Low-temperature (120 K) structure and vibrational spectrum of protonated proton sponge: the adduct of 1,8-bis(dimethylamino)naphthalene (DMAN) with 4,5- dicyanoimidazole (DCI)
✍ Scribed by Eugeniusz Grech; Zbigniew Malarski; Wanda Sawka-Dobrowolska; Lucjan Sobczyk
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 111 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0894-3230
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✦ Synopsis
Low-temperature (120 K)
studies of the structure of the DMAN Á DCI adduct indicate that in symmetrical [NHN] hydrogen bridge of 2.571 (1) A ˚length (2.579(2) A ˚at room temperature) there is a disorder of the H-atom occupying two positions at nitrogen atoms with a distance of 0.94(3) A ˚. The comparison with the situation at room temperature seems to show a very low barrier for the proton transfer. The low-frequency vibrations with the participation of the whole N(CH 3 ) 2 groups observed in Raman and inelastic incoherent neutron scattering (IINS) spectra of about 100 cm À1 excited at room temperature cause the fundamental level of the protonic mode to penetrate or exceed the barrier. The bending CNC vibrations of about 500 cm À1 are strongly coupled with the protonic mode leading to Evans holes in the band ascribed to the 0 → 0 À transition. This hypothesis is consistent with the literature data relating to theoretical studies on H 3 NHNH 3 , which show that the barrier for the proton transfer disappears at the hydrogen bond length of about 2.55 A ˚.