• ARUNACHALAM RAMANAN

      Articles written in Journal of Chemical Sciences

    • Crystallization of organically templated phosphomolybdate cluster-based solids from aqueous solution

      Minakshi Asnani Dinesh Kumar T Duraisamy Arunachalam Ramanan

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      The paper reports the synthesis and structural characterization of several organic-inorganic solids involving phosphomolybdate clusters. The Strandberg-type {P2Mo$^{\text{VI}}_5$O23} and the lower-valent {P4Mo$^V_6$O31} cluster based solids were isolated in the presence of $en$ (ethylenediamine) by controlling pH of the reaction medium. The lower-valent cluster invariably requires the presence of a suitable metal cation for further stabilization. A detailed investigation of the system was carried out where three different weak acids viz. oxalic acid, succinic acid and glycine were used in the entire pH range (1-12). Our results establish that the organic amine ($en$) is alone capable of reducing the molybdenum core in the absence of an organic acid at a suitable pH. Hence, pH of the reaction medium combined with suitable temperature favours the formation of lower-valent phosphomolybdate cluster. Higher pH favours the precipitation of a new sodium hydrogen phosphate.

    • What Triggers Supramolecular Isomerism in Nonmolecular Solids? A case study of Copper Pyridazine Halides

      JENCY THOMAS ARUNACHALAM RAMANAN

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      Molecular recognition and aggregation occurring in solution are critical events towards the nucleation and growth of a crystal. However, controlling aggregation towards a particular supramolecular assembly is difficult due to lack of information on its thermodynamics and kinetics. Hence, the occurrence of supramolecularisomers is hardly recognized. In this paper, therefore, we demonstrate a retrosynthetic analysis to interpret the occurrence of isostructures and supramolecular isomers and predict the possibility of new phases in copperhalide-pyridazine- H₂O system. A significant feature of this paper is the use of crystal engineering tools, namely, synthons and tectons to interpret the phase diagram of a system. The structure-synthesis correlation discussed here provides chemical insight to evolve a synthetic protocol to interpret and predict the possibilityof supramolecular isomers in metal organic solids.

    • From molecules to materials: Structural landscape of zinc terephthalates grown from solution

      MANISHA JADON MANJU SRIVASTAVA PRASUN KUMAR ROY ARUNACHALAM RAMANAN

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      Nucleation of crystals from solution is a universal phenomenon that significantly impacts thedevelopment of advanced functional materials. In this context, metal organic frameworks (MOFs) whichencompass a plethora of metal and multidentate organic ligand architectures offer potential applications inareas such as gas storage, gas separation and catalysis. The experimental and theoretical proceduresemployed, however, lack insights into the chemistry of molecular aggregation which is key to formulatesynthetic protocols towards obtaining solids with desired structural features. Monitoring crystallization on areal timescale, especially at supersaturation involving a relatively small number of molecules, calls foradvanced imaging and spectroscopic techniques supported by logical theoretical models. In this perspective,we have examined the crystal structures of zinc terephthalates grown from solution reported in the CambridgeStructural Database with an objective to rationalize the aggregation of molecular species occurring in thesolution transforming into a crystal with a defined stoichiometry and dimensionality of zinc terephthalatecoordination interaction. The structural chemistry described here addresses the influence of solvent, particularly water in the formation of MOF-5 and other related solids.

      A neutral 1:1 zinc terephthalate complex drives the nucleation and growth of all crystals known in the structural landscape of zinc salt-terephthalic acid-solvent.

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