Complexation studies of phosphorus containing bis and tris (Benzocrown ether) moieties

The complexation behaviour between salts of Li+-Rb+ in CD3CN and tris(benzo crown ether)s 2a,b X=P(NMeN=CH-B15C5)(3) (X = O, S) and tri[bis(benzocrown ether)] [N=P(NMeN=CH-B15C5)(2)](3) 3 was investigated by C-13 NMR spectrosc opy. Using the program RMNSTAB, the complexation constants for the differen t possible complexes (M2L, ML and ML2 were L represents one benzo-15-crown- 5) were obtained and were compared with those of the corresponding monomer material. A remarkable "biscrown effect'' for compounds 2a,b and 3 was foun d, especially for potassium and rubidium by the predominant formation of st able ML2 complexes. The strong chelate effect make these ligands highly eff icient extracting agents for alkali metal picrate salts of K+, Rb+ and Cs+, as shown by UV-Vis spectroscopy.