Department of Chemistry
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Item Encapsulation of a Ni salen complex in zeolite Y: an experimental and DFT study(RSC, 2015) Ray, SaumiIt is observed that for a square planar Ni(II)-Schiff base complex of the general formula {Ni(II)L}, where L is {L: N,N′-bis(5-hydroxy-salicylidene)ethylenediamine}, when encapsulated in a supercage of zeolite Y the bulky guest complex adopts a non-planar geometry without disturbing the integrity of the zeolite framework. Detailed comparative characterization is carried out to understand the structural change of the guest complex as a result of steric and electronic interactions with the host framework. UV-Vis spectroscopic studies of the encapsulated and ‘neat’ complex show a significant blue shift in the d–d transition after encapsulation and the diamagnetic ‘neat’ complex exhibits paramagnetism after encapsulation. DFT studies of the Ni(II)-Schiff base complex have been carried out for different spin states in neat and encapsulated form and the UV-Vis spectra are simulated using TD-DFT to understand the observed spectra in detail.Item Enhanced catalytic activity and magnetization of encapsulated nickel Schiff-base complexes in zeolite-Y: a correlation with the adopted non-planar geometry(RSC, 2016) Ray, SaumiSquare planar Ni(II)-Schiff base complexes when encapsulated in a supercage of zeolite Y have shown altered optical, magnetic properties and catalytic activities in comparison to their corresponding free states. Different characterization techniques like XRD analysis, SEM-EDX, AAS, FTIR, UV-Visible spectroscopy and magnetic studies as well as detailed theoretical studies altogether show the differences in the properties of complexes in free and encapsulated states. All these studies have suggested that the largest complex deviates by the maximum amount from its free-state properties and a fascinating correlation between the extent of deviation from molecular dimension and modified catalytic activity of encapsulated complexes is observed.Item Encapsulated Schiff base nickel complex in zeolite Y: Correlation between catalytic activities and extent of distortion supported by experimental and DFT studies(Elsiever, 2017-06-01) Ray, SaumiIt is observed that planar Ni(II)–Schiff base complexes of general formulae NiL with L as N, Ń-bis(4-hydroxy salicylidene)ethylenediamine (4-OH-salen) when encapsulated in the supercage of zeolite Y, the complex adopts non-planar geometry. The detailed characterization studies of the 4-OH-Ni-salen complex when compared with Ni-salen complex encapsulated in zeolite Y (Ni-salen-Y) Choudhary et al. (2016) have suggested that the complex undergoes more distortion in order to accommodate itself inside the supercage of zeolite-Y. Optical spectroscopic studies show relatively more blue shifted and intensified d-d transition for 4-OH-Ni-salen complex after encapsulation. We also report the catalytic activities and enhanced magnetization of encapsulated complex though it is diamagnetic in the ‘free’ state. DFT studies of these complexes have been carried out in different spin states and electronic spectra are simulated to have better insight about the geometries adopted by the guest complexes inside the host framework.Item The functionality of the hybrid systems driven by molecular dimension of the guest copper Schiff-base complexes entrapped in Zeolite-Y(Wiley, 2019-01) Ray, SaumiOn encapsulation inside the supercage of zeolite-Y planar Cu (II)–Schiff base complexes show the modified structural, optical and functional properties. The electronic effect of the different substituent groups present in the catalyst plays the decisive role towards their reactivity in the homogeneous phase but after the encapsulation in zeolite Y, reactivity is mainly governed by the molecular dimensions of the guest complexes rather than the electronic factor of the substituent groups attached on them. These systems are well characterized with the help of different characterization tools like XRD analysis, SEM - EDX, AAS, FTIR, XPS, DSC, TGA, BET and UV–Visible spectroscopy and the comparative optical and catalytic studies have provided a rational explanation of enhanced reactivity of zeolite encapsulated metal complexes for various oxidation reactions compared to their corresponding solution states.Item An insight into the catalytic activity of palladium Schiff-base complexes towards the Heck coupling reaction: routes via encapsulation in zeolite-Y(RSC, 2019) Ray, SaumiA small set of palladium Schiff-base complexes were synthesized and entrapped in the supercage of zeolite-Y. All these novel complexes in both states were systematically characterized with the help of different characterization tools like XRD, SEM-EDS, thermal analysis, XPS, IR, electronic spectroscopic and theoretical studies. These systems were thoroughly studied for their catalytic activities towards the Heck coupling reaction between bromobenzene and styrene. The aim was to meticulously compare the performance of the homogeneous catalysts, i.e., neat palladium Schiff-base complexes with that of their heterogeneous encapsulated analogs. The experimental as well as theoretical electronic structure studies suggested significant structural modification of the guest Pd(II)–Schiff-base complexes after encapsulation in zeolite Y. These complexes manifested modified catalytic activities towards the Heck coupling reaction. The theoretical studies reinforced the correlation between the modified catalytic properties and structural alteration of these complexes on encapsulation. These heterogeneous catalysts essentially demonstrated the benefits of easy separation and reusability as compared to the homogeneous analogues.Item Zeolite-Y encapsulated cobalt(II) Schiff-base complexes employed for photocatalytic dye-degradation and upcycling CO2(RSC, 2020-12) Ray, SaumiPlanar cobalt(II) Schiff-base complexes show modified structural and functional properties after encapsulation inside zeolite-Y. In the free-state, the reactivity of the cobalt(II) Schiff-base complexes is primarily controlled by the electronic effects of the different substituent groups present in the complexes. However, the encapsulation of these complexes within the supercages of zeolite-Y causes the alteration of the electron density around the metal center and subsequently modifies the reactivity. We have intended to study two environment-friendly reactions, i.e., degradation of rhodamine B dye and transformation of CO2 with catalysts containing relatively lower metal content like cobalt(II) salophen complexes encapsulated in zeolite-Y. To comprehend these systems well, XRD analysis, SEM-EDX, FTIR, XPS, TGA, BET, and UV–visible spectroscopy and DFT studies have been performed. XRD and BET studies along with XPS, experimental and theoretical electronic spectroscopic studies clearly revealed successful encapsulation of the guest complex with some alteration of the electronic environment around the metal center. Catalytic studies identified that encapsulated complexes exhibit the better results for dye degradation. Zeolite-Y encapsulated 5-methoxy cobalt(II) sal-1,2-phen (CoL5-Y) could degrade 89.6% of the dye while neat CoL5 could only degrade 30.2%. Comparative studies of structural and catalytic modifications allowed a rational explanation of enhanced reactivity of zeolite encapsulated metal complexes for the degradation of rhodamine B dye compared to their corresponding free-states. The catalysts showing the maximal and minimal activities for dye degradation in the series, i.e., CoL1, CoL1-Y, CoL5, and CoL5-Y, have been tested for coupling of CO2 and styrene oxide. The TON for CO2 uptake using the heterogeneous catalyst CoL5-Y was found to be 2949, while using the homogeneous counterpart, it was only 339