Nuclear Magnetic Shielding Constants of Halogens in X^- and XO₄^-(X = F, Cl, Br, I) – Relativistic and Electron-Correlation Effects –

Abstract

A series of calculations of halogen nuclear magnetic shielding constants and chemical shifts in X^- and XO₄^- (X = F, Cl, Br, I) were carried out to discuss the relativistic and electron-correlation effects and, especially, the non-additivity of both effects. The second-order Douglas-Kroll-Hess method was used as a relativistic method, and the Moller-Plesset method was applied to the generalized UHF wave function. The calculated chemical shifts in ClO₄^- and IO₄^- agree reasonably well with the observed ones, though there are no experimental values in FO₄^- and BrO₄^-. The relativistic effect was quite large especially in IO₄^- as reported previously, while the electron-correlation effect is significant in both FO₄^- and IO₄^-. The non-additivity of the relativistic and the electron-correlation effects in magnetic shielding constants is unexpectedly large in IO₄^-, and therefore a relativistic electron-correlated method is crucial for describing accurate heavy-element nuclear magnetic shielding constants and chemical shifts.