Ab initio ²⁷Al NMR chemical shift calculation for the clusters of Al(OH)₄^-, Al(OH)₅^2- and Al(OH)₆^3-

The effect of coordination number on ²⁷Al NMR chemical shift was studied using ab initio molecular orbital calculation. In order to mimic Al of four-, five-and six-coordinations Al, the clusters of Al(OH)₄^-, Al(OH)₅^2- and Al(OH)₆^3- were employed for the calculation. The obtained shifts for Al(OH)₄^-, Al(OH)₅^2- and Al(OH)₆^3- were +70.3, +31.5 and -3.9 ppm, respectively, and were in reasonable agreement with observed shifts of Al-containing oxides. Present calculation supports the assignment of + 30 ppm peak observed in aluminosilicate glasses as five-coordination state. Ab initio molecular orbital calculation can be used to establish the correlation between local structure and NMR chemical shift of Al-containing materials.