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 ( ortho 4 and meta 8) 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.