Susobhan Biswas

Enhanced UV detection by transparent graphene oxide/ZnO composite thin films

All solution processed transparent thin films of graphene oxide (GO) and zinc oxide (ZnO) in different compositions prepared by a simple two-step chemical synthesis method have been studied for their UV detection properties. The preparation of GO through oxidation of graphite flakes is followed by sol–gel spin coating deposition of the GO–ZnO composite films on glass substrates. The surface morphology, microstructure and composition of the samples have been studied to confirm the formation of composite thin films comprising wurtzite-ZnO nanocrystallites and GO flakes. Optical studies demonstrate that both the transparency and optical band gap of the samples as estimated from wavelength dependent transmittance curves decrease with the increase of GO content in the films, while the charge carrier concentration increases by 5 fold. The in-plane current–voltage (I–V) measurements with two silver electrodes on the GO–ZnO film show a significant enhancement of the photosensitivity in comparison to ZnO films when they are exposed to UV light of different intensities. The response time (t90-response) is nearly three times smaller for GO–ZnO composite films as compared to that of pure ZnO. This improvement is attributed to the defect state modulation and carrier density improvement of the thin films with incorporation of GO, which is encouraging to propel optical, electrical and hence optoelectronics applicability of ZnO composite based transparent devices.

Synthesis, characterization, and density functional study of some manganese(III) Schiff-base complexes

Some Mn(III) complexes of N,N′-(2-hydroxy)propylenebis(acetylacetoneimine) (abbreviated to H2L1) and N,N′-(2-hydroxy)propylenebis(2-imino-3-oximino)butane (abbreviated to H2L2), [Mn(III)(Lig)(X)] (where Lig stands for the dianion of the Schiff-base ligands and X stands for CH3COO−, Cl−, Br−, I−) were synthesized. The complexes are characterized with the help of elemental analyses, magnetic moments, spectroscopic data (UV-Vis, infrared), and molecular weight determination (measured by Rasts method). The structures of the complexes were obtained using density functional theory (DFT). DFT calculation shows that 1–4 and 8 are trigonal-bipyramidal whereas 5–7 are square-pyramidal.

Synthesis and characterization of oxovanadium(IV), vanadium(IV) and oxovanadium(V) complexes of tetradentate Schiff bases. Attempted preparation of vanadium-carbon bonded compounds through desilylation

Condensation of 1,3-diaminopropane-2-ol with diacetylmonoxime, acetylacetone, salicylaldehyde and orthohydroxyacetophenone yielded the tetradentate Schiff bases N,N′-(2-hydroxy)propylenebis{(2-imino-3-oximino)butane} (H2dampnol), N,N′-(2-hydroxy)propylenebis(acetylacetoneimine) (H2acacpnol), N,N′-(2-hydroxy)propylenebis-(salicyalaldimine) (H2salpnol) and N,N′-(2-hydroxy)propylenebis(7-methylsalicylaldimine) (H2ohacpnol), respectively. The ligands form complexes with oxovanadium(IV), vanadium(IV) and oxovanadium(V) salts. Some mixed ligand complexes involving σ-bonded phenyl and benzyl radical along with tetradentate ligand, H2L (where, H2L stands for H2dampnol, H2acacpnol, H2salpnol or H2ohacpnol) of the types [(L)V(C6H5)2]CH3OH and [(L)V(CH2Ph)2]CH3OH have been synthesized, characterized and also provide the syntheses of some new organovanadium(IV) complexes. Silylation coupled with desilylation have been employed as a route to new organovanadium(IV) complexes. All the complexes have been characterized with the help of elemental analyses, molar conductance values, molecular weights, magnetic moments and spectroscopic (IR, UV-Vis, ESR) data.

Synthesis, characterization and coordination behavior of 2-(1-carboxyl-2-hydroxyphenyl)thiazolidine

The reaction of 3-formylsalicylic acid with 2-aminoethanethiol produces 2-(1-carboxyl-2-hydroxyphenyl)thiazolidine (H2chptz) which remains in equilibrium in solution with its corresponding Schiff base, 3-carboxysalicylidenethioethanolimine (H3mcsalim) having an NSO-donor set of atoms. The reactions of the thiazolidine ligand with different metal salts leading to the synthesis of many new metal complexes and organometallic derivatives have been studied. For all the complexes the dianion of the Schiff base, H3mcsalim acts as a tridentate NSO donor ligand. The reactions of [(Hmcsalim)Ti(π-C5H5)Cl] and [(Hmcsalim)Sn(Me)Cl], isolated in this study, with Me3SiE (where, E stands for SMe, NMe2 and C≡CPh) have also been studied. The elemental analyses, magnetic susceptibilities, molar conductance values, EPR-study, CV, molecular weights and spectroscopic (UV-Vis, IR, 1H NMR) data characterize all the compounds under study. Based upon these data the geometry of the compounds has also been proposed.

Synthesis and Characterization of Some Mononuclear Complexes of the Schiff Base {N,N′‐2,2′‐Bis(Aminoethyl)Methylaminebis‐(3‐Carboxysalicylaldimine)}

Reaction of 3‐formylsalicylic acid with diethylenetriamine yielded the Schiff base {N,N′–2,2′‐bis(aminoethyl)methylaminebis(3‐carboxysalicylaldimine)}, abbreviated as H4fsadien. The interaction of H4fsadien with CoCl2 · 6H2O, Ni(OAc)2 · 4H2O, Cu(OAc)2 · H2O, Zn(OAc)2 · 2H2O, Na2MoO4 · 2H2O, WO2(acac)2, (NH4)2[MoOCl5], (pyH)2[Mo(SCN)6], FeSO4 · 7H2O and FeCl3 · 6H2O under varied reaction conditions have been studied. The reactions of some of the new metal complexes isolated in this study have also been investigated with a view to develop new preparative methods. The Schiff base H4fsadien was found to act as a dibasic tetradentate ligand or as a dibasic pentadentate ligand, by using N2O2 or N3O2 donor sites, respectively. Elemental analyses, molecular weights, magnetic moment values, molar conductances and spectroscopic (IR, UV‐Vis and 1H NMR) data characterize the complexes. The authors are thankful to the Regional Sophisticated Instrumentation Centre, the Central Drug Research Institute, Lucknow, for elemental analyses and spectroscopic data. One of the authors (SS) is grateful to the University of Kalyani for Junior Research Fellowship.

Synthesis and characterization of a new thiohydrazone ligand, 3-carboxy-2-hydroxybenzaldehydemorpholine N-thiohydrazone and its metal complexes

The reaction of 3-formylsalicylic acid with morpholine N-thiohydrazide in ethanol leading to the formation of a new thiohydrazone, 3-carboxy-2-hydroxybenzaldehydemorpholine N-thiohydrazone (H2chbmth) is described. This thiohydrazone ligand remained as the thio-keto form in the solid state. However, thioketo- and a small amount of the thiol-tautomeric forms (H2chbmth and H3chbmthol, respectively) remain in equilibrium in solution. The reactions of the ligand with different metal salts (in 1 : 1 molar ratio) leading to the synthesis of many new metal complexes have been studied. Depending on pH of the reaction medium and the nature of the metal salt used, the ligand is found to be monobasic tridentate, dibasic tridentate, monobasic bidentate or neutral bidentate giving complexes [Co(H2chbmth)2]X2, [X = NO3 (11), ½SO4 (13)]; [Cd(H2chbmth)(H2O)2]SO4 (21); [M(Hchbmth)X], [M = Cu(II) and X = Cl (1), NO3 (2), CH3COO (4); M = Ni(II) and X = Cl (6), NO3 (7); M = Co(II) and X = NO3 (12), CH3COO (14); M = Zn and X = Cl (17), CH3COO (18); M = Hg(II) and X = Cl (23), CH3COO (24)]; [Ni(H2chbmthol)(acac)] (9); [Co(Hchbmth)Cl]·2H2O (10), [Cu(Hchbmth)H2O]½SO4 (3); [Cu(Hchbmthol)]2 (5); [M(Hchbmthol)X], [M = Ni(II) and X = H2O (8); M = VO(II) and X = H2O (15); M = Pd(II) and X = H2O (16); M = Zn(II) and X = NH3 (19); M = Cd(II) and X = H2O (20), NH3 (22); M = Hg(II) and X = NH3 (25)]. In situ reactions of metal salts with the ligand components (i.e. 3-formylsalicylic acid and morpholine N-thiohydrazide) in ethanol resulted the same complexes. The complexes are characterized by elemental analyses, magnetic susceptibilities, molar conductances, molecular weights and spectroscopic (IR, ESR, 1H NMR and UV-visible) data.

A pharmaceutical cocrystal with potential anticancer activity

The design of pharmaceutical cocrystals has become a prime thrust of crystal engineering and the pharmaceutical industry in recent times – but the use of pharmaceutical cocrystals as regular drugs is yet to be explored. Quinoxaline acts as a basic skeleton of several potential anticancer drugs. We have successfully cocrystallized quinoxaline with another organic molecule 3-thiosemicarbano-butan-2-one-oxime (TSBO, a virus replication inhibitor) and examined the anticancer activity of the cocrystal. The crystal structure of the cocrystal was determined by single crystal X-diffraction study. According to thermogravimetric study the cocrystal exhibits better thermal stability than quinoxaline. UV-Vis spectroscopic study has shown that in solution state the behavior of the cocrystal and the physical mixture of its components (mixture of quinoxaline and TSBO) are significantly different. The solubility of the cocrystal in distilled water has been found to be 31.9 mg mL−1. The cocrystal exhibits a specific cytotoxic effect on lung cancer cells (A549) at 10−7 M concentration while it shows growth inhibitory effect on normal cells. The detailed mechanistic study of the cytotoxicity of the cocrystal suggests that it follows the mitochondrial mediated cell death pathway through activation of Caspase 9 and Bax. It also shows anticancer activity on breast cancer cells (MCF-7).

Co-crystals of 2,3-Dimethylquinoxaline (DMQ) and Dimethylglyoxime (DMG) in 1:1 and 1:2 Ratios and Hirshfeld Surface Analysis

Two co-crystals of 2,3-dimethylquinoxaline (DMQ) and dimethylglyoxime (DMG) have been synthesized and characterized by single crystallographic X-ray, IR and thermal studies. Co-crystal I is colorless while co-crystal II is orange in color. In the co-crystals, both hydrogen-bonding and π··· interactions assemble both DMQ and DMG within the crystal structure. For co-crystal I, 2D supramolecular sheet structure is formed by utilizing both hydrogen bonding and π··· interactions, while for co-crystal II supramolecular 1D chain motifs are formed by O–H···N hydrogen bonding interactions which are held together by C–H···O interactions to form 2D supramolecular network. These 2D supramolecular networks are further stacked by π···π and C–H···π interactions of aromatic rings of DMQ leading to the formation of 3D supramolecular structure. Examination of the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that most of the close contacts are associated with weak interactions. The fingerprint plots indicate that these weak interactions have significant role in crystal packing. Thermogravimetric analyses of the co-crystals have been carried out.Graphical AbstractTwo concomitant co-crystals of active pharmaceutical ingredients (API) 2,3-dimethylquinaxoline (DMQ) and co-crystallizing agent dimethylglyoxime (DMG) have been synthesized and characterized by X-ray crystal structure, IR analysis along with their detailed Hirshfeld surfaces analyses.

Synthesis and Characterization of Some New Manganese(II) Complexes, Manganese(III) Heterochelates, and µ‐Dioxo‐dimanganese(IV) Complexes Involving Tetradentate Schiff Bases

Abstract Condensation of 1,3‐diaminopropane‐2‐ol with diacetylmonoxime and acetylacetone yielded the tetradentate Schiff bases N,N′‐(2‐hydroxy)propylene‐bis{(2‐imino‐3‐oximino)butane} (H2L1) and N,N′‐(2‐hydroxy)propylene‐bis(acetylacetoneimine) (H2L2), respectively. The ligands form mononuclear manganese(II) complexes of the type [Mn(II)(L1)] (1) and [Mn(II)(L2)] (3), which are used for the formation of the manganese(III) heterochelates of the type [Mn(III)(L)(L‐L)] (where H2L = H2L1 or H2L2; L‐L = anion of acetylacetone or salicylaldehyde). Cationic heterochelates of the type [Mn(L)(L‐L)]ClO4 where H2L = H2L1 or H2L2 and L‐L = ethylenediamine and N,N′‐propylene‐bis(benzaldimine) (L3) have been synthesized by the reactions of bis(acetylacetonato)manganese(II) or bis(salicylaldehydato)manganese(II) with the preformed Schiff bases or by the reactions of [Mn(II)(L1)] or [Mn(II)(L2)] with L‐L in absolute alcohol under reflux. Some of the complexes, synthesized here, may be used as precursors in the synthesis of higher nuclearity manganese complexes. Air oxidation of [Mn(II)(L1)] (1) and [Mn(II)(L2)] (3) in DMF yielded the dark‐brown µ‐dioxo‐bis‐[N,N′‐(2‐hydroxy)propylene‐bis{(2‐imino‐3‐oximino)butane}]dimangenese(IV) (2) and µ‐dioxo‐bis[N,N′‐(2‐hydroxy)propylene‐bis{(acetylacetoneimine)}]dimangenese(IV) (4) complexes, respectively. All of the complexes have been characterized with the help of elemental analyses, molar conductance values, molecular weights, magnetic moments, and spectroscopic (IR, UV‐VIS, ESR) data.

Oxygen transfer from peroxometalates as a new and general route to the synthesis of oxopolymetalates: rational synthesis of Mo2O72-, MO6O192- and MO7O246-. Evidence of a M2O72- with linear M-O-M axis

Abstract The oxopolymolybdates, [Mo 2 O 7 ] 2- , [Mo 6 O 19 ] 2- and [Mo 7 O 24 ] 6- have been obtained via oxygen transfer reaction from a peroxomolybdate [Mo 2 O 2 (μ 2 -O)(O 2 ) 4 (H 2 O) 2 ] 2- , obtained by the treatment of HOOH on MoO 3 . In the case of dimolybdate, the oxygen acceptor is Ph 3 P, while Ph 3 GeCI functions as an oxygen receptor for the generation of higher polymolybdates. Three dimensional X-ray structure analysis indicates that (PPN) 2 [MO 2 O 7 ] contains a linear Mo-O-Mo axis and MoO 3 oxygens in each fragment are staggered with respect to those of the other. The structural identity of the PPh 4 and PPN salts of hexamolybdate and the PPh 4 salt of heptamolybdate has been established by their superimposable X-ray powder diffractogram with those of the respective authentic samples prepared. This work presents further evidences in favour of our recent contention that peroxometalates serve as a useful precursor intermediate for the synthesis of oxopolymetalates.