Theoretical and Experimental 27Al NMR Chemical Shift Studies on End-Group Aluminates Linked to Different Silicate Species

Aluminium-27 nuclear magnetic resonance spectroscopy (Al-27 NMR) does not yield fully resolved spectra for end-group aluminates attached to different silicate species. For example, the chemical shifts of all q(1) (end-group aluminates) lying in the range delta = 72.2-77 ppm are observed on average at delta approximate to 74.6 ppm in an NMR spectrum. With the aim of better characterisation of different q(1) linked units, we first made some attempts to resolve the signals that might arise from different q(1) linkages through the application of suitable experimental methods and then followed up this work by applying some calculation methods. Some of the observed differences and evidence have not been previously detected experimentally, but were clearly apparent from our calculations (Table 1) as well as in our experimental data. Therefore, in such a situation, theoretical calculations of NMR chemical shifts can be very helpful and can provide some missing information.