Fluxional template

Scheme 35 Fluxional template for radical enantioselective conjugate additions...

For halide ligands, a coordination number of four (/u4-X) is rare. Self-assembly of ds metal centers and halides around a pyramidal halide gives tetrapalladium complexes. In this unprecedented case the metallamacrocycle owes its formation to the halide acting as a template.347 The complexes (PPN)[Pd4(Fmes)4] (Fmes = 2,4,6-tris(trisfluoromethyl)phenyl) display fluxional behavior in solution in noncoordinating solvents.347... 

If the above scheme indeed holds in crystal nucleation, the conclusion is that a mother solution does not contain crystalline nuclei of all possible crystal polymorphs, but contains the mother of all polymorphs, a fluxional dropletready to evolve in several different crystalline directions. The mechanism of this process could be a mirror image of surface melting while in surface melting the isotropic surface layer rushes in toward complete melting, in crystallization within the nanoparticle the molecular ordering of the inner core successively templates the growing outer layer. 

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