Crystal and Substituent Effects on Paramagnetic NMR Shifts in Transition-Metal Complexes
Autoři
NOVOTNÝ, Jan (203 Česká republika, domácí), Lukáš JEREMIAS (203 Česká republika, domácí), Patrick René NIMAX (276 Německo, domácí), Stanislav KOMOROVSKY (703 Slovensko), Ivo HEINMAA (233 Estonsko) a Radek MAREK (203 Česká republika, garant, domácí)
Vydání
Inorganic Chemistry, American Chemical Society, 2021, 0020-1669
Nuclear magnetic resonance (NMR) spectroscopy of paramagnetic molecules provides detailed information about their molecular and electron-spin structure. The paramagnetic NMR spectrum is a very rich source of information about the hyperfine interaction between the atomic nuclei and the unpaired electron density. The Fermi-contact contribution to ligand hyperfine NMR shifts is particularly informative about the nature of the metal−ligand bonding and the structural arrangements of the ligands coordinated to the metal center. In this account, we provide a detailed experimental and theoretical NMR study of compounds of Cr(III) and Cu(II) coordinated with substituted acetylacetonate (acac) ligands in the solid state. For the first time, we report the experimental observation of extremely paramagnetically deshielded 13C NMR resonances for these compounds in the range of 900−1200 ppm. We demonstrate an excellent agreement between the experimental NMR shifts and those calculated using relativistic density-functional theory. Crystal packing is shown to significantly influence the NMR shifts in the solid state, as demonstrated by theoretical calculations of various supramolecular clusters. The resonances are assigned to individual atoms in octahedral Cr(acac)3 and square-planar Cu(acac)2 compounds and interpreted by different electron configurations and magnetizations at the central metal atoms resulting in different spin delocalizations and polarizations of the ligand atoms. Further, effects of substituents on the 13C NMR resonance of the ipso carbon atom reaching almost 700 ppm for Cr(acac)3 compounds are interpreted based on the analysis of Fermi-contact hyperfine contributions.
Návaznosti
GA18-05421S, projekt VaV
Název: Rozvoj paramagnetické NMR spektroskopie pro supramolekulární systémy (Akronym: SUPRAMAG)
Investor: Grantová agentura ČR, Rozvoj paramagnetické NMR spektroskopie pro supramolekulární systémy
GA21-06991S, projekt VaV
Název: Relativistické efekty v paramagnetické NMR spektroskopii (Akronym: RELMAG)
Investor: Grantová agentura ČR, Relativistické efekty v paramagnetické NMR spektroskopii
LM2018140, projekt VaV
Název: e-Infrastruktura CZ (Akronym: e-INFRA CZ)
Investor: Ministerstvo školství, mládeže a tělovýchovy ČR, e-Infrastruktura CZ