Fluorine-19 NMR from retrosynthesis to NMR crystallography

Abstract

Recently, the need for more accurate structure description that will allow to analyze possible retrosynthesis of microporous compounds has led us to use and develop new structural strategies to access structure determination by solid state NMR techniques. At first, an example, AlPO4-CJ2, between crystallogenesis and crystal structure is explored. AlPO4-CJ2 has been studied by hydrothermal in-situ NMR. A soluble species exists in supersaturated liquid as well as the product of redissolution of AlPO4-CJ2. This species, the prenucleation building units (PNBU) is different from structural buildings units (SBU) the sub-ensembles of the crystal. How this PNBU gets into the structure and becomes therefore a structural building unit (SBU) is our main question. To answer it, an HETCOR experiment between fluorine and aluminum has been performed. This experiment shows that when the PNBU enters the solid, it forms at the same time than growing the solid, a fluorinated bridge. On ULM-18 after structure elucidation positioning hydrogen, a dynamic charge compensation mechanism is proposed for the solid formation. On TMPGaPO, a set of 2D experiments using radio frequency driven dipolar recoupling (RFDR) on 19F, Double Quanta on 31P and HETCOR between 19F and 31P allowed analyzing the topology of the network.