From a Single Molecule to Molecular Crystal Architectures: Structural and Energetic Studies of Selected Uracil Derivatives

A comprehensive analysis of crystal packing and energetic features of the selected uracil derivatives (i.e., 1-methyluracil, 1,5-dimethyluracil, 5-fluorouracil, 2-thiouracil, 4-thiouracil, 2,4-dithiouracil, and 6-methyl-2-thiouracil) is reported. High-quality X-ray diffraction data sets of the studied compounds were subjected to the TAAM procedure (Transferable Aspherical Atom Model based on the Hansen–Coppens formalism), which gave results comparable both with the optimized and neutron-diffraction-derived geometries. Crystal packing motifs were investigated with the aid of Hirshfeld surface fingerprint plots. Most of the structures form hydrogen-bonded layers kept together by π-stacking interactions. The only exception is 2,4-dithiouracil, which exhibits a rather complex 3D network based on N–H···S and C–H···S contacts. The TAAM procedure allows also for a quite reliable reconstruction of the electron density distribution in a crystal structure. It was therefore possible to rationalize the existence of s...