A study of C-F center dot center dot center dot 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 (H-1, C-13, and F-19) spectra a nd X-ray crystallographic analyses of 1 and its metal complexes showed clea r evidence of the interaction. Short C-F Mt distances (C-F . . .K+, 2.755 a nd 2.727 Angstrom; C-F . . . Cs+, 2.944 and 2.954 Angstrom) were observed i n the crystalline state of K+ subset of 1 and Cs+ subset of 1. Furthermore, the C-F bond lengths were elongated by the interaction with the metal cati ons. 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 imply ing the C-F . . .M+ interaction were observed in the NMR (H-1, C-13,and F-1 9) spectra. In particular, Cs-133-F-19 spin coupling (J = 54.9 Hz) was obse rved in the Cs+ complex.