Ab initio structure determination of monoclinic 2,2-dihydroxymethylbutanoic acid from synchrotron radiation powder diffraction data: combined use of direct methods and the Monte Carlo method

The crystal structure of 2,2-dihydroxymethylbutanoic acid (C6H12O4) in mono clinic form has been determined ab initio from synchrotron radiation powder diffraction data. Two O and five C atoms were first derived by direct meth ods. Two missing O atoms and one C atom were found by the Monte Carlo metho d without applying constraint to their relative positions. Positional and i sotropic displacement parameters of these non-H atoms were refined by the R ietveld method. Molecules are linked by hydrogen bonds and they make sheetl ike networks running parallel to the (010) plane. The Monte Carlo method is demonstrated to be a powerful tool for finding missing atoms in partially solved structure.