NMR Chemical Shift and Quadrupolar Interaction Parameters of Carbon-Coordinated 27Al in Aluminium Carbide, Al4C3

Aluminium carbide, Al4C3, was characterised by C-13 and Al-27 solid-state NMR spectroscopy. The C-13 NMR spectra display two resonances with an intensity ratio of 1: 2, which is in agreement with the reported crystal structure. The Al-27 NMR spectra of Al4C3 under both static and MAS conditions were deconvoluted into two spectral components, belonging to the two aluminium species Al1 and Al2 in the crystal structure of Al4C3. The spectral fit allowed for determination of the relatively large quadrupolar coupling constants (chi approximate to 16 MHz) of both Al-27 species. One aluminium species displayed a tendency of having a. of slightly smaller magnitude compared to the other. By carrying out DFT calculations of the EFG tensor at the Al-27 sites using the Wien2k software, we could tentatively assign the smaller. site to be the crystallographic Al1 species. Also, the isotropic chemical shift for the carbon-coordinated aluminium in Al4C3 could be determined, being in the range of 111 to 120 ppm. This is somewhat larger than those shift values observed for Al-27 in nitrogen coordination.