Nature of NMR Shifts in Paramagnetic Octahedral Ru(III) Complexes with Axial Pyridine-Based Ligands

Overview

Journal Inorg Chem

Specialty Chemistry

Date 2023 Feb 10

PMID 36763803

Authors

Jan Chyba

Anna Hruzikova

Michal Knor

Petra Pikulova

Katerina Markova

Jan Novotny

Radek Marek

Affiliations

Soon will be listed here.

Abstract

In recent decades, transition-metal coordination compounds have been extensively studied for their antitumor and antimetastatic activities. In this work, we synthesized a set of symmetric and asymmetric Ru(III) and Rh(III) coordination compounds of the general structure (Na/K/PPh/LH) [-ML(eq)L(ax)] (M = Ru or Rh; L(eq) = Cl, = 4; L(eq) = ox, = 2; L(ax) = 4-R-pyridine, R = CH, H, CH, COOH, CF, CN; L(ax) = DMSO-) and systematically investigated their structure, stability, and NMR properties. H and C NMR spectra measured at various temperatures were used to break down the total NMR shifts into the orbital (temperature-independent) and hyperfine (temperature-dependent) contributions. The hyperfine NMR shifts for paramagnetic Ru(III) compounds were analyzed in detail using relativistic density functional theory (DFT). The effects of (i) the 4-R substituent of pyridine, (ii) the axial ligand L(ax), and (iii) the equatorial ligands L(eq) on the distribution of spin density reflected in the "through-bond" (contact) and the "through-space" (pseudocontact) contributions to the hyperfine NMR shifts of the individual atoms of the pyridine ligands are rationalized. Further, we demonstrate the large effects of the solvent on the hyperfine NMR shifts and discuss our observations in the general context of the paramagnetic NMR spectroscopy of transition-metal complexes.

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