Crystal structure and infrared and Raman spectra of tetramethylammonium di-µ-fluoro-bis[aquadifluoro-oxovanadate(IV)]

Abstract

The title complex, [NMe₄]₂[V₂O₂F₆(OH₂)₂], has been isolated from an aqueous solution of VF₄ and [NMe₄]F. The crystal structure has been determined from three-dimensional counter X-ray data. The compound crystallizes in the triclinic space group P with a= 7.012(1), b= 8.119(1), c= 9.047(1)Å, α= 65.84(1), β= 83.21(1), γ= 73.09(1)°, and Z= 1. Least-squares refinement of the structure based on 1 552 observations led to an R factor of 0.046. The structure consists of dimeric units [{VOF₃(OH₂)}₂]^2– possessing a centre of inversion, which are linked in chains by short hydrogen bonds [O–H ⋯ F 2.564(5)Å]. The geometry around vanadium is distorted octahedral with vanadium-fluorine distances ranging from 1.894(4) to 2.173(3), V–O 1.607(5), V–OH₂ 2.074(3), V–V 3.292(1)Å, and V–F–V 105.5(1)°. The i.r. (250–4 000 cm^–1) and Raman spectra of [NMe₄]₂[V₂O₂F₆(OH₂)₂] and its deuteriated and anhydrous derivatives are reported and interpreted according to the structure. The spectrum of the cation shows only influences of the solid-state forces. Stretching vibrations of the VO bonds appear either in the Raman (980 cm^–1) or the i.r. (968 cm^–1). Hydrogen bonds give rise to a strong absorption manifesting one of the strongest interactions in hydrates (3 205 and 3 030 cm^–1). The shift (ν_H/ν_D= 1.34) and the reduction in band width (factor of 1.8) upon deuteriation have expected values. The spectra of the product of reversible dehydration indicate the absence of a centre of inversion in the anionic portion.