Sulfate ion encapsulation in caged supramolecular structures assembled by second-sphere coordination

A tripodal tris(3-pyridylurea) receptor (L) assembles with metal sulfate salts MSO(4) (M = Mn, Zn) to afford supramolecular cages [SO(4)subset of L(2)] that encapsulate the SO(4)(2-) ion via multiple hydrogen bonds in a three-dimensional structure held by second-sphere coordination; (1)H NMR and negative-ion mode ESI-MS spectra reveal significantly strong sulfate binding in solution.