Controversy about the reference compound for correct chemical shift determination of 195Pt nuclei
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 27 March 2010
Bogdan, Nowak
Several groups exploring the 195Pt NMR in solids, including metallic and magnetic materials, use different standards for chemical shift (Knight shift) determination. Commonly applied H2PtCl6 and Na2PtCl6 (IUPAC δ scale) lead to considerable underestimation of the shifts since H2PtCl6 has considerable own 195Pt NMR shift due to its Van Vleck paramagnetism.In this Letter new results on 195Pt NMR in heavy fermion system CeInPt4 are presentedand rationalized scale for the Knight shift determination is discussed.
Off-resonance effects in two-dimensional exchange NMR at zero- field
Publication year: 2010Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 March 2010
Mariusz, Maćkowiak , Nicolay, Sinyavsky
The effects of off-resonance irradiation in 2D exchange NMR at zero-field are analysed. A theoretical treatment of the 2D exchange NMR pulse sequence is presented and applied to the quantitative study of exchange processes in molecular crystals. It takes into account the off-resonance irradiation, which critically influences the spin dynamics. The response of a system of spins I=3/2 in zero applied field to the three-pulse sequence is analysed. The mixing dynamics by exchange and the expected cross-peak intensities as a function of the frequency offset has been derived. It is shown that the off-resonance effects are of crucial importance for the quantitative description of the exchange spectra. The theory is successfully tested for the exchange spectra of hindered trichloromethyl groups of p-chloroanilinium trichloroacetate, where the conventional approach without taking into account the off-resonance phenomena has failed.
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