Ion-pair binding by mixed N,S-donor 2-ureidopyridine ligands.

The synthesis of a simple ambidentate ligand 1-(3-methylsulfanyl-phenyl)-3-pyridin-2-yl-urea (L) capable of binding metal ions via a pyridyl nitrogen atom or thioether sulfur donor is reported. The pyridyl functionality is located adjacent to an anion binding urea group allowing this region of the ligand to bind contact ion-pairs by simultaneous coordination and hydrogen bonding interactions. This intimate ion-pair binding coordination mode is demonstrated by the X-ray crystal structures of [Ag(L)]X (X = CH(3)CO(2)(-), 1; NO(3)(-), 2). The non-coordinating PF(6)(-) anion is not bound as an ion-pair in [Ag(L)](PF(6)) (3) and the urea NH groups exhibit short contacts to carbonyl oxygen and pi-systems. The X-ray crystal structure of [Ag(L)(4)]BF(4) (4) is also reported, showing the ligand to be exclusively S-bound. Anion binding by L and its silver(I) complex is also explored by solution (1)H NMR spectroscopic methods.