The [NHN]- homoconjugated anions:: X-ray diffraction, IR and multinuclear MR studies

X-ray diffraction, IR and NMR studies are reported on chemically symmetric [NHN](-) anions formed by 1,8-bis(4-toluene-sulphonamido)naphthalene, 1,8-bis(trifluoroacetamido)naphthalene, 1,8-diamino-2, 4,5,7-tetranitronaphthalen and di-4-nitroimidazolyl-5-sulphide after abstraction of a proton by means of the proton sponge (DMAN), and in the 2:1 adducts of 4,5-dicyanoimidazole and 2-amino-4,5-dicyanoimidazole with DMAN as well as in the conjugated tetrazole-tetrazolate anion. The anionic NHN- hydrogen bonds studied so far are markedly weaker as compared with NHN+ cationic ones of similar geometry. They are characterized by an asymmetric, in the scale of vibrations,H-atom localization in the bridge with the protonic (NHN)- band located usually in the region 2600-3000cm(-1)!. The delta(1)H value in acetonitrile of the bridge proton in [NHN]- anions studied until now is between 14.1 and 16.4 ppm, while that in protonated DMAN is 18.7 ppm. The studies on N-15 chemical shift and N-15-H-1 coupling constant yielded additional information on the symmetry of [NHN]- bridges and localization of the bridge H-atom. (C) 1998 Elsevier Science B.V..All rights reserved.