Diprotonation of Guanidine in Superacidic Solutions.

Morgenstern, Yvonne; Zischka, Florian; Kornath, Andreas

Guanidinium chloride reacts with the superacidic solutions HF/MF5 (M=As, Sb) at a molar ratio of 1:2 under formation of the diprotonated guanidinium salts [C(NH2)2(NH3)][AsF6]2 and [C(NH2)2(NH3)][SbF6]2. The compounds were characterized by using infrared and Raman spectroscopy. Furthermore, single‐crystal X‐ray structure analysis of the guanidinium(2 ) salts [C(NH2)2(NH3)][SbF6]2⋅HF, [C(NH2)2(NH3)]2[Ge3F16]⋅HF, and [C(NH2)2(NH3)]2[Ge3F16]⋅2 HF and the guanidinium(1 ) salt [C(NH2)3][SbF6] is reported. The discussion of the experimental data is supported by quantum‐chemical calculations of the [C(NH2)2(NH3)]2 and [C(NH2)3] ions to investigate the modification of the resonance stabilization during the protonation process at the PBE1PBE/6–311G (3df,3pd) level of theory. The planar CN3 skeleton of the guanidinium(2 ) ion has two carbon–nitrogen bonds in the range 1.286(4)–1.293(4) Å and one carbon–nitrogen bond of 1.453(4) Å, which can be explained with a decreased resonance stabilization relative to the guanidinium(1 ) ion. Twice as positive: Salts of diprotonated guanidine have been isolated from superacidic solutions, even though the monoprotonated species is known as a remarkably stable cation. The guanidinium(2 ) salts are characterized by single‐crystal X‐ray structure analysis and vibrational spectroscopy for the first time (see picture).

PROTON transfer reactions; GUANIDINE; GUANIDINIUM chlorides; SOLUTION (Chemistry); RAMAN spectroscopy; QUANTUM chemistry

Chemistry - A European Journal, 2018, Vol 24, Issue 65, p17311

0947-6539

Academic Journal

10.1002/chem.201803726