Organic Selenocyanates as Halide Receptors: From Chelation to One-Dimensional Systems

Organic selenocyanates were recently identified as strong chalcogen bond donors. They also play an important role in biochemistry. Here, we show that 1,2-bis(selenocyanatomethyl)benzene (1) and 1,2,4,5-tetrakis(selenocyanatomethyl)-benzene (2) crystallize from dimethylformamide (DMF) to afford solvates where two ortho-SeCN moieties act as a chelate toward the carbonyl oxygen atom of DMF through strong Se⋯O chalcogen bonds. This result led us to explore their ability to also chelate halide anions (Cl ^- , Br ^- ) in solution as well as in the solid state, an important issue in view of applications in crystal engineering or organocatalysis. NMR titration experiments provide an association constant between 1 and Cl ^- of 148 M ^-1 . We also observed the recurrent formation of cocrystal salts from the association of the ChB donors 1 and 2 with the onium salts Ph ₄ PCl, Ph ₄ PBr, and Bu ₄ NCl. We demonstrate that not only μ ₂ -halide but also μ ₄ -halide structures can be stabilized though ChB interactions, leading to the formation of complex polymeric anionic networks. Continuous shape measure calculations of these μ ₄ -halide structures demonstrate that seesaw symmetry best describes the μ ₄ -Br ^- bromide structures, while the smaller chloride anions tend to favor a close-to-tetrahedral μ ₄ -Cl ^- organization, which is also confirmed by density functional theory calculations. Electrostatic surface potential calculations further demonstrate the efficiency of this chelating ortho-bis(selenocyanatomethyl) motif in 1 and 2, with V _s,max values reaching 50 kcal mol ^-1 , to be compared with the simplest benzyl selenocyanate (36.4 kcal mol ^-1 ) or the reference halogen bond donor F ₅ C ₆ -I (35.7 kcal mol ^-1 ) in the same conditions.