title: Slow Magnetic Relaxations in Cobalt(II) Tetranitrate Complexes. Studies of Magnetic Anisotropy by Inelastic Neutron Scattering and High-Frequency and High-Field EPR Spectroscopy.
abstract: Three mononuclear cobalt(II) tetranitrate complexes (A)2[Co(NO3)4] with different countercations, Ph4P+(1), MePh3P+(2), and Ph4As+(3), have been synthesized and studied by X-ray single-crystal diffraction, magnetic measurements, inelastic neutron scattering (INS), high-frequency and high-field EPR (HF-EPR) spectroscopy, and theoretical calculations. The X-ray diffraction studies reveal that the structure of the tetranitrate cobalt anion varies with the countercation. 1 and 2 exhibit highly irregular seven-coordinate geometries, while the central Co(II) ion of 3 is in a distorted-dodecahedral configuration. The sole magnetic transition observed in the INS spectroscopy of 1-3 corresponds to the zero-field splitting (2(D2+ 3E2)1/2) from 22.5(2) cm-1in 1 to 26.6(3) cm-1in 2 and 11.1(5) cm-1in 3. The positive sign of the D value, and hence the easy-plane magnetic anisotropy, was demonstrated for 1 by INS studies under magnetic fields and HF-EPR spectroscopy. The combined analyses of INS and HF-EPR data yield the D values as +10.90(3), +12.74(3), and +4.50(3) cm-1for 1-3, respectively. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal the slow magnetization relaxation in 1 and 2 at an applied dc field of 600 Oe, which is a characteristic of field-induced single-molecule magnets (SMMs). The electronic structures and the origin of magnetic anisotropy of 1-3 were revealed by calculations at the CASPT2/NEVPT2 level.
authors.affiliation: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210023, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210023, People's Republic of China.
authors.forename: Hui-Hui
authors.initials: HH
authors.lastname: Cui
authors.affiliation: Department of Chemistry, University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Shelby E
authors.initials: SE
authors.lastname: Stavretis
authors.affiliation: Department of Chemistry, University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Seth C
authors.initials: SC
authors.lastname: Hunter
authors.affiliation: Jiangsu Key Laboratory for NSLSCS, School of Physical Science and Technology, Nanjing Normal University , Nanjing 210023, People's Republic of China.
authors.forename: Yi-Quan
authors.initials: YQ
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210023, People's Republic of China.
authors.forename: Xue-Tai
authors.identifier: http://orcid.org/0000-0001-5518-5557
authors.initials: XT
authors.lastname: Chen
authors.affiliation: Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology , Wuhan 430074, People's Republic of China.
authors.forename: Yi-Chen
authors.initials: YC
authors.lastname: Sun
authors.affiliation: Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology , Wuhan 430074, People's Republic of China.
authors.forename: Zhenxing
authors.initials: Z
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210023, People's Republic of China.
authors.forename: You
authors.initials: Y
authors.lastname: Song
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Podlesnyak
authors.affiliation: Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology , Wuhan 430074, People's Republic of China.
authors.forename: Zhong-Wen
authors.initials: ZW
authors.lastname: Ouyang
authors.affiliation: Department of Chemistry, University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Zi-Ling
authors.initials: ZL
authors.lastname: Xue