X-ray charge density study of the 6-methyluracil derivative in the crystal: Revealing, consequences, and multipole refinement of minor static disorder

Orbital‐Free Quantum Crystallographic View on Noncovalent Bonding: Insights into Hydrogen Bonds, π⋅⋅⋅π and Reverse Electron Lone Pair⋅⋅⋅π Interactions

“…The wavefunction-derived ELF is generally more expanded compared to the AST-approximate one, which in turn has a smoother character, e.g., less distinct maxima near the N atoms and not so pronounced maxima at the location of LPs of the O atom. As we described previously, 84 the theoretical ELF shows two distinct maxima at each nitrogen atom N1 and N3 above and below the molecular plane, which is additionally supported by the found Laplacian minima. Localization of π-density at nitrogen atom N1 from the side of LPs•••π interaction is less pronounced than that from the N1•••C5 contact (Figure S10).…”

“…The former approximation shows a distinct "double-humped" peak of ELF on covalent bonds [35] (Figure S2b), which seems like an inheritance of the Laplacian and contradicts the exact theoretical ELF. [85] AST-approximated ELF (Figure 1c) exhibits single peaks on covalent bonds and a more uniform distribution in the regions of ED accumulation and VSCC near the carbonyl oxygen atoms. Notably, the important difference between the AST-based ELF and wavefunction-derived one is the more expanded character of the latter (vide infra).…”

“…DMPU crystallizes in the monoclinic space group P2 1 /c with one molecule in the asymmetric cell. [85] Intermolecular contacts discussed above participate in the formation of DMPU crystal structure in the following way (Figure 3). One can identify the one-dimensional hydrogen-bonded zig-zag chains along the longest axis 0b of the unit cell, which are formed by the shortest O2•••H9 hydrogen-bonds.…”

“…Comparison with the more common bonding descriptors enhanced the understanding of both the nature of donor-acceptor bonding and the behavior of advanced physical quantities used. We have recently performed a high-resolution X-ray diffraction experiment on 1,6-dimethyl-3-(prop-2-yn-1yl)pyrimidine-2,4(1H,3H)-dione (DMPU) 84 , a derivative of 6-methyluracil, which presented itself as an attractive research object due to the rather diverse set of noncovalent interactions, such as nonclassical hydrogen bonds essential for organic crystals as well as more rare but not less important π-stacking interactions. The structural formula and atom labels for DMPU are shown in Scheme 1.…”

“…We have recently performed a high-resolution X-ray diffraction experiment on 1,6-dimethyl-3-(prop-2-yn-1-yl) pyrimidine-2,4(1H,3H)-dione (DMPU), [85] a derivative of 6-methyluracil, which presented itself as an attractive research object due to the rather diverse set of noncovalent interactions, such as nonclassical hydrogen bonds essential for organic crystals as well as more rare but not less important π-stacking interactions. A more interesting feature of the crystal structure is an intriguing short intermolecular contact [C =]O•••N(sp 2 ), which is surprisingly strong -among the strongest in the crystal.…”