Sulfate binding with a tripodal tris(4-pyridylurea) receptor

The tris(2-aminoethyl)amine (tren)-based tris(4-pyridylurea) receptor L has been synthesized and its anion binding properties were studied. The ligand forms a 2:1 (host/guest) complex with MgSO₄, [SO₄ ^2-âŠL₂], in which a sulfate ion is encapsulated by six urea groups from the two ligands through multiple hydrogen bonds. The metal ions do not coordinate to the pyridyl groups but exist as the hydrate [Mg(H₂O)₆]²⁺ and interact with the [SO₄âŠL₂] capsules in the outer coordination sphere to form a three dimensional extended structure. The anion binding behavior of ligand L in solution was studied. The tripodal tris(4-pyridylurea) receptor (L) was synthesized and its anion binding properties studied. The ligand forms a 2:1 (H/G) complex with MgSO₄, [SO₄ ^2-âŠL₂], in which a sulfate ion is encapsulated by six urea groups as in the analogous complex of the 3-pyridyl-substituted ligand. The anion binding behavior of ligand L in solution was studied.