Stabilization of molecular LiF and LiFHF inside metallamacrocyclic hosts
Complexes of molecular LiF and LiFHF were synthesized using the metallamacrocyclic receptors [(cymene)Ru-(C5H3NO2)](3) (1), [(CpRh)-Rh-*(C5H3NO2)](3) (2), and [(CpIr)-Ir-*(C5H3NO2)](3) (3). LiBF4 complexes of 1-3 were prepared and subsequently treated with F- or FHF- to give the desired products in an anion-exchange reaction. All complexes were characterized by multinuclear NMR spectroscopy (H-1, C-13, F-19, Li-7). Strong scalar coupling between Li-7 and F-19 is observed for the LiF and the LiFHF complexes ((1)J(LiF) = 91-103 Hz). The LiFHF adduct of 1 displays fluxional behavior with fast exchange of the two fluorine atoms. The structures of the complexes 1.LiBF4, 2.LiBF4, 1.LiF, 2-LiF, 1-LiFHF, and 3-LiFHF were determined by single-crystal X-ray analysis. Li-F bond lengths between 1.77 and 1.81 Angstrom were found. The LiFHF complexes show a hydrogen difluoride anion coordinated in a bent fashion via one fluorine atom to the lithium ion.