Structure and IR Spectra of Protonated 1,8-Bis(dimethylamino)naphthalene Proton Sponge

A review of X-ray diffraction studies (including those not published so far) on a number of salts composed of l,8-bis(dimethylamino)naphthalene (DMAN) and various proton donors is presented. The symmetry of intramolecular NHN+ bridges in protonated DMAN changes depending on the counteranion and the resulting lattice potential in the neighbourhood of a bridge. Symmetrical NHN+ bridges in solid protonated DMAN arc characterized by a low frequency v(NHN) stretching vibration at about 500-000 cm-1. The symmcüy causes a broadening and some diminishing of integrated intensity of the band and a shift of its centre of gravity towards higher frequencies. In some cases, an additional absorption at about 2000 cm-1 appears. Quite differently behave the protonated DMAN species in acetonitrile solution. In all cases, the so called continue appear, extending between 200-3000 cm-1. In the case of moderately strong proton donors (both for OH and N-N acids) complicated ionic equilibria arc evidenced, in which protonated DMAN.H + cations, free molecules of DMAN and homoconjugated OHO" or NHN" anions participate