• Dillip Kumar Chand

      Articles written in Journal of Chemical Sciences

    • Synthesis, structure and applications of [cis-dioxomolybdenum(VI)-(ONO)] type complexes

      Rajan Deepan Chakravarthy Dillip Kumar Chand

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      Oxo-molybdenum chemistry is of great interest since such units are found in the active sites of a majority of molybdo-enzymes. In order to mimic the biological systems, a number of oxo-molybdenum complexes have been synthesised and studied. This review describes synthesis, structure and applications of oxomolybdenum complexes particularly cis-MoO2(L)(D) where L stands for a dianionic tridentate ONO ligand and D for a donor solvent molecule/monodentate ligand. The ligand moieties are derived from Schiff base, hydrazide Schiff base and other related tridentate ligands L(H)2. The coordination geometry around the Mo center in these complexes can be best described as a distorted octahedron in which the ONO-tridentate ligand occupies meridional position with two anionic oxygen donors mutually trans and are cis to the oxygen centers of the cis-dioxo group. Mostly the applications of cis-MoO2-(ONO) type complexes seen in literature are oxo transfer reactions like epoxidation, sulfoxidation and phosphine oxidation reactions.

    • Synthesis of azamacrocycle stabilized palladium nanoparticles: Controlled size and one-dimensional growth

      Jeyaraman Athilakshmi Dillip Kumar Chand

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      Palladium nanoparticles (PdNPs) of uniform size in the range of 3-5 nm are prepared in MeOH and MeCN:MeOH by solvent-assisted reduction of palladium acetate in the presence of a hexaazamacrocyclic ligand, L1. For the mixed solvent system different ratio of the solvents was tried i.e., 1:1, 1:3 and 3:1. In all cases the concentration and ratio of Pd(II) to L1 was maintained at 2mM:1mM. In another experiment NPs were prepared in MeOH by lowering the concentration of L1 to 0.5mM, where chain-like assemblies of PdNPs was observed. Importantly, the solutions are found to be stable at RT for months.

    • Self-assembly of self-assembled molecular triangles

      Mili C Naranthatta V Ramkumar Dillip Kumar Chand

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      A rare variety of self-assembledmolecular triangle [Pd3(bpy)3(imidazolate)3](NO3)3, 1 is prepared by the combination of Pd(bpy)(NO3)2 with imidazole, at 1:1 ratio, in acetonitrile-water. Deprotonation of imidazole happened during the course of the complexation reaction where upon the metallomacrocycle is formed. The bowl-shaped trinuclear architecture of 1 is crafted with three peripheral bpy units capable of 𝜋 - 𝜋 stacking interactions. While the solution state structure of 1 can be best described as a trinuclear complex, in the solidstate well-fashioned intermolecular $\pi - \pi$ and CH-𝜋 interactions are observed. Thus, in the solid-state further self-assembly of already self-assembled molecular triangle is witnessed. The triangular panels are arranged in a linear manner utilizing intermolecular 𝜋 - 𝜋 interactions where upon two out of three bpy units of each molecule participated in the chain formation.

    • Role of peripheral phenanthroline groups in the self-assembly of self-assembled molecular triangles

      Mili C Naranthatta V Ramkumar Dillip Kumar Chand

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      Self-assembled molecular triangles [Pd3(phen)3(imidazolate)3](NO3)3, 1a and [Pd3(phen)3 (imidazolate)3](PF6)3, 1b are prepared by the combination of imidazole with Pd(phen)(NO3)2 and Pd(phen) (PF6)2, respectively. Imidazole was deprotonated during the complexation reactions and the imidazolate so formed acted as a bis-monodentate bridging ligand to form the bowl-shaped trinuclear architectures of 1a/b. Relative orientation of the imidazolate moieties can be best described as syn,anti,anti as observed in the crystal structure of 1b. However, in solution state, slow conformational changes are assumed on the basis of 1HNMR spectral data. The molecular triangles are crafted with three peripheral phen units capable of 𝜋−𝜋 stacking interactions. Well-fashioned intermolecular 𝜋−𝜋 interactions are observed in the solid-state, wherein further self-assembly of already self-assembled triangle is observed.

    • Linear and circular helicates: A brief review


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      Helical self-assembled coordination complexes are broadly classified under linear and circular helicates. While the number of strands of the ligand units in a molecule of the linear helicates is used for further classifications such as single-stranded, double-stranded and so on, the circular helicates are not classified further. The compositions of helicates are considered as MxLy where the terms x and y stand for the number of metal ion(s) and ligand strands, respectively. However, more than one type of metal centers/ligand in helicates are also known. The linear helicates of a given number of strands are further classified under the number of metal centers such as binuclear, trinuclear and so on. Representative examples are included to exemplify the varieties of helicates.

    • Multicomponent click reactions catalysed by copper(I) oxide nanoparticles (Cu2ONPs) derived using Oryza sativa


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      A procedure for the expedient synthesis of well-characterized Cu(I) oxide nanoparticles (Cu2-ONPs) from Cu(II) salts by employing Rice (Oryza sativa) as a cheap and ready source of reducing as well as stabilizing agent has been demonstrated. The judicious choice of rice as a catalyst has helped in the symbiotic combination of two events: viz., acidic hydrolysis of starch to form glucose and the subsequent formal reduction of Cu2+ by the in-situ generated monosaccharide reducing sugar (glucose) under the alkaline condition to produce Cu2O. Further, rice was also found to be effectively stabilizing the nanoparticles from agglomeration. Optical and microscopic techniques were suitably employed for the characterization of the nanoparticles of approximately 10 nm size. Furthermore, the specifically generated nanoparticles were foundto be active catalysts in an aqueous medium for Azide-alkyne Huisgen cycloaddition (Click reaction) under base free condition via one-pot multi-component addition for the synthesis of mono-, bis- and tris-1,2,3-triazoles in good to excellent yields.

    • Copper nanoparticles (CuNPs) catalyzed chemoselective reduction of nitroarenes in aqueous medium


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      A procedure for practical synthesis of CuNPs from CuSO4.5H2O is established, under appropriatereaction conditions, using rice (Oryza sativa) as an economic source of reducing as well as a stabilizing agent.Optical and microscopic techniques are employed for the characterization of the synthesized CuNPs and thesizes of the particles were found to be in the range of 8 ± 2 nm. The nanoparticles are used as a catalyst forchemoselective reduction of aromatic nitro compounds to corresponding amines under ambient conditionsand water as a reaction medium.

      CuNPs are synthesized using hydrolysed rice and used as catalyst for chemoselective reduction of nitroarenes to their corresponding amines in water.

    • Self-assembled discrete and polymeric cobalt(II) complexes of a carboxylate appended tripodal tetradentate ligand: reactivity with aerial dioxygen or aqueous hydrogen peroxide


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      Three new cobalt(II) complexes [Co(μ2-L)]3(ClO4)3.2H2O, 1, [Co(L)(NO3)], 2 and {[Co(μ2-L)(MeOH)](BPh4).(MeOH)}n, 3 are prepared where L stands for 2-(bis(pyridin-2-ylmethyl)amino)acetate. Single crystal X-ray diffraction analysis confirmed the trinuclear core for 1, and 1-D polymericstructure for 3. It is proposed that these complexes are largely mononuclear in solution state. Reactivity of thecomplexes with aerial dioxygen, in presence of Et3N, invariably produced a common complexed cation[Co(L)(pic)]+ where pic stands for picolinate. The novelty of the finding is in terms of the presence of bothintact ligand (i.e L) and a fragment of the ligand (i.e. pic) in the same complex. Crystal structures of theisolated complexes [Co(L)(pic)](ClO4), 4a and [Co(L)(pic)](NO3), 4b confirmed the solid state structures.The Co(II) center of a complex is oxidized to Co(III) and the bound ligand moiety afforded a picolinate unit(due to oxidative Cpicolyl-Namine bond cleavage). The picolinate unit then connects with another molecule of aCo(III) complex containing L in its original form. Oxidation of a representative complex using H2O2 alsoresulted [Co(L)(pic)]+, but a stable binuclear dihydroxo bridged Co(III) complex [Co(L)(μ2-OH)]2(ClO4)2, 5was formed when controlled amount of H2O2 (1 equiv) was employed.

      Synopsis: Three new Co(II) complexes of 2-(bis(pyridin-2-ylmethyl)amino)acetate (L) are prepared. Reactivity of the complexes with aerial dioxygen, in presence of Et3N, invariably produced Co(III) complexes having the common complexed cation [Co(L)(picolinate)]+. Picolinate is generated due to the oxidative cleavage of bound L.

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