scholarly journals Two Tautomers of Thiobarbituric Acid in One Crystal: The Experimental Charge Density Perspective

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 223
Author(s):  
Anita M. Grześkiewicz ◽  
Maciej Kubicki

High-quality crystals of a certain polymorphic form of thiobarbituric acid containing both keto and enol tautomers in the asymmetric unit were obtained. High-resolution X-ray diffraction data up to sinθ/λ = 1.0 Å−1 were collected and subsequently successfully used for the refining of the multipolar model of electron density distribution. The use of a crystal containing both ketone and enol forms allowed a direct comparison of the topological analysis results and a closer look at the differences between these two forms. The similarities and differences between the deformation densities, electrostatic potentials, Laplacian maps and bond characteristics of the tautomers were analysed. Additionally, the spectrum of the intermolecular interactions was identified and studied from classical, relatively strong N-H···O and O-H···O hydrogen bonds through weaker N-H···S hydrogen bonds to weak interactions (for instance, C-H···O, C-H···S and N···O). The results of these studies point toward the importance of including both the geometrical features and the details of the electron density distribution in the analysis of such weak interactions.

2007 ◽  
Vol 63 (1) ◽  
pp. 49-55 ◽  
Author(s):  
Yu. V. Ivanov ◽  
E. L. Belokoneva

The electron density distribution in the layer silicate datolite, Ca[BOH(SiO4)], was analyzed using high-precision single-crystal X-ray diffraction data (Mo Kα, T = 293 K). The Hansen–Coppens multipole model and Bader's topological analysis of the electron density provides a basis for the quantitative characterization of the bonded interaction of datolite. The results are presented both in the form of maps of the electron density distribution and its Laplacian, and in a compact way in terms of the critical points of the electron density. The relative electronegativities are also discussed. It was shown that closed-shell type interactions exist between Ca and O atoms, whereas Si—O and B—O bonds exhibit an intermediate nature with a strong covalent component. An analysis of the topology of the electrostatic potential demonstrates the relevance of considering this physical property to obtain a complete picture of structure-forming factors.


2019 ◽  
Vol 2019 (6) ◽  
pp. 875-884 ◽  
Author(s):  
Maxim G. Chegerev ◽  
Alexandr V. Piskunov ◽  
Kseniya V. Tsys ◽  
Andrey G. Starikov ◽  
Klaus Jurkschat ◽  
...  

2009 ◽  
Vol 65 (5) ◽  
pp. 600-611 ◽  
Author(s):  
Ruimin Wang ◽  
Christian W. Lehmann ◽  
Ulli Englert

The experimental electron-density distributions in crystals of five chain polymers [M(μ-X)2(py)2] (M = Zn, Cd; X = Cl, Br; py = 3,5-substituted pyridine) have been obtained from high-resolution X-ray diffraction data sets (sin θ/λ > 1.1 Å−1) at 100 K. Topological analyses following Bader's `Atoms in Molecules' approach not only confirmed the existence of (3, −1) critical points for the chemically reasonable and presumably strong covalent and coordinative bonds, but also for four different secondary interactions which are expected to play a role in stabilizing the polymeric structures which are unusual for Zn as the metal center. These weaker contacts comprise intra- and inter-strand C—H...X—M hydrogen bonds on the one hand and C—X...X—C interhalogen contacts on the other hand. According to the experimental electron-density studies, the non-classical hydrogen bonds are associated with higher electron density in the (3, −1) critical points than the halogen bonds and hence are the dominant interactions both with respect to intra- and inter-chain contacts.


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