KHF2 Research Articles

The Polarized Infrared Spectrum of Potassium Bifluoride at − 185°C

Observations on the reflection spectrum of potassium bifluoride have recently been reported [1] which appear to confirm the symmetrical linear structure of the bifluoride ion in this crystal. Some time ago absorption spectra of single crystals of KHF2 using polarized infrared radiation were obtained in this laboratory which both confirm this work and supplement it. Owing to the improved resolution of complex absorption regions which we obtained at low temperatures it seems worthwhile to present these results briefly. The spectrum is possibly unique in the wealth of combination and overtone bands which arise from a crystal of structure so simple that a detailed interpretation may be anticipated.

Nature of the Hydrogen Bond in Potassium Hydrogen Fluoride

In 1941 Ketelaar1 published accurate measurements on the infra-red absorption and reflexion spectra of potassium hydrogen fluoride (KHF2). The two strong peaks of 1450 and 1222 cm.−1 were interpreted as a doubling of the fundamental asymmetric valence frequency v3 belonging to the vibration of a proton between two F− ions. The doubling was assumed to be caused by a double-minimum potential curve of the type occurring in the NH3 molecule. The splitting of the lowest vibrational level was estimated to be 25 cm.−1 and the distance between the two equilibrium positions 0.70 A.

The Double Minimum Problem Applied to Potassium Hydrogen Fluoride

The doublet character of the infra-red absorption line at 2.67μ of solid potassium hydrogen fluoride is due to the ``tunnel effect.'' The proton has two potential minima between the fluorine nuclei in the FHF− ion. The distance of a minimum to the center of the ion is 0.26A. The height of the potential hill is 33,400 calories.

Raman effect investigations of aqueous solutions of potassium hydrogen fluoride and hydrofluoric acid

Raman effect investigations of aqueous solutions of potassium hydrogen fluoride and hydrofluoric acid

Infra-Red Absorption Studies X. The Infra-Red Absorption of Hydrogen Fluoride in the Vapor State and in Solution in an Inert Solvent

The infra-red absorption of hydrogen fluoride has been observed both with the prism and the grating spectrometer. The absorption in the vapor for the single molecules is as previously reported by Imes. At slightly longer wave-lengths a very strong absorption band due to the hydrogen bonding in the associated molecules is observed. In solution in carbon tetrachloride the single molecule spectrum undergoes considerable modification and no association is observed. This fact is rather surprising. The infra-red absorption of a thin crystal of potassium hydrogen fluoride was studied in order to fix the frequency of the hydrogen in the FHF- ion.

Structure and thermal properties

The effect on the lattice spacings of substituting deuterium for hydrogen has been investigated for pentaerythritol, CuS0 4 5H 2 0, SrCl 2 6H 2 0, furmaric acid, KH 2 P0 4 , NaHS0 4 , urea, and KHF 2 . The main conclusion is that when the crystal structure contains hydroxyl bonds the isotope effect is small, and when it contains hydrogen bonds there is a marked expansion, which disturbs the lattice sufficiently to lead to the separation of potassium phosphate in a new crystal structure. The effect for potassium hydrogen fluoride does not suggest a short hydrogen bond in this compound. Short hydrogen bonds seem to require special resonance forces for their explanation.

A Redetermination of the Fluorine-Fluorine Distance in Potassium Bifluoride

A Redetermination of the Fluorine-Fluorine Distance in Potassium Bifluoride

The molecular structures of carbon and silicon tetrafluorides.

The tetrahedral structure of the halides of Group IV is well established. The relation of the molecular constants to the force field governing the motion of the atoms is less certain; in particular, some difficulty has been found in reconciling the interatomic distances obtained by electrons diffraction with those deduced by other means. We have obtained certain of these molecular constants from an examination of the infra-red absorption spectra of gaseous carbon and silicon tetrafluorides. Preparative Carbon tetrafluoride was formed by the direct action of fluorine on carbon. The halogen was generated by the electrolysis of fused potassium bifluoride in a copper vessel, the anode being a graphite rod; the gas was passed through a hard glass tube packed with sodium fluoride and then through charcoal. A stream of dry nitrogen had been passed through the absorbents and the molten electrolyte for some hours. The resulting gas was condensed in a liquid air trap, and separated; after evaporation through silver nitrate solution to remove oxygen and silicon fluorides, and through soda-lime to remove hydrogen fluoride and CO 2 , it was again condensed and fractionally distilled, as far as was possible with the small yields obtained, over a small temperature range at about - 130° C.