Structural (X-ray diffraction), infrared spectroscopic, and theoretical MP2 and DFT studies on the HBr and DBr adducts of 1,8-bis(dimethylamino)2,7-dimethoxynaphthalene ((CH3O)2.DMAN) were performed. This particular proton sponge has been chosen for its strong basicity and display of the buttressing effect influencing the hydrogen bond dynamics and properties. The studies revealed a symmetric, planar DMAN.H+ cation with a short (NHN)+ hydrogen bond of 2.567(3) A. The X-ray diffraction results suggest that the proton is in the central position in the bridge, while the calculations show two potential energy minima with the zero point energy level close to the top of the barrier. The infrared spectra display an (NHN)+ band at 488 cm(-1) and an (NDN)+ band at 235 cm(-1), respectively. It gives the isotopic ratio of 2.08, the highest value reported to date. Such a result suggests a peculiar shape of the potential for the proton motion, characterized by an extremely high positive anharmonicity. The calculations reproduce this particular potential, yielding an ISR value displaying a very good agreement with the experimental one. The anharmonic frequencies, however, show the discrepancy between the observed and calculated transitions.

A new proton sponge, 2,7-dibromo-1,8-bis(dimethylamino)naphthalene (Br2DMAN), 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 Br2DMAN.HBr salt, symmetrical (NHN)+ hydrogen bonding of length 2.547(3) Å 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 ∼560 cm−1 assigned to the ν(NHN) protonic transition. Deuteration leads to a shift of this band to ∼340 cm−1, so that the isotopic ratio νH/νD (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 N…N hydrogen bond length is 2.575 Å, while the distance between the minima equals to ca. 0.5 Å 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.

No abstract

No abstract