Monolayer aggregation of a series of atypical amphiphilic β-diketone rare earth complexes at air/liquid interface

Monolayer aggregation of a series of atypical amphiphilic rare earth complexes REL3Phen [RE=Eu(III), Sm(III), Tb(III); L=acac (acetylacetone), TFA (trifluoroacetylacetone), HFA (hexafluoroacetylacetone), TTA (thenoyltrifluoroacetone); Phen=1, 10-phenanthroline] were investigated at the air/liquid interface by π-A isotherms, Brewster angle microscopy (BAM) and transmission electron microscopy (TEM). When the complexes were mixed with arachidic acid (AA), respectively, stable monolayers could be formed. The rare earth complexes could be divided into two classes according to the π-A isotherm shape that whether there was a plateau period or not. Complexes with β-diketones acac, TFA and HFA were in one class, while complexes with the β-diketone TTA were in another. All the rare earth complexes formed microcrystals at the air/liquid interface. However, the former complex microcrystals oriented with the same crystal plane facing to all directions upon compression; while the latter complex microcrystals oriented with the same crystal plane facing to the same direction. Differences between monolayer behaviors of the two classes of complexes were discussed by comparing the structure of β-diketone ligands. A possible structural model of the rare earth complexes in the mixed monolayers with AA at air/liquid interface was proposed.