Issue 7, 2023

Magnetic and relaxation properties of vanadium(iv) complexes: an integrated 1H relaxometric, EPR and computational study

Abstract

We report a detailed study of the magnetic and relaxation properties of a series of oxovanadium(IV) complexes comprising the aqua ion [VO(H2O)5]2+ and [VO(ox)2]2− (ox = oxalate), [VO(nta)] (nta = nitrilotriacetate), [VO(dtpa)]3− (dtpa = diethylenetriaminepentaacetate) and [VO(acac)2] (acac = acetylacetonato) in solution. The complexes were characterized using continuous wave (X-band) and pulsed (Q-band) EPR measurements and 1H nuclear magnetic relaxation dispersion (NMRD) studies in the 0.01–120 MHz 1H Larmor frequency range. The 51V A-tensor parameters obtained from the analysis of EPR spectra are in good agreement with those obtained using theoretical calculations at the DFT and coupled-cluster levels (DLPNO-CCSD), while g-tensors were obtained with CASSCF/NEVPT2 calculations. EPR measurements reveal significant differences in the electronic Te1 and Tem relaxation times, with [VO(acac)2] showing a markedly different behaviour due to the trans coordination geometry. The NMRD profiles measured at different temperatures have contributions from both the outer- and inner-sphere mechanisms, with the latter showing contributions from the dipolar and scalar mechanisms. The rotational correlation times (τR) obtained from the fitting of NMRD and EPR data are in good mutual agreement. The scalar mechanism depends on the hyperfine coupling constants of the coordinated water molecule Haiso, which were obtained from the fitting of the NMRD profiles and DFT calculations. Finally, the analysis of the data provided information on the exchange rate of coordinated water molecules, which display mean residence times of ∼7–17 μs at 298 K.

Graphical abstract: Magnetic and relaxation properties of vanadium(iv) complexes: an integrated 1H relaxometric, EPR and computational study

Supplementary files

Article information

Article type
Research Article
Submitted
12 Dec. 2022
Accepted
20 Janv. 2023
First published
20 Janv. 2023
This article is Open Access
Creative Commons BY license

Inorg. Chem. Front., 2023,10, 1999-2013

Magnetic and relaxation properties of vanadium(IV) complexes: an integrated 1H relaxometric, EPR and computational study

V. Lagostina, F. Carniato, D. Esteban-Gómez, C. Platas-Iglesias, M. Chiesa and M. Botta, Inorg. Chem. Front., 2023, 10, 1999 DOI: 10.1039/D2QI02635J

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