Faculty Publications
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Item Distal Synergistic Effect in Bimetal-Organic Framework for Superior Catalytic Water Oxidation(American Chemical Society, 2023) Bhoi, U.; Ray, S.; Bhand, S.; Ninawe, P.; Roy, D.; Rana, S.; Tarafder, K.; Ballav, N.Metal-organic frameworks (MOFs) are emerging as promising electro-catalysts for the oxygen evolution reaction (OER). The bimetallic design strategy was further adopted in MOFs to elevate the OER performance by a synergistic effect. The proximal metal-oxygen-metal bonding configuration with typical 3dπ-2pπ-3dπ interaction was apparently essential for an effective electronic coupling between the metal centers. Here, we report an example of distal synergy in a bimetal-organic framework exhibiting a better OER activity than the monometallic counterparts, as well as the conventional proximal synergy. To achieve a current density of 10 mA·cm-2, our electrodeposited bimetallic MOF, Co-Ni(TCNQ)2(H2O)2 (TCNQ = 7,7,8,8-tetracyanoquinodimethane), on a glassy-carbon electrode required an overpotential value of 220 mV. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed distinctive electronic coupling between the Co(II)-3d7 and Ni(II)-3d8 centers, despite being 9 Å apart, leading to an overall charge delocalization in the structure via TCNQ. © 2023 American Chemical Society.Item Excitonic cuprophilic interactions in one-dimensional hybrid organic-inorganic crystals(Royal Society of Chemistry, 2024) Hassan, N.; Nagaraja, S.; Saha, S.; Tarafder, K.; Ballav, N.The everlasting pursuit of hybrid organic-inorganic lead-free semiconductors has directed the focus towards eco-friendly copper-based systems, perhaps because of the diversity in chemistry, controlling the structure-property relationship. In this work, we report single crystals of a Cu(i) halide-based perovskite-like organic-inorganic hybrid, (TMA)Cu2Br3, (TMA = tetramethylammonium), consisting of unusual one-dimensional inorganic anionic chains of -(Cu2Br3)-, electrostatically stabilized by organic cations, and the Cu(i)-Cu(i) distance of 2.775 Å indicates the possibility of cuprophilic interactions. X-ray photoelectron spectroscopy measurements further confirmed the presence of exclusive Cu(i) in (TMA)Cu2Br3 and electronic structure calculations based on density functional theory suggested a direct bandgap value of 2.50 eV. The crystal device demonstrated an impressive bulk photovoltaic effect due to the emergence of excitonic Cu(i)-Cu(i) interactions, as was clearly visualized in the charge-density plot as well as in the Raman spectroscopic analysis. The single crystals of a silver analogue, (TMA)Ag2Br3, have also been synthesized revealing a Ag(i)-Ag(i) distance of 3.048 Å (signature of an argentophilic interaction). Unlike (TMA)Cu2Br3, where more density of states from Cu compared to Br near the Fermi level was observed, (TMA)Ag2Br3 exhibited the opposite trend, possibly due to variation in the ionic potential influencing the overall bonding scenario. © 2024 The Royal Society of Chemistry.Item Thermally-driven conformational twist in organic azobenzene linker activates molecular doping effect in thin films of lanthanide MOFs(Royal Society of Chemistry, 2025) Bhoi, U.; Kalyani, M.; Ananthram, K.S.; Saha, S.; Acharya, A.; Hassan, N.; Raj, M.; Tarafder, K.; Ballav, N.Azobenzene-based photo-switchable molecules have shown significant potential in stimuli-responsive systems, especially when incorporated into metal–organic frameworks (MOFs). This study reports thin films of lanthanide-based metal–organic frameworks (Ln-MOFs) with 4,4?-azobenzene dicarboxylic acid (H2ADA) as the organic linker – Tb-ADA, Eu-ADA, and Gd-ADA – using an electrodeposition method. Upon heating to 400 K, a reversible structural transition was observed via variable temperature grazing-incidence X-ray diffraction (GIXRD) and Raman spectroscopy, not due to trans–cis isomerization but rather a thermally-induced conformational twist of the ADA linker. Density functional theory (DFT) combined with molecular dynamics (MD) simulations supports this interpretation, revealing high-energy atropisomeric states stabilized by MOF confinement. Molecular doping of these films with 7,7,8,8-tetracyanoquinodimethane (TCNQ) significantly enhanced their electrical conductivity, increasing by two orders of magnitude at 400 K. This enhancement is attributed to improved ?–? stacking and charge-transfer interactions facilitated by the conformational twist. Temperature-dependent X-ray photoelectron spectroscopy (XPS) confirmed redox activity in TCNQ@Tb-ADA films, showing reversible conversion between Tb(iii) and Tb(iv), with back electron transfer at 400 K restoring Tb(iii). These findings introduce a new mechanism of thermally-driven conformational switching in MOFs and open avenues for developing responsive electronic materials based on azobenzene linkers. This journal is © The Royal Society of Chemistry, 2025Item Rotational Flexibility in Dication Drives Ambient Temperature Ferroelectricity in an Organic–Inorganic Hybrid Halide(John Wiley and Sons Inc, 2025) Hassan, N.; Panday, R.; Chandru, P.G.; Ananthram, K.S.; Jose, T.M.; Bhoi, U.; Sieradzki, A.; Zar?ba, J.K.; Boomishankar, R.; Tarafder, K.; Ballav, N.Organic–inorganic hybrid halides (OIHHs) have gained attention as potential ferroelectric materials due to structure-property synergy of the organic and inorganic constituents. This study introduces an unusual Ag(I)-based ternary OIHH, (4,4?-bpy)Ag2Br4, featuring rotational flexibility in the organic dication to induce asymmetry into the structure. The compound crystallizes in a monoclinic crystal system with a non-centrosymmetric polar P21 space group at room-temperature and undergoes a structural phase transition to a centrosymmetric phase (P21/c) at Curie temperature (Tc) of 330 K which was further supported by differential scanning calorimetry (DSC), second harmonic generation (SHG) signals, dielectric anomaly, current-voltage (I–V) profiles, and X-ray photoelectron spectroscopy (XPS) data. Ferroelectricity is confirmed through polarization–electric field (P–E) hysteresis loops and piezoresponse force microscopy (PFM), exhibiting switchable polar domains. Density functional theory (DFT) calculations revealed electronic structures of the ferroelectric and paraelectric phases, identified the (?-AgBr2)nn? inorganic anionic chain contributing to the net polarization, and in general, complemented the experimental results. Comparative studies with structurally analogous Ag(I)-based OIHHs lacking dication rotational freedom endorse the critical role of organic flexibility in driving ferroelectricity. This study provides insights into the role of organic dications in controlling ferroelectric behavior and offers a promising pathway for developing coinage metal-based OIHH ferroelectric materials. © 2025 Wiley-VCH GmbH.