Architecture of silsesquioxanes

The family of silsesquioxanes includes compounds where each silicon atom is linked to three oxygen atoms and connected to an organic function or the hydrogen atom. The preparation of silsesquioxanes by sol-gel chemistry offers large possibilities for obtaining functional and smart materials, thanks to the large variety of available organoalkoxysilanes and the stability of the Si-C bond. However, only the deep understanding of oligomer growth and assembling and the knowledge of building blocks structural features can direct the synthesis approach toward the production of materials with desired functionalities. The main targets of this chapter include the influence of synthesis conditions on solgel preparation of silsesquioxanes, with focus on organoalkoxysilane hydrolytic condensation, and the characterization of oligo- and polysilsesquioxanes aimed at controlling structural features for tuning structure-property relationships. The structural characterization by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) analyses and the contribution of theoretical studies to the understanding of silsesquioxane architecture are discussed in this chapter, but it is worth of noting that many different techniques contributed in elucidating silsesquioxane structures.