A study of C-F.M+ interaction: alkali metal complexes of the fluorine-containing cage compound

The C-F.M(+) interaction was investigated by employing a cage compound 1 that has four fluorobenzene units. The NMR ((1)H, (13)C, and (19)F) spectra and X-ray crystallographic analyses of 1 and its metal complexes showed clear evidence of the interaction. Short C-F.M(+) distances (C-F.K(+), 2.755 and 2.727 A; C-F.Cs(+), 2.944 and 2.954 A) were observed in the crystalline state of K(+) subset 1 and Cs(+) subset 1. Furthermore, the C-F bond lengths were elongated by the interaction with the metal cations. By calculating Brown's bond valence, it is shown that the contribution of the C-F unit to cation binding is comparable or greater than the ether oxygen in the crystalline state. Representative spectroscopic changes implying the C-F.M(+) interaction were observed in the NMR ((1)H, (13)C, and (19)F) spectra. In particular, (133)Cs-(19)F spin coupling (J = 54.9 Hz) was observed in the Cs(+) complex.