Molecular Recognition by Chalcogen Bond: Selective Charge‐Transfer Crystal Formation of Dimethylnaphthalene with Selenadiazolotetracyanonaphthoquinodimethane

The title nonplanar electron acceptor (1) fused with a selenadiazole ring selectively forms a crystalline charge‐transfer complex (CT crystal) with 2,6‐dimethylnaphthalene (2,6‐DMN). On the other hand, the sulfur analogue (2) has less recognition ability and forms CT crystals with both 2,6‐ and 2,7‐DMN. X‐ray analyses of 1, 2, and their CT crystals revealed that the Se⋅⋅⋅N chalcogen bond (ChB) in 1 is strong enough to determine the crystal packing with the formation of a cavity suitable for 2,6‐DMN. On the contrary, ChB through S⋅⋅⋅N contact in 2 competes with other weak interactions such as a C−H⋅⋅⋅N hydrogen bond. The stronger ChB involving Se is the key for 1 to separate 2,6‐DMN (>97 wt %) from a complex isomer mixture containing ca. 10 wt % each of 2,6‐ and 2,7‐DMN by a simple, efficient and straightforward mixing‐filtration‐heating process. Highly selective cocrystallization with 2,6‐dimethylnaphthalene (2,6‐DMN) allows the title selenadiazole‐based electron acceptor to separate 2,6‐DMN from the isomer mixture by an effective Se⋅⋅⋅N chalcogen bond whereas the sulfur congener shows only low selectivity due to the competing C−H⋅⋅⋅N hydrogen bond, which overwhelms the S⋅⋅⋅N bond.