On the Use of Solomon Echoes in 27Al NMR Studies of Complex Aluminium Hydrides

The quadrupole coupling constant C-Q and the asymmetry parameter eta have been determined for two complex aluminium hydrides from Al-27 NMR spectra recorded for stationary samples by using the Solomon echo sequence. The thus obtained data for KAlH4 (C-Q=(1.30 +/- 0.02) MHz, eta=(0.64 +/- 0.02)) and NaAlH4 (C-Q=(3.11 +/- 0.02) MHz, eta<0.01) agree very well with data previously determined from MAS NMR spectra. The accuracy with which these parameters can be determined from static spectra turned out to be at least as good as via the MAS approach. The experimentally determined parameters (delta(iso), C-Q and eta) are compared with those obtained from DFT-GIPAW (density functional theory - gauge-including projected augmented wave) calculations. Except for the quadrupole coupling constant for KAlH4, which is overestimated in the GIPAW calculations by about 30 %, the agreement is excellent. Advantages of the application of the Solomon echo sequence for the measurement of less stable materials or for in situ studies are discussed.

Automated summary

The quadrupole coupling constants and asymmetry parameters of two complex aluminium hydrides were determined using Al-27 NMR spectra recorded for stationary samples with the Solomon echo sequence. The results for KAlH4 and NaAlH4 agreed well with previous MAS NMR spectra data. The accuracy of static spectra determination was found to be comparable to the MAS approach. Comparisons were made with DFT-GIPAW calculations, showing excellent agreement except for one parameter being overestimated in the calculations.