Spectroscopic studies on charge transfer complexes of 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane with a series of electron acceptors

The interaction of the mixed oxygen-nitrogen cyclic base 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (D18C6) with various pi-acceptors, picric acid (HPA), chloranilic acid (H(2)CA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has been studied spectrophotometrically in CHCl3 and MeOH at 25 degrees C. The obtained complexes have been formulated as {[}(D18C6H(2))(PA)(2)], {[}(D18C6H(2))(CA)] and {[}(D18C6)(DDQ)]. The electronic absorption, H-1 NMR and infrared spectra of the obtained complexes indicate a strong interaction between the donor and acceptors associated with a proton migration from HPA and H(2)CA to the donor followed by intramolecular hydrogen bonding. The equilibrium constants, K-C, for the complexes are shown to be dependent on the structure of the used acceptors.