Co-crystals of an organic triselenocyanate with ditopic Lewis bases: recurrent chalcogen bond interactions motifs.

Organic selenocyanates R-Se-CN can act as an amphoteric chalcogen bond (ChB) donor (through the Se atom) and acceptor (through the N atom lone pair). Co-crystallization of tri-substituted 1,3,5-tris(selenocyanatomethyl)-2,4,6-trimethylbenzene (1) is investigated with different ditopic Lewis bases acting as chalcogen bond (ChB) acceptors to investigate the outcome of the competition, as ChB acceptor, between the nitrogen lone pair of the SeCN group and other Lewis bases involving pyridinyl or carbonyl functions. In the presence of tetramethylpyrazine (TMP), benzoquinone (BQ) and para-dinitrobenzene (pDNB) as ditopic Lewis bases, a recurrent oligomeric motif stabilized by six ChB interactions is observed, involving six SeCN groups and the ChB acceptor sites of TMP, BQ and pDNB in the 2:1 adducts (1)2·TMP, (1)2·BQ and (1)2·pDNB.