Paramagnetic enhanced proton spin-lattice relaxation in the Ni2+ hexa-aquo complex

A theoretical and molecular dynamics simulation study of the Bloembergen-Morgan decomposition approach

P.-O. Westlund, T. Larsson, Olle Teleman

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

A reinterpretation of the experimental NMR proton spin-lattice dispersion curve of the Ni2+(H2O)6 complex is presented within a general slow-motion theory. The extended pseudo rotation (PR) model developed allows for cross-correlation effects between the nuclear spin-electron spin dipole-dipole and zero field splitting (ZFS) interaction. It is shown that the decomposition approach, treating the electron spin relaxation and the reorientational dynamic of the dipole-dipole correlation function as independent processes is not generally valid. For the Ni-hexa-aquo complex the transient ZFS interaction and the reorientational correlation time change by about 20 per cent due to the correlation effects. Molecular dynamics (MD) simulation of a divalent ion in water provided the timescale of the dynamics present in the PR and the Smoluchowsky models. The structure and dynamics of the octahedral complex is described. The transient ZFS interaction generated by the low frequency vibration modes n(M ↔ OH2) is characterized by a correlation time τv = 0·2 ps and the timescale of the orientational motion of the PR model is in the range τv = 1-10 ps. The fast E- and A-symmetric vibrations cause partial averaging of the ZFS interaction. The timescale of the ligand orientational modes, wag, twist and rock modes are comparable with the electron spin dynamics. The reinterpretation of the NMRD curve suggests that the dynamics described by the single exponential reorientational correlation time, τR reflects the wag, twist and rock modes rather than the overall reorientation of the whole metal-aquo complex. The simulations also suggest that the relatively short proton-metal ion distance obtained from the interpretation of the NMRD curve reflects neglect of outer sphere contributions rather than oversimplification of electron spin dynamics.

Original languageEnglish
Pages (from-to)1365 - 1384
Number of pages20
JournalMolecular Physics
Volume78
Issue number6
DOIs
Publication statusPublished - 1993
MoE publication typeA1 Journal article-refereed

Fingerprint

Spin-lattice relaxation
Molecular Dynamics Simulation
spin-lattice relaxation
Molecular dynamics
Protons
electron spin
Electrons
molecular dynamics
Decomposition
Spin dynamics
decomposition
protons
dipoles
Computer simulation
Vibration
spin dynamics
simulation
Rocks
Ions
curves

Cite this

@article{768bf2cfcc594b0fb46ab7a848ca6689,
title = "Paramagnetic enhanced proton spin-lattice relaxation in the Ni2+ hexa-aquo complex: A theoretical and molecular dynamics simulation study of the Bloembergen-Morgan decomposition approach",
abstract = "A reinterpretation of the experimental NMR proton spin-lattice dispersion curve of the Ni2+(H2O)6 complex is presented within a general slow-motion theory. The extended pseudo rotation (PR) model developed allows for cross-correlation effects between the nuclear spin-electron spin dipole-dipole and zero field splitting (ZFS) interaction. It is shown that the decomposition approach, treating the electron spin relaxation and the reorientational dynamic of the dipole-dipole correlation function as independent processes is not generally valid. For the Ni-hexa-aquo complex the transient ZFS interaction and the reorientational correlation time change by about 20 per cent due to the correlation effects. Molecular dynamics (MD) simulation of a divalent ion in water provided the timescale of the dynamics present in the PR and the Smoluchowsky models. The structure and dynamics of the octahedral complex is described. The transient ZFS interaction generated by the low frequency vibration modes n(M ↔ OH2) is characterized by a correlation time τv = 0·2 ps and the timescale of the orientational motion of the PR model is in the range τv = 1-10 ps. The fast E- and A-symmetric vibrations cause partial averaging of the ZFS interaction. The timescale of the ligand orientational modes, wag, twist and rock modes are comparable with the electron spin dynamics. The reinterpretation of the NMRD curve suggests that the dynamics described by the single exponential reorientational correlation time, τR reflects the wag, twist and rock modes rather than the overall reorientation of the whole metal-aquo complex. The simulations also suggest that the relatively short proton-metal ion distance obtained from the interpretation of the NMRD curve reflects neglect of outer sphere contributions rather than oversimplification of electron spin dynamics.",
author = "P.-O. Westlund and T. Larsson and Olle Teleman",
year = "1993",
doi = "10.1080/00268979300100911",
language = "English",
volume = "78",
pages = "1365 -- 1384",
journal = "Molecular Physics",
issn = "0026-8976",
publisher = "Taylor & Francis",
number = "6",

}

Paramagnetic enhanced proton spin-lattice relaxation in the Ni2+ hexa-aquo complex : A theoretical and molecular dynamics simulation study of the Bloembergen-Morgan decomposition approach. / Westlund, P.-O.; Larsson, T.; Teleman, Olle.

In: Molecular Physics, Vol. 78, No. 6, 1993, p. 1365 - 1384.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Paramagnetic enhanced proton spin-lattice relaxation in the Ni2+ hexa-aquo complex

T2 - A theoretical and molecular dynamics simulation study of the Bloembergen-Morgan decomposition approach

AU - Westlund, P.-O.

AU - Larsson, T.

AU - Teleman, Olle

PY - 1993

Y1 - 1993

N2 - A reinterpretation of the experimental NMR proton spin-lattice dispersion curve of the Ni2+(H2O)6 complex is presented within a general slow-motion theory. The extended pseudo rotation (PR) model developed allows for cross-correlation effects between the nuclear spin-electron spin dipole-dipole and zero field splitting (ZFS) interaction. It is shown that the decomposition approach, treating the electron spin relaxation and the reorientational dynamic of the dipole-dipole correlation function as independent processes is not generally valid. For the Ni-hexa-aquo complex the transient ZFS interaction and the reorientational correlation time change by about 20 per cent due to the correlation effects. Molecular dynamics (MD) simulation of a divalent ion in water provided the timescale of the dynamics present in the PR and the Smoluchowsky models. The structure and dynamics of the octahedral complex is described. The transient ZFS interaction generated by the low frequency vibration modes n(M ↔ OH2) is characterized by a correlation time τv = 0·2 ps and the timescale of the orientational motion of the PR model is in the range τv = 1-10 ps. The fast E- and A-symmetric vibrations cause partial averaging of the ZFS interaction. The timescale of the ligand orientational modes, wag, twist and rock modes are comparable with the electron spin dynamics. The reinterpretation of the NMRD curve suggests that the dynamics described by the single exponential reorientational correlation time, τR reflects the wag, twist and rock modes rather than the overall reorientation of the whole metal-aquo complex. The simulations also suggest that the relatively short proton-metal ion distance obtained from the interpretation of the NMRD curve reflects neglect of outer sphere contributions rather than oversimplification of electron spin dynamics.

AB - A reinterpretation of the experimental NMR proton spin-lattice dispersion curve of the Ni2+(H2O)6 complex is presented within a general slow-motion theory. The extended pseudo rotation (PR) model developed allows for cross-correlation effects between the nuclear spin-electron spin dipole-dipole and zero field splitting (ZFS) interaction. It is shown that the decomposition approach, treating the electron spin relaxation and the reorientational dynamic of the dipole-dipole correlation function as independent processes is not generally valid. For the Ni-hexa-aquo complex the transient ZFS interaction and the reorientational correlation time change by about 20 per cent due to the correlation effects. Molecular dynamics (MD) simulation of a divalent ion in water provided the timescale of the dynamics present in the PR and the Smoluchowsky models. The structure and dynamics of the octahedral complex is described. The transient ZFS interaction generated by the low frequency vibration modes n(M ↔ OH2) is characterized by a correlation time τv = 0·2 ps and the timescale of the orientational motion of the PR model is in the range τv = 1-10 ps. The fast E- and A-symmetric vibrations cause partial averaging of the ZFS interaction. The timescale of the ligand orientational modes, wag, twist and rock modes are comparable with the electron spin dynamics. The reinterpretation of the NMRD curve suggests that the dynamics described by the single exponential reorientational correlation time, τR reflects the wag, twist and rock modes rather than the overall reorientation of the whole metal-aquo complex. The simulations also suggest that the relatively short proton-metal ion distance obtained from the interpretation of the NMRD curve reflects neglect of outer sphere contributions rather than oversimplification of electron spin dynamics.

U2 - 10.1080/00268979300100911

DO - 10.1080/00268979300100911

M3 - Article

VL - 78

SP - 1365

EP - 1384

JO - Molecular Physics

JF - Molecular Physics

SN - 0026-8976

IS - 6

ER -