• A Ramanan

      Articles written in Journal of Chemical Sciences

    • Influence of organic cations on the crystal packing of decavanadate containing solids

      A Ramanan Prasun Roy T Duraisamy Sanjeev Sharma P Ayyappan

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    • Morpholinium intercalated vanadophosphates

      Sanjeev Sharma A Ramanan J J Vittal

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      The present paper reports the formation of two morpholinium (Morp) incorporated solids precipitated from aqueous vanadate solution acidifed with phosphoric acid: a zero-dimensional, mixed-valent phosphovanadate cluster containing solid, [Morp]6[PVO4 ⊂ VIV3VV11O32(OH)6].2H2O,1 and a two-dimensional layered solid, [Morp]0.23[VIV,VOPO4]1.1H2O,2. While2 precipitates out from the reaction mixture in the presence of a reducing agent hydrazine hydrate,1 crystallises out in its absence.

    • Hydrothermal synthesis of a new ethylenediammonium intercalated vanadyl phosphate, (H3NCH2CH2NH3)0.5[V0.324+V0.685+O2PO4{P(OH)2}0.44]0.44]

      P Ayyappan Minakshi Asnani A Ramanan Y Piffard

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      In this paper we report the hydrothermal synthesis and characterisation of a new ethylenediammonium intercalated vanadyl phosphate, (H3NCH2CH2NH3)0.5 [V0.324+V0.685+O2PO4P(OH)20.44]. The phase purity of the solid was established using powder X-ray diffraction, single crystal X-ray diffraction, TGA, DTA, FTIR, UV-Vis and magnetic susceptibility measurements. Crystal data: orthorhombic,Pnma,a = 90289,b = 8.8962 andc = 15.9813 Å,V = 1283.7Å3,Z = 8. The structure contains layers made of VO5 square pyramids and PO4 tetrahedra; adjacent layers are connected through disordered tetrahedral PO2(OH)2 units. Ethylenediammonium cations occupy cavities in between the layers.

    • Direct hydrothermal synthesis of metal intercalated hexagonal molybdates, M+xMo6−x/3O18−x(OH)x.yH2O (M = Li, Rb, Cs, NH4)

      S Upreti A Ramanan

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      Here we report direct hydrothermal synthesis of a few hexagonal molybdates with composition, Mx/+Mo6−xEmphasis>/3/6+O18−x(OH)x.yH2O (M = Li, Rb, Cs, NH4). The molybdates crystallize in the space groupP63/m with a r∼ 10.5 andc r∼ 3.7 Å . Unlike previous studies, our work suggests that hexagonal molybdates could be stabilized in the presence of monovalent cations with varying ionic size (smaller lithium to larger cesium) under hydrothermal condition. The phases showed exceptional thermal stability till 550°C.

    • Formation of high nuclearity mixed-valent polyoxovanadates in the presence of copper amine complexes

      Jency Thomas Sanjeev Sharma S E Lofland K V Ramanujachary A Ramanan

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      Two new Müller-type clusters, a one-dimensional solid [Cu(en)]24[Cl ⊂V15O36]−12H2O1, and a three-dimensional solid [Cu(pn)]24[Cl ⊂V18O42]·12H2O2, have been synthesised by employing identical hydrothermal conditions except varying the nature of organic diamine.1 crystallised in a chiral space groupP212121 witha = 12.757(1),b = 18.927(2) andc = 28.590(3) Å, andZ =4.2 crystallised in a tetragonal system with space groupP4/nnc,a = 15.113(1) andc = 18.542(3) Å, andZ = 2. Mixed-valent vanadium ions in structures1 and2 have been established both by magnetisation and bond-length bond-valence measurements. Chemistry of formation of high nuclearity polyoxovanadate clusters is discussed.

    • Two new polyoxovanadate clusters templated through cysteamine

      K Pavani S Upreti A Ramanan

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      Two new fully oxidized polyoxovanadate cluster-based solids (C4N2S2H14)2[H2V10O28]·4H2O,1 and (C4N2S2H14)5[H4V15O42]2·l0H2O,2 are crystallized under self-assembly process in the presence of cysteamine. In both1 and2, cysteamines are oxidized forming disulphide linkages and occur as counter cations. The organic cations assemble around V10O28 cluster anions in1 whereas they aggregate around V15O42 clusters in 2· pH appears to be the structure determinant in the occurrence of decavanadate cluster in1 and pentadecavanadate in2, with the same counter cation.

    • Nanostructured phosphomolybdates

      J Thomas K R Kannan A Ramanan

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      Phosphomolybdate nanorods were synthesized using dodecyl pyridinium cations as structure directing agent. Composition and morphology of the nanorods were established by powder X-ray diffraction, energy dispersive X-ray analysis, fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy and scanning electron microscopy. Effect of synthetic variables such as pH and nature of templating agent on structure and morphology of the nanorods under ambient condition is discussed.

    • Crystallization of copper(II) sulfate based minerals and MOF from solution: Chemical insights into the supramolecular interactions

      M Singh D Kumar J Thomas A Ramanan

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      Crystallization of solids, molecular or non-molecular from solution is a supramolecular reaction. Nucleation of a lattice structure at supersaturation can be conceived to result from a critical nucleus, a high energy intermediate (supramolecular transition state). Conceptualization of a structure for the critical nucleus in terms of aggregation of tectons through non-covalent interactions provides chemical insights into the architecture of a solid. The retrosynthetic analysis of copper-based minerals and materials offers an elegant description for the crystal packing. It addresses the influence of the geometry, functionality and reactivity of copper tecton(s) in directing a specific supramolecular aggregation. The mechanistic approach provides guiding principles to chemists to account for the experimentally crystallized solids and a platform to practice structure-synthesis correlation. Rationalization of the same composition with different atomic arrangements (polymorphs), compositional variation leading to different pseudopolymorphs, degree of hydration (anhydrous to hydrated), water clusters, role of solvent, etc. can all be justified on molecular basis. Also, the method gives predictive components including directions to synthesize new solids. In a nutshell, the paper is an attempt to generalize the crystallization of inorganic solids from solution by recognizing supramolecular interactions between metal tectons and gain insights for designing new MOF.

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