Synthesis and anion recognition studies of new oligomethylene bis(nitrophenylureylbenzamide) receptors

A new series of oligomethylene bis(nitrophenylureylbenzamide) receptors were synthesized varying the relative position of the urea and amide groups (ortho4 and meta8) and the length of the oligomethylene chain (C(2) to C(8)). An anion recognition study was performed with TBAX salts (X = AcO(−), BzO(−), F(−), H(2)PO(4)(−), and HP(2)O(7)(3−)) by UV-vis and (1)H NMR. The flexibility of these receptors allows a cooperative effect of both ureylbenzamide units in the receptors. Noteworthy, the ortho position favored the 1 : 1 stoichiometry in the complexes with the carboxylates. The formation of 2 : 1 receptor–anion complexes with both types of receptors 4 and 8 and with hydrogen pyrophosphate and high log K values obtained were very significant in this work. The NMR studies evidenced the formation of supramolecular complexes, even in a competitive solvent, such as DMSO.