Potassium fluoride–malonic acid, KF·CH2(CO2H)2: X-ray crystal structure determination and infrared spectrum reveals very short hydrogen bonds

Abstract

Crystals of the adduct KF·CH₂(CO₂H)₂, grown from aqueous solution, are unstable with evolution of HF. They show a remarkable cleavage. An X-ray crystal structure determination reveals a polymeric crystal arrangement of alternate malonic acid molecules and fluoride ions. Five different malonic acid–fluoride chains can be distinguished within the unit cell and there is a range of hydrogen bond lengths with R(O ⋯ F)= 2.41–2.49(4)Å. In most of these bonds one proton appears nearer the fluoride so that in effect the chains are composed of alternate HF molecules and hydrogen malonate ions, [⋯ O₂^–C–CH₂–CO₂H ⋯ F–H ⋯ O₂^–C–CH₂–CO₂H ⋯ F–H ⋯]_n.