Potassium fluoride–succinic acid adduct: a fully refined X-ray crystal-structure determination, ab initio calculations of a model system, and the infrared spectrum of a very strong hydrogen-bonded system

Abstract

The title complex KF·(CH₂CO₂H)₂, grown from aqueous solution, is orthorhombic, space group Pnam, with a= 7.0680(1), b= 5.5710(1), c= 16.846(2)Å, and Z= 4. Its structure, determined by X-ray diffraction techniques and refined to R 0.035, consists of infinite chains of fluoride ions joined to two succinic acid molecules by very short hydrogen bonds of R(O ⋯ F)= 2.441(3)Å. The complex [F(HCO₂H)₂]^– has been used as a model for the purpose of ab initio calculations on this doubly hydrogen-bonded fluoride, and these show a theoretical hydrogen-bond energy of 179 kJ mol^–1 for each bond. The i.r. spectrum of KF·(CH₂CO₂H)₂ shows eight very broad bands in several regions of the spectrum and these are assigned to the vibrational modes of this unique O–H ⋯ F^–⋯ H–O hydrogen-bonded system.