DISORDER IN THE INTRAMOLECULAR [N-H...N]+ HYDROGEN-BOND - THE REDETERMINATION OF THE CRYSTAL AND MOLECULAR-STRUCTURE AT LIQUID-NITROGEN TEMPERATURE OF 8-DIMETHYLAMINOMETHYL-1-DIMETHYLAMMONIOMETHYLNAPHTHALENE NITRATE

1,8-Bis(dimethylaminomethyl)naphthalene (DMAMN) is a "proton sponge", and protonation leads to the formation of a strong intramolecular [N-H ... N]+ hydrogen bond. In the recently reported room-temperature structure of the salt [DMAMNH]+.NO3-, P. Brzezinski, T. Glowiak, E. Grech, Z. Malarski and L. Sobczyk, J. Chem. Soc., Perkin Trans. 2, (1991) 1643, the intramolecular hydrogen bond displays an unusual geometry with a nearly symmetrical position of the H atom implying long N-H distances. In order to obtain accurate information on the geometry of this [N-H ... N]+ hydrogen bond and to investigate the possible occurrence of disorder, the structure was redetermined at liquid nitrogen temperature (100 K). The salt crystallizes in space group P2(1)/c (as at room temperature) with a = 11.0004(6), b = 11.5132(6), c = 12.2636(7) angstrom, beta = 91.863(4)-degrees and Z = 4. The structure was refined to R = 0.037 for 2811 unique reflections. Difference Fourier syntheses of the N ... N region and the results of refinement revealed disordering of the H atoms over two positions. Refinement of the population parameter resulted in stable N(1)-H and N(2)-H distances of 0.83(6) and 1.04(3) angstrom, and population parameters of 0.34 and 0.66, respectively. The extremely long N-H distance at room temperature may be interpreted as the result of increased disordering at elevated temperatures. Because of the absence of intermolecular N-H...O hydrogen bonds, the packing is chiefly determined by C-H...O interactions, all of which involve the charged oxygen acceptors of the nitrate anion. The average C...O and H...O distances and C-H...O angles of nine interactions are 3.393, 2.35 angstrom and 157-degrees, respectively.