Ligand Optimization of Exchange Interaction in Co(II) Dimer Single Molecule Magnet by Machine Learning

Abstract

Designing single-molecule magnets (SMMs) for potential applications in quantum computing and high-density data storage requires tuning their magnetic properties, especially the strength of the magnetic interaction. These properties can be characterized by first-principles calculations based on density functional theory (DFT). In this work, we study the experimentally synthesized Co(II) dimer (Co 2 (C 5 NH 5 ) 4 (μ-PO 2 (CH 2 C 6 H 5 ) 2 ) 3 ) SMM with the goal to control the exchange energy, ΔE J , between the Co atoms through tuning of the capping ligands. The experimentally synthesized Co(II) dimer molecule has a very small ΔE J < 1 meV. We assemble a DFT data set of 1081 ligand substitutions for the Co(II) dimer. The ligand exchange provides a broad range of exchange energies, ΔE J , from +50 to −200 meV, with 80% of the ligands yielding a small ΔE J < 10 meV. We identify descriptors for the classification and regression of ΔE J using gradient boosting machine learning models. We compare one-hot encoded, structure-based, and chemical descriptors consisting of the HOMO/LUMO energies of the individual ligands and the maximum electronegativity difference and bond order for the ligand atom connecting to Co. We observe a similar overall performance with the chemical descriptors outperforming the other descriptors. We show that the exchange coupling, ΔE J , is correlated to the difference in the average bridging angle between the ferromagnetic and antiferromagnetic states, similar to the Goodenough−Kanamori rules.

A Machine Learning Approach to Decipher the Origin of Magnetic Anisotropy in Three-Coordinate Cobalt Single-Ion Magnets

“…21,33 The AI/ML approach has been demonstrated recently for spin state of spin crossover systems and exchange coupling in transition metal complexes. 34,35 For spin crossover systems using artificial neural networks (ANN) with a high percentage of https://doi.org/10.26434/chemrxiv-2024-97555 ORCID: https://orcid.org/0000-0001-6133-3026 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 .i.e.…”

Interlayer interaction-force-tuned magnetic responses in CoII-tetrazolate–carboxylate system from canted antiferromagnet to field-induced metamagnet

“…In this context, Co(II)-derived coordination polymers (CPs) with anisotropic spins tightly aggregated through short coordinative linkages have become excellent candidates for molecular magnets due to their large spin-orbit coupling, well-optimized anisotropy via ligand field (octahedral, tetrahedral, square-pyramidal, trigonal-bipyramid, and square-planar), 10 tunable strength of exchange coupling through tailorable short mediators (N 3 − , COO − , CN − , oxalate, triazolyl, 11 and tetrazolyl [12][13][14], and secondary interactions between low-dimensional chains or layers. [15][16][17][18][19][20][21][22] In addition, such materials have the real possibility of displaying high critical temperatures, particularly in the case of three-dimensional ferromagnets.…”

Weak interchain interaction-dominated magnetic responses in water-extended cobalt(ii)-chains: from magnetic ordering to single-chain magnet

“…6–8 Single-ion anisotropy, strong intrachain exchange coupling, and weak interchain interactions are found to be highly essential for the molecular magnetism of the resulting SCMs. 9–15 Due to its intrinsic spin–orbit coupling and skillfully optimized ligand-field anisotropy, the high-spin cobalt( ii ) ion with the d 7 configuration has widely emerged as a star carrier for high-performance SCMs. 16 In particular, among the various accessible coordination numbers from two to eight, hexa-coordinated cobalt( ii )-derived SCMs with saturated first-sphere coordination (perfect octahedron, compressed or elongated tetragonal bipyramid, and pseudo-trigonal prism) have been extensively designed by manipulating the donor types and bridging connectors.…”