Oxo-anion binding by protonated (dimethylphenyl)(pyridyl)ureas

The anion coordination chemistry of two protonated urea-based ligands, N-(2,4-dimethylphenyl)-N′-(3-pyridy1)urea (1) and N-(2,6-dimethylphenyl)- N′-(3-pyridy1)urea (2) is reported. Reaction of 1 or 2 with inorganic oxo-acids such as perchloric, nitric or sulfuric acid affords the adducts (3-6) of the corresponding anions with protonated ligands (1H⁺ and 2H ⁺). The solid-state structures of the anion complexes display a rich variety of hydrogen bond motifs involving the urea NH groups, carbonyl, protonated pyridyl NH⁺ fragment, water molecules, and the anions. While complexes with ligand 1 (3 and 4) crystallize as monohydrate, compounds with 2 (5 and 6) are solvent-free, which leads to notable differences in their hydrogen bond patterns. When crystallized from the acid mixture HClO ₄/HNO₃ or HClO₄/H₂SO₄ both 1 and 2 selectively bind the perchlorate anion.