THE [NHN](-) HOMOCONJUGATED ANIONS - X-RAY-DIFFRACTION, IR AND MULTINUCLEAR MR STUDIES

X-ray diffraction, IR and NMR studies are reported on chemically symme tric [NHN](-) anions formed by 1,8-bis(4-toluene-sulphonamido)naphthal ene, 1,8-bis(trifluoroacetamido)naphthalene, 1,8-diamino-2, 4,5,7-tetr anitronaphthalen and di-4-nitroimidazolyl-5-sulphide after abstraction of a proton by means of the proton sponge (DMAN), and in the 2:1 addu cts 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 wi th NHN+ cationic ones of similar geometry. They are characterized by a n asymmetric, in the scale of vibrations,H-atom localization in the br idge 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 shi ft and N-15-H-1 coupling constant yielded additional information on th e symmetry of [NHN]- bridges and localization of the bridge H-atom. (C ) 1998 Elsevier Science B.V..All rights reserved.