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Title: Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies

Molecular dynamics is a fundamental property of metal complexes. These dynamic processes, especially for paramagnetic complexes under external magnetic fields, are in general not well understood. Quasielastic neutron scattering (QENS) in 0–4 T magnetic fields has been used to study the dynamics of Co(acac) 2(D 2O) 2 (1- d 4, acac = acetylacetonate). At 80–100 K, rotation of the methyl groups on the acac ligands is the dominant dynamical process. This rotation is slowed down by the magnetic field increase. Rotation times at 80 K are 5.6(3) × 10 –10 s at 0 T and 2.04(10) × 10 –9 s at 4 T. The QENS studies suggest that methyl groups in these paramagnetic Co(II) molecules do not behave as isolated units, which is consistent with results from earlier magnetic susceptibility studies indicating the presence of intermolecular interactions. DFT calculations show that unpaired electron spin density in 1 is dispersed to the atoms of both acac and H 2O ligands. Methyl torsions in 1- d 4 have also been observed at 5–100 K in inelastic neutron spectroscopy (INS). In conclusion, the QENS and INS results here help understand the dynamics of the compound in the solid state.
Authors:
 [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [2] ;  [2] ; ORCiD logo [2] ; ORCiD logo [1]
  1. Univ. of Tennessee, Knoxville, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 20; Journal Issue: 32; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1484105
Alternate Identifier(s):
OSTI ID: 1463037

Stavretis, Shelby E., Mamontov, Eugene, Moseley, Duncan H., Cheng, Yongqiang, Daemen, Luke L., Ramirez-Cuesta, Anibal J., and Xue, Zi -Ling. Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies. United States: N. p., Web. doi:10.1039/c8cp01660g.
Stavretis, Shelby E., Mamontov, Eugene, Moseley, Duncan H., Cheng, Yongqiang, Daemen, Luke L., Ramirez-Cuesta, Anibal J., & Xue, Zi -Ling. Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies. United States. doi:10.1039/c8cp01660g.
Stavretis, Shelby E., Mamontov, Eugene, Moseley, Duncan H., Cheng, Yongqiang, Daemen, Luke L., Ramirez-Cuesta, Anibal J., and Xue, Zi -Ling. 2018. "Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies". United States. doi:10.1039/c8cp01660g.
@article{osti_1484105,
title = {Effect of magnetic fields on the methyl rotation in a paramagnetic cobalt(ii) complex. Quasielastic neutron scattering studies},
author = {Stavretis, Shelby E. and Mamontov, Eugene and Moseley, Duncan H. and Cheng, Yongqiang and Daemen, Luke L. and Ramirez-Cuesta, Anibal J. and Xue, Zi -Ling},
abstractNote = {Molecular dynamics is a fundamental property of metal complexes. These dynamic processes, especially for paramagnetic complexes under external magnetic fields, are in general not well understood. Quasielastic neutron scattering (QENS) in 0–4 T magnetic fields has been used to study the dynamics of Co(acac)2(D2O)2 (1-d4, acac = acetylacetonate). At 80–100 K, rotation of the methyl groups on the acac ligands is the dominant dynamical process. This rotation is slowed down by the magnetic field increase. Rotation times at 80 K are 5.6(3) × 10–10 s at 0 T and 2.04(10) × 10–9 s at 4 T. The QENS studies suggest that methyl groups in these paramagnetic Co(II) molecules do not behave as isolated units, which is consistent with results from earlier magnetic susceptibility studies indicating the presence of intermolecular interactions. DFT calculations show that unpaired electron spin density in 1 is dispersed to the atoms of both acac and H2O ligands. Methyl torsions in 1-d4 have also been observed at 5–100 K in inelastic neutron spectroscopy (INS). In conclusion, the QENS and INS results here help understand the dynamics of the compound in the solid state.},
doi = {10.1039/c8cp01660g},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 32,
volume = 20,
place = {United States},
year = {2018},
month = {7}
}

Works referenced in this record:

Generalized Gradient Approximation Made Simple
journal, October 1996
  • Perdew, John P.; Burke, Kieron; Ernzerhof, Matthias
  • Physical Review Letters, Vol. 77, Issue 18, p. 3865-3868
  • DOI: 10.1103/PhysRevLett.77.3865

Projector augmented-wave method
journal, December 1994

From ultrasoft pseudopotentials to the projector augmented-wave method
journal, January 1999