The use of spectroscopic data in the least-squares refinement of diffraction-obtained structure parameters. An example: K₂C₂O₄.H₂O

A method is presented in which parameters obtained from vibrational spectroscopy are used in the least-squares refinement of positional and thermal parameters obtained from diffraction data. The method involves the calculation of those contributions to the temperature factors not well described by the second-rank tensor approximation conventionally used in crystal structure determinations. Expressions are given for the temperature-factor contributions from vibrational motion on an arc and from anharmonic linear motion. The method is applied to the water molecule in dipotassium oxalate monohydrate, 2K⁺.C₂O^-₄.H₂O. Refinements using vibrational data are compared with a conventional refinement; the latter are shown to give considerable systematic errors in the geometrical parameters for the water molecule.