Publications by authors named "Tanmoy Ghosh"

22 Publications

  • Page 1 of 1

Synthesis of Ni(ii)-Mn(ii) complexes using a new mononuclear Ni(ii) complex of an unsymmetrical NO donor ligand: structures, magnetic properties and catalytic oxidase activity.

Dalton Trans 2021 Apr 17;50(13):4686-4699. Epub 2021 Mar 17.

Department of Chemistry, University College of Science, University of Calcutta, 92 APC Road, Kolkata 700009, India.

A new Ni(ii) complex [NiL] (complex 1) of an asymmetrically di-condensed NO donor Schiff base ligand, N-salicylidene-N'-3-methoxysalicylidene-1,3-propanediamine (HL), has been synthesized and utilized for the synthesis of three heterometallic complexes, [(NiL)Mn(NCS)(CHOH)]·CHOH (2) [(NiL)Mn(N(CN))(CHOH)]·CHOH (3) and [(NiL)Mn(N)(μ-N)(CHOH)] (4). Single crystal X-ray diffraction analyses show that complexes 2 and 3 have linear trinuclear structures where two tridentate O donor (NiL) units are coordinated to the central octahedral Mn(ii) centre, whereas complex 4 has a centrosymmetric tetranuclear structure where two binuclear (NiL)Mn units are linked via two phenoxido and two μ-N bridges. Among the heterometallic complexes (2-4), only 4 is active towards the catalytic oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone. The turnover number for the aerobic oxidation of 3,5-DTBC is 935 h. ESI-mass spectra have been recorded to scrutinize the mechanistic pathway of this catalytic reaction. Variable temperature magnetic susceptibility measurements suggest that complexes 2-4 are antiferromagnetically coupled with coupling constants (J) of -4.84 and -5.23 cm for complexes 2 and 3, respectively and J = -2.20 cm, J = 1.13 cm and J = -1.12 cm for complex 4. DFT calculations have been used to rationalize the magnetic super-exchange in complexes 2-4, by computing the theoretical coupling constants and analyzing the spin density plots.
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http://dx.doi.org/10.1039/d0dt04337kDOI Listing
April 2021

NHC-Mediated Stetter-Aldol and Imino-Stetter-Aldol Domino Cyclization to Naphthalen-1(2)-ones and Isoquinolines.

Org Lett 2021 Mar 4;23(6):2178-2182. Epub 2021 Mar 4.

Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700009, India.

N-Heterocyclic carbene-catalyzed tandem Stetter-aldol reaction of phthalaldehyde and α,β-unsaturated ketimines has been developed to afford functionalized naphthalen-1(2)-one derivatives as the formal [4+2] annulation product. Interestingly, the reaction of aldimines led to the formation of isoquinoline derivatives instead of the expected indanone derivatives as a [4+1] annulation product.
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http://dx.doi.org/10.1021/acs.orglett.1c00337DOI Listing
March 2021

Metavalent Bonding in GeSe Leads to High Thermoelectric Performance.

Angew Chem Int Ed Engl 2021 Feb 22. Epub 2021 Feb 22.

New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore, 560064, India.

Orthorhombic GeSe is a promising thermoelectric material. However, large band gap and strong covalent bonding result in a low thermoelectric figure of merit, zT≈0.2. Here, we demonstrate a maximum zT≈1.35 at 627 K in p-type polycrystalline rhombohedral (GeSe) (AgBiTe )  , which is the highest value reported among GeSe based materials. The rhombohedral phase is stable in ambient conditions for x=0.8-0.29 in (GeSe) (AgBiTe )  . The structural transformation accompanies change from covalent bonding in orthorhombic GeSe to metavalent bonding in rhombohedral (GeSe) (AgBiTe )  . (GeSe) (AgBiTe ) has closely lying primary and secondary valence bands (within 0.25-0.30 eV), which results in high power factor 12.8 μW cm  K at 627 K. It also exhibits intrinsically low lattice thermal conductivity (0.38 Wm  K at 578 K). Theoretical phonon dispersion calculations reveal vicinity of a ferroelectric instability, with large anomalous Born effective charges and high optical dielectric constant, which, in concurrence with high effective coordination number, low band gap and moderate electrical conductivity, corroborate metavalent bonding in (GeSe) (AgBiTe ) . We confirmed the presence of low energy phonon modes and local ferroelectric domains using heat capacity measurement (3-30 K) and switching spectroscopy in piezoresponse force microscopy, respectively.
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http://dx.doi.org/10.1002/anie.202101283DOI Listing
February 2021

Enhanced atomic ordering leads to high thermoelectric performance in AgSbTe.

Science 2021 02;371(6530):722-727

New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India.

High thermoelectric performance is generally achieved through either electronic structure modulations or phonon scattering enhancements, which often counteract each other. A leap in performance requires innovative strategies that simultaneously optimize electronic and phonon transports. We demonstrate high thermoelectric performance with a near room-temperature figure of merit, ~ 1.5, and a maximum ~ 2.6 at 573 kelvin, by optimizing atomic disorder in cadmium-doped polycrystalline silver antimony telluride (AgSbTe). Cadmium doping in AgSbTe enhances cationic ordering, which simultaneously improves electronic properties by tuning disorder-induced localization of electronic states and reduces lattice thermal conductivity through spontaneous formation of nanoscale (~2 to 4 nanometers) superstructures and coupling of soft vibrations localized within ~1 nanometer around cadmium sites with local strain modulation. The strategy is applicable to most other thermoelectric materials that exhibit inherent atomic disorder.
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http://dx.doi.org/10.1126/science.abb3517DOI Listing
February 2021

Family of Isomeric Cu-Ln (Ln = Gd, Tb, and Dy) Complexes Presenting Field-Induced Slow Relaxation of Magnetization Only for the Members Containing Gd.

Inorg Chem 2021 Jan 22;60(1):438-448. Epub 2020 Dec 22.

Department of Chemistry, University College of Science, University of Calcutta, 92 APC Road, Kolkata 700009, India.

The strategic design and synthesis of two isomeric Cu complexes, [CuL] and [CuL], of asymmetrically dicondensed NO-donor Schiff-base ligands (where HL and HL are -salicylidene-'-3-methoxysalicylidenepropane-1,2-diamine and -3-methoxysalicylidene-'-salicylidenepropane-1,2-diamine, respectively) have been accomplished via a convenient Cu template method. These two complexes have been used as metalloligands for the synthesis of three pairs of Cu-Ln isomeric complexes [CuL(μ-NO)Ln(NO)(HO)]·CHCN (for complexes -, L = L, and for complexes -, L = L and Ln = Gd, Tb, and Dy, respectively), all of which have been characterized structurally. In all six isomorphous and isostructural complexes, the decacoordinated Ln centers and pentacoordinated Cu centers possess sphenocorona and square-pyramidal geometries, respectively. The isomeric pair of Cu-Gd compounds shows field-induced slow relaxation of magnetization, although they present the typical isotropic behavior of Gd complexes, indicating that slow relaxation is not due to the usual energy barrier originating from the magnetic anisotropy. The isostructural derivatives with the ion-anisotropic lanthanides Tb and Dy do not show slow magnetic relaxation with or without a direct-current bias field, demonstrating that the magnetic response of the isotropic system Cu-Gd occurs through different mechanisms than the rest of the Ln cations.
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http://dx.doi.org/10.1021/acs.inorgchem.0c03129DOI Listing
January 2021

Evidence of Highly Anharmonic Soft Lattice Vibrations in a Zintl Rattler.

Angew Chem Int Ed Engl 2021 Feb 16;60(8):4259-4265. Epub 2020 Dec 16.

New Chemistry Unit, School of Advanced Materials and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore, 560064, India.

Here, we present lattice dynamics associated with the local chemical bonding hierarchy in Zintl compound TlInTe , which cause intriguing phonon excitations and strongly suppress the lattice thermal conductivity to an ultralow value (0.46-0.31 W m  K ) in the 300-673 K. We established an intrinsic rattling nature in TlInTe by studying the local structure and phonon vibrations using synchrotron X-ray pair distribution function (PDF) (100-503 K) and inelastic neutron scattering (INS) (5-450 K), respectively. We showed that while 1D chain of covalently bonded transport heat with Debye type phonon excitation, ionically bonded Tl rattles with a frequency ca. 30 cm inside distorted Thompson cage formed by . This highly anharmonic Tl rattling causes strong phonon scattering and consequently phonon lifetime reduces to ultralow value of ca. 0.66(6) ps, resulting in ultralow thermal conductivity in TlInTe .
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http://dx.doi.org/10.1002/anie.202013923DOI Listing
February 2021

Complementary amide-based donor-acceptor with unique nano-scale aggregation, fluorescence, and band gap-lowering properties: a WORM memory device.

Nanotechnology 2020 Oct 22;32(2):025208. Epub 2020 Oct 22.

Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700009, India.

Organic fluorescent semiconducting nanomaterials have gained widespread research interest owing to their potential applications in the arena of high-tech devices. We designed two pyrazaacene-based compounds, their stacked system, and the role of gluing interactions to fabricate nanomaterials, and determined the prospective band gaps utilizing the density functional theory calculation. The two pyrazaacene derivatives containing complementary amide linkages (-CONH and -NHCO) were efficiently synthesized. The synthesized compounds are highly soluble in common organic solvents as well as highly fluorescent and photostable. The heterocycles and their mixture displayed efficient solvent dependent fluorescence in the visible region of the solar spectrum. Notably, the compounds were associated through complementary NH•••O = C type hydrogen bonding, π-π stacking, and hydrophobic interactions, and thereby afforded nanomaterials with a low band gap. Fascinatingly, the fabricated stacked nanomaterial system exhibited resistive switching behavior, leading to the fabrication of an efficient write-once-read-many-times memory device of crossbar structure.
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http://dx.doi.org/10.1088/1361-6528/abba5aDOI Listing
October 2020

Joining of Trinuclear Heterometallic Cu-M (M = Mn, Cd) Nodes by Nicotinate to Form 1D Chains: Magnetic Properties and Catalytic Activities.

Inorg Chem 2020 Oct 1;59(20):14989-15003. Epub 2020 Oct 1.

Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India.

In the present work, four new heterometallic coordination complexes, {[(CuL)Mn(nic)(HO)](ClO)(0.5HO)} (), {[(CuL)Cd(nic)(HO)](ClO)(HO)} (), [(CuL)Mn(nic)]·2CHOH (), and [(CuL)Cd(nic)]·2CHOH () (where HL = ,'-bis(α-methylsalicylidene)-1,3-propanediamine and nic = nicotinate ion), have been synthesized and characterized by single-crystal X-ray crystallography. In complexes and , the nicotinate ion acts as a bifunctional linker (N,O donor) and joins the linear trinuclear nodes to form 1D polymeric chains. However, in complexes and , the nicotinate ion uses only the oxygen atoms of the carboxylic acid (O donor) to bind to the metal centers, forming discrete linear trinuclear units, while the pyridyl nitrogen (N donor atom) remains free. The dc magnetic susceptibility measurements show that the Cu and Mn ions are antiferromagnetically coupled in both and , with exchange coupling constants () of -20.57 ± 0.08 and -9.38 ± 0.08 cm, respectively. Among the four complexes, and show catechol oxidase and phenoxazinone synthase like catalytic activities. The turnover numbers () of complexes and for catecholase activity are 1121 and 720 h, respectively, at an optimum pH of 8.0 and for phenoxazinone synthase activity are 429 and 398 h, respectively, at an optimum pH of 9.7. The higher values of for both reactions are attributable to a water molecule coordinated to the central Mn atom that facilitates the substrate-catalyst binding. An ESI-mass spectral analysis indicates that trinuclear heterometallic species, e.g., [(CuL)Mn(nic)(HO)] for and [(CuL)Mn(nic)] for , are the active species that bind to the substrate, and on that basis, probable mechanisms through the formation of radical intermediates have been proposed.
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http://dx.doi.org/10.1021/acs.inorgchem.0c01733DOI Listing
October 2020

Complementary amide-based donor-acceptor with unique nano-scale aggregation, fluorescence, and bandgap lowering properties: a WORM memory device.

Nanotechnology 2020 Sep 21. Epub 2020 Sep 21.

Chemistry, University of Calcutta, Kolkata, West Bengal, INDIA.

Organic fluorescent semiconducting nanomaterials have gained widespread research interest owing to their potential applications in the arena of high-tech devices. We have designed two pyrazaacene-based compounds, their stacked system, the role of gluing interactions to fabricate nanomaterials, and determined the prospective bandgaps utilizing the DFT calculation. The two pyrazaacene derivatives containing complementary amide linkages (-CONH and -NHCO) were efficiently synthesized. The synthesized compounds are highly soluble in common organic solvents as well as highly fluorescent and photostable. The heterocycles and their mixture displayed efficient solvent dependent fluorescence in the visible region of the solar spectrum. Notably, the compounds were associated through complementary NH•••O=C type hydrogen bonding, π-π stacking, and hydrophobic interactions and thereby afforded nanomaterials with a low bandgap. Fascinatingly, the fabricated stacked nanomaterial system exhibited resistive switching behavior leading to the fabrication of an efficient write once read many times (WORM) memory device of crossbar structure.
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http://dx.doi.org/10.1088/1361-6528/abba5aDOI Listing
September 2020

Green Synthesis, Characterization and Application of Natural Product Coated Magnetite Nanoparticles for Wastewater Treatment.

Nanomaterials (Basel) 2020 Aug 18;10(8). Epub 2020 Aug 18.

Department of Chemistry, Cooch Behar Panchanan Barma University, Vivekananda Street, Cooch Behar 736101, West Bengal, India.

Adsorption of organic pollutants, toxic metal ions, and removal of harmful bacteria can give us clean and pure drinkable water from wastewater resources. Respective magnetite nanoparticles (MNPs) were synthesized using a cheaper and greener way in an open-air environment with the use of crude latex of (JC) and leaf extract of (CT). Characterization of MNPs had been performed by dynamic light scattering (DLS), Ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, powdered X-ray diffraction (XRD), and field emission scanning electron microscope (FE-SEM). The size ranges of the synthesized MNPs were observed in between 20-42 nm for JC-FeO and within 26-35 nm for CT-FeO by FE-SEM images. The effect of synthesized magnetic nanoparticles in wastewater treatment (bacterial portion), dye adsorption, toxic metal removal as well as antibacterial, antioxidant, and cytotoxic activities were studied. This purification will lead to an increase in the resources of pure drinking water in the future.
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http://dx.doi.org/10.3390/nano10081615DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7466664PMC
August 2020

Intrinsically Ultralow Thermal Conductivity in Ruddlesden-Popper 2D Perovskite CsPbICl: Localized Anharmonic Vibrations and Dynamic Octahedral Distortions.

J Am Chem Soc 2020 Sep 28;142(36):15595-15603. Epub 2020 Aug 28.

School of Advanced Materials and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India.

Fundamental understanding of the correlation between chemical bonding and lattice dynamics in intrinsically low thermal conductive crystalline solids is important to thermoelectrics, thermal barrier coating, and more recently to photovoltaics. Two-dimensional (2D) layered halide perovskites have recently attracted widespread attention in optoelectronics and solar cells. Here, we discover intrinsically ultralow lattice thermal conductivity (κ) in the single crystal of all-inorganic layered Ruddlesden-Popper (RP) perovskite, CsPbICl, synthesized by the Bridgman method. We have measured the anisotropic κ value of the CsPbICl single crystal and observed an ultralow κ value of ∼0.37-0.28 W/mK in the temperature range of 295-523 K when measured along the crystallographic -axis. First-principles density functional theory (DFT) analysis of the phonon spectrum uncovers the presence of soft (frequency ∼18-55 cm) optical phonon modes that constitute relatively flat bands due to localized vibrations of Cs and I atoms. A further low energy optical mode exists at ∼12 cm that originates from dynamic octahedral rotation around Pb caused by anharmonic vibration of Cl atoms induced by a 3s lone pair. We provide experimental evidence for such low energy optical phonon modes with low-temperature heat capacity and temperature-dependent Raman spectroscopic measurements. The strong anharmonic coupling of the low energy optical modes with acoustic modes causes damping of heat carrying acoustic phonons to ultrasoft frequency (maximum ∼37 cm). The combined effect of soft elastic layered structure, abundance of low energy optical phonons, and strong acoustic-optical phonon coupling results in an intrinsically ultralow κ value in the all-inorganic layered RP perovskite CsPbICl.
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http://dx.doi.org/10.1021/jacs.0c08044DOI Listing
September 2020

Ferroelectric Instability Induced Ultralow Thermal Conductivity and High Thermoelectric Performance in Rhombohedral -Type GeSe Crystal.

J Am Chem Soc 2020 Jul 30;142(28):12237-12244. Epub 2020 Jun 30.

Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S. A. S. Nagar, Manauli 140306, India.

The orthorhombic phase of GeSe, a structural analogue of layered SnSe (space group: ), has recently attracted attention after a theoretical prediction of high thermoelectric figure of merit, zT > 2. The experimental realization of such high performance in orthorhombic GeSe, however, is still elusive (zT ≈ 0.2). The rhombohedral phase of GeSe, a structural analogue of GeTe (space group: 3), previously stabilized at high pressure (2 GPa) and high temperature (1600 K), is promising due to its theoretically predicted ferroelectric instability and the higher earth abundance of Se compared to Te. Here, we demonstrate high thermoelectric performance in the rhombohedral crystals of GeSe, which is stabilized at ambient conditions by alloying with 10 mol % AgBiSe. We show ultralow lattice thermal conductivity (κ) of 0.74-0.47 W/mK in the 300-723 K range and high zT ≈ 1.25 at 723 K in the -type rhombohedral (GeSe)(AgBiSe) crystals grown using Bridgman method. First-principles density functional theoretical analysis reveals its vicinity to a ferroelectric instability which generates large anomalous Born effective charges and strong coupling of low energy polar optical phonons with acoustic phonons. The presence of soft optical phonons and incipient ferroelectric instability in (GeSe)(AgBiSe) are directly evident in the low temperature heat capacity () and switching spectroscopy piezoresponse force microscopy (SS-PFM) experiments, respectively. Effective scattering of heat carrying acoustic phonons by ferroelectric instability induced soft transverse optical phonons significantly reduces the κ and enhances the thermoelectric performance in rhombohedral (GeSe)(AgBiSe) crystals.
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http://dx.doi.org/10.1021/jacs.0c03696DOI Listing
July 2020

Development, Characterization and Pharmacological Evaluation of Antiblemish Cream Containing Herbal Oils.

Recent Pat Drug Deliv Formul 2020 ;14(3):223-232

Department of Pharmaceutics, Faculty of Pharmacy, M. S. Ramaiah University of Applied Sciences, Bengaluru -560054, Karnataka, India.

Background: Many topical agents are available in the market, which interfere with the pigmentation process at different levels. They are often known to cause side effects ranging from irritation to tumor over chronic use.

Objective: The present study was designed to develop and characterize an anti blemish cream containing herbal oils.

Methods: A herbal cream was formulated using dill, nagarmotha and black cumin oil and subjected to evaluation of its anti blemish potential against stress augmented UV-B rays-induced hyperpigmentation. Topical oil in water type of creams containing 2%, 4% and 6% of each oil was formulated using herbal oils. The formulated cream was characterized for solubility, pH, particle size, grittiness, viscosity, stability, phase separation, shelf life and spreadability, and found to be stable. Acute dermal toxicity was carried out individually for dill, nagarmotha and black cumin oil according to the OECD guidelines 402. Hyperpigmentation was induced in all the experimental animals by stress-augmented UV-B irradiation method. The animals were treated for 30 days (twice daily) with standard and test formulations by topical administration, whereas the disease group was left untreated. The skin of the animals was subjected to photographical study as well as grading for pigmentation and irritation before and after treatment. After the treatment period, the serum antioxidant levels were estimated and histopathology, histochemical studies of skin were performed.

Results: The animals treated with test formulations containing 2%, 4%, and 6% of herbal oil showed significant improvement in pigmentation compared to disease control as it is evident in photographic biochemical, histopathological and histochemical studies.

Conclusion: Thus, it was concluded that the developed anti-blemish cream containing herbal oils possesses significant anti-blemish potential. This study necessitates further evaluations in human subjects as it could have a high positive therapeutic value in the treatment of hyperpigmentation.
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http://dx.doi.org/10.2174/1872211314666200601163458DOI Listing
January 2020

Highly Converged Valence Bands and Ultralow Lattice Thermal Conductivity for High-Performance SnTe Thermoelectrics.

Angew Chem Int Ed Engl 2020 Jun 28;59(27):11115-11122. Epub 2020 Apr 28.

New Chemistry Unit, International Centre for Materials Science and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore, 560064, India.

A two-step optimization strategy is used to improve the thermoelectric performance of SnTe via modulating the electronic structure and phonon transport. The electrical transport of self-compensated SnTe (that is, Sn Te) was first optimized by Ag doping, which resulted in an optimized carrier concentration. Subsequently, Mn doping in Sn Ag Te resulted in highly converged valence bands, which improved the Seebeck coefficient. The energy gap between the light and heavy hole bands, i.e. ΔE decreases to 0.10 eV in Sn Ag Mn Te compared to the value of 0.35 eV in pristine SnTe. As a result, a high power factor of ca. 24.8 μW cm  K at 816 K in Sn Ag Mn Te was attained. The lattice thermal conductivity of Sn Ag Mn Te reached to an ultralow value (ca. 0.3 W m  K ) at 865 K, owing to the formation of Ag Te nanoprecipitates in SnTe matrix. A high thermoelectric figure of merit (z T≈1.45 at 865 K) was obtained in Sn Ag Mn Te.
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http://dx.doi.org/10.1002/anie.202003946DOI Listing
June 2020

The Effect of Guest Metal Ions on the Reduction Potentials of Uranium(VI) Complexes: Experimental and Theoretical Investigations.

Chemistry 2020 Feb 28;26(7):1612-1623. Epub 2020 Jan 28.

Department of Chemistry, University College of Science, University of Calcutta, 92 A.P.C. Road, Kolkata, 700 009, India.

Two mononuclear uranyl complexes, [UO L ] (1) and [UO L ]⋅0.5 CH CN⋅0.25 CH OH (2), have been synthesized from two multidentate N O donor ligands, N,N'-bis(5-methoxysalicylidene)diethylenetriamine (H L ) and N,N'-bis(3-methoxysalicylidene)diethylenetriamine (H L ), respectively, and have been structurally characterized. Both complexes 1 and 2 showed a reversible U /U couple at -1.571 and -1.519 V, respectively, in cyclic voltammetry. The reduction potential of the U /U couple shifted towards more positive potential on addition of Li , Na , K , and Ag metal ions to acetonitrile solutions of complex 2, and the resulting potential was correlated with the Lewis acidity of the metal ions and was also justified by theoretical DFT calculations. No such shift in reduction potential was observed for complex 1. All four bimetallic products, [UO L Li ](ClO ) (3), [UO L Na(ClO )] (4), [UO L Ag(NO )(H O)] (5), and [(UO L ) K(H O) ]PF (6), formed on addition of the Li , Na , Ag , and K metal ions, respectively, to acetonitrile solutions of complex 2, were isolated in the solid state and structurally characterized by single-crystal X-ray diffraction. In all the species, the inner N O donor set of the ligand encompasses the equatorial plane of the uranyl ion and the outer open compartment with O O' donor sites hosts the second metal ion.
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http://dx.doi.org/10.1002/chem.201904253DOI Listing
February 2020

Realization of Both n- and p-Type GeTe Thermoelectrics: Electronic Structure Modulation by AgBiSe Alloying.

J Am Chem Soc 2019 Dec 2;141(49):19505-19512. Epub 2019 Dec 2.

Successful applications of a thermoelectric material require simultaneous development of compatible n- and p-type counterparts. While the thermoelectric performance of p-type GeTe has been improved tremendously in recent years, it has been a challenge to find a compatible n-type GeTe counterpart due to the prevalence of intrinsic Ge vacancies. Herein, we have shown that alloying of AgBiSe with GeTe results in an intriguing evolution in its crystal and electronic structures, resulting in n-type thermoelectric properties. We have demonstrated that the ambient rhombohedral structure of pristine GeTe transforms into cubic phase in (GeTe)(AgBiSe) for ≥ 25, with concurrent change from its p-type electronic character to n-type character in electronic transport properties. Such change in structural and electronic properties is confirmed from the nonmonotonic variation of band gap, unit cell volume, electrical conductivity, and Seebeck coefficient, all of which show an inflection point around ∼ 20, as well as from the temperature variations of synchrotron powder X-ray diffractions and differential scanning calorimetry. First-principles density functional theoretical (DFT) calculations explain that the shift toward n-type electronic character with increasing AgBiSe concentration arises due to increasing contribution of Bi p orbitals in the conduction band edge of (GeTe)(AgBiSe). This cubic n-type phase has promising thermoelectric properties with a band gap of ∼0.25 eV and ultralow lattice thermal conductivity that ranges between 0.3 and 0.6 W/mK. Further, we have shown that (GeTe)(AgBiSe) has promising thermoelectric performance in the mid-temperature range (400-500 K) with maximum thermoelectric figure of merit, , reaching ∼1.3 in p-type (GeTe)(AgBiSe) at 467 K and ∼0.6 in n-type (GeTe)(AgBiSe) at 500 K.
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http://dx.doi.org/10.1021/jacs.9b11405DOI Listing
December 2019

Chitosan-grafted tetrapolymer using two monomers: pH-responsive high-performance removals of Cu(II), Cd(II), Pb(II), dichromate, and biphosphate and analyses of adsorbed microstructures.

Environ Res 2019 12 23;179(Pt B):108839. Epub 2019 Oct 23.

Advanced Polymer Laboratory, Department of Polymer Science and Technology, Government College of Engineering and Leather Technology (Post-Graduate), Maulana Abul Kalam Azad University of Technology, Salt Lake, Kolkata, 700106, West Bengal, India. Electronic address:

For circumventing the cumbersome and expensive multifunctional and multipolymer adsorbents for high-performance removals of hazardous water-contaminant(s), chitosan-g-[2-acrylamido-2-methyl-1-propanoic acid (AMPS)-co-2-(3-acrylamidopropanamido)-2-methylpropane-1-sulfonic acid (APAMPS)-co-2-(N-(3-amino-3-oxopropyl)acrylamido)-2-methylpropane-1-sulfonic acid (NAOPAMPS)-co-acrylamide (AM)] (i.e., chitosan-g-tetrapolymer), a multifunctional scalable and reusable hydrogel, was synthesized by grafting of chitosan and in situ attachments of N-H functionalized NAOPAMPS and APAMPS hydrophilic acrylamido-monomers during free-radical solution-polymerization of the two ex situ added AMPS and AM monomers in water. The response surface methodology was employed to synthesize one hydrogel envisaging the optimum balance between swelling and stability for the superadsorption of Cu(II), Cd(II), Pb(II), CrO, and HPO. The in situ attachments of NAOPAMPS and APAMPS, grafting of chitosan into tetrapolymer, structures and properties, pH-responsive abilities, superadsorption mechanism, and reusability were understood via in depth microstructural analyses of adsorbed and/or unadsorbed chitosan-g-tetrapolymer(s) through H/C NMR, FTIR, XPS, TGA, XRD, DLS, and pH. The maximum adsorption capacities of Cd(II), Cu(II), Pb(II), CrO, and HPO were 1374.41, 1521.08, 1554.08, 47.76, and 32.76 mg g, respectively.
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http://dx.doi.org/10.1016/j.envres.2019.108839DOI Listing
December 2019

Ultrathin Free-Standing Nanosheets of BiOSe: Room Temperature Ferroelectricity in Self-Assembled Charged Layered Heterostructure.

Nano Lett 2019 Aug 1;19(8):5703-5709. Epub 2019 Aug 1.

New Chemistry Unit , Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) , Jakkur, Bangalore 560064 , India.

Ultrathin ferroelectric semiconductors with high charge carrier mobility are much coveted systems for the advancement of various electronic and optoelectronic devices. However, in traditional oxide ferroelectric insulators, the ferroelectric transition temperature decreases drastically with decreasing material thickness and ceases to exist below certain critical thickness owing to depolarizing fields. Herein, we show the emergence of an ordered ferroelectric ground state in ultrathin (∼2 nm) single crystalline nanosheets of BiOSe at room temperature. Free-standing ferroelectric nanosheets, in which oppositely charged alternating layers are self-assembled together by electrostatic interactions, are synthesized by a simple, rapid, and scalable wet chemical procedure at room temperature. The existence of ferroelectricity in BiOSe nanosheets is confirmed by dielectric measurements and piezoresponse force spectroscopy. The spontaneous orthorhombic distortion in the ultrathin nanosheets breaks the local inversion symmetry, thereby resulting in ferroelectricity. The local structural distortion and the formation of spontaneous dipole moment were directly probed by atomic resolution scanning transmission electron microscopy and density functional theory calculations.
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http://dx.doi.org/10.1021/acs.nanolett.9b02312DOI Listing
August 2019

Investigation on the structure and thermoelectric properties of CuTe binary compounds.

Dalton Trans 2019 Jan;48(3):1040-1050

Thermoelectric Materials and Device Laboratory, Department of Physics, Indian Institute of Science, Bangalore, 560012, India.

Cu2Te is a superionic conductor that belongs to the Phonon Liquid Electron Crystal class of thermoelectric (TE) materials. Despite the simple chemical formula, the crystal structures and phases in the Cu2Te system have not been understood properly. In this work, we study the structural and TE properties of Cu2Te (CT2), Cu1.6Te (CT1.6) and Cu1.25Te (CT1.25). The samples were synthesized via a solid-state reaction method. Powder X-ray diffraction analysis revealed that the samples have different crystal structures depending upon the Cu : Te stoichiometry. The elemental compositional analysis showed that all the samples are copper deficient. This is due to the precipitation of metallic copper on the surface of the ingot arising from the thermal dissociation of Cu2Te. The transport properties were measured in the temperature range 300 K-600 K. The electrical conductivity (σ) decreases with an increase in temperature indicating a metal-like behaviour for all the samples. The positive Seebeck coefficients (S) for all the samples indicates that majority charge carriers are holes. The sample CT2 has a higher S (29.5 μV K-1 at 573 K) and a lower σ (2513 S cm-1 at 573 K) due to a lower carrier (hole) concentration compared to the other two samples. With the increase in Cu deficiency, the hole concentration increases, and this leads to higher electronic thermal conductivity in the samples CT1.6 and CT1.25. The maximum thermoelectric figure of merit of 0.03 at 524 K is achieved for the sample CT2 owing to its higher power factor (0.24 mW m-1 K-2) and lower thermal conductivity (3.8 W m-1 K-1). The present study bridges the gap between the theoretical predictions and experimental observations involving the various possible structures in this system. Furthermore, we have shown that the Cu vacancies are detrimental to the thermoelectric performance of Cu2Te.
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http://dx.doi.org/10.1039/c8dt04351eDOI Listing
January 2019

Exploitation of the Flexidentate Nature of a Ligand To Synthesize Zn(II) Complexes of Diverse Nuclearity and Their Use in Solid-State Naked Eye Detection and Aqueous Phase Sensing of 2,4,6-Trinitrophenol.

Inorg Chem 2018 Dec 5;57(24):15216-15228. Epub 2018 Dec 5.

Department of Chemistry, University College of Science , University of Calcutta , 92, A.P.C. Road , Kolkata 700 009 , India.

Three Zn(II) complexes, [Zn(HL)(NO)]·HO (1), [(ZnL)(μ-OH)](NO)·0.5HO (2), and [(ZnL)( o-van)(μ-OCH)(μ-OH)](NO) (3), have been synthesized by exploiting the flexidentate nature of a multidentate Schiff base ligand, HL ( N, N'-bis(3-methoxysalicylidene)diethylenetriamine), by changing the reaction conditions and stoichiometry of the reactants. All three complexes are highly fluorescent in solution as well as in solid and have been used as luminescence sensors toward nitrophenol explosives in both the media. In aqueous/methanol medium, these complexes show very high selectivity and sensitivity with detection limit in ppb (2.03) or nM level (8.89 nM) for picric acid. The yellow color of all three Zn(II) complexes changes to red on mixing with small amount (∼5%) of picric acid in solid state, revealing the potential of these complexes for practical use in naked eye detection of 2,4,6-trinitrophenol (TNP) or picric acid in ambient light. In order to identify the host-guest interactions between Zn(II) complex and TNP, single crystals of the adduct of TNP with Zn(II) complex, [Zn(HL)(HO)][CHNO] (4), were grown. Its X-ray crystal structure reveals that two picrate ions are attached to a dinuclear host with the help of H-bonding and π···π interactions, throwing light into the quenching mechanism and selectivity of detection.
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http://dx.doi.org/10.1021/acs.inorgchem.8b02497DOI Listing
December 2018

Stabilizing n-Type Cubic GeSe by Entropy-Driven Alloying of AgBiSe : Ultralow Thermal Conductivity and Promising Thermoelectric Performance.

Angew Chem Int Ed Engl 2018 Nov 15;57(46):15167-15171. Epub 2018 Oct 15.

New Chemistry Unit and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore, India.

The realization of n-type Ge chalcogenides is elusive owing to intrinsic Ge vacancies that make them p-type semiconductors. GeSe crystallizes into a layered orthorhombic structure similar to SnSe at ambient conditions. The high-symmetry cubic phase of GeSe is predicted to be stabilized by applying 7 GPa external pressure or by enhancing the entropy by increasing to temperature to 920 K. Stabilization of the n-type cubic phase of GeSe at ambient conditions was achieved by alloying with AgBiSe (30-50 mol %), enhancing the entropy through solid solution mixing. The interplay of positive and negative chemical pressure anomalously changes the band gap of GeSe with increasing the AgBiSe concentration. The band gap of n-type cubic (GeSe) (AgBiSe ) (0.30≤x≤0.50) has a value in the 0.3-0.4 eV range, which is significantly lower than orthorhombic GeSe (1.1 eV). Cubic (GeSe) (AgBiSe ) exhibits an ultralow lattice thermal conductivity (κ ≈0.43 W m  K ) in the 300-723 K range. The low κ is attributed to significant phonon scattering by entropy-driven enhanced solid-solution point defects.
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http://dx.doi.org/10.1002/anie.201809841DOI Listing
November 2018