Chalcogen–chalcogen secondary bonding interactions in trichalcogenaferrocenophanes

Abstract

The solid-state structures of all members in the series of trichalcogenaferrocenophanes [Fe(C₅H₄E)₂E′] (E, E′ = S, Se, Te) (1–9) have been explored to understand the trends in secondary bonding interactions (SBIs) between chalcogen elements sulfur, selenium, and tellurium. To complete the series, the crystal structures of the four hitherto unknown complexes [Fe(C₅H₄S)₂Te] (3), [Fe(C₅H₄Se)₂S] (4), [Fe(C₅H₄Se)₂Te] (6), and [Fe(C₅H₄Te)₂S] (7) have been determined in this contribution. The packings of all complexes 1–9 were considered by DFT calculations at the PBE0/pob-TZVP level of theory using periodic boundary conditions. The intermolecular close contacts were considered by QTAIM and NBO analyses. The isomorphous complexes [Fe(C₅H₄S)₂S] (1), [Fe(C₅H₄S)₂Se] (2), and [Fe(C₅H₄Se)₂Se] (5a) form dimers via weak interactions between the central chalcogen atoms of the two trichalcogena chains of adjacent complexes. In the second isomorphous series consisting of [Fe(C₅H₄Se)₂S] (4) and 5b, the complexes are linked together into continuous chains by short contacts via the terminal selenium atoms. The intermolecular chalcogen–chalcogen interactions are significantly stronger in complexes [Fe(C₅H₄S)₂Te] (3), [Fe(C₅H₄Se)₂Te] (6), and [Fe(C₅H₄Te)₂E′] (E′ = S, Se, Te) (7–9), which contain tellurium. The NBO comparison of donor–acceptor interactions in the lattices of [Fe(C₅H₄S)₂S] (1), [Fe(C₅H₄Se)₂Se] (5a and 5b), and [Fe(C₅H₄Te)₂Te] (9) indeed shows that the n(5p_Te)² → σ*(Te–Te) interactions in 9 are the strongest. All other interaction energies are significantly smaller even in the case of tellurium. The computed natural charges of the chalcogen atoms indicate that electrostatic effects strengthen the attractive interactions in the case of all chalcogen atoms.