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Investigations on Squaric Acid in Superacidic Media
Author(s) -
Schickinger Manuel,
Cibu Denise,
Zischka Florian,
Stierstorfer Karin,
Jessen Christoph,
Kornath Andreas
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201802516
Subject(s) - squaric acid , chemistry , protonation , monoclinic crystal system , crystallography , dication , crystal structure , molecule , organic chemistry , ion
The syntheses of [OC(COX) 3 ][MF 6 ] and [(COX) 4 ][MF 6 ] 2 ⋅2 HF were carried out in superacidic media XF/MF 5 (M=As, Sb; X=H, D). The degree of protonation is highly dependent on the stoichiometric ratio of the Lewis acid with regard to squaric acid. The salts of diprotonated squaric acid were characterized by Raman spectroscopy and, in the case of [(COH) 4 ][MF 6 ] 2 ⋅2 HF (M=As, Sb), by single‐crystal X‐ray structure analyses. [(COH) 4 ][AsF 6 ] crystallizes in the monoclinic space group P 2 1 / n with two formula units per unit cell. Analysis of the vibrational spectra was achieved with the support of quantum chemical calculations of the cation [(COH) 4 ] 2+ ⋅4 HF on the PBE1PBE/6‐311G++(3df,3pd) level of theory. Furthermore, a salt of monoprotonated squaric acid, [OC(COH) 3 ][AsF 6 ], was characterized by a single‐crystal X‐ray structure analysis. It crystallizes in the monoclinic space group P 2 1 / n with four formula units per unit cell. The protonation of squaric acid leads to a change of the carbon skeleton, which is discussed for the entire series, starting with the dianion of squaric acid and ending with the tetrahydroxy dication.