Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: A comparison of three relativistic computational methods

• Autores: Arcisauskaite, V.; Melo, J.I.; Hemmingsen, L.; Sauer, S.P.A.
• Año de publicación: 2011
• Idioma: inglés
• Tipo de recurso: artículo
• Fuente: J Chem Phys 2011;135(4)
• Materia: Atomic numbers; Basis sets; Coulomb potential; Exchange-correlations; Experimental data; Functionals; Gaussians; Linear response; NMR shielding; Nuclear magnetic resonance shielding; Point nuclei; Relativistic effects; Shielding constants; Small components; Spin densities; Spin orbits; Two-component; Zeroth-order regular approximations; Atoms; Bromine; Chemical compounds; Chemical shift; Chlorine; Electric fields; Iodine; Mercury (metal); Resonance; Magnetic shielding; mercury; mercury derivative; article; chemistry; comparative study; computer analysis; methodology; nuclear magnetic resonance spectroscopy; quantum theory; Computing Methodologies; Magnetic Resonance Spectroscopy; Mercury Compounds; Mercury Isotopes; Quantum Theory
• Institución: Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales

We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL2 (L = Cl, Br, I, CH 3) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH3)2 within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by ∼2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr 2 and HgI2 when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of ∼500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by ∼100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible. © 2011 American Institute of Physics.
Fil:Melo, J.I. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.