Abstract
The effects of the various xenon and krypton isotopes on the nuclear shielding of ^19^F in xenon and krypton difluoride in solution were studied by ^19^F NMR spectroscopy. For both molecules, linear relationships were observed between the oneβbond secondary isotope shift of the ^19^F nucleus, ^1^Ξ; ^19^F(^mβ²/128^Xe) and ^1^Ξ ^19^F(^mβ²/78^Kr), and the relative mass factor, (mβ² β m)/mβ², and also between the shifts and the quadratic mean bond displacement, γ(Ξ__r__)^2^γ. On the basis of the latter correlation and the linear relationship between γΞ__r__γ and γ(Ξ__r__)^2^γ for the linear combination of the first and second derivatives of the ^19^F shielding, the values β1742 and β5804 ppm Γ
^β2^, respectively, were determined. Further, the temperature dependence of the ^129^Xe and ^19^F chemical shifts and the ^129^Xe, ^19^F indirect spinβspin coupling of XeF~2~ were determined. The ^129^Xe chemical shift is extremely sensitive to temperature with ΞΞ΄/Ξ__T__ = β0.4718 ppm K^β1^, whereas for ^19^F ΞΞ΄/Ξ__T__ = +0.0042 ppm K^β1^. In contrast, the ^129^Xe, ^19^F indirect spinβspin coupling is independent of temperature over the range 243β303 K, the mean value being 5644.2 Β± 0.6 Hz.