Meenakshi Dan

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.

A simple single-source precursor route to the nanostructures of AlN, GaN and InN

In an effort to find a simple and common single-source precursor route for the group 13 metal nitride semiconductor nanostructures, the complexes formed by the trichlorides of Al, Ga and In with urea have been investigated. The complexes, characterized by X-ray crystallography and other techniques, yield the nitrides on thermal decomposition. Single crystalline nanowires of AlN, GaN and InN have been deposited on Si substrates covered with Au islands by using the complexes as precursors. The urea complexes yield single crystalline nanocrystals under solvothermal conditions. The successful synthesis of the nanowires and nanocrystals of these three important nitrides by a simple single-precursor route is noteworthy and the method may indeed be useful in practice.

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.

Amine-templated metal squarates

Two layered amine-templated cobalt squarates, [C 6 N 2 H 14 ] 2 [Co 2 (C 4 O 4 ) 3 (H 2 O) 4 ], I, and [C 3 N 2 H 5 ] 2 [Co 2 (C 4 O 4 ) 3 (H 2 O) 4 ], II, have been prepared under hydrothermal conditions. Both I and II contain chains formed by dimers comprising two cobalt atoms bound to the squarate units, the chains being connected through hydrogen bond interactions. An amine-templated cobalt squarate of the formula [C 4 N 2 H 12 ][Co(C 4 O 4 ) 2 (H 2 O) 4 ][H 2 O] 2 , III, as well as its Ni, Zn and Cd analogues have been prepared by room temperature reactions. III has a layered architecture wherein the cobalt-squarate monomers are linked by the amine molecules. Co and Zn analogues of [Ni(C 4 O 4 )(H 2 O) 2 (C 3 N 2 H 4 )] with ligating imidazole units have also been prepared and characterized.

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.

Transformation of a 4-membered ring zinc phosphate SBU to a sodalite-related 3-dimensional structure through a linear chain structure

A zero-dimensional zinc phosphate, comprising a 4-membered ring, is shown to spontaneously transform at room temperature, to a linear chain structure consisting of corner-shared 4-membered rings, the latter transforming to a 3-dimensional sodalite-related structure under mild conditions.