We have linked two porphyrazinedithiolates of the type Ni[pz((S-)2:R6)] (R = 4- tert-butylphenyl) by mutual chelation of a nickel ion. The trinuclear metal-linked porphyrazine dimer 9 is a monoanion, and it exhibits the classical EPR signal of Ni(III) bis(dithiolene) complexes. The absorption spectrum of the Ni(III)-linked dimer complex suggests that delocalization between the porphyrazine rings and the bridging [NiS4]- unit is significant.

No abstract

Over the last decade, the diversity of metal oxide materials prepared using sol-gel techniques has increased significantly. This transformation can be attributed, in part, to the development of the technique known as epoxide-initiated gelation. The process utilizes organic epoxides as initiators for the sol-gel polymerization of simple inorganic metal salts in aqueous or alcoholic media. In this approach, the epoxide acts as an acid scavenger in the sol-gel reaction, driving the hydrolysis and condensation of hydrated metal species. This process is general and applicable to the synthesis of a wide range of metal oxide aerogels, xerogels, and nanocomposites. In addition, modification of synthetic parameters allows for control over the structure and properties of the sol-gel product. This method is particularly amenable to the synthesis of multi-component or composite sol-gel systems with intimately mixed nanostructures. This chapter describes both the reaction mechanisms associated with epoxide-initiated gelation as well as the variety of materials that have been prepared using this technique. IntroductionAerogels [1, 2] are a special class of open-cell foams that exhibit many interesting properties, such as low mass densities, continuous porosities, and high surface areas. These unique properties are derived from the aerogel microstructure, which typically consists of three-dimensional networks of interconnected nanometer-sized primary particles. Because of their unusual chemical and textural properties, aerogels have been investigated for a wide variety of applications, including catalysis, sorption, insulation, energy storage, and even for cosmic dust collection (Parts VIII-XV). To further expand the utility of these materials, recent efforts have focussed the development of new synthetic processes that can be used to tailor both the composition and structure of aerogels for different applications. Aerogels are typically prepared using sol-gel chemistry, a process that involves the transformation of molecular precursors into highly cross-linked inorganic or organic gels that can then be dried using special techniques to preserve the tenuous solid network. For organic and carbon

No abstract