Sulfonyl-bridged oligo(benzoic acid)s 7 n (n = 2-4) are prepared from the corresponding triflate esters (8 n ) of sulfur-bridged oligophenols by palladium-catalyzed methoxycarbonylation of the triflate moieties, followed by hydrolysis of the resulting methyl esters, and subsequent oxidation of the sulfur bridges. X-ray analysis reveals that dimer 7 2 forms supramolecular zig-zag chains through intermolecular hydrogen bonds between the carboxy groups. As for the crystal of trimer 7 3, two molecules are associated through two couples of intermolecular hydrogen bonds between terminal and central carboxy groups to form a cyclic dimer, which connects with two adjacent dimers with the remaining carboxy groups to construct an infinite columnar structure. Tetramer 7 4 adopts a monomolecular cyclic structure through intramolecular hydrogen bonds between the terminal carboxy groups, and a molecule connects with each of two adjacent molecules through two couples of intermolecular hydrogen bonds between inner carboxy and sulfonyl groups. Solvent extraction experiments reveal that the oligo(benzoic acid)s exhibit high extractability toward lanthanoid ions (Ln3+); the performance follows the order 7 4 ≈ 7 3 > 7 2 . Moderate extraction selectivity is observed for the extraction of Pr3+, Gd3+, and Yb3+ with 7 2 . X-ray crystallographic analysis of cluster [Tb4L4(H 2O)6](Et3NH)4, which was prepared from 7 4 (H4L) and Tb(NO3)3· 6H2O in the presence of Et3N, reveals that no sulfonyl oxygens coordinate to the metal centers. This indicates that the high extractability of 7 4 originates from the electron-withdrawing nature of the sulfonyl function, which increases the acidity of two adjacent carboxy groups.
|Number of pages||10|
|Journal||Journal of Inclusion Phenomena and Macrocyclic Chemistry|
|Publication status||Published - 2014 Apr|
- Lanthanoid ion
- Oligo(benzoic acid)
- Solvent extraction
- Sulfonyl group