Chalcogen-chalcogen secondary bonding interactions in trichalcogenaferrocenophanes

The solid-state structures of all members in the series of trichalcogenaferrocenophanes [Fe(C5H4E)(2)E'] (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)(2)Te] (3), [Fe(C5H4Se)(2)S] (4), [Fe(C5H4Se)(2)Te] (6), and [Fe(C5H4Te)(2)S] (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)(2)Se] (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)(2)Te] (3), [Fe(C5H4Se)(2)Te] (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)(2)S] (1), [Fe(C5H4Se)(2)Se] (5a and 5b), and [Fe(C5H4Te)(2)Te] (9) indeed shows that the n(5pT(e))(2) -> sigma*(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.