RESUMO
The (1)J((11)B(19)F) spin-spin coupling of gaseous BF(3) was observed in (11)B NMR spectra as a function of density in a wide range of temperatures. Following the extrapolation of the measured values to the zero-density limit, the coupling constant free from intermolecular effects (1)J(0)((11)B(19)F) was obtained for each temperature. In contrast to previous investigations, the final results indicate a nonlinear dependence of (1)J(0)((11)B(19)F) on temperature. In the corresponding ab initio calculations of spin-spin coupling constants performed at the coupled cluster singles and doubles (CCSD) level to obtain a reliable result for this coupling constant we had to take into account large vibrational corrections.
Assuntos
Boranos/química , Boro/química , Fluoretos/química , Espectroscopia de Ressonância Magnética/normas , Temperatura , Espectroscopia de Ressonância Magnética/métodos , Teoria Quântica , Padrões de ReferênciaRESUMO
Gas-phase NMR spectra of (11)B, (10)B, and (19)F in BF(3) are reported, and high-level ab initio calculations of the corresponding NMR shielding constants are described. Extrapolation of the measured resonance frequencies to the zero-density limit ensures that the results correspond to the ab initio values for an isolated molecule. Simultaneous measurements of (3)He resonance frequencies and application of the calculated shielding constants allow us to determine improved values of the nuclear magnetic dipole moments of (11)B and (10)B. The magnetic moments of both isotopes are also determined independently by comparing with the (19)F spectral parameters (frequencies and shielding constants). The separately derived nuclear magnetic moments are in good agreement, whereas the literature moments of both (11)B and (10)B are noticeably less accurate.
