• Samar K Das

      Articles written in Journal of Chemical Sciences

    • Synthesis and characterization of a chiral dimeric copper(II) complex: Crystal structure of [Cu2(μ-Cl)2(HL)2]·H2O(H2L = S-(−)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol)

      Chullikkattil P Pradeep Panthapally S Zacharias Samar K Das

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      Synthesis and characterization of an optically active binuclear dichloro-bridged copper(II) complex [Cu2(μ-Cl)2(HL)2]·H2O 1 (H2L = S-(−)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol) of a Schiff-base derived from salicylaldehyde and (S)-(+)-2-phenylglycinol are described. Compound 1 crystallizes in the orthorhombic chiral P212121 space group with Z = 4, a = 10·21(2), b = 11·574(3), c = 25·364(9). Each copper shows square pyramidal geometry with O2NCl2 coordination and the Cu2Cl2 core geometry adopts a butterfly shape. Crystals of 1 were further characterized by elemental analysis, IR, UV-visible and EPR spectroscopy and circular dichroism (CD) studies.

    • ‘Ionic crystals’ consisting of trinuclear macrocations and polyoxometalate anions exhibiting single crystal to single crystal transformation: breathing of crystals


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      Ion pairing of trinuclear macrocation cluster (known as basic carboxylate), [M ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ¹⁺ and a Keggin type polyoxometalate cluster anion [SiW ₁₂O₄₀] ⁴⁻ is stabilized with a number of crystal water molecules in composite type compounds [M ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄[SiW ₁₂O₄₀] ·xH ₂O · 2ClCH ₂COOH [M = Fe ³⁺, x = 18(1); M = Cr ³⁺x = 14(2)]. When the crystals of 1 are heated at 85◦C and 135◦C for 3.5 hours in an open atmospheric condition, it goes to [Fe ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] ·10H ₂O ·2ClCH ₂COOH (dehydrated 1-85o ≡ 1'), and [Fe ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] · 8H ₂O · 2ClCH ₂COOH (dehydrated 1-135o ≡ 1'') respectively with the loss of considerable amount of lattice water molecules retaining their single crystallinity. On the other hand, the single crystals of compound 2, upon heating at 85◦C or 135◦C for 3.5 hours, undergo ‘crystal-to-crystal transformation’ to the single crystals of [Cr ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW₁₂O₄₀]·8H₂O·2ClCH ₂COOH (dehydrated 2 ≡ 2'). Crystal structure analyses show that the parent compounds 1 and 2 undergo molecular rearrangement (molecular motion in the solid state) in respective dehydrated compounds. Remarkably, these dehydrated crystals (1', 1'' and 2'), upon exposure to water vapor at an ambient condition, regenerate the crystals of parent compounds 1 and 2, respectively

    • A gas–liquid interface synthesis in polyoxometalate chemistry: potential bag filter for volatile organic amines


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      Diffusion of piperidine and pyridine into an acidified aqueous solution of Na2MoO4, yield compounds [(pipH)4][Mo8O26] · 4H2O (pip = piperidine = C5H11N) (1) and [(pyH)4][Mo8O26] (py =pyridine = C5H5N) (2), respectively. Compound 1 possesses supramolecular 3-D network and the relevant connectivity pattern generates channels of approximate dimensions of 10.76 × 11.57´A° 2, in which the piperidinium cations are located as guests. Multidimensional supramolecular frameworks (3-D in compound 1 and 2-D layer type of network in compound 2) have been made possible, as the organic cations and polyoxometalate (POM) anions are glued together by significant hydrogen bonding interactions. The synthesis of compounds 1 and 2 provides a unique ‘gas–liquid’ synthetic route in POM chemistry that result in organic–inorganic hybrid materials with structural diversities. This synthetic approach, first time in POM chemistry, can be described as a potential bag filter for volatile organic amines.

    • Cobalt based functional inorganic materials: Electrocatalytic water oxidation


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      Water splitting is considered to be one of the most promising sources of sustainable energy, as it can produce hydrogen (H2) fuel. To have successful water splitting in a sustained manner, it is necessary to develop efficient and robust catalysts that can perform water oxidation, the bottleneck process of water splitting either electrochemically or photochemically. Here, we have presented a brief descriptive analysis of different aspects of designing such catalysts in connection with our recent works on the same field. The focus of the article is to discuss contemporary works in the field of designing cobalt-based heterogeneous water oxidation electrocatalysts. To the best of our knowledge, although cobalt is the most extensively studied 1st row transition metal for water oxidation catalysis reaction, no such report has been found where the simplest cobalt complex, [Co(H2O6]2+ , has been employed as a water oxidation catalyst. Not only that, reports of cobalt-based simple and small molecular catalysts are also not very frequent. With the help of our recent works, we have tried to detail here a wide aspect of the study on cobalt-based simple and small molecular catalysts, starting from the reasons behind the scarcity of such water oxidation catalysts, to development of new ideas addressing the challenges in utilization of such small cobalt complexes for water oxidation catalyst. Here, we have addressed the scope of encapsulation chemistry in designing robust and efficient heterogeneous water oxidation catalysts using cobalt-based small molecular guest species. With the help of structural insight, gained from the recent results, we published in the field of water oxidation catalysis; here, we try to formulate a general approach that can help to prepare water oxidation catalyst based on host-guest chemistry. The article critically evaluates our recent results in connection with the approach of addressing the problem.

    • Supramolecular inorganic chemistry leading to functional materials


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      Functional inorganic materials are very important today to meet the needs of our society. The most demanding needs are sustainable and clean energy (it would be nice if that can be achieved from water splitting), smart materials for sensing toxic volatile as well as water-soluble substances (health care) andefficient catalysts that can cycle multiple times without deterioration for useful chemical reactions. Supramolecular chemistry, that plays a vital role to design and synthesize such functional molecules, controls over the intermolecular interactions, thereby the molecular recognition processes leading to molecularfunctions, e.g., sensing, catalysis, etc. This article deals with inorganic supramolecular chemistry of a number of mono-nuclear coordination complexes to selected di-nuclear systems through trinuclear metal basic carboxylates,mostly in their solid-state, leading to the functional inorganic materials. We have demonstrated that some of the very old inorganic systems can be explored in the light of supramolecular chemistry to describe them as functional materials, which have potential in serving our society to some extent

    • Polyoxometalate based hybrid compound as a pre-catalyst for electrocatalytic water reduction at neutral pH


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      Polyoxometalate (POM) supported metal complex has proved to be a suitable catalyst for waterreduction/oxidation in recent studies. To catalyze hydrogen evolution reaction (HER), we have employed aPOM-based inorganic-organic hybrid compound [CuII(2,2′-bpy)(H2O)2Cl][CuII(2,2′-bpy)(H2O)2Al(OH)6-Mo6O18].4H2O (1) with a spiral-chain-like structure consisting of Anderson type polyoxometalate,[Al(OH)6Mo6O18]3- onto which Cu-complex, [Cu(H2O)2(bpy)]2+ fragments are supported. This compoundacts as a pre-catalyst towards forming the active catalyst for catalyzing hydrogen evolution reaction (HER) bywater reduction in a neutral medium. The active catalyst derived from this compound 1 achieves a currentdensity of 1 mA/cm2 at an overpotential of 348 mV. The turnover frequency calculated for the active catalystis found to be 1.780 [mol H2 (mol Cu)-1s-1] with the Faradaic efficiency of 85%.

      A unique electrochemical structural rearrangement under the electrochemical condition observed for a chain-like structured Cu-complex supported on Anderson type polyoxometalate,[CuII(2,2′-bpy)(H2O)2Cl][CuII(2,2′-bpy)(H2O)2Al(OH)6-Mo6O18].4H2O (1) resulting in the formation of the active catalyst for the electrochemical HER activity. The active catalyst achieves the current density of 1 mA/cm2 with an overpotential of 348 mV with faradic efficiency of 85% at neutral pH.

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