| Research Abstract |
The C-F…M^+ interaction was investigated by observation of the NMR spectroscopic changes and complexation studies between metal cations and the cage compounds 1 and 2 which have six fluorobenzene units (1) or four fluorobenzene units and two diethyleneoxa units (2) as donor atoms. As a result, the interaction was detected with all of the metal cations which form complexes with 1 and 2. The stability of the complexes of 1 and 2 was determined by the properties of the metal cations (ionic radii and degree of hydrolysis), not by the hard-soft nature of the cations. Crystallographic analyses of T1^+ ⊂ 1 and La^<3+> ⊂ 2 provided structural information (interatomic distances and bond angles), and the bond strengths, C-F…M^+, O…M^+, and N…M^+, were estimated by Brown's equation based on the structural data. Short C-F…T1^+ (2.952 〜 3.048) distances were observed in the complex T1^+ ⊂ 1. The C-F bond lengths in the complexes, T1^+ ⊂ 1 and La^<3+> ⊂ 2, are elongated compared to those of the meta
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l-free compounds. Interestingly, no solvent molecules including water molecules were coordinated to La^<3+> in the La^<3+> ⊂ 2. The stabilization energy of cation-dipole interaction was calculated based on the data from X-ray crystallographic analysis, and it is roughly consistent with the【-!【horizontally divided triangle】】H values estimated in solution. Thus, the C-F…M^+ interaction can be expressed by the cation-dipole interaction. This result explains the fact that compound 1 which has fluorine atom as hard donor strongly binds soft metals such as Ag^+ and T1^+. Furthermore, it was concluded that the fluorobenzene unit has a poor electron-donating ability compared to that of ether oxygen or amine nitrogen, and thus the ratio of the coordination bond in C-F…M^+ is small. The specific and remarkable changes in the ^1H, ^<13>C, and ^<19>F NMR spectra were observed accompanied by the complexation between M^+ and the hosts 1 and 2. These spectral features are important tools for the investigation of the C-F…M^+ interaction. Furthermore, F…T1^+ spin couplings were observed at room temperature in the T1^+ ⊂ 1, 2 (J_<F-T1> = 2914 Hz for T1^+ ⊂ 1 and 4558 Hz for T1^+ ⊂ 2), and these are clear and definitive evidence of the interaction. Less
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