Abstract
Two-dimensional (2D) coordination polymer (CP) [CoIII(CN)6]2[CoII(TODA)]3·7H2O (TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane, Co-TODA) was reported earlier to show field-induced slow magnetic relaxation, displaying single-ion magnet (SIM) behaviors. Most SIMs are molecular compounds with fewer adopting coordination polymer (CP) or metal-organic framework (MOF) structures. In the current work, magnetic and phonon properties of Co-TODA have been studied by advanced spectroscopies and computations. The combined use of far-IR magneto-spectroscopy (FIRMS) and variable-temperature (VT) high-frequency and -field electron paramagnetic resonance (HFEPR) gives spin Hamiltonian (SH) parameters: Axial zero-field splitting (ZFS) parameter D as +38.0(1.0) ≤ D ≪ +40.2(1.0) cm-1 and rhombic ZFS parameter E as 0 ≪ |E| ≤ 7.3(1.0) cm-1, showing that Co-TODA has the easy-plane magnetic anisotropy. Two CoII centers in the CP, as determined by synchrotron single-crystal X-ray diffraction at 15(2) K, show similar magnetic properties indistinguishable in FIRMS at 5.3(3) K or in HFEPR at 5-150 K. Ab initio calculations explore the origin of the magnetic anisotropy and magnetostructural correlations. VT inelastic neutron scattering (INS) spectra of Co-TODA have been obtained to show the phonon properties of the CP. Density functional theory (DFT) calculations, giving both a calculated INS spectrum and spin distributions in Co-TODA, demonstrate that, compared with other high-spin CoII complexes, the larger the spin density on a metal ion, the larger the ZFS in the complex. Pulsed X-band EPR studies probe relaxations of the CoII ions from the MS = +1/2 to -1/2 state in the ground Kramers doublet (KD), yielding spin-lattice (T1) and spin-spin relaxation (T2) times. The work reported here highlights the versatility and power of the spectroscopic techniques and computations in the characterization of magnetic and phonon properties of a CP and the understanding of its magnetic anisotropy.
| Original language | English |
|---|---|
| Pages (from-to) | 13268-13283 |
| Number of pages | 16 |
| Journal | Journal of Physical Chemistry C |
| Volume | 126 |
| Issue number | 31 |
| DOIs | |
| State | Published - Aug 11 2022 |
Funding
US National Science Foundation (CHE-1900296 and CHE-2055499 to Z.-L.X.), Natural Science Grant of China (no. 21973046 to Y.-Q.Z.), and a Shull Wollan Center Graduate Research Fellowship (to P.T.) are acknowledged for partial support of the research. Part of this work was performed at the National High Magnetic Field Laboratory, which is supported by NSF Cooperative Agreement No. DMR-1644779 and the State of Florida. Neutron scattering experiments were conducted at the VISION beamline at ORNL’s Spallation Neutron Source, which is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences (BES), U.S. Department of Energy (DOE), under Contract No. DE-AC0500OR22725 with UT Battelle, LLC. The computing resources were made available through the VirtuES and the ICEMAN projects, funded by Laboratory Directed Research and Development program and Compute and Data Environment for Science (CADES) at ORNL. NSF’s ChemMatCARS Sector 15 is supported by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under Grant Number NSF/CHE-1834750. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. The authors thank Adam T. Hand and Michael J. Jenkins for help with FIRMS experiments.