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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.

The vibrational spectra of chloranilic acid (2,5-dihydroxy-3,6-dichloro-[1,4]-benzoquinone) in the solid state were studied by using inelastic neutron scattering (INS), infrared (IR) and Raman (R) spectroscopy. The spectra were compared with simulated spectra using the Gaussian and Climax programs. Sufficiently good agreement between the experimental and theoretical (DFT) spectra is observed although the calculations show that in the crystalline state a bifurcation of hydrogen bonds takes place. Relatively strong intermolecular interactions are noticeable when the experimental (x-ray) and calculated bond lengths and angles with participation of OH groups are compared. The studies of the deuterium isotope effect in the IR and R spectra enabled us to analyse the lowfrequency out-of-plane vibrations and particularly the (OH) and (OD) modes. In the case of the (OH) and (OD) vibrations, one observes a strong asymmetry of the bands (low-frequency wings), which can be interpreted in terms of a coupling of the (OH) mode with low-frequency ones damped by the lattice phonons and no fine structure of the (OH) and (OD) bands is observed.

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In searching for new molecular materials the crystals of 1:1 complexes of tetramethylpyrazine (TMP) with chloranilic acid (CLA) were grown. In the crystalline lattice of TMP.CLA infinite chains of hydrogen bonded components are formed. Very strong (d (O···N) = 2.692(2)Å) hydrogen bonds without proton transfer are present. The components of the complex form stacks of parallel arrangement with the distance typical of van der Waals interaction. One can conclude that in packing, interactions via hydrogen bonds play a decisive role. In the IR spectrum one observes a broad, continuous absorption with well resolved trio typical of strong hydrogen bonds. A detailed analysis of IR and Raman spectra in the low frequency region related to deformation vibrations of CH 3 groups shows that strong interaction via hydrogen bonding only slightly affects the dynamics of these groups.

The crystal and molecular structures of 4,4(')- and 6,6(')-dimethyl-2,2(')-bipyridyl complexes with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) have been determined and compared with those of the complex with the 5,5(')-derivative, which is known to possess interesting antiferroelectric properties. In the crystalline state, all three compounds form hydrogen bonded chains with N(+)-H···O(-) and O-H···N bridges on both sides of the bipyridyl constituent. The comparison of three derivatives indicates that the N(+)-H···O(-) hydrogen bonds are shortest for the 5,5(')-dimethyl complex. The 4,4(')- and 6,6(')-derivatives do not show any ferroelectric feature. The 6,6(')-one is, however, characterized by a continuous phase transition, revealed in the differential scanning calorimetry, dilatometric, and dielectric characteristics. The tunneling splitting measured by neutron backscattering in the energy range ±30 μeV for the neat dimethyl bipyridyls and their complexes with CLA indicates that the different splittings are primarily due to the crystal packing effect and that charge transfer between interacting compounds plays only a minor role.

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