Lariat ethers with fluoroaryl side-arms: A study of CF⋯metal cation interaction in the complexes of N-(o-fluoroaryl)azacrown ethers

New lariat ethers, N-(o-fluorophenyl)aza-15-crown-5 (F-A15C5) and N,N'-bis(o-fluorophenyl)diaza-18-crown-6 (F(2)-A(2)18C6), were prepared by the N-arylation of the corresponding azacrown ethers. The interaction of the ligands with metal cations was studied in solution by (1)H and (19)F NMR (in acetone-d(6)) and UV spectroscopy (MeOH) confirming the formation of complexes of F(2)-A(2)18C6 with K(+), Na(+), Ag(+), Ba(2+), Pb(2+) and of F-A15C5 with Na(+) and giving evidence of CFmetal cation interaction. Cation binding constants (beta, evaluated by UV titration method), demonstrate that F-A15C5 and F(2)-A(2)18C6 form more stable complexes than their fluorine-free analogs. The effect depends on the nature of the metal cation and is at a maximum for hard, singly charged cations (up to 3 logbeta units for K(+) complex of F(2)-A(2)18C6). The X-ray structures of complexes [Pb(F(2)-A(2)18C6)(H(2)O)](ClO(4))(2) () and [Ba(F(2)-A(2)18C6)(ClO(4))(2)] () reveal short Pb-F (2.805 A) and Ba-F (2.965 A) contacts. Complex is centrosymmetric (C(i)), while complex has C(2) symmetry with one-side coordination of o-fluorophenyl groups to Pb(2+). This "one-side" coordination mode of Pb(2+) is indicative of a partial localization of the Pb(2+) lone pair.