Crystal structures of some acid salts of monobasic acids. Part 18. Potassium hydrogen bisphenylacetate, redetermined by neutron diffraction

Abstract

The crystal structure of the title compound, KH[C₈H₇O₂]₂, has been redetermined by neutron diffraction and refined to R 2.8% for 991 reflections. The short, and formally symmetrical, hydrogen bond has O ⋯ H ⋯ O 2.454(3)Å. and the estimated relative vibrational motion of the proton has its maximum nearly parallel to the bond, with root-mean-square amplitude 0.18 Å. The vibrations of the other atoms are discussed, with their interpretation by various rigid-body models. The most satisfactory model is probably that which treats the ten heavier atoms of each phenylacetate residue as an independent rigid body. A small error in the monoclinic β angle affects earlier work on this structure, though its effects on derived molecular geometry are marginally significant only on the results of the 1 968 X-ray work. Amended cell dimensions are: a= 28.449(6), b= 4.480(1), c= 11.887(2)Å, β= 89.60(2)°. Geometric results of the X-ray analysis have been recalculated with these parameters and the agreement with neutron-diffraction results is satisfactory.