Anion binding with a tripodal amine

Binding studies of the tren-based amine, L (N,N',N''-tris(2-benzylaminoethyl)amine), with inorganic anions and two crystal structures, [H3L][H2PO4](3).H3PO4 and [H3L][Br](3), are reported. NMR titration results indicate that the ligand binds H2PO4- and HSO4- more strongly than NO3 and halides. In the crystal structure of the phosphate complex, the ligand is triprotonated with the three arms pointing outward in a trigonal-planar-like arrangement, Four phosphate species are associated with the receptor, and have been assigned as three H2PO4- counterions located between each of the tren arms, and an additional H3PO4 Molecule above the quasi-planar tren. The structure of the bromide complex is slightly different, although again the tren receptor is triprotonated and quasi-planar, but in this case C-2v-like symmetry is seen with two of the arms pointed in the same direction with a bromide ion in between. The other two bromides lie outside of the tren arms.