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-dimethylammoniomethyl-naphthalene nitrate

Abstract

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] +·NO − 3, P. Brzezinski, T. Głowiak, 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 = 11.004(6), b = 11.5132(6), c = 12.2636(7) Å, β = 91.863(4)° 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) Å, 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 Å and 157°, respectively.