Browsing by Author "Ajit N. Gupta"

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Cooperative influence of ligand frameworks in sustaining supramolecular architectures of Ni(II)/Pd(II) heteroleptic dithio-dipyrrin complexes via non-covalent interactions
(Elsevier Ltd, 2015) Vinod Kumar; Vikram Singh; Ajit N. Gupta; Santosh Kumar Singh; Michael G.B. Drew; Nanhai Singh
The impact of the ligand frameworks on the crystal stabilization of the novel heteroleptic complexes [M(bzdpm)(xant)] (M = Ni(II) 1, Pd(II) 2, xant- = 4-methoxyphenylethylxanthate, bzdpmH = 5-benzyl dipyrromethene) and [Ni(dmbzdpm)(dtc)] 3 (dmbzdpmH = 5-N,N-dimethylbenzyl dipyrromethene; dtc- = N-pyridyl-N-ferrocenylmethyl dithiocarbamate) has been investigated. In these planar complexes, the supramolecular structures of 1 and 2 are stabilized via C-H⋯O and CH⋯π interactions. The structure of 3 revealed a centrosymmetric dimer formed by two C-H...N intermolecular hydrogen bonds between the nitrogen atom of the pyridyl group and a hydrogen atom on a neighboring molecule. The dimers thus formed are held together by C-H...π (NiCS2, chelate) interactions, sustaining a 2-D supramolecular architecture and constructing an unprecedented cyclic analog of benzene. The intermolecular interaction energies for the C-H...N and C-H...π (NiCS2, chelate) interactions have been estimated to assess their nature. The palladium complex 2 shows luminescent characteristics in solution at room temperature. © 2015 Elsevier Ltd. All rights reserved.
Effect of pyridyl substituents leading to the formation of green luminescent mercury(ii) coordination polymers, zinc(ii) dimers and a monomer
(Royal Society of Chemistry, 2014) Vikram Singh; Vinod Kumar; Ajit N. Gupta; Michael G.B. Drew; Nanhai Singh
Pyridine-2, -3 and -4 functionalized dithiocarbamate ligands yielded the coordination polymers with mercury, namely [{Hg(L)2}n] (L = L1, C5H4NCH2NCS2CH 2C7H5O2 (1); L2, C5H 4NCH2NCS2CH3 (2); L3, C 5H4NCH2NCS2CH2C 4H3O (3); and L4, C5H4NCH 2NCS2CH2CH2C6H 5 (4)), [PhHg(L3)] (5), and mononuclear [Hg(L5)2], L5 = C5H4NCH2NCS2CH2C 6H5 (6). Unexpectedly, the pyridine-2-functionalized ligand, L6, C5H4NCH2NCS2CH 2C6H5 gave a cyclized product, benzyl-2H-imidazo[1,5-a]pyridine-3-thione (7), C14H 13N2S, instead of a mercury complex. Complexes with zinc were also characterized, namely dinuclear [Zn2(L5)4] (8) and [Zn2(L7)4], L7 = CH3CH2O 2C5H9NCS2 (9) and a mononuclear complex [Zn(L8)2], L8 = C4H3NCH 3CH2NCS2CH2C6H 5 (10). These ten compounds have been characterized by microanalysis and X-ray crystallography. Complexes (1, 2) and 3 are 1-D and 2-D coordination polymers in which the ligands are uniquely bonded in the bridging-chelating mode in a μ2, κ3-N, S, S fashion establishing square pyramidal five-coordinate and octahedral six-coordinate geometries about the Hg atom respectively. The structure of 4 is also a 1-D coordination polymer formed via bridging sulphur bonds with a five-coordinate distorted geometry about the mercury atom. 6 is a mononuclear mercury(ii) complex forming an interesting polymeric 1-D architecture through intermolecular Hg⋯S interactions. 8 is the first example of a homoleptic dinuclear zinc(ii) dithiocarbamate complex bridged through ligand L5 in a μ2, κ3-N, S(11), S(13) bridging-chelating manner. L7 and L8 form a typical S, S-bridged dimer 9 and a mononuclear complex 10. The nature of the Hg-N and Zn-N bonds in the coordination polymers 1, 2 and 3 and in the dinuclear 8 has been assessed by DFT calculations. Complexes 1-9 are luminescent in both solution and solid phases; especially, significant red shifted green emission in the solid phase for the coordination polymers 1, 2 and 3 shows good structure-property correlations. © 2014 the Partner Organisations.
Exploring the coordinative behaviour and molecular architecture of new PhHg(II)/Hg(II) dithiocarbamate complexes
(Elsevier S.A., 2014) Manoj K. Yadav; Gunjan Rajput; Ajit N. Gupta; Vinod Kumar; Michael G.B. Drew; Nanhai Singh
New dithiocarbamate (dtc) complexes of the form [(PhHg)2L] (L = bis(furfurylaminomethyl)benzene dtc L1 (1)), [PhHg(L)] (L = ethyl-1- piperazinecarboxylate dtc L2 (2), thiomorpholine dtc L3 (3), N-(N-methyl-2-pyrrole)-N-(methyl-3-pyridyl) dtc L4 (4), N-(N′-methyl-2- pyrrole)-N-(methyl-benzyl) dtc L5 (5)) and [Hg(L)2] (L = bis(N-methyl-3-pyridyl) dtc L6 (6), L4 (7), L5 (8)) have been synthesized and fully characterised; their structures revealed by X-ray crystallography. 1-5 show similar structures with the metal atoms forming two strong bonds, to carbon and one sulfur atom from the bidentate ligand in an approximate linear arrangement with an additional weak bond to the second sulfur atom. However the complexes show very different packing arrangements. 1 is a less common type of dinuclear organomercury complex containing two dithiocarbamate units linked by a 1,4-dibenzyl group. In 6, the metal lies at the centre of a distorted square plane coordinated by two L6 ligands, axially bonded by sulfur atoms on the adjacent molecules in a 2-D polymeric chain. In 7 and 8 the Hg atom is tetrahedrally coordinated to four sulfur atoms from two bidentate ligands. Complexes 2, 5, 7 and 8 show luminescence in solution. © 2014 Elsevier B.V. All rights reserved.
Highly efficient and recyclable pre-catalysts based on mono- and dinuclear heteroleptic Cu(I) dithio- PPh3 complexes to produce variety of glycoconjugate triazoles
(Elsevier B.V., 2019) Avadhesh K. Singh; Chote Lal Yadav; Kunj Bihari Mishra; Santosh K. Singh; Ajit N. Gupta; Vinod Kumar Tiwari; Michael G.B. Drew; Nanhai Singh
Highly efficient and reusable pre-formed mono- and dinuclear heteroleptic copper(I) dithiocarbamate and dithiocarbimate complex based catalysts, [Cu(PPh3)2(L)] and [Cu2(PPh3)4(L)] (L = N-(4-methylpyridyl)-N-(3-methylpyridyl)dithiocarbamate− L1 1, N-methylfuryl-N-methylthiophenedithiocarbamate- L2 2; 4-chlorobenzenesulfonyl dithiocarbimate2- L3 3, 4-bromobenzenesulfonyldithiocarbimate2- L4 4) have been utilized in the cycloaddition reactions of azide and alkyne to form a variety of glycoconjugate triazoles in Click chemistry. These new pre-catalysts have been characterized by elemental (C, H, N) analysis, IR, UV–vis., 1H, 13C{1H}, and 31P{1H} NMR spectroscopy and their structures have been revealed by X-ray crystallography. In the structures of (1,2)/(3,4) the copper atoms are situated within a four coordinate (P2S2)/(P2NS) distorted tetrahedral geometry. Notably in the dinuclear complexes 3 and 4, the dithiocarbimate ligands are bonded in a S, S- chelating mode to one copper atom and simultaneously bridge the other copper centre via N, S- donor atoms. 1-4 are strongly luminescent in CH2Cl2 solution at room temperature. © 2019 Elsevier B.V.
Impact of ferrocenyl and pyridyl groups attached to dithiocarbamate moieties on crystal structures and luminescent characteristics of group 12 metal complexes
(Elsevier B.V., 2016) Vinod Kumar; Krishna K. Manar; Ajit N. Gupta; Vikram Singh; Michael G.B. Drew; Nanhai Singh
Metal-directed self assembly of ferrocenyl based pyridyl functionalized dithiocarbamates afforded the novel macrocyclic metal-organic coordination polymers, [M(L)2]∞(M = Zn(II), L = L2 (N-ferrocenylmethyl-N-pyridin-4-ylmethyl) dithiocarbamate 2, M = Cd(II), L = L1 (N-ferrocenylmethyl-N-pyridin-3-ylmethyl) dithiocarbamate 3); dimers [M(L1)2]2(M = Zn(II) 1, Hg(II) 4) and a mononuclear [Cd(L2)(phen)], (phen = 1,10-phenanthroline) complex 5. These complexes have been characterised by elemental analysis, IR, UV–Vis.,1H and13C NMR spectroscopy and their structures have been investigated by X-ray crystallography. In 2 and 3 the metal ions are six-coordinate with two bidentate dithiocarbamate ligands L1 and L2 in an equatorial plane and axially bonded by two Py(N) of the dithiocarbamate ligands on neighbouring molecules thus establishing distorted octahedral geometry (MS4N2) in 2-D polymeric structures. In L1 where the Py(N) is in the 3-position, a centrosymmetric dinuclear complex 1 is formed in which the metal ions adopt square pyramidal geometry. In 1–4, the dithiocarbamate ligands are uniquely bonded to the metal centres in a μ2, κ3-N, S, S bridging-chelating manner. In all the complexes the supramolecular structures are sustained via [Formula presented] … π (MS2C, chelate) interactions. These unusual interactions have been supported by theoretical calculations. All the complexes show luminescent emissions in the solid phase. © 2016 Elsevier B.V.
Influence of functionalities on the structure and luminescent properties of organotin(IV) dithiocarbamate complexes
(Elsevier, 2015) Ajit N. Gupta; Vinod Kumar; Vikram Singh; Amit Rajput; Lal Bahadur Prasad; Michael G.B. Drew; Nanhai Singh
Five new organotin(IV) dithiocarbamate complexes of the form R2SnL2 (R = nBu, L = L1, (4-phenylpiperazine-1-dithiocarbamate) 1, L2, (N-benzyl-N′-methyl-4-pyridyldithiocarbamate) 2; Ph, L3, (N-benzyl-N′-methyl-3-pyridyldithiocarbamate) 3) and Ph3SnL (L = L4, (N,N′-di(methyl-3-pyridyldithiocarbamate)) 4, L5, (4-ethoxycarbonylpiperidine-1-dithiocarbamate) 5) have been synthesized and characterized by elemental analysis, spectroscopy (IR, UV-Vis., 1H, 13C and 119Sn NMR) and their structures have been investigated by single crystal X-ray crystallography. In (1,2) the structure has C2 symmetry with the tin atom in a highly distorted octahedral six-coordinate geometry in which the bidentate ligands are asymmetrically bonded and the two nBu groups subtend an angle at the metal of 140.7(1), 141.4(3)°. By contrast 3, also with C2 symmetry, with phenyl substituents, is closely octahedral. In 3 the Py(N) on the dtc backbone interacts with the H37 on the adjacent molecule via unconventional C-H-N hydrogen bonding forming a six membered benzene like (C2H2N2) structure. In 4 and 5 five coordinate TBP geometry is established; 4 contains two molecules in the asymmetric unit (4A and 4B). In 4 the Py(N) on the dithiocarbamate unit uniquely interacts with the tin atom on the neighbouring molecule with Sn-N contacts at 3.11 Å. The C-H-π (CG) interactions between CG of 4A and H34 of 4B are also observed. These interactions have been supported by theoretical calculations. All the complexes luminesce in CH2Cl2 solution at room temperature except for 1; the strongest luminescent behaviour is found in 4. TGA analysis of 3 and 5 show a double and single step decomposition respectively. © 2015 Elsevier B.V.
Influence of ligand environment on the structure and properties of silver(I) dithiocarbamate cluster-based coordination polymers and dimers
(Royal Society of Chemistry, 2014) Vinod Kumar; Vikram Singh; Ajit N. Gupta; Krishna K. Manar; Lal Bahadur Prasad; Michael G. B. Drew; Nanhai Singh
Luminescent silver(i) homo- and heteroleptic pyridyl functionalised dithiocarbamate (dtc) complexes of the form, [{Ag(L)}4] ∞ (L = N-benzyl-N-methylpyridyldtc (L1) 1, bis-(N- methylpyridyl)dtc (L2) 2) and [Ag(L)PPh3]2 (L = L1 (3), L2 (4)) have been synthesized and characterized by elemental analysis, TGA, spectroscopy (IR, 1H, 13C and 31P NMR and UV-Vis) and X-ray crystallography. Complexes 1 and 2 are isomorphous and have a tetranuclear cluster-based coordination polymeric structure. In these tetranuclear silver(i) cluster subunits the four Ag atoms form a distorted tetrahedron. Complexes 3 and 4 are also isostructural and have centrosymmetric structures in which each Ag atom forms a distorted tetrahedral coordination geometry. All complexes are weakly conducting and exhibit semiconductor behaviour. 1-4 are strongly luminescent in solid phase; a correlation between their structure and luminescent properties has been established. © the Partner Organisations 2014.
Influence of ligand environments on the structures and luminescence properties of homoleptic cadmium(ii) pyridyl functionalized dithiocarbamates
(Royal Society of Chemistry, 2014) Vinod Kumar; Vikram Singh; Ajit N. Gupta; Krishna K. Manar; Michael. G.B. Drew; Nanhai Singh
Novel homoleptic pyridyl-3(N) functionalised dithiocarbamate complexes having polymeric, [Cd(L)2] (L = L1, C5H 4NCH2NCS2CH2C6H 5 (1), L2, (C5H4NCH2) 2NCS2 (2), L3, C5H4NCH 2NCS2CH2C4H3O (3) and L4, C5H4NCH2NCS2CH2C 4H3S (4)); dinuclear, [Cd(L)2]2 (L = L5, (C8H6NCH2NCS2CH 2NC5H4) (5)) and trinuclear, [Cd(L6) 2]3 (L6 = CH3C6H4CH 2NCS2CH2C4H3O) (6)) structures have been synthesised and characterized by elemental analysis, IR, UV-vis, and 1H and 13C NMR spectroscopy and their structures have been elucidated by X-ray crystallography. In 1-4, the cadmium(ii) ions are six-co-ordinate with two bidentate dithiocarbamate ligands (L1-L4) in an equatorial plane and axially bonded by Py(N) of the dithiocarbamate ligands on adjacent molecules, thus adopting a distorted octahedral geometry (CdS4N2) in 2-D polymeric structures. Complexes 1 and 2 are isomorphous and have similar structures to those of 3 and 4, although they differ significantly in architecture and topology. In 3 and 4, the metal atoms occupy centrosymmetric sites. In marked contrast to these polymeric structures, complex 5 derived from ligand L5 containing a bulky indolyl substituent proved to be a dinuclear complex. In 5, the metal atom has a square pyramidal geometry. As in 1-4, the dithiocarbamate ligand in 5 is uniquely bonded to the metal centres in a μ2,κ3- N,S,S bridging-chelating fashion. Ligand L6 containing furfuryl and tolulyl substituents yielded a spectacular centrosymmetric trinuclear complex 6 with the central metal atom in an octahedral environment and the two outer metal atoms in square pyramidal environments in which the dithiocarbamate ligands are bonded in a μ2,κ2-S,S chelating-bridging and S,S chelating manner within the same molecule. To the best of our knowledge, 1-4 and 5 and 6 are the first examples of 2-D coordination polymeric, dinuclear and trinuclear cadmium dithiocarbamates. All the complexes show bright luminescence emission in the solid state; the coordination polymers 1 and 2 are strongly luminescent. This journal is © the Partner Organisations 2014.
Intermolecular anagostic interactions in group 10 metal dithiocarbamates
(Royal Society of Chemistry, 2014) Ajit N. Gupta; Vinod Kumar; Vikram Singh; Krishna K. Manar; Michael G. B. Drew; Nanhai Singh
New functionalized homoleptic xanthate and dithiocarbamates of the form [M(L)2] (M = Ni(ii), L = L1 (4-methoxyphenethylxanthate) 1, L2 (4-ethoxycarbonylpiperidine-1-dithiocarbamate) 2, L3 (N,N′-difurfuryldithiocarbamate) 3; M = Pt(ii), L3, 4, M = Pd(ii), L4 (N-benzyl-N′-3-methylpyridyldithiocarbamate) 5) have been synthesized and characterized using microanalyses, and their structures have been investigated by X-ray crystallography. All five complexes are centrosymmetric with the central metal in a distorted square planar structure; the distortion varies in the order Pt > Pd > Ni. In 3, 4 and 5 the ligand framework and crystal packing effects force the methylene proton on the substituents into close proximity with the metal centers, forming intermolecular C-H⋯M (M = Ni, Pt and Pd) anagostic interactions and generating a 1-D polymeric chain; 4 and 5 are the first examples containing Pt and Pd that exhibit such interactions. Similar anagostic interactions are also observed in 2 but are rather weaker. These interactions have been supported by theoretical calculations. The xanthate complex 1 displays unique S⋯S intermolecular interactions leading to a 1-D polymeric chain, while no significant intermolecular interactions involving the metal centres have been found. The supramolecular structures are sustained by weaker O⋯H, S⋯H, C-H⋯π and C-H⋯π (chelate, CS2M) interactions. 1 is weakly conducting (σrt = 1.39 × 10-7 S cm-1) but shows semiconductor behaviour in the 303-363 K range. The platinum complex 4 shows luminescent properties in solution. This journal is © the Partner Organisations 2014.
Intermolecular Tl⋯H-C anagostic interactions in luminescent pyridyl functionalized thallium(i) dithiocarbamates
(Royal Society of Chemistry, 2015) Vinod Kumar; Vikram Singh; Ajit N. Gupta; Michael G. B. Drew; Nanhai Singh
Crystal structures of novel pyridyl functionalised [Tl(L)]∞ (L = (N-benzyl-N-methylpyridyl) dithiocarbamate(L1) 1, bis(N-methylpyridyl) dithiocarbamate(L2) 2, (N-methyl(1,4-benzodioxane-6-yl)-N-methylpyridyl)dithiocarbamate(L3) 3, (N-ferrocenyl-N-methylpyridyl) dithiocarbamate(L4) 4) complexes revealed rare intermolecular C-H⋯Tl anagostic and C-S⋯Tl interactions forming a six-membered chelate ring about the metal center, which have been assessed by DFT calculations. The strong thallophilic bonding is responsible for the strong luminescent characteristics of the complexes in the solid phase. This journal is © 2015 The Royal Society of Chemistry.
Microstructure, dielectric and ferroelectric properties of CaCu3-xZnxTi4-xCexO12 ceramics prepared via semi-wet route
(University of Novi Sad, Faculty of Technology, 2024) Anuj Kumar Gond; Atendra Kumar; Anees A. Ansari; Sunil Kumar; Sumit Kumar; Ajit N. Gupta; Akhilesh Kumar; Youngil Lee; Kamdeo Mandal; Himanshu Shekher; Laxman Singh
In this work, the effect of bi-substitution of Zn and Ce at Cu and Ti sites on microstructure and dielectric properties of CaCu3Ti4O12 ceramics was investigated. The doped CaCu3-xZnxTi4-xCexO12 (CCZTC-x) powders (where x = 0.1, 0.2 and 0.3) were successfully synthesized via semi-wet route and the corresponding ceramics were obtained by sintering at 950°C for 14 h in air. The presence of major cubic CaCu3Ti4O12 phase along with minor secondary CuO phase was observed by X-ray diffraction analysis. Scanning electron microscopy analyses confirmed microstructure consisting of cubic-shaped grains and grain sizes of 0.76, 0.87 and 0.98 μm, for the ceramics with x = 0.1, 0.2 and 0.3, respectively. The high value of relative dielectric constant of 1500 at 100Hz was found for the sample with x = 0.3, which may be regarded as having semiconducting grains surrounded by insulating grain boundaries. In addition, conductivity of the sintered samples decreases with doping concentrations and the activation energies of the samples with x = 0.1, 0.2 and 0.3 are 0.93, 0.76 and 0.74 eV, respectively. © 2024 University of Novi Sad, Faculty of Technology. All rights reserved.
Photosensitizing activity of ferrocenyl bearing Ni(ii) and Cu(ii) dithiocarbamates in dye sensitized TiO2 solar cells
(2014) Vikram Singh; Ratna Chauhan; Ajit N. Gupta; Vinod Kumar; Michael G.B. Drew; Lal Bahadur; Nanhai Singh
Biferrocene bearing planar metal dithiocarbamates, namely, [M(FcCH 2dtc)2] (dtc = furan-2-ylmethyldithiocarbamate, M = Cu(ii) 1, Ni(ii) 4; dtc = benzo[d][1,3]dioxol-5-ylmethyl dithiocarbamate, M = Cu(ii) 2, Ni(ii) 5; dtc = pyridin-2-ylmethyldithiocarbamate, M = Cu(ii) 3, Ni(ii) 6; Fc = ferrocenyl; Fe(η5-C5H5) (η5-C5H4-)), have been synthesized and characterized by microanalysis, magnetic susceptibility and cyclic voltammetry. Structures of 1, 2 and 4 have been obtained by single crystal X-ray diffraction. These complexes with pyridyl, piperonyl and furfuryl as heteroaromatic groups in the dithiocarbamate ligands have been exploited as sensitizers in dye sensitized TiO2 solar cells for converting sunlight into electrical energy. Light-to-electrical energy conversion efficiencies achieved using these sensitizers are considerably greater than those obtained with analogous compounds previously reported by us. The overall conversion efficiency (η) is found to be dependent upon the nature of the heteroaromatic conjugated linkers and increases in the order η (ferrocenylfurfuryl) > η (ferrocenylpiperonyl) > η (ferrocenylpyridyl) all values being lower than that obtained in the reference Ru dye N719 under similar experimental conditions. The conversion efficiencies also vary with the metal being higher for Ni (4, 5 and 6) than for Cu complexes (1, 2 and 3). The X-ray structural analyses reveal the existence of rare M⋯H-C intermolecular anagostic interactions involving the metal atom in chain motifs in 1 and 4, which are retained in solution as evidenced by 1H NMR spectroscopy. © 2014 The Royal Society of Chemistry.
Polyoxomolybdate(VI) anion stabilized by ammonium cation via CS 2 elimination from N-benzyl-N-methylferrocenyl dithiocarbamate
(2012) Abhinav Kumar; Vikram Singh; Ajit N. Gupta; Manoj K. Yadav; Vinod Kumar; Nanhai Singh
A new polyoxomolybdate [(FcCH 2)NH 2(CH 2C 6H 5)] 4[Mo 8O 26] has been obtained by the reaction of ammonium molybdate and potassium N-benzyl-N-methylferrocenyl dithiocarbamate in mild acidic condition. The resulting cluster has been characterized by microanalyses, electronic absorption, photoluminescence, IR, and 1H NMR spectroscopy, and its electrochemical properties. Quantum chemical calculations have been performed in order to explain the CS 2 elimination from the dithiocarbamate moiety. Single-crystal X-ray analysis of this compound reveals that the ammonium cation generates an intricate 2-D supramolecular architecture. Copyright © 2012 Taylor and Francis Group, LLC.
Syntheses, crystal structures and conducting properties of new homoleptic copper (II) dithiocarbamate complexes
(Elsevier S.A., 2013) Ajit N. Gupta; Vikram Singh; Vinod Kumar; Amit Rajput; Laxman Singh; Michael G.B. Drew; Nanhai Singh
Five new homoleptic dithiocarbamate complexes of the general formula [Cu(L)2] [L = L1 (N-benzyl-N-furfuryl dithiocarbamate) (1); L2 (N,N-difurfuryldithiocarbamate) (2); L3 (4-ethoxycarbonylpiperidine-1-dithiocarbamate) (3); L4 (4-ethoxycarbonylpiperazine-1-dithiocarbamate) (4) and L5 (N-benzyl-N-3-methylpyridyl dithiocarbamate) (5) have been prepared and characterized by elemental analysis, spectroscopy (IR, UV-Vis, EPR), magnetic moment determination and cyclic voltammetry; their structures have been elucidated by X-ray crystallography. Variations in sterically demanding substituents on the dithiocarbamate units lead to different structures. 1, 2, 3 and 4 are Cu(dtc)2 moieties in which the copper atoms occupy square planar environments which are connected via weak interactions in axial positions to form centrosymmetric dimers. The weak Cuâ̄S distances vary significantly in the four complexes. By contrast 5 is a monomer with two molecules in the asymmetric unit. The supramolecular architecture in the five complexes has been sustained in the solid state by, C-Hâ̄S, C-Hâ̄O, πâ̄π and C-Hâ̄π (chelate, CuS2C) interactions. The electrical properties of all the complexes studied by the impedance spectroscopic technique in the 303-373 K temperature range show semiconducting properties with σrt = 10 -7-10-5 S cm-1 and Ea = 0.23-0.66 eV. The dielectric properties of the complexes have been measured at variable frequency (100 Hz-5 MHz) in the 303-373 K range; and show notably that complex 3 has a high dielectric constant. © 2013 Elsevier B.V. All rights reserved.
Syntheses, crystal structures and optical properties of heteroleptic copper(I) dithio/PPh3 complexes
(Elsevier Ltd, 2014) Ajit N. Gupta; Vikram Singh; Vinod Kumar; Lal Bahadur Prasad; Michael G.B. Drew; Nanhai Singh
New heteroleptic copper(I) dithiocarbamate and xanthate complexes of the general formula [(PPh3)2CuL] (L = N-(4-pyridyl)-N- furfuryldithiocarbamate L1 (1), thiomorpholinedithiocarbamate L2 (2), phenylpiperazinedithiocarbamate L3 (3), furfurylxanthate L4 (4) and pyridine-4-xanthate L5 (5) have been synthesized by metathesis reactions of the precursor complex [Cu(PPh3)2NO3] and potassium salts of the ligands (KL) in an equimolar ratio. These complexes have been characterized by elemental analysis and spectroscopy (IR, UV-Vis., 1H, 13C and 31P NMR), and their structures have been elucidated by X-ray crystallography. In all the five structures, the copper atoms are found to reside within a four coordinate (P2S 2) distorted tetrahedral geometry. The non-linear optical properties of 1-5 and the electronic absorption bands of 1 and 5 have been studied by DFT and TD-DFT methods, respectively. All the complexes are strongly luminescent in dichloromethane solution at room temperature. The pressed pellet σrt values of ∼10-8-10-5 S cm -1 show their weakly conducting behavior. © 2014 Elsevier Ltd. All rights reserved.
Synthesis, crystal structures and conducting properties of heteroleptic nickel(II) 1,1-dithiolate-bpy/dppe ligand complexes
(Elsevier Ltd, 2015) Ajit N. Gupta; Vinod Kumar; Vikram Singh; Krishna K. Manar; Avadhesh K. Singh; Michael G.B. Drew; Nanhai Singh
New heteroleptic complexes, [Ni(LL′)] (L = 2-(methylene-1,1′-dithiolato)-5,5′-dimethylcyclohexane-1,3-dione (L1), L′ = 2,2′-bipyridyl (bpy) 1; L = 2-(methylene-1,1′-dithiolato)-1,3-indandione (L2), L′ = 1,2-bis(diphenylphosphino)ethane (dppe) 2) have been synthesized and characterized by elemental analysis, IR, NMR and UV-Vis spectroscopy, and their structures have been determined crystallographically. In the two structures, the Ni atom lies at the centre of a distorted square plane. In 1, the ligand L1 is uniquely bonded to the Ni atom in an adjacent molecule in a μ2, κ2 S,S-chelating-bridging manner, forming a weak dimer with a Ni...S distance of 2.96 Å, which is shorter than the sum of the van der Waal's radii of the Ni and S atoms. In 2 the steric restrictions of the bulky dppe ligand hindered any dimerization, but result in the formation of a rare intramolecular C-H...Ni anagostic interaction between the ortho hydrogen atom of the phenyl ring and the nickel centre, which has been assessed by theoretical calculations. The supramolecular structures of 1 and 2 are sustained by π(chelate)...π(bpy), C-H...O, C-H...π(chelate) and C-H...π(Ar) interactions. The two compounds are weakly conducting (σrt = 10-7-10-5 S cm-1), but show semiconducting behavior in the 303-363 K temperature range. © 2015 Elsevier Ltd. All rights reserved.
Synthesis, Crystal Structures and Photosensitizing Activities of Ni(II) and Pd(II) Heteroleptic Dithiolate–dppf Complexes
(Wiley-Blackwell, 2017) Krishna K. Manar; Ajit N. Gupta; Arun K. Gupta; Lal B. Prasad; Pankaj Srivastava; Michael G. B. Drew; Nanhai Singh
New heteroleptic complexes, [M(dithiolate-dppf)] (M=Ni(II) 1,Pd(II) 2, dithiolate=2-(methylene-1,1′-dithiolato)-1,3-indandione (L1); Pd(II) 3, 2-(methylene-1,1′-dithiolato)-5,5′-dimethylcyclohexane-1,3-dione (L2); dppf = 1,1′-bis(diphenylphosphino)ferrocene) have been synthesized and characterized by elemental analysis, spectroscopy (IR, UV-Vis., 1H, 13C and 31P NMR) and cyclic voltammetry. X-ray crystallography revealed distorted square planar geometry with P2MS2 cores in 1–3, displaying M⋯H−C intramolecular anagostic interactions. Complexes 1–3 show luminescent characteristics in CH2Cl2 solution at room temperature emanating from the MLCT charge-transfer state. Based on their optical and electrochemical properties, the sensitizing activities of 1–3 have been explored; the Ni complex 1 has shown significant light to electrical energy conversion efficiency with η value of 0.78%. All the three complexes with σrt, 10−6-10−7 S cm−1 and Ea=1.00-1.35 eV are weakly conducting but show semiconducting characteristic in the 303–363 K temperature range. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Unusual C-H⋯Ni anagostic interactions in new homoleptic Ni(II) dithio complexes
(2013) Gunjan Rajput; Vikram Singh; Ajit N. Gupta; Manoj Kumar Yadav; Vinod Kumar; Santosh Kumar Singh; Akhilesh Prasad; Michael G. B. Drew; Nanhai Singh
Six new homoleptic complexes of the general form [Ni(L2)] [L = L1 (9-fluorenylmethyl)xanthate (1); L2 (cyclobutylmethyl)xanthate (2); L3 (1-benzyl-4-hydroxypiperidine)xanthate (3); L4 (N-benzyl-N-methylpyridyl) dithiocarbamate (4); L5 (N-methylfuryl-N-methylpyridyl)dithiocarbamate (5); L6 (N-benzyl-N-methylfuryl)dithiocarbamate (6)] have been prepared and characterized by microanalysis, spectroscopy (IR, 1H and 13C NMR, UV-Vis) and their structures have been elucidated by X-ray crystallography. In all complexes the metals are four coordinate with square planar coordination geometries although in the crystal structures of 2 and 4 significant C-H⋯Ni anagostic intermolecular interactions in axial positions are found which involve the metal atom in chain motifs. As far as we are aware 2 and 4 are unique examples of homoleptic metal dithio complexes exhibiting such type of anagostic interactions. In the remaining complexes (1, 3, 5 and 6) supramolecular frameworks are stabilised by S⋯S, C-H⋯S, C-H⋯π and π⋯π non-covalent interactions. All six complexes are weakly conducting (σrt = 10 -11-10-8 S cm-1; Ea = 0.37-1.40 eV) and show semiconductor behaviour in the 303-393 K temperature range. © 2013 The Royal Society of Chemistry.