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), [Cp*Rh(C5H3NO2)]3 (2), and [Cp*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 (1H, 13C, 19F, 7Li). Strong scalar coupling between 7Li and 19F is observed for the LiF and the LiFHF complexes (1JLiF = 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 Å were found. The LiFHF complexes show a hydrogen difluoride anion coordinated in a bent fashion via one fluorine atom to the lithium ion.