Diprotonation of Guanidine in Superacidic Solutions.

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 [Ge3 F16 ]⋅HF, and [C(NH2 )2 (NH3 )]2 [Ge3 F16 ]⋅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.