From Molecular Precursors

Corriu RJP (2000) Ceramics and nanostructures from molecular precursors. Ange-wandte Chemie-International Edition 39(8), 1376-1398... 

Size-Selective Precipitation from Molecular Precursors... 

The conceptual connection between cluster and solid-state chemistries is the unifying theme of the first seven chapters. Complementary empirical connections between cluster and solid-state chemistries are emphasized in this final chapter. That is, the synthesis of solid-state materials from molecular precursors including clusters permits the strengths of molecular synthesis to be used in the development of new materials. On the other hand, the utilization of Zintl clusters as novel reagents in solution permits the advantages of thermodynamically driven solid-state synthesis to be transferred to the production of clusters in solution. Most of the examples discussed could have been included in earlier chapters, but are gathered here to serve as a review as well as a stimulus to creative thought for future research in cluster and materials chemistries. 

Sol-gel chemistry has been extensively studied during the past decade. The basic reactions, hydrolysis, condensation, and complexation, involved in the formation of oxide networks from molecular precursors are now quite well described. The sol-gel process brings new opportunities in the field of materials science. It allows a powderless processing of glasses and ceramics. Coatings can be easily deposited directly from the solution onto a wide variety of substrates. Many patents have been taken and several products are now on the market. Other industrial applications will undoubtedly be developed during the next few years. 

C. W. Hills, S. Nashner, A.I. Frenkel, J.R. Shapley, R.G. Nuzzo, Carbon support effects on bimetallic Pt-Ru nanoparticles formed from molecular precursors. Langmuir 1999, 15, 690-700. 

Reactions to Form Compounds Containing ZintI Anions 10.2.2.3.2. From Molecular Precursors. 

Preparation of BN catalyst supports from molecular precursors. 

The conversion of the molecular precursors into boron nitride requires a ceramisation under an ammonia flow. Ammonia is used as a reductive atmosphere, and its ability to replace halo or amino groups on the borazine framework is well known [12,13]. Ammonia is also a curing reagent in the borazine polymerisation [25]. So, for the preparation of BN from molecular precursors, one usually needs to perform a low temperature ceramisation, up to 600°C at least, under an ammonia flow. The conversion of each precursor into BN has been studied using TGA up to 1000°C in order to optimise the ceramisation conditions and the properties of the obtained ceramic. The measurements were realised in a pure ammonia flow up to 650°C and then under nitrogen. The three tested compounds presented original behaviours related to their formulation and their reactivity towards ammonia. 

An obvious criterion is that the mineral moieties of interest have to be able to be dispersed in a suitable solvent in large enough concentrations. We have seen several examples of how this can be achieved by exfoliation or by direct self-assembly from molecular precursors. This dispersion step is probably one of the most delicate points to fulfill. 

GL Rice, SL Scott. Characterization of silica-supported vanadium(V) complexes derived from molecular precursors and their ligand exchange reactions. Langmuir 13 1545-1551,1997. 

There are two technically important methods by which extended Si/0 systems can be formed from molecular precursors. The first is by reaction of chlorosilanes with oxygen at high temperatures, while the second is by hydrolysis and condensation reactions of chloro- or alkoxysilanes. Chapters 32 and 33 deal with the structural evolution of siloxane structures in such reactions from an experimental and theoretical viewpoint. M. Binnewies et al. compare the stepwise formation of Si-0 networks from SiCU for both the combustion and hydrolysis reactions. The stability and reactivity of intermediate chlorosiloxanes is an important issue in this work. Both the initial process in the reaction of SiCfi with O2 and the growth of larger siloxane cages are investigated theoretically in the contribution of K. Jug. 

Fig. 1. General synthetic approach to ceramics starting from molecular precursors...

The synthesis of nanoparticles inside MOFs is another, still more special example of reactions inside the framework. Nanoparticles trapped inside MOF cavities, with a high number of reactive surface atoms, are indeed reactive species as well. Their synthesis inside the porous hosts, starting from molecular precursors, anticipates the caging effect of the framework. To prevent the clusters from growing to larger, bulk agglomerates, the space confinement of the framework pores is utilized naturally. 

Baldus, H.P., and M. Jansen. 1997. Novel high-performance ceramics amorphous inorganic networks from molecular precursors. 

The first of the so-called ship-in-bottle porphyrin systems, in which the porphyrin macrocycle is synthesized from molecular precursors inside the zeolite cavities, was... 

Gadet, V., Bujoli-Doeuff, M., Force, L., Verdaguo, M., El Malki, K., de Roy, A., Besse, J. P., Chappert, C., Veillet, P., and Rem, J. P. Towards high Tc ferro and ferrimagnetic bi and tridimensional materials from molecular precursors. NATO ASI Series (Eds D. Gatteschi O. Kahn J.S. Millw F. Falacio) Reidel (in press). 

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