Spin-state energetics and magnetic anisotropy in penta-coordinated Fe() complexes with different axial and equatorial ligand environments

• Published in: Physical chemistry chemical physics : PCCP 2023-07, Vol.25 (26), p.1768-17691
• Main Authors: Joshi, Shalini, Roy Chowdhury, Sabyasachi, Mishra, Sabyashachi
• Format: Article
• Language: English
• Subjects: Anisotropy; Electron states; Halides; Ligands; Magnetic anisotropy; Quantum tunnelling
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp02182c

The penta-coordinated trigonal-bi-pyramidal (TBP) Fe( iii ) complex (PMe 2 Ph) 2 FeCl 3 shows a reduced magnetic anisotropy in its intermediate-spin (IS) state as compared to its methyl-analog (PMe 3 ) 2 Fe( iii )Cl 3 . In this work, the ligand environment in (PMe 2 Ph) 2 FeCl 3 is systematically altered by replacing the axial -P with -N and -As, the equatorial -Cl with other halides, and the axial methyl group with an acetyl group. This has resulted in a series of Fe( iii ) TBP complexes modelled in their IS and high-spin (HS) states. Lighter ligands -N and -F stabilize the complex in the HS state, while the magnetically anisotropic IS state is stabilized by -P and -As at the axial site, and -Cl, -Br, and -I at the equatorial site. Larger magnetic anisotropies appear for complexes with nearly degenerate ground electronic states that are well separated from the higher excited states. This requirement, largely controlled by the d-orbital splitting pattern due to the changing ligand field, is achieved with a certain combination of axial and equatorial ligands, such as -P and -Br, -As and -Br, and -As and -I. In most cases, the acetyl group at the axial site enhances the magnetic anisotropy compared to its methyl counterpart. In contrast, the presence of -I at the equatorial site compromises the uniaxial type of anisotropy of the Fe( iii ) complex leading to an enhanced rate of quantum tunneling of magnetization. Ligand environment influences the magnetic anisotropy of the penta-coordinated trigonal-bi-pyramidal Fe( iii ) complex (PMe 2 Ph) 2 FeCl 3 in its intermediate-spin state.