• Srinivasan Natarajan

      Articles written in Journal of Chemical Sciences

    • A synthetic iron phosphate mineral, spheniscidite, [NH4]+[Fe2(OH)(H2O)(PO4)2]H2O, exhibiting reversible dehydration

      Amitava Choudhury Srinivasan Natarajan

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      Spheniscidite, a synthetic iron phosphate mineral has been synthesized by hydrothermal methods. The material is isotypic with another iron phosphate mineral, leucophosphite. Spheniscidite crystallizes in the monoclinic spacegroupP21/n. (a=9·845(1),b=9·771(3),c=9·897(1),β=102·9°,V=928·5(1),Z=4,M=372·2,dcalc=2·02 g cm−3 andR=0·02). The structure consists of a network of FeO6 octahedra vertex-linked with PO4 tetrahedra forming 8-membered one-dimensional channels in which the NH4+ ions and H2O molecules are located. The material exhibits reversible dehydration and good adsorption behaviour. Magnetic susceptibility measurements indicate that the solid orders antiferromagnetically.

    • Inorganic-organic hybrid framework solids

      Srinivasan Natarajan

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      Recent developments in the area of hybrid structures are overviewed with special emphasis on iron phosphate-oxalate materials. The structure of the iron phosphate-oxalates consists of iron phosphate chains or layers that are connected by oxalate moieties completing the architecture. The compounds exhibit interesting magnetic properties originating from the super-exchange interactions that are predominantly anti-ferromagnetic, involving the iron phosphates and the oxalate moieties. One of the materials,IV, also exhibits interesting adsorptive properties reminiscent of aluminosilicate zeolites. The aluminum phosphate-oxalate,VII, indicates that hybrid structures can be formed with zeolite architecture.

    • Synthesis of a 4-membered ring zinc phosphate monomer and its condensation self-assembly into an open-framework structure

      S Neeraj Srinivasan Natarajan C N R Rao

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    • Hydrothermal synthesis and structure of framework cobalt phosphates

      Amitava Choudhury Srinivasan Natarajan C N R Rao

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    • Synthesis and characterization of submicron-sized mesoporous aluminosilicate spheres

      Gautam Gundiah M Eswaramoorthy S Neeraj Srinivasan Natarajan C N R Rao

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      Mesoporous aluminosilicate spheres of 0.3–0.4 Μm diameter, with different Si/Al ratios, have been prepared by surfactant templating. Surface area of these materials is in the 510–970 m2 g-1 range and pore diameter in the 15–20 å range.

    • A two-dimensional yttrium phthalate coordination polymer, [Y4(H2O)2(C8H4O4)6], exhibiting different coordination geometries

      A Thirumurugan Srinivasan Natarajan

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      A hydrothermal reaction of a mixture of Y(NO3)3, 1,2-benzenedicarboxylic acid (1,2-BDC) and NaOH gives rise to a new yttrium phthalate coordination polymer, [Y4H2O2C8H4O4)6],I. The Y ions inI are present in four different coordination environments with respect to the oxygen atoms (CN6 = octahedral, CN7 = pentagonal bipyramid, CN8 = dodecahedron and CN9 = capped square anti-prism). The oxygen atoms of the 1,2-BDC are fully deprotonated, and show variations in their connectivity with Y atoms. The Y atoms themselves are connected through their vertices forming infinite Y-O-Y one-dimensional chains. The Y-O-Ychains are cross-linked by the 1,2-BDC anions forming a corrugated layer structure. The layers are supported by favourableπ…π interactions between the benzene rings of the 1,2-BDC anions. The variations in the coordination environment of the Y atoms and the presence of Y-O-Y interactions along with the favourableπ…π interactions between the benzene rings from different layers are noteworthy structural features. Crystal data: triclinic, space group =P−1 (no. 2),a = 12.6669 (2),b = 13.8538 (2),c = 16.0289 Å,α = 75.20 (1),β = 69.012 (1),γ= 65.529 (1)°,V = 2371.28 (7) Å3,Dcalc = 1.922 g cm−1, μ(MoKα) = 4.943 mm−1. A total of 9745 reflections collected and merged to give 6566 unique reflections (Rint = 0.0292) of which 5252 withI>2σ(I) were considered to be observed. FinalR2 = 0.0339,wR2 = 0.0724 andS = 1.036 were obtained for 704 parameters.

    • A lanthanum pyromellitate coordination polymer with three-dimensional structure

      S V Ganesan Srinivasan Natarajan

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      A new three-dimensional metal-organic coordination polymer, [La2(H2O)2(H2BTEC)(BTEC)], 1, was hydrothermally synthesized and characterized by single crystal X-ray diffraction. The three-dimensional framework is built up from La2O16 dimers connected by carboxylate anions. The polymer exhibits strong photoluminescence at room temperature with the main emission band at 390 nm (λex = 338 nm). Crystal data: triclinic, space group P(−1),a = 6.4486(3),b = 9.4525(5),c = 9.6238(5) Å, α= 88.24(1), β = 74.67(2), γ= 76.76(1)°,V = 550.45(5)

    • Hydrothermal synthesis and structure of [(C4N2H12)3][P2Mo5O23]·H2O and [(C3N2H12)3][P2Mo5O23]·4H2O

      S V Ganesan Srinivasan Natarajan

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      Two new compounds, [(C4N2H12)3][P2Mo5O23]·H2O,I, and [(C3N2H12)3][P2Mo5O23]4H2O,II, have been prepared employing hydrothermal methods in the presence of aliphatic organic amine molecules. Both the compounds possess the same polyoxoanion, pentamolybdatobisphosphate, (P2Mo5O23)6-. The anions consist of a ring of five MoO6 distorted octahedra with four edge connections and one corner connection. The phosphate groups cap the pentamolybdate ring anion on either side. The anion is stabilized by strong hydrogen bonds involving the hydrogen atoms of the amine molecules and the oxygen atoms of the polyoxoanion and water molecules. Crystal data:I, monoclinic, space group = P21/n (no. 14), mol. wt. = 1192.1,a = 9.4180(1),b = 18.1972(3),c = 19.4509(1) å, Β = 103.722(1)‡,V = 3238.37(7) å3, Z = 4;II, triclinic, space group = P1 (no. 2), mol. wt. = 1210.1,a 9.5617(9),b = 13.3393(12),c = 13.7637(12) å, α = 88.735(1), Β = 75.68(1), γ = 87.484(2)‡,V = 1699.2(3) å3.

    • Synthesis, structure and magnetic properties of the polyoxovanadate cluster [Zn2(NH2(CH2)2NH2)5][{Zn(NH2(CH2)2NH2)2}2{V18O42(H2O)}].xH2O (x ∼ 12), possessing a layered structure].xH2O (x ∼ 12), possessing a layered structure

      Srinivasan Natarajan K S Narayan Swapan K Pati

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      A hydrothermal reaction of a mixture of ZnCl2, V2O5, ethylenediamine and water gave rise to a layered poly oxovanadate material [Zn2(NH2(CH2)2NH2)5][{Zn(NH2(CH2)2NH2)2}5{V18O42(H2O)}].xH2O (x ∼ 12) (I) consisting of [V18O42]12− clusters. These clusters, with all the vanadium ions in the +4 state, are connected together through Zn(NH2(CH2)2NH2)2 linkers forming a two-dimensional structure. The layers are also separated by distorted trigonal bipyramidal [Zn2(NH2(CH2)2NH2)5] complexes. The structure, thus, presents a dual role for the Zn-ethyl-enediamine complex. The magnetic susceptibility studies indicate that the interactions between the V centres inI are predominantly antiferromagnetic in nature and the compound shows highly frustrated behaviour. The magnetic properties are compared to the theoretical calculations based on the Heisenberg model, in addition to correlating to the structure. Crystal data for the complexes are presented.

    • The use of hydrothermal methods in the synthesis of novel open-framework materials

      Srinivasan Natarajan Sukhendu Manual Partha Mahata Vandavasi Koteswara Rao Padmini Ramaswamy Abhishek Banerjee Avijit Kumar Paul K V Ramya

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      The preparation of inorganic compounds, exhibiting open-framework structures, by hydrothermal methods has been presented. To illustrate the efficacy of this approach, few select examples encompassing a wide variety and diversity in the structures have been provided. In all the cases, good quality single crystals were obtained, which were used for the elucidation of the structure. In the first example, simple inorganic network compounds based on phosphite and arsenate are described. In the second example, inorganic-organic hybrid compounds involving phosphite/arsenate along with oxalate units are presented. In the third example, new coordination polymers with interesting structures are given. The examples presented are representative of the type and variety of compounds one can prepare by careful choice of the reaction conditions.

    • Magnetic behaviour in metal-organic frameworks — Some recent examples

      Partha Mahata Debajit Sarma Srinivasan Natarajan

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      The article describes the synthesis, structure and magnetic investigations of a series of metal-organic framework compounds formed with Mn+2 and Ni+2 ions. The structures, determined using the single crystal X-ray diffraction, indicated that the structures possess two- and three-dimensional structures with magnetically active dimers, tetramers, chains, two-dimensional layers connected by polycarboxylic acids. These compounds provide good examples for the investigations of magnetic behaviour. Magnetic studies have been carried out using SQUID magnetometer in the range of 2-300 K and the behaviour indicates a predominant anti-ferromagnetic interactions, which appears to differ based on the M-O-C-O-M and/or the M-O-M (M = metal ions) linkages. Thus, compounds with carboxylate (Mn- O-C-O-Mn) connected ones, [C3N2H5][Mn(H2O){C6H3(COO)3\}], I, [{Mn(H2O)3}{C12H8O(COO)2}]$\cdots$H2O, II, [{Mn(H2O)}{C12H8O(COO)2}], III, show simple anti-ferromagnetic behaviour. The compounds with Mn-O/OH-Mn connected dimer and tetramer units in [NaMn{C6H3(COO)3}], IV, [Mn2($\mu_3$-OH) (H2O)2{C6H3(COO)3}]$\cdot$2H2O, V, show canted-antiferromagnetic and anti-ferromagnetic behaviour, respectively. The presence of infinite one-dimensional -Ni-OH-Ni- chains in the compound, [NiR_2R(HR_2RO)($\mu_3$-OH)2(C8H5NO4], VI, gives rise to ferromagnet-like behaviour at low temperatures. The compounds, [Mn3{C6H3(COO)3}$2], VII and [{Mn(OH)}2{C12H8O(COO)2}], VIII, have two-dimensional infinite -Mn-O/OH-Mn- layers with triangular magnetic lattices, which resemble the Kagome and brucite-like layer. The magnetic studies indicated canted-antiferromagnetic behaviour in both the cases. Variable temperature EPR and theoretical magnetic modelling studies have been carried out on selected compounds to probe the nature of the magnetic species and their interactions with them.

    • Effect of metal ion doping on the photocatalytic activity of aluminophosphates

      Avijit Kumar Paul Manikanda Prabu Giridhar Madras Srinivasan Natarajan

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      The metal ions (Ti+4, Mg+2, Zn+2 and Co+2) have been substituted in place of Al$^{+3}$ in aluminophosphates (AlPOs). These compounds were used for the first time as possible photocatalysts for the degradation of organic dyes. Among the doped AlPOs, ZnAlPO-5, CoAlPO-5, MgAlPO-11, 18 and 36 did not show any photocatalytic activity. MgAlPO-5 showed photocatalytic activity and different loading of Mg (4, 8, 12 atom % of Mg) were investigated. The activity can be enhanced by the increasing of concentration of the doped metal ions. TiAlPO-5 (4, 8, 12 atom % of Ti) showed the highest photocatalytic activity among all the compounds and its activity was compared to that of Degussa P25 (TiO2). The activity of photocatalysts was correlated with the diffuse reflectance and photoluminescence spectra.

    • The relevance of metal organic frameworks (MOFs) in inorganic materials chemistry

      Srinivasan Natarajan Partha Mahata Debajit Sarma

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      The metal organic frameworks (MOFs) have evolved to be an important family and a corner stone for research in the area of inorganic chemistry. The progress made since 2000 has attracted researchers from other disciplines to actively engage themselves in this area. This cooperative synergy of different scientific believes have provided important edge and spread to the chemistry of metal-organic frameworks. The ease of synthesis coupled with the observation of properties in the areas of catalysis, sorption, separation, luminescence, bioactivity, magnetism, etc., are a proof of this synergism. In this article, we present the recent developments in this area.

    • A Reactive Intermediate, [Ni5(C6H4N3)6(CO)4], in the Formation of Nonameric Clusters of Nickel, [Ni9(C6H4N3)12(CO)6] and [Ni9(C6H4N3)12(CO)6].2(C3H7NO)

      Subhradeep Mistry Srinivasan Natarajan

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      Three new molecular compounds, [Ni5(bta)6(CO)4], I, [Ni9(bta)12(CO)6], II, [Ni9(bta)12(CO)6].2(C3H7NO), III, (bta = benzotriazole) were prepared employing solvothermal reactions. Of these, I have pentanuclear nickel, whereas II and III have nonanuclear nickel species. The structures are formed by the connectivity between the nickel and benzotriazole giving rise to the 5- and 9-membered nickel clusters. The structures are stabilised by extensive $\pi \ldots \pi$ and C-H$\ldots \pi$ interactions. Compound II and III are solvotamorphs as they have the same 9-membered nickel clusters and have different solvent molecules. To the best of our knowledge, the compounds I-III represent the first examples of the same transition element existing in two distinct coordination environment in this class of compounds. The studies reveal that compound I is reactive and could be an intermediate in the preparation of II and III. Thermal studies indicate that the compounds are stable upto 350°C and at higher temperatures (∼800°C) the compounds decompose into NiO.Magnetic studies reveal that II is anti-ferromagnetic.

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