Exploring the persistence of the fluorinated thiolate 2,3,5,6-S(C6F4H-4) motif to establish πF-πF stacking in metal complexes: A Crystal Engineering Perspective

Abstract

 Stacking interactions are versatile because they are involved in many processes, such as protein folding, DNA stacking, and drug recognition. However, from the point of view of Crystal Engineering, there is an incipient knowledge of its exploitation. A comparison of these interactions with hydrogen bonds shows a huge difference in their employment as a reliable non-covalent interaction. And different reasons can be listed to explain why hydrogen bonding can be considered a more robust interaction than  stacking. For instance, hydrogen bonds encompass a wide energy range (25-40 kJ/mol). From this, these interactions can be classified as strong, moderate, and weak. Hence, the first two can be considered highly to moderately directional to be exploited in Crystal Engineering. This aspect is relevant for them to be used in a relatively reliably way in this area of Supramolecular Chemistry. On the other hand, in the case of  stacking, the energy range is 0-10 kJ/mol, thus implying that hydrogen bonds or any other energetically more robust contact would predominate in the competition for establishing packing interactions in a given arrangement. In this sense, if stacking is pretended to be exploited from the point of view of Crystal Engineering, one of the points that must be ensured is that this interaction will be the one energetically predominant. However, although there are other factors to consider, it seems that energetics is the dominant one. In this line, our research group has obtained and studied many single-crystalline structures of coordination and organometallic compounds containing fluorinated thiolates. This being particularly true in the case of the thiolate 2,3,5,6-S(C6F4H-4) bound to different metals, where it has been observed that they preferentially tend to establish FF stacking interactions, results that have been reported in several papers. Thus, from this perspective, we have explored, using ConQuest (CCDC) a number of structures to observe how feasible is to find stacking in coordination and organometallic compounds containing the thiolate 2,3,5,6-S(C6F4H-4).