Anion Cluster: Assembly of Dihydrogen Phosphates for the Formation of a Cyclic Anion Octamer

Structural characterization of a dihydrogen phosphate complex of triprotonated tris­[2-(2-thienylmethylamino)­ethyl] amine shows that eight dihydrogen phosphate anions are assembled around the host by strong interactions of H-bond donors and acceptors to form a new type of cyclic anion octamer as (H2PO4¯)8, an analogy of cyclic water octamer. The presence of an anion cluster has also been identified by electrospray ionization mass spectrometry and 31P NMR experiments.