Tris chelating phosphate complexes of bis(thio)urea ligands

Two bisurea (L, L) and one bisthiourea (L ) ligands were synthesized and their anion coordination behavior was studied. These ligands can readily form the tris chelates [PO (L)] (1, 5, and 6) with phosphate ion (PO) in the solid state, in which the anion is coordinated by six urea groups through 12 hydrogen bonds. Solution binding studies by H NMR and UV-vis spectroscopy revealed different binding properties of the ligands toward phosphate ion. While the bis(p-nitrophenyl)- substituted bisurea L retains the 3:1 (host to guest) binding ratio in solution, the diethyl derivative L only forms 1:1 complex with phosphate ion. The more acidic thiourea L undergoes deprotonation/decomposition in the presence of phosphate ion. Moreover, the sulfate complex (2) of L and bicarbonate (3) and carbonate (4) complexes of L have also been obtained, which show lower coordination numbers both in the solid state and in solution. © 2013 American Chemical Society.