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
C2v-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.