A new proton sponge, 2,7-dibromo-1,8-bis(dimethylamino)naphthalene (Br(2)DMAN), and its protonated (HBr) or deuterated (DBr) forms were studied by using x-ray diffraction and infrared spectroscopy, as well as ab initio and density functional theory calculations. In the crystalline lattice of the Br(2)DMAN(.)HBr salt, symmetrical (NHN)(+) hydrogen bonding of length 2.547(3) A is observed. No deuterium geometrical isotope effect was detected. The structure refinement suggests disordering of protons between two equivalent positions at the nitrogen atoms. These findings are in agreement with infrared spectra, which are characterized by an intense band centered at similar to560 cm(-1) assigned to the nu(NHN) protonic transition. Deuteration leads to a shift of this band to similar to340 cm(-1), so that the isotopic ratio nu(H)/nu(D) (ISR) of 1.65 is characteristic of an unusual potential for the proton motion. The results of MP2 calculations are in fairly good agreement with the experimental data. The theoretical (NN)-N-... hydrogen bond length is 2.575 A, while the distance between the minima equals to ca. 0.5 A with a barrier height of 0.70 kcal/mol. The calculated difference between the 0-->1 proton (deuteron) levels is 509 (284) cm(-1), giving an ISR value of 1.76. (C) 2003 American Institute of Physics.