Abstract
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). The QENS and INS results here help understand the dynamics of the compound in the solid state.
Original language | English |
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Pages (from-to) | 21119-21126 |
Number of pages | 8 |
Journal | Physical Chemistry Chemical Physics |
Volume | 20 |
Issue number | 32 |
DOIs | |
State | Published - 2018 |
Funding
The authors thank Drs S. O. Diallo and Craig. M. Brown for their helpful discussions and preliminary data collection. We appreciate suggestions of Profs. Xue-Tai Chen and You Song. Acknowledgement is made to the Donors of the American Chemical Society Petroleum Research Fund, National Science Foundation (CHE-1633870 to Z.-L. X.) and Shull Wollan Graduate Research Fellowship (to S. E. S.) for partial support of the research. Research at the Oak Ridge National Laboratory's Spallation Neutron Source was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Computational resources for the VASP calculations were made available through the VirtuES and ICE-MAN projects, funded by the Laboratory Directed Research and Development at ORNL. We acknowledge the technical and scientific support of the staff at the SNS and the NIST for preliminary QENS data. The authors thank Drs S. O. Diallo and Craig. M. Brown for their helpful discussions and preliminary data collection. We appreciate suggestions of Profs. Xue-Tai Chen and You Song. Acknowledgement is made to the Donors of the American Chemical Society Petroleum Research Fund, National Science Foundation (CHE-1633870 to Z.-L. X.) and Shull Wollan Graduate Research Fellowship (to S. E. S.) for partial support of the research. Research at the Oak Ridge National Laboratory’s Spallation Neutron Source was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Computational resources for the VASP calculations were made available through the VirtuES and ICE-MAN projects, funded by the Laboratory Directed Research and Development at ORNL. We acknowledge the technical and scientific support of the staff at the SNS and the NIST for preliminary QENS data.