Arunachalam Ramanan

Novel self-assembled decavanadate clusters forming 1D molecular chains and 2D molecular arrays: [HMTA-H···H2O][HMTA-CH2OH][H3V10O28{Na(H2O)4}]·4H2O and [Na2(H2O)10] [H3V10O28 {Na(H2O)2}]·3H2O

Abstract Two novel materials, [HMTA-H··H2O] [HMTA-CH2OH] [H3V10O28[Na(H2O)4}]·4H2O, 1 and [Na2(H2O)10][H3V10O28[Na(H2O)2}]·3H2O, 2 containing decavanadate clusters interconnected through hydrated sodium cations forming 1D molecular chains and 2D molecular arrays have been self-assembled from acidified, aqueous vanadate solution in the presence of organic bases, hexamethylenetetramine and 1,3,5-triazine respectively.

Copper pyrazole directed crystallization of decavanadates: synthesis and characterization of {Cu(pz)}4[{Cu(pz)3}2V10O28] and (Hpz)2[{Cu(pz)4}2V10O28]·2H2O

Crystal engineering of two new fully oxidized decavanadate based 1-D solid {Cu(pz)4}[{Cu(pz)3}2V10O28], 1 and a 2-D inorganic–organic hybrid solid (Hpz)2[{Cu(pz)4}2V10O28]·2H2O, 2 have been effected under self-assembly condition. 1 contains 1-D anionic chains of the composition [{Cu(pz)3}2V10O28] intercalated with {Cu(pz)4}2+ as counter cations. 2 contains 2-D anionic sheets of the composition [{Cu(pz)4}2V10O28] incorporating pyrazolium counter cations and water molecules. Self-assembly of 1 and 2 is interpreted in terms of molecular recognition between reasonable soluble molecular species in the supramolecular reaction along the mechanistic approach proposed by Ramanan and Whittingham for rationalising metal–organic framework structures. Low temperature magnetic measurements of 1 and 2 show copper in divalent state with Curie behaviour. Crystal data: 1, triclinic, space group P-1, a = 11.671(1) A, b = 11.976(1) A, c = 12.900(1) A, α = 100.226(2)°, β = 105.549(3)°, γ = 118.571(2)°, Z = 1; 2, triclinic, space group P-1, a = 11.582(2) A, b = 11.659(1) A, c = 12.451(1) A, α = 114.660(3)°, β = 107.439(2)°, γ = 91.639(3)°, Z = 2.

Microbial mineralization of struvite: A promising process to overcome phosphate sequestering crisis

Due to extensive exploitation of non-renewable phosphate minerals, their natural reserves will exhaust very soon. This necessitates looking for alternatives and an efficient methodology through which indispensable phosphorus can be harvested back. The current study was undertaken to explore the potential of a metallophilic bacterium Enterobacter sp. EMB19 for the recovery of phosphorus as phosphate rich mineral. A very low phosphate concentration strategy was adopted. The process led to the mineralization of phosphorus as homogeneous struvite crystals. For each gram of Epsom salt added, the cells effectively mineralized about 20% of the salt into struvite. The effect of different inorganic sources, culture profile and plausible mechanism involved in crystal formation was also explored. The synthesized struvite crystals typically possessed a prismatic crystal habit. The characterization and identification of the crystals were done using single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), energy dispersive X-ray analysis (EDAX) and fourier transform infrared (FTIR). The thermal characteristics were studied using thermo gravimetric analysis (TGA) and differential scanning calorimetric (DSC) processes. The synthesis of struvite by this bacterium seems to be a promising and viable strategy since it serves dual purpose (i) obtaining phosphorus and nitrogen rich fertilizer and (ii) conservation of natural phosphate reserves. This study is very significant in the sense that the process may be used for harvesting and synthesizing other valuable minerals. Also, it will provide new insights into phosphate biomineralization mechanisms.

Oxalate Bridged Copper Pyrazole Complex Templated Anderson-Evans Cluster Based Solids

The synthesis of four new Anderson-Evans type cluster based solids was carried out from an aqueous solution containing sodium molybdate, chromium chloride, cupric chloride and pyrazole at room temperature: [{Cr3O(CH3COO)6(H2O)3}2{H7CrMo6O24}]·24H2O, 1; [{Cu2(ox)(pz)4}{H7CrMo6O24}]·11H2O, 3; [{Cu(pz)2(H2O)2}{Cu2(ox)(pz)4}{H5CrMo6O24}]·8H2O, 4; and [{Cu(pz)3Cl}{Cu2(ox)(pz)4}{H6CrMo6O24}]·8H2O, 5. In 1, the discrete Anderson-Evans cluster aggregates with trimeric chromium acetate cationic complex through supramolecular interactions. In 3–5, the Anderson-Evans cluster is covalently linked into a 1D chain through oxalate bridged copper pyrazole units. In 3, the chains are further stabilized by water oligomers. In 4 and 5, the chains are covalently linked into 2D sheets by different copper pyrazole complexes. The oxalate molecules in 3–5 are probably generated in situ in the reaction medium, through a reductive coupling of dissolved carbon dioxide assisted by copper pyrazole units.

Nax/2Bi1-x/2MoxV1-xO4 and Bi1-x/3MoxV1-xO4 : New Scheelite-related phases

Abstract New Scheelite-related solid solutions of the compositions Na x /2 Bi 1− x /2 Mo x V 1− x O 4 (0≤ x ≤1) and Bi 1− x /3 Mo x V 1− x O 4 (0≤ x ≤0.2) have been synthesised by the substitution of Na and Mo at the A and B sites respectively of the ABO 4 type ferroelastic BiVO 4 . The phases were characterised using chemical analysis, powder X-ray diffraction, scanning electron microscopy, EDAX, and Raman spectroscopy. While almost a continuous solid solution is obtained for the series Na x /2 Bi 1− x /2 Mo x V 1− x O 4 , the absence of Na at the A-site results only in a narrow stability region for the other series, Bi 1− x /3 Mo x V 1− x O 4 where 0≤ x ≤0.2. Raman spectra of selected samples at room temperature also suggest that vanadium and molybdenum atoms are disordered at the tetrahedral sites.

Hydrolytically stable ZIF-8@PDMS core–shell microspheres for gas–solid chromatographic separation

Metal organic frameworks (MOFs) with exceptionally high surface areas, shape selectivity and availability of multiple active sites are suitable materials to serve as solid stationary phase for chromatographic applications. Packed columns filled with conventionally prepared MOFs result in high pressure drops and low column efficiency, mainly due to the presence of small irregular shaped crystals and broader size distribution. In this paper, we report the successful utilization of the hydrolytically stable microcrystalline zinc imidazolate (ZIF-8), a well-known MOF immobilized on a thermally stable polymer i.e., polydimethylsiloxane (PDMS) for application as a stationary phase towards gas–solid chromatographic separations. A gas chromatography (GC) column (2 m × 2.5 mm) packed with the ZIF-8@PDMS core–shell microspheres demonstrate efficient separation of liquid and gas mixtures including xylene isomers and natural gas mixtures. We also successfully used the stationary phase for quantification of ethanol concentration in aqueous samples; the column did not undergo any structural change suggesting its excellent hydrolytic stability.

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

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.

Toughening of epoxy resin using Zn4O (1,4-benzenedicarboxylate)3 metal–organic frameworks

In this paper, we have demonstrated the potential of the well-known microporous MOF 5 towards toughening of a cycloaliphatic epoxy resin by preparing Epoxy–MOF 5 composites (0.1–0.7% w/w). Introduction of MOF 5 led to significant stiffening and improvement in dynamic properties as indicated by a 68% increase in impact strength and a 230% increase in fracture energy at an optimal loading of 0.3% w/w. A comparison of the mechanical response under different strain rates established the strain rate sensitivity of the composites, which is of relevance under blast loading conditions. We also performed fractographic analysis of the ruptured surface to understand the underlying mechanism behind the improvement in toughness.

Two new polyoxovanadate clusters templated through cysteamine

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.

Core–shell polysiloxane–MOF 5 microspheres as a stationary phase for gas–solid chromatographic separation

Core–shell poly(dimethylsiloxane) (PDMS)–MOF 5 microspheres were prepared by directed crystallization of MOF 5 on thermally stable PDMS beads. The microspheres were evaluated for their potential use as a stationary phase for gas-chromatographic separation of permanent gases and liquids, where the issues associated with pressure drop were circumvented. The successful demonstration of this simple and versatile methodology widens the scope for large-scale application of Metal–Organic Frameworks (MOFs) in chromatographic separation.