Charge density in crystalline citrinin from X-ray diffraction at 19 K

For the fungal metabolite citrinin, C 13 H 14 O 5 , the total experimental electron distribution ρ( r ) and its Laplacian have been obtained from an extensive set (36 564 measurements) of single-crystal X-ray diffracted intensities at a temperature of 19 ± 2 K. Relevant steps in data collection and processing are reported. The resulting 7698 independent intensity data have been analysed with a multipole (pseudoatoms) formalism. The topological properties of ρ( r ) have been determined according to the quantum theory of atoms in molecules. CC and CO bond path lengths have been obtained by numerical integration; their values are found to be well correlated with those of the electron density at the bond critical points. Topological features have been used to characterize the extension of the conjugated system of the molecule, and to confirm the stability of its rings, particularly the two formed by intramolecular H bonds. Maps of are presented, showing details in the valence charge distribution and providing a very sensitive tool for analysing dependence of the density on the model adopted to interpret X-ray data. The known chemical reactivity of the molecule towards nucleophiles at a Csp 2 atom is confirmed by the shape of the molecular reactive surface (the zero envelope of ). Key words: experimental electron density, low-temperature X-ray diffraction, topological analysis, Laplacian of ρ.