Fluoride und Fluorosäuren, VII [1]. Kristallstrukturen von Säurehydraten und Oxoniumsalzen, XXII [2]. Hydratbildung der Trifluoressigsäure sowie Strukturen eines Monohydrats und eines Tetrahydrats [3]. / Fluorides and Fluoro Acids, VII [1] Crystal Structures of Acid Hydrates and Oxonium Salts, XXII [2]. Hydrate Formation of Trifluoroacetic Acid and Structures of a Monohydrate and a Tetrahydrate [3]

Abstract

<jats:p>The liquidus and solidus lines of the quasi binary system CF<jats:sub>3</jats:sub>COOH-H<jats:sub>2</jats:sub>O were determined by low temperature difference thermal analysis and the resulting phase relations controlled by X-ray powder diffraction. Formation of a monohydrate and a tetrahydrate, melting congruently at -43 and -16 °C, respectively, is confirmed. In addition a metastable form of the monohydrate and a low temperature form of the tetrahydrate, stable below -47 °C, are indicated. The crystal structures of the stable high temperature forms were determined. From these the monohydrate (tetragonal, space group I42d, Z = 16) is a true acid hydrate, CF<jats:sub>3</jats:sub>COOH-H<jats:sub>2</jats:sub>O, and the tetrahydrate (triclinic, P1̅, Z = 2) a hydrated oxonium salt, (H<jats:sub>5</jats:sub>O<jats:sub>2</jats:sub>)<jats:sup>+</jats:sup>[H(CF<jats:sub>3</jats:sub>COO)<jats:sub>2</jats:sub>]<jats:sup>-</jats:sup> · 6H<jats:sub>2</jats:sub>O.</jats:p>

Synthesis and characterization of trifluoromethylcarboxonium salts

“…The former carbonyl bond is slightly elongated compared to the CO double bond length (1.197(10) Å) found in the crystal structure of the monohydrate of trifluoroacetic acid. 14 The C–C bond does not exhibit significant differences from the C–C bond distances in CF 3 COOH·H 2 O. Both the C–O bond lengths and O–C–O/C–C–O bond angles are consistent with values found in other protonated carboxylic acids.…”