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

Abstract

Activation of σ-holes on selenium atoms through the oxidation of the tetrathiafulvalene core in selenomethyl-substituted TTFs was evaluated in comparison 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, with all of them showing a partial degree of charge transfer, ρ, in the range of ±0.5–±0.6, with alternating stacks of DDAADDAA patterns with TCNQ and DADADA patterns with TCNQF and TCNQF₂. No ChB interactions were identified in the latter two co-crystals, where MeSe and MeS- were disordered in 50 : 50 distribution, as also observed in the structure of neutral 1. Alternatively, in the co-crystal with TCNQ, dissymmetric Se/S distribution (69 : 31) was associated with a strong Se⋯NC ChB interaction involving the majority Se atom. A similar preferential ChB interaction with Se was 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.