Calculation of the chemical shielding constants of 95Mo in the clusters of [MoO mS 4 − m(CuX) n] 2− ( X = CN, Cl; m = 0–2, n = 1–3) by the finite perturbation theory-CNDO/2 method

Abstract

By using a semi-empirical molecular orbital method within the framework of the finite perturbation theory (FPT), the FPT-CNDO/2 method, which has been successfully adapted to the study of the 95Mo chemical shielding in molybdate and thiomolybdate [MoO m S 4 − m ] 2− ( m = 0–4) anions, theoretical calculation of the chemical shielding constants of 95Mo in the MoCuS clusters [MoO m S 4 − m (CuX) n ] 2− ( X = CN, Cl; m = 0–2, n = 1–3) has been carried out to extend the study of MoCuS clusters. Factors determining the regular change of 95Mo chemical shielding constants in the MoCuS clusters are discussed and the Mo d-orbital exponent is deduced to be the most sensitive one. The deduction is verified in the calculation by varying the Mo d-orbital exponent. The scaling coefficient of the linear regression between the calculated and the experimental results changes from 2.956 to 0.834 as the Mo d-orbital exponent reduces from 3.22 to 3.05, and the value of 3.10 produces the best linear regression. The deviation in the linear regression is attributed to the basic approximation of the CNDO/2 semi-empirical method.