Chemical Shift in Paramagnetic Systems

Vaara, Juha

doi:10.1016/b978-0-444-59411-2.00003-4

Cited by 12 publications

(11 citation statements)

References 69 publications

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“…The EPR parameters ( g and A ) ,, for Ru(III) complexes were calculated by using the ADF 2017 program . The calculations were performed at the two-component (SO-ZORA) level of theory by using the PBE0 functional, the TZ2P or QZ4P basis set, and the COSMO solvent model.…”

Section: Methodsmentioning

confidence: 99%

Zwitterionic Ru(III) Complexes: Stability of Metal–Ligand Bond and Host–Guest Binding with Cucurbit[7]uril

et al. 2020

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A wide range of ruthenium-based coordination compounds have been reported to possess potential as metallodrugs with anticancer or antimetastatic activity. In this work, we synthesized a set of new zwitterionic Ru(III) compounds bearing ligands derived from N-alkyl (R) systems based on pyridine, 4,4′-bipyridine, or 1,4-diazabicyclo[2.2.2]octane (DABCO). The effects of the ligand(s) and their environment on the coordination stability have been investigated. Whereas the [DABCO-R]+ ligand is shown to be easily split out of a negative [RuCl4]− core, positively charged R-pyridine and R-bipyridine ligands form somewhat more stable Ru(III) complexes and can be used as supramolecular anchors for binding with macrocycles. Therefore, supramolecular host–guest assemblies between the stable zwitterionic Ru(III) guests and the cucurbit[7]uril host were investigated and characterized in detail by using NMR spectroscopy and single-crystal X-ray diffraction. Paramagnetic 1H NMR experiments supplemented by relativistic DFT calculations of the structure and hyperfine NMR shifts were performed to determine the host–guest binding modes in solution. In contrast to the intramolecular hyperfine shifts, dominated by the through-bond Fermi-contact mechanism, supramolecular hyperfine shifts were shown to depend on the “through-space” spin–dipole contributions with structural trends being satisfactorily reproduced by a simple point-dipole approximation.

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Section: Methodsmentioning

confidence: 99%

Zwitterionic Ru(III) Complexes: Stability of Metal–Ligand Bond and Host–Guest Binding with Cucurbit[7]uril

et al. 2020

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“…Soncini -van der Heuvel [18] theories, analyzed as in Reference [21] indicates that a total of ten terms may contribute to the total shift tensor (Table 1), three of which contain the dipolar hyperfine interaction (terms 2, 7, and 9 in Table 1) and which may be used in a classical point-dipole approximation for long-range pseudocontact shifts, see References [17,49] for a detailed discussion of the various mechanisms.…”

Section: Definitions and Conventions For Nmr Parametersmentioning

confidence: 99%

“…The situation in the molecular pNMR shift theory has been reviewed in References [47,49,50]. It is noteworthy that, in contrast to the situation in the SSNMR of diamagnetic systems for which periodic DFT methods [4] are routinely used [51], so far no periodic implementation of the modern first-principles pNMR theory with ZFS exist.…”

Section: Introductionmentioning

confidence: 99%

Assignment of solid-state 13C and 1H NMR spectra of paramagnetic Ni(II) acetylacetonate complexes aided by first-principles computations

Rouf

Jakobsen

Mareš

et al. 2017

Solid State Nuclear Magnetic Resonance

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Recent advances in computational methodology allowed for first-principles calculations of the nuclear shielding tensor for a series of paramagnetic nickel(II) acetylacetonate complexes, [Ni(acac)L] with L = HO, DO, NH, ND, and PMePh have provided detailed insight into the origin of the paramagnetic contributions to the total shift tensor. This was employed for the assignment of the solid-state H andC MAS NMR spectra of these compounds. The two major contributions to the isotropic shifts are by orbital (diamagnetic-like) and contact mechanism. The orbital shielding, contact, as well as dipolar terms all contribute to the anisotropic component. The calculations suggest reassignment of the C methyl and carbonyl resonances in the acac ligand [Inorg. Chem.53, 2014, 399] leading to isotropic paramagnetic shifts of δ(C) ≈ 800-1100 ppm and ≈180-300 ppm for C for the methyl and carbonyl carbons located three and two bonds away from the paramagnetic Ni(II) ion, respectively. Assignment using three different empirical correlations, i.e., paramagnetic shifts, shift anisotropy, and relaxation (T) were ambiguous, however the latter two support the computational results. Thus, solid-state NMR spectroscopy in combination with modern quantum-chemical calculations of paramagnetic shifts constitutes a promising tool for structural investigations of metal complexes and materials.

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“…To achieve reliable results it is necessary to assess each component, and calibrate the most effective approach against an often-limited set of experimental values for similar chemical species. Detailed overviews of the evaluation of spin Hamiltonian parameters in the context of modern computational chemistry are available from Vaara [16], Bolvin [17] and Autschbach [18]. We shall mostly be concerned with studying the effect of zero field splitting (ZFS) on the predicted 1 H, 13 C, 29 Si shifts of six compounds.…”

Section: Introductionmentioning

confidence: 99%

Modelling the Effect of Zero-Field Splitting on the 1H, 13C and 29Si Chemical Shifts of Lanthanide and Actinide Compounds

2019

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The prediction of paramagnetic NMR (pNMR) chemical shifts in molecules containing heavy atoms presents a significant challenge to computational quantum chemistry. The importance of meeting this challenge lies in the central role that NMR plays in the structural characterisation of chemical systems. Hence there is a need for reliable assignment and prediction of chemical shifts. In a previous study [Trends in Physical Chemistry, 17, 25–57, (2017)] we looked at the computation of pNMR chemical shifts in lanthanide and actinide complexes using a spin Hamiltonian approach. In that study we were principally concerned with molecules with S = 1/2 ground states. In the present work we extend that study by looking at the effect of zero field splitting (ZFS) for six complexes with S = 3/2 ground states. It is shown that the inclusion of ZFS can produce substantial shifts in the predicted chemical shifts. The computations presented are typically sufficient to enable assignment of experimental spectra. However for one case, in which the peaks are closely clustered, the inclusion of ZFS re-orders the chemical shifts making assignment quite difficult. We also observe, and echo, the previously reported importance of including the paramagnetic spin-orbit hyperfine interaction for 13 C and 29 Si atoms, when these are directly bound to a heavy element and thus subject to heavy-atom-light-atom effects. The necessary computations are very demanding, and more work is needed to find theoretical and computational approaches that simplify the evaluation of this term. We discuss the computation of each term required in the spin Hamiltonian. The systems we study in this work are restricted to a single heavy atom ion (one Nd(III) and five U(III) complexes), but typify some of the computational complexity encountered in lanthanide and actinide containing molecules.

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Chemical Shift in Paramagnetic Systems

Cited by 12 publications

References 69 publications

Zwitterionic Ru(III) Complexes: Stability of Metal–Ligand Bond and Host–Guest Binding with Cucurbit[7]uril

Zwitterionic Ru(III) Complexes: Stability of Metal–Ligand Bond and Host–Guest Binding with Cucurbit[7]uril

Assignment of solid-state 13C and 1H NMR spectra of paramagnetic Ni(II) acetylacetonate complexes aided by first-principles computations

Modelling the Effect of Zero-Field Splitting on the 1H, 13C and 29Si Chemical Shifts of Lanthanide and Actinide Compounds

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