J. N. Behera

Organically-templated metal sulfates, selenites and selenates

The literature on inorganic open-framework materials abounds in the synthesis and characterization of metal silicates, phosphates and carboxylates. Most of these materials have an organic amine as the template. In the last few years, it has been shown that anions such as sulfate, selenite and selenate can also be employed to obtain organically templated open-framework materials. This tutorial review provides an up-to-date survey of organically templated metal sulfates, selenites and selenates, prepared under hydrothermal conditions. The discussion includes one-, two-, and three-dimensional structures of these materials, many of which possess open architectures. The article should be useful to practitioners of inorganic and materials chemistry, besides students and teachers. The article serves to demonstrate how most oxy-anions can be used to build complex structures with metal-oxygen polyhedra.

Organically templated rare earth sulfates with three-dimensional and layered structures

Amine-templated rare earth sulfates of the compositions: [Ln2(H2O)2(SO4)5][C2N2H10]2, I, with Ln = La, Pr or Nd, [Nd2(SO4)4(H2O)2][C4N2H12], II, [Ln2(SO4)4][C2N2H10], III, with Ln = La or Nd, [La2(SO4)4][C3N2H12], IV and [Ln2(SO4)4(H2O)4][C6N2H14]2[C2N2H8][SO4][H2O]3, with V, Ln = La, Pr or Nd, have been synthesized under hydrothermal conditions. Both I and II have three-dimensional architectures with I possessing eight-membered apertures surrounding 16-membered apertures, and II having 12 membered apertures. Both III and V have interesting layered structures with LnO3 layers possessing (6, 3) net topology and the amine located in between the layers. V has a layered structure wherein the SO4 tetrahedra and the LnO9 polyhedra join together to form (4, 4) net sheets, with two different amines as well as the sulfate ions residing in the interlamellar space.

An organically templated Co(II) sulfate with the kagome lattice.

An amine-templated cobalt(II) sulfate with the kagome lattice, prepared for the first time, exhibits magnetic properties comparable to those of the analogous Fe(III) compounds.

3D cuboidal vanadium diselenide embedded reduced graphene oxide hybrid structures with enhanced supercapacitor properties

The electrochemical supercapacitor performance of a VSe2-reduced graphene oxide (RGO) hybrid has been reported for the first time. The hybrid was synthesized via a one-step hydrothermal route at different concentrations of graphene oxide, i.e. 0.15, 0.3, and 0.75 wt%. Enhanced supercapacitor performances were observed in the case of the hybrid obtained at 0.3 wt% of GO. It showed a specific capacitance of ∼680 F g-1 at a mass normalised current of 1 A g-1 which was ∼6 and ∼5 fold higher than those of bare VSe2 and bare RGO, respectively. Furthermore, a high energy density of ∼212 W h kg-1, power density of ∼3.3 kW kg-1, and ∼81% retention of the initial capacitance even after 10 000 cycles of charge-discharge were observed.

Supercapacitors based on patronite–reduced graphene oxide hybrids: experimental and theoretical insights

Here we report the hydrothermal synthesis and detailed study on supercapacitor applications of a patronite hybrid, VS4/reduced graphene oxide, which showed an enhanced specific capacitance of ∼877 F g−1 at a current density of 0.5 A g−1. In comparison to bare vanadium sulfide and reduced graphene oxide, the hybrid showed ∼6 times and ∼5 times higher value of specific capacitance, respectively. The obtained energy density (117 W h kg−1) and power density (20.65 kW kg−1) are comparable to those of other reported transition metal sulfides and their graphene hybrids. Theoretical calculations using density functional theory confirm an enhanced quantum capacitance of VS4/graphene composite systems, owing primarily to the shifting of the graphene Dirac cone relative to the band gap of VS4. The results infer that the hybrid has the potential to be used as a high performance supercapacitor electrode.

Chemical design of materials: A case study of inorganic open-framework materials

Inorganic open-framework materials are discussed as a case study in the chemical design of materials. Investigations of open-framework zinc phosphates have demonstrated that the formation of the complex 3D architectures may involve a process wherein 1D ladders or chains, and possibly 0D monomers comprising four-membered rings, transform to the higher-dimensional structures. The 1D ladder and the four-membered rings appear to be important building units of these structures. At one stage of the building-up process, spontaneous self-assembly of a low-dimensional structure such as the ladder could occur, followed by the crystallization of a 3D structure. Accordingly, many of the higher-dimensional structures retain structural features of the 0D or 1D structure. It is significant that a four-membered ring zinc phosphate spontaneously yields a linear chain phosphate at room temperature, on addition of piperazine, the chain transforming to a sodalite-type 3D structure under mild conditions. The occurrence of a hierarchy of structures from 0-3 dimensions is found in open-framework metal oxalates as well. Interestingly, the 3D sodalite structure is generated readily by the assembly of metal squarates, possessing the four-membered ring motif. It is noteworthy that open-framework structures are also formed by oxyanions such as sulfate, selenite, and selenate. Transformations of molecules to complex architectures are a worthy area of study, defining a new direction in the chemistry of materials.

The first organically templated open-framework metal selenate with a three-dimensional architecture

A three-dimensional metal selenate of the formula [C2N2H10][La2(SeO4)4(H2O)3].H2O, comprising La2Se4 building units and possessing 12-membered channels, has been prepared in an acidic medium under hydrothermal conditions.

Pyrazine-based donor tectons: synthesis, self-assembly and characterization

Two new supramolecular building blocks derived from pyrazine are introduced. These molecules, having pendant pyridine units covalently linked to central pyrazine ring, are structurally rigid with pre-defined bite angles. Therefore they can act as donor tectons in design of supramolecular hexagons using coordination driven self-assembly protocol. Multinuclear NMR (including 1H DOSY) and mass spectrometry have been utilized to confirm the purity and stoichiometry of these self assembled hexagonal ensembles. PM6 molecular modeling studies corroborate their hexagonal shape and nanoscalar dimensions.

H-bond supported coordination polymers of transition metal sulfites with different dimensionalities

Three new transition metal–sulfite coordination complexes namely [(C6N4H18)NaCo(SO3)2(H2O)3], (1), [(C3N2H10)2NaCo(SO3)2(H2O)2]·H2O, (2), and [(C6N4H18)Zn3(SO3)3], (3), have been synthesized under hydrothermal conditions in the presence of various organic amines where the amine behaves as an organic ligand. The complexes were characterized by PXRD, TGA and FTIR techniques. 1 shows the formation of a zero dimensional structure whereas 2 and 3 show two dimensional layer structures. The difference between 1 and 2 is due to the usage of different amines. The tetradentate amine in 1 dictates the coordination of sulfite groups in a cis-manner leading to the formation of a zero dimensional structure whereas in 2 the bidentate amine forces the sulfite group coordination in a trans-manner resulting in a two dimensional structure. In 3, the tetradentate amine caps one of the Zn centres, however the other two unique zinc ions coordinate with the sulfite anion to form interconnected cyclic dimers which gives a two dimensional layer structure. The subtle changes in the hydrogen bonding pattern and its consequence on the overall lattice to give a three dimensional network for 1 and 2 and two dimensional layer structure for 3 have been emphasized in detail.

Syntheses, crystal structure, electrochemistry and luminescence properties of lanthano–germanotungstates

A series of sandwich-type early lanthanoid substituted complexes: [Ln(α-GeW11O39)2]13− [Ln = LaIII (La-1) and CeIII (Ce-2)] and acetate-bridged hybrid dimeric complexes: [{Ln(μ-CH3COO)GeW11O39(H2O)}2]12− [Ln = PrIII (Pr-3), NdIII (Nd-4) and SmIII (Sm-5)] were synthesized by the interaction of a trilacunary Na10[GeW9O34]·18H2O precursor with Ln(NO3)3·nH2O in a potassium acetate buffer at pH 4.7. All these compounds were isolated as mixed sodium/potassium salts and structurally characterised by various analytical techniques such as single-crystal X-ray diffraction, FT-IR, ICP-AES, UV/vis, photoluminescence spectroscopy, thermogravimetric analysis, 13C and 1H NMR spectroscopy, magnetism and electrochemistry. The FT-IR spectra suggest that compounds (La-1a and Ce-2a) and (Pr-3a–Sm-5a) are isomorphous. We also synthesized analogous acetate-bridged dimeric complexes (Pr-3a to Sm-5a) with mid and late lanthanoid ions (Ln = EuIII, GdIII, TbIII, DyIII, HoIII, ErIII, TmIII and YbIII) using a procedure published elsewhere and also investigated other features such as electrochemistry and magnetic and photochromic properties. The molecular complexes Pr-3a, Sm-5a, Eu-6a, Tb-8a, Dy-9a, Ho-10a, Er-11a and Tm-12a show good photochromic behaviour at room temperature. Magnetic studies of La-1a, Ce-2a, Pr-3a, Nd-4a and Sm-5a were performed at room temperature and the molecular complexes were found to exhibit ferromagnetic behaviour.