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.