Magnetic resonance properties of metal-containing nanosystems

by J (Juho) Roukala

Institution: University of Oulu
Year: 2016
Keywords: Monte Carlo simulation; density functional theory; electronic structure; magnetic resonance parameters; nuclear magnetic resonance spectroscopy; special relativity
Posted: 02/05/2017
Record ID: 2064062
Full text PDF: http://urn.fi/urn:isbn:9789526213279


Abstract This thesis presents computational first-principles investigations of nuclear magnetic resonance (NMR) parameters in metal-containing nanosystems. Special attention is paid to the relativistic effects observed in the vicinity of heavy elements. Small transition metal complexes are used to assess the feasibility of a quasirelativistic density functional theory (DFT) approach for calculating nuclear magnetic shielding tensors of increasingly heavy metal nuclei, followed by applications of the concept to larger systems. Nuclear magnetic shielding constants, shielding anisotropies, and chemical shifts with respect to metal ions are calculated in dimethyl and water complexes of the group-12 transition metals 67Zn, 111/113Cd, and 199/201Hg, using Hartree–Fock and DFT methods with relativistic corrections from the Breit–Pauli Perturbation Theory (BPPT). Four-component relativistic Dirac–Hartree–Fock and correlated, nonrelativistic ab initio calculations are used to benchmark the BPPT and DFT methods, respectively. The DFT/BPPT approach, combined with Monte Carlo simulations at finite temperatures, is subsequently used to calculate the chemical shift of a guest 129Xe inside a tetrahedral, iron-based cage. Complementing experiments, the encapsulation of xenon is verified, and empirically elusive details are revealed about the guest dynamics. Finally, the full shielding tensors of 31P and 195Pt and the indirect spin–spin coupling constants between the two nuclei are studied in five crystalline platinum(II) dialkyldithiophosphato complexes, concentrating on the solid-state chemical shift anisotropy and asymmetry parameters of phosphorus and platinum. The NMR parameters are calculated using DFT and the two-component zerothorder regular approximation (ZORA) for relativistic effects, combining molecular and solid-state models to incorporate indispensable contributions due to spin–orbit and crystal lattice corrections for the shielding tensors. Four-component matrix-Dirac–Kohn–Sham shielding calculations are used to benchmark the ZORA method. Qualitative, in cases nearly quantitative agreement is obtained with experiments, allowing the validation of the X-ray structures of the complexes, as well as a deeper analysis of the differences between them, including the major contributions to the NMR parameters. The results presented here demonstrate that computational NMR, a branch of relativistic quantum chemistry, is applicable and useful in studying nanoscale systems containing heavy elements, such as transition metals. Approximations are necessary to enable the treatment of large and complex targets, but sufficient accuracy is achieved for supplementing experiments with reliable and useful data that provides additional insight and analysis possibilities.