotential (640 mV) with a high turnover frequency (TOF) of 524.57 s−1 and demonstrates good stability in acidic conditions. Furthermore, catalytic (working) electrodes are prepared by immobilizing the complexes onto the surface of activated carbon cloth (CC) for electrocatalytic HER under heterogeneous conditions. An impressive HER performance was again obtained with catalytic electrode 3@CC in 1.0 M KOH, achieving a current density of −10 mA cm−2 at an overpotential of 262 mV. Chronoamperometric (CA) studies showed no significant decay of the initial current density for 10 h, indicating the excellent stability of 3@CC. Additionally, UV-Vis and NMR spectral studies of the recovered catalyst after electrocatalysis revealed no structural changes, demonstrating its robustness under reaction conditions. © 2024 The Royal Society of Chemistry.
Chlorocobaloxime containing N-(4-pyridylmethyl)-1,8-naphthalamide peripheral ligands: synthesis, characterization and enhanced electrochemical hydrogen evolution in alkaline medium
(Royal Society of Chemistry, 2022) Jitendra Kumar Yadav; Baghendra Singh; Sarvesh Kumar Pal; Nanhai Singh; Prem Lama; Arindam Indra; Kamlesh Kumar
Two new discrete cobaloxime based complexes with the general formula [ClCo(dioxime)2L] (1 and 2), L1 = N-(4-pyridylmethyl)-1,8-naphthalamide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalamide have been synthesized and characterized by various spectroscopic techniques such as FT-IR, 1H, 13C{1H} NMR and PXRD. The molecular structures of both complexes have also been determined using single crystal X-ray crystallography. The solid state molecular structures revealed distorted octahedral geometry around the Co(iii) central metal ion with two dioximes in the equatorial plane and axial positions are occupied by chloro and pyridine nitrogen of N-(4-pyridylmethyl)-1,8-naphthalamide ligands. Both complexes exhibit weaker non-covalent interactions (C-H⋯O, C-H⋯Cl and C-H⋯π(Centroid) in complex 1 whereas C-H⋯O and C-H⋯Br in complex 2) resulting in the formation of dimeric and 1D supramolecular structures. Furthermore, these complexes are immobilized onto the surface of activated carbon cloth (CC) and their electrocatalytic performance for the hydrogen evolution reaction (HER) has been investigated in alkaline and acidic media as well as buffer solution. In alkaline medium, we found that complex 2 exhibited impressive electrocatalytic HER activity and produced a current density of −10 mA cm−2 at an overpotential of 260 mV, whereas complex 1 produced the same current density at an overpotential of 334 mV. An electrochemical impedance spectroscopy (EIS) spectral study revealed the faster charge transfer kinetics of complex 2 than that of complex 1. Similarly, the low Tafel slope (100 mV dec−1) for the HER with complex 2 indicates faster HER kinetics compared to complex 1. The chronoamperometric study showed that complex 2 is stable under electrocatalytic HER conditions for 5 h without losing the initial current density and it has also been established that the complex structure is retained after electrocatalysis. © 2023 The Royal Society of Chemistry.
Homoleptic Ni(ii) dithiocarbamate complexes as pre-catalysts for the electrocatalytic oxygen evolution reaction
(Royal Society of Chemistry, 2022) Sarvesh Kumar Pal; Baghendra Singh; Jitendra Kumar Yadav; Chote Lal Yadav; Michael G. B. Drew; Nanhai Singh; Arindam Indra; Kamlesh Kumar
Four new functionalized Ni(ii) dithiocarbamate complexes of the formula [Ni(Lx)2] (1-4) (L1 = N-methylthiophene-N-3-pyridylmethyl dithiocarbamate, L2 = N-methylthiophene-N-4-pyridylmethyl dithiocarbamate, L3 = N-benzyl-N-3-pyridylmethyl dithiocarbamate, and L4 = N-benzyl-N-4-pyridylmethyl dithiocarbamate) have been synthesized and characterized by IR, UV-vis, and 1H and 13C{1H} NMR spectroscopic techniques. The solid-state structure of complex 1 has also been determined by single crystal X-ray crystallography. Single crystal X-ray analysis revealed a monomeric centrosymmetric structure for complex 1 in which two dithiocarbamate ligands are bonded to the Ni(ii) metal ion in a S^S chelating mode resulting in a square planar geometry around the nickel center. These complexes are immobilized on activated carbon cloth (CC) and their electrocatalytic performances for the oxygen evolution reaction (OER) have been investigated in aqueous alkaline solution. All the complexes act as pre-catalysts for the OER and undergo electrochemical anodic activation to form Ni(O)OH active catalysts. Spectroscopic and electrochemical characterization revealed the existence of the interface of molecular complex/Ni(O)OH, which acts as the real catalyst for the OER. The active catalyst obtained from complex 2 showed the best OER activity achieving 10 mA cm−2 current density at an overpotential of 330 mV in 1.0 M aqueous KOH solution. © 2022 The Royal Society of Chemistry.
Ni(ii)-Dithiocarbamate and -diphosphine coordination complexes as pre-catalysts for electrochemical OER activity
(Royal Society of Chemistry, 2024) Sarvesh Kumar Pal; Toufik Ansari; Chote Lal Yadav; Nanhai Singh; Prem Lama; Arindam Indra; Kamlesh Kumar
Electrochemical water oxidation holds immense potential for sustainable energy generation, splitting water into clean-burning hydrogen and life-giving oxygen. However, a key roadblock lies in the sluggish nature of the oxygen evolution reaction (OER). Finding stable, cost-effective, and environmentally friendly catalysts with high OER efficiency is crucial to unlock this technology's full potential. Here, we have synthesized four new cationic heteroleptic Ni(ii) complexes having the formula [Ni(S^S)(P^P)]PF6 (1-4) where S^S represents bidentate dithiocarbamate ligands (N,N-bis(benzyl)dithiocarbamate and N-benzyl-N-3-picolyldithiocarbamate) and P^P represents diphosphine ligands (1,2-bis(diphenylphosphino)ethane (dppe) and 1,1-bis(diphenylphosphino)ferrocene (dppf)). The complexes were characterized by UV-Vis, FT-IR, and multinuclear NMR spectroscopic techniques. Single crystal X-ray structures of all complexes are also reported. The molecular structures showed a distorted square planar geometry around the Ni(ii) center defined by a bidentate S^S dithiolate chelating ligand and a P^P diphosphine chelating ligand. Interestingly, the complexes exhibit weak non-covalent interactions, contributing to the overall supramolecular structures. The role of complexes in water oxidation has been investigated electrochemically in a 1.0 M KOH solution after immobilization onto the surface of activated carbon cloth (CC). Detailed analyses revealed that the complexes are promising precatalysts for generating active Ni(OH)2/NiO(OH) as a true oxygen evolution reaction (OER) catalyst at CC upon anodic activation. Notably, the catalyst derived from complex 4@CC exhibited the highest OER activity with a Tafel slope of 93 mV per decade and reaching a current density of 10 mA cm−2 at a low overpotential of 250 mV in a 1.0 M KOH solution. This study reveals the significance of dithiocarbamate and diphosphine ligands in facilitating the conversion of Ni(ii) complexes into highly active OER catalysts. © 2025 The Royal Society of Chemistry.
Oxidase-Like Nanozyme Activity of Ultrathin Copper Metal–Organic Framework Nanosheets With High Specificity for Catechol Oxidation
(John Wiley and Sons Inc, 2025) Ajit Kumar Kumar Singh; D. R. Sharma; Devesh Kumar Singh; Sonu Sarraf; Aviru Kumar Basu; Vellaichamy Ganesan; Avishek Saha; Arindam Indra
In nature, catechol oxidase catalyzes the oxidation of o-diphenol to o-quinone to produce a series of highly important polyphenolic natural products. Although mimicking the functionality of natural enzyme using a nanozyme was found to be beneficial, attaining a high specificity is challenging. Herein, we have explored the thickness-dependent oxidase activity and specificity of Cu-metal-organic framework (MOF) nanosheets. The unique synthetic method offers control over the thickness of the Cu-MOF nanosheets. The ultrathin (4 nm) Cu-MOF (Cu-UMOF) nanosheets as an oxidase nanozyme exhibit high specificity for catechol oxidation without having any peroxidase activity. Interestingly, the thicker (20–30 nm) Cu-MOF nanosheets showed poor catechol oxidase and peroxidase activity. The binuclear Cu-center, coordinative, and electronic unsaturation tuned electronic structure in Cu-UMOF, resulting in higher specificity for catechol oxidation than thicker Cu-MOF. © 2024 Wiley-VCH GmbH.
Visible light-driven molecular oxygen activation for oxidative amidation of alcohols using lead-free metal halide perovskite
(Royal Society of Chemistry, 2024) Vishesh Kumar; Ved Vyas; Deepak Kumar; Ashish Kumar Kushwaha; Arindam Indra
Herein, we report the modulation of the band structures of halide perovskite Cs2CuBr4 by tuning the synthesis methods. The photocatalyst PC-1, synthesized by the hot injection method, has a more negative conduction band minima (CBM) than the photocatalyst PC-2, synthesized at room temperature. As a result, PC-1 can activate molecular O2 more efficiently to initiate the radical-mediated dehydrogenation of alcohols. The more positive valence band maxima (VBM) of PC-1 also facilitates amine oxidation to the corresponding radical. Further, improved charge separation and transport and a decrement in the photogenerated charge carrier recombination have been detected for PC-1 to enhance photocatalytic activity. PC-1 showed improved yields for a series of structurally diverse amides (highest yield = 98%) by oxidative amidation of alcohols under visible light irradiation. © 2024 The Royal Society of Chemistry.