Abstract
Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs). Small structural changes can alter the magnetic properties, and accurate experimental methods to investigate magnetic anisotropy are therefore critical. Here, we investigate two five-coordinated Co(ii) SMMs, [CoCl2Cltpy] (1) and [CoBr2Cltpy] (2) (Cltpy = 4′-chloro-2,2′:6′,2′′-terpyridine), through multiple techniques. Ab initio theoretical calculations performed on the two compounds show that both possess axial magnetic anisotropy with the magnetic easy axis pointing towards one of the terminal halogen atoms. Theoretical calculations on SMMs are typically done on isolated molecular species, and to validate this approximation the magnetic anisotropy was further studied through experimental techniques. EPR measurements confirm an axial anisotropy of 1, and magnetic measurements provide experimental Zero-Field Splitting (ZFS) parameters, showing that the values from theoretical calculations are slightly overestimated. The X-ray electron density determined from 20 K single-crystal synchrotron X-ray diffraction data provides estimated d-orbital populations also suggesting axial magnetic anisotropy in both systems, and furthermore suggesting a more pronounced axiality in 1 compared to 2. This is in good agreement with the results obtained from both magnetic measurements and theoretical calculations. The magnetic anisotropy of 1 is quantified experimentally through polarized powder neutron diffraction via the site susceptibility method, confirming an axial magnetic anisotropy of the compound. A slight deviation in the easy axis direction is observed between experimental and theoretical results. This, together with the overestimation of the ZFS parameters from theoretical calculations, shows that experimental investigation of the magnetic anisotropy of SMMs is of high relevance.
| Original language | English |
|---|---|
| Pages (from-to) | 16610-16624 |
| Number of pages | 15 |
| Journal | Chemical Science |
| Volume | 16 |
| Issue number | 36 |
| DOIs | |
| State | Published - Sep 17 2025 |
Funding
The study was supported by the Villum Foundation (25861), the Danish Ministry for Higher Education and Sciences (Q-MAT lighthouse), Aarhus University Research Foundation, the Danish National Research Foundation (DNRF189), the Novo Nordisk Foundation, the Carlsberg Foundation and Danscatt. Jacob Overgaard is thanked for initial conceptualisation and discussion. This research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to HB-2A/POWDER on proposal number IPTS-28520.1. The authors would like to acknowledge the staff at the BL02B1 beamline at SPring-8 for measuring and providing the single-crystal diffraction data, Jacob Svane for collecting PXRD data, and Kim-Khuong Huynh for help with collecting magnetic data. We thank the Copenhagen Pulse EPR Facility, supported by a Research Infrastructure – Large Equipment and Facilities grant (NNF21OC0068806) from the Novo Nordisk Foundation. The numerical results presented in this work were obtained at the Centre for Scientific Computing, Aarhus.64 The study was supported by the Villum Foundation (25861), the Danish Ministry for Higher Education and Sciences (Q-MAT lighthouse), Aarhus University Research Foundation, the Danish National Research Foundation (DNRF189), the Novo Nordisk Foundation, the Carlsberg Foundation and Danscatt. Jacob Overgaard is thanked for initial conceptualisation and discussion. This research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to HB-2A/POWDER on proposal number IPTS-28520.1. The authors would like to acknowledge the staff at the BL02B1 beamline at SPring-8 for measuring and providing the single-crystal diffraction data, Jacob Svane for collecting PXRD data, and Kim-Khuong Huynh for help with collecting magnetic data. We thank the Copenhagen Pulse EPR Facility, supported by a Research Infrastructure - Large Equipment and Facilities grant (NNF21OC0068806) from the Novo Nordisk Foundation. The numerical results presented in this work were obtained at the Centre for Scientific Computing, Aarhus.64