NMR of microporous compounds - From in situ reactions to solid paving

Alumino- and gallo-phosphate materials present a large variety of structure s. Among them, two new families the ULM and the MIL provide a large class o f microporous compounds. A systematic study has been undertaken for underst anding the main steps of solids formation. As these materials form under hy drothermal conditions, we developed in-situ NMR devices and methods for fol lowing pH and concentration of species during crystal formation. Coordinati on state of aluminum evolution during synthesis suggests a general mechanis m for the structural building unit formation. This mechanism is analyzed by quantitative evolution of liquid and solid phases in situ and ex situ. The dynamics of the different stages is therefore followed and the main steps of phase dissolution and crystallization are sequenced. Nucleation, which i s the most delicate step of evolution to characterize, is shown to witness unexpected chemical bond formation not seen in steps before. These chemical bonds formed during nucleation and crystal growth are demonstrated by comp aring building agents in solution and crystal structure. (C) 1999 Elsevier Science B.V. All rights reserved.