1-Dimethylamino-2,7-dimethoxy-8-methylamino-3,5-dinitronaphthalene and 1,2,4-tribromo-6-dimethylamino-5-methylaminoacenaphthylene: first examples of N—H...N hydrogen bond contraction/expansion in neutral 1,8-diaminonaphthalenes

1-Dimethylamino-2,7-dimethoxy-8-methylamino-3,5-dinitronaphthalene and 1,2,4-tri-bromo-6-dimethylamino-5-methylaminoacenaphthylene containing the N,N,N′-trimethyl-1,8-diaminonaphthalene fragment with the substituted aromatic ring were studied by X-ray diffraction. Both systems are stabilized by an intramolecular hydrogen bond. The characteristics of the latter are determined by the influence of either the ortho substituents or the peri-annelated five-membered ring. In the former case, the intramolecular hydrogen bond is substantially shortened (N...N, 2.628(5) Å) due to the “buttressing effect” of the o-OMe groups, whereas the peri-dibromoethylene bridge and the Br substituent at position 4 cause a substantial elongation of the intramolecular hydrogen bond (N...N, 2.75(2) and 2.76(1) Å) in the latter case. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2414–2417, November, 2005.