Adduct Formation between Organic Oxoanions and Hexaazamacrocycles

Five adducts formed by organic acids and two hexaazamacrocycles, 1,4,7,10,13,16-hexaazacylooctadecane (L1) and 1,2-[bis(1,4,7-triazacyclononan-1-yl]ethane (L2), viz., (H6L1)(ox)2(Hox)2 (1), (H6L1)(TFA)6(H2O)2
(2), (H2L1)(pic)2(H2O)5 (3), (H3L1)(BNPP)3(H2O)5 (4) and (H4L2)(C12H8N2O8P2)4(H2O)0.5, or (H4L2)(BNPP)4(H2O)0.5
(5) (ox = C2O42-, TFA = CF3CO2-, pic = C6H4NO2-, and BNPP = (O2NC6H4O)2PO2-), were crystallized from aqueous
solutions containing the azamacrocycles and the organic oxoanions. Crystal structure determinations have allowed
an examination of hydrogen bonding and electrostatic interactions contributing to the supramolecular architectures.
The flexible L1 ligand is found in degrees of protonation ranging from fully protonated to diprotonated, with anions
binding both above and below the cavity to balance the charge on the macrocycle. Of particular interest are compounds
4, which contains the only structurally characterized example of [18]aneN6 in a triprotonated state, and 3, which
exhibits the second example of the macrocycle hosting two ammonium groups. For the bis(tacn) macrocycle, the
anions were found to bind only on one side of the macrocycle. With the exception of 4, the macrocycles display the
ability to chelate a single anionic oxygen atom. All the structures except 1 employ water in assisting the formation
of stable lattices, sometimes showing complex and unique formations including a water−phosphate cage in 4.