Activation of chalcogen bonding in tetrathiafulvalene derivatives with Se/S differentiation

Abstract

Activation of σ-hole on selenium atoms through oxidation of the tetrathiafuvalene core in selenomethyl-substituted TTFs was evaluated in competition with the less activatable thiomethyl moieties in 4,5-bis(methylseleno)-4',5'-bis(methylthio)-tetrathiafulvalene 1. Three charge-transfer complexes with TCNQ, TCNQF and TCNQF2 were structurally characterized showing in all of them a partial degree of charge transfer ρ in the range ±0.5/±0.6, with alternated stacks of DDAADDAA pattern with TCNQ, DADADA with TCNQF and TCNQF2. No ChB interactions were identified in two latter co-crystals, where the MeSe− and MeS− are disordered in a 50:50 distribution, as observed also in the structure of neutral 1. On the other hand, in the co-crystal with TCNQ, the dissymmetric Se/S distribution (69:31) is associated with a strong Se•••NC ChB interaction of the majority Se atom. A similar preferential ChB interaction with Se is observed in the perchlorate salt (1)ClO4, where the majority Se atom (71:29 Se/S distribution) interacts through Se•••O ChB with the ClO4− anion.