Crystal Engineering, Electron Conduction, Molecular Recognition and Reactivity by Chalcogen Bonds in Tetracyanoquinodimethanes Fused with [1,2,5]Chalcogenadiazoles

Studies on a series of tetracyanoquinodimethanes (TCNQs) fused with [1,2,5]chalcogenadiazole rings reveals that chalcogen bonds (ChBs), through E center dot center dot center dot=C (E = S or Se) contacts, are a decisive factor in determining their crystal structures, with the formation of one- or twodimensional networks in a lateral direction. For anion-radical salts generated by one-electron reduction, electron conduction occurs in the direction of the network due to intermolecular electronic interactions involving ChBs. Based on the reliable synthon E center dot center dot center dot N=C for crystal engineering, molecular recognition occurs so that solid-state molecular complexes are selectively formed with certain donors, such as xylenes, among their isomers by charge-transfer-type clathrate formation. The inclusion cavity of the clathrate might provide a reaction environment for photoinduced electron transfer in the solid state. The accommodation of multiple conformers of overcrowded ethylene exhibiting thermo/mechanochromism is another example of a novel function that can be realized by ChBs through E center dot center dot center dot N=C contacts. Therefore, these chalcogenadiazolo-TCNQs endowed with the ability to form ChBs are promising materials for the development of novel solid-state functions. 1 Introduction 2 Bis[1,2,5]thiadiazolo-TCNQ (BTDA) 2.1 Chalcogen Bonds in Crystal Structures of BTDA and its Se Analogues 2.2 Electronic Effects of Chalcogen Bonds in Organic Conductors Consisting of BTDA 2.3 Molecular Recognition by Chalcogen Bonds in Molecular Complexes of BTDA 2.4 Single-Crystalline-State Photoreactions of Molecular Complexes of BTDA 2.5 Overcrowded Ethylene Composed of a BTDA Substructure 3 TCNQ Analogues Fused with a [1,2,5]Chalcogenadiazole 3.1 Crystal Structures of Chalcogenadiazolo-TCNQs 3.2 Crystal Structures of Chalcogenadiazolo-TCNNQs: An E center dot center dot center dot N=C Chalcogen Bond versus a Weak C-H center dot center dot center dot N=C Hydrogen Bond 3.3 Molecular Recognition by Chalcogen Bonds in TCNNQ Derivatives 4 Outlook