AB-INITIO AL-27 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 Al-27 NMR chemical shift was stud ied using ab initio molecular orbital calculation. In order to mimic A l 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 a greement with observed shifts of Al-containing oxides. Present calcula tion supports the assignment of +30 ppm peak observed in aluminosilica te glasses as five-coordination state. Ab initio molecular orbital cal culation can be used to establish the correlation between local struct ure and NMR chemical shift of Al-containing materials.