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A study on theQn(mAl) complexes by 29SiNMR chemical shift calculation

S.N.Azizi, M.Yousefpour

Valuable insights into Qn(mAl) complexes can be achieved when the NMR results are combined with the calculated data. 29Si NMR chemical shift calculation has been used to investigate the Qn local structures about the Si in a series of aluminosilicate solutions. By using the gauge-including atomic orbitalmethod at the self-consistent-field and Hartree-Fock theory levels, the ab-initio calculations of the 29Si NMR chemical shifts for non cyclic or chain formoligomers of Qn units of aluminosilicate species have been performed. The GIAO-HF-SCF calculations were carried out using, three different basis sets: 6-31G**6-31+G** and 6-311+G(2d,p). This data convincingly shows the right sequence of aluminosilicate anions through the different structures Qn-q1 connectivity. The results, especially with 6- 31+G** and 6-311+G(2d,p),with a fewexceptions are satisfactory. Theoretical calculations of NMR spectroscopic properties can be very helpful and can provide the missing information.