Combining the useful properties of lanthanides with self-assembled structures provides the opportunity to produce innovative new technologies with a multitude of applications and advantages. Of global interest, are their uses within modern technologies, such as permanent magnets in wind turbines and electric car batteries.
(1R,2R)-1,2-diaminocyclohexane was used to synthesise a ditopic salen ligand, LN1. Synthetic methods included mono-protection of one of the amine groups on the cyclohexane ring, followed by a Schiff base reaction on the unprotected amine using 5-bromosalicylaldehyde, to form an ammonium salt. A 2:1 equivalence of the ammonium salt with 2,6-dihydroxynapthalene-1,5-dicarbaldehyde was reacted in a one-pot synthesis, forming the ditopic ligand, LN1. As part of each synthetic step, 1H NMR, 13C NMR, and IR was recorded, where possible, in order to confirm formation of the desired products.
Investigation into the effect of concentration on the self-assembly of macrocyclic complexes was carried out through serial dilutions of a solution consisting of the ligand, LN1, with Y(OTf)3, a proxy-lanthanide. DOSY NMR analysis followed, which recorded the log diffusion coefficient, a measurement of speed, of each species. Based on the approximation that a larger species would have a significantly lower value than a species of a smaller size, identifying the log diffusion coefficient was of significance when determining complex size. Measurements obtained from DOSY NMR were related to computationally calculated values, in order to estimate an approximate identity for each species.
Successful formation of the square macrocyclic complex was reported within the ligand – lanthanide samples when at concentrations of 2 x 10-2 mol dm-3 and 1 x 10-2 mol dm-3. The 1 x 10-2 mol dm-3 concentration displayed also a trimeric, dimeric, and monomeric variation of the complex, suggesting this concentration neared the lower self-assembly concentration (LSAC). The 2 x 10-3 mol dm-3 concentration showed only the monomeric form of the complex. All serial dilutions were taken in a CD3CN/CD3OH solvent mixture.
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