Vibrational and 119Sn Mössbauer spectra and X-ray crystal structure of ammonium tetrafluorodimethylstannate(IV)

Abstract

Ammonium tetrafluorodimethylstannate(IV) has been prepared and characterized by IR, Raman and 119Sn Mössbauer spectroscopies. The Mössbauer parameters place this compound at the frontier between the dimethyltin(IV) compounds that gave rise to the quadrupole splitting (QS) vs. CSNC angle correlation, and the dimethyltin(IV) salts of strong protic acids and superacids. The Mössbauer QS, as well as the IR and Raman spectra, indicate that the CSNC angle is 180°. The IR-active v(SnF) E u mode appears at 345 cm −1, and this mode is related to the Mössbauer QS for trans-[SnF 4L 2] because strong donors have a negative partial quadrupole splitting (pqs) and weaken the SnF bond. The IR spectrum also suggests the existence of normal (not polyfurcated) NH⋯F hydrogen bonds. The X-ray crystal structure contains two crystallographically independent centrosymmetric [Me 2SnF 4] 2- anions, but only one kind of NH 4 + cation. The cations and the anions are linked by nearly linear NH⋯F hydrogen bonds giving rise to a three-dimensional network. The average SnF distance is 2.127 Å and the usefulness of covalent radii to predict accurate bond distances is challenged. An equation to calculate the average SnF distance in complexes [SnF 4L 2] from the Mössbauer QS is proposed.