Magnetic Shielding of 19F in XeF2

Abstract

The rigid-lattice second moment of the 19F nuclear magnetic resonance of XeF2 has been measured as a function of the external magnetic field. The experimental shielding anisotropy | Δσ | = 105 ± 10 × 10−6 does not agree closely with a value of σ⊥ − σ‖ = − 506 × 10−6 previously calculated using a localized orbital model. The field-independent rigid-lattice second moment is ∼ 0.4 G2 larger than that calculated from crystallographic data, probably because of large amplitude vibrations in XeF2. The temperature dependences of the second moment and of the spin–lattice relaxation time are also reported.

NMR spectroscopic study of xenon fluorides in the gas phase and of XeF2 in the solid state

“…Inclusion of the 1 J( 129 Xe-19 F) coupling constant (À5550 Hz) as well as the heteronuclear dipolar coupling between 19 F and 129 Xe in XeF 2 (3940 Hz) in the simulations reproduced the skewing observed for the 129 Xe satellites. The 19 F SA determined in the present study is in good agreement with the value found previously based on second-moment measurements at three different field strengths [6].…”

“…The spin-1/2 nuclides, 129 Xe and 19 F, have found extensive use in the characterization of xenon compounds, nearly all of which are derived from the parent binary fluorides, XeF 2 , XeF 4 , and XeF 6 . Both nuclides have high receptivities, with 19 F having a receptivity relative to that of 1 H of 0.834, and 129 Xe (natural abundance, 26.44%) a receptivity 32.4 times that of natural abundance 13 C. The large number of experimental NMR parameters for xenon compounds in solution [1] is in marked contrast with the relative paucity of NMR data that have been reported for xenon compounds in the solid state [2][3][4][5][6]. The gas-phase NMR spectroscopy of xenon compounds has been neglected with no NMR spectroscopic measurements having been reported.…”

“…Jameson and Gutowsky [11] have predicted extraordinarily large 129 Xe SA values for XeF 2 of 5125 or 7185 ppm using low-level MO calculations. An experimental study of solid XeF 2 , measuring 19 F second moments at three different magnetic field strengths predicted a 19 F SA of 105 AE 10 ppm [6]. Jokisaari et al [12] have studied 19 F and 129 Xe T 1 relaxation times of XeF 2 in CH 3 CN solvent at variable field strengths and temperatures and deduced shielding anisotropies for 19 F (205 or 105 ppm) and 129 Xe (4722 or 2416 ppm).…”

Magnetic Shielding of 19F in XeF4

“…29 M2=M2(field independent) + (4/45)[( uz-ux )2 +(uy-u z )(uy-u x )]H02. (1) The equation is completely general and is not changed by a permutation of x, y, and z, which results in U x , U y , and U z being indistinguishable. In the case of axial symmetry, Ux=Uy and Eq.…”

“…3 for the rigid lattice and above the motional transition relate to Eqs. (1) and (3), respectively. In addition, the total absolute shielding may be expressed as (4) From the shape of the higher temperature resonance in Fig.…”