Chalcogen bonding interactions in a series of aromatic selenocyanates
Résumé
Selenium atoms in aromatic selenocyanates are characterized by the occurrence of two and sigma;-holes, a stronger one in the prolongation of the NC-Se bond and a weaker one in the prolongation of the Ar-Se bond. The crystal structures of several bis(selenocyanato) derivatives, prepared by a method originally developed for ortho bis-substituted derivatives, illustrate very well this difference, with a short NC-SeMIDLINE HORIZONTAL ELLIPSISNC ChB interaction organizing the molecules into 1D motifs with reduction ratio (RR) values in the range of 0.87-0.91 (RR is defined as the interatomic distance over the van der Waals contact), complemented with Ar-SeMIDLINE HORIZONTAL ELLIPSISNC ChB interactions between antiparallel chains involving the second and sigma;-hole, with larger RR values in the range of 0.92-0.94. Comparison with benzylic selenocyanates shows that this secondary lateral interaction involving the weaker and sigma;-hole is notably enhanced in these novel aromatic compounds. The structure of co-crystals of the para derivative (1,4-diselenocyanatobenzene) with (E)-1,2-di(4-pyridyl)ethylene (bpen) is characterized by an extremely short NC-SeMIDLINE HORIZONTAL ELLIPSISNbpen distance at 2.693(2) and ANGS;, i.e. a RR value of 0.78, complemented with interaction of the second and sigma;-hole with the and pi; system of the double bond of bpen. Selenium atoms in aromatic selenocyanates exhibit two sizeable and sigma;-holes, leading to recurrent supramolecular organizations with chalcogen-bonded (ChB) chain-like motifs and antiparallel arrangement of the chains through weaker ChB.
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