Ab initio structure determination of 5-anilinomethylene-2,2-dimethyl-1,3-dioxane-4,6-dione from laboratory powder data--a combined use of X-ray, molecular and solid-state DFT study

The crystal structure of the title compound was solved from laboratory powder diffraction data in the triclinic group P\bar 1 by simulated annealing using the program DASH. Since Rietveld refinements yielded inaccurate geometries the structure was finally refined by geometry optimization using energy minimization in the solid state with the DFT/plane-waves approach. The molecule is essentially planar and its Meldrum's acid moiety (2,2-dimethyl-1,3-dioxane-4,6-dione) has a flattened boat conformation. The bond orders in the molecule estimated using a natural bond-orbitals formalism correlate with the optimized bond lengths. The structure in the solid state is based on dimer units in which the molecules are held by N-H...O and C-H...O hydrogen bonds in addition to electrostatic interactions. These units interact through weak C-H...O hydrogen bonds. It is suggested that structure refinement by energy minimization at the DFT level of theory may in many cases successfully replace Rietveld refinement.