AlPO_4-CJ2 crystallogenesis has been followed by in-situ NMR and its solid state structure has been investigated by solid state NMR. The 4Ring units, that are connected to form the framework of the structure, have a bridging group which is fractionally occupied by fluorine or hydroxide. In solution the 4R unit does not exhibit this bridge. From the mechanistic description of the structure formation. it appears that the bridge forms at inclusion of the 4R into the crystal. Two phenomena are evidenced clearly in this study. First there is a definite relation between the species pre-existing in solution and the units identified in the crystal. However, both species differ by an isomerization. Second, nucleation and crystal growth differ for the mechanism of unit inclusion. At nucleation, units connect through the networking bonds. When the critical size of nucleation has been reached a clipping process transform the network into a crystallite by forming the proper conformation of bonds. In the case of AlPO_4-CJ2 the main aspect of this conformational transformation is the formation of the bridge in the 4R and the coordination change of one aluminum atom giving rise to some distances adjustment to allow for lattice formation. This phenomenon evidenced through the bridged formation of A1PO_4-CJ2 is of general significance in crystal formation. It may occur through covalent bonding as well as with hydrogen bonds or Coulombic interaction.
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