Version 2 2019-11-19, 15:12Version 2 2019-11-19, 15:12
Version 1 2019-11-12, 17:34Version 1 2019-11-12, 17:34
journal contribution
posted on 2019-11-19, 15:12authored byAgata Owczarzak, Zbigniew Dutkiewicz, Rafał Kurczab, Wojciech Pietruś, Maciej Kubicki, Anita M. Grześkiewicz
The reasons behind the formation of S···S
contacts
in thioamides, the most important compounds with terminal sulfur atoms,
were investigated by means of experimental charge density studies
and theoretical calculations. As this interaction is to some extent
similar to the much better-known halogen bond, geometrical analysis
was performed using previously determined halogen bond formation criteria.
To investigate the most representative thioamides, three compounds,
namely, 6-amintothiouracil hydrate (ATU·H2O, 1), 2-imidazolidinethione (IMT, 2), and 2-thiazolidinethione
(TT, 3), were selected. In all three structures, relatively
short S···S contacts displaying different geometries
were observed. Furthermore, different symmetry elements (mirror plane
in ATU, inversion center in TT, and translation in IMT) determined
the mutual orientation of the sulfur atoms in contact. The structural
analysis and calculations proved that the isolated S···S
dimers are unstable and that they are stabilized by “staple”
molecules, which are any molecules present in the crystal structure
that interact with both molecules forming the S···S
contact. Several types of staple molecules were identified, differing
in the area of interaction with the S···S dimer molecule.
The analysis of the data in the Cambridge Structural Database showed
that the staple structures can be found in 77% of all structures with
short S···S contacts (shorter than 3.4 Å) and
in more than half of the structures with the contacts within the van
der Waals radius limit. The calculations show that the smaller the
distance between sulfur atoms in the S···S dimer, the
greater the amount of energy needed for dimer stabilization. Consequently,
the presence of a staple is essential.