Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)-Iron Complexes Containing Redox-Active -Diimine Ligands. Academic Article uri icon


  • Incorporating radical ligands into metal complexes is one of the emerging trends in the design of single-molecule magnets (SMMs). While significant effort has been expended to generate multinuclear transition metal-based SMMs with bridging radical ligands, less attention has been paid to mononuclear transition metal-radical SMMs. Herein, we describe the first -diiminato radical-containing mononuclear transition metal SMM, namely, [2-PhTttBu]Fe(AdNCHCHNAd) (1), and its analogue [2-PhTttBu]Fe(CyNCHCHNCy) (2) (PhTttBu = phenyltris(tert-butylthiomethyl)borate, Ad = adamantyl, and Cy = cyclohexyl). 1 and 2 feature nearly identical geometric and electronic structures, as shown by X-ray crystallography and electronic absorption spectroscopy. A more detailed description of the electronic structure of 1 was obtained through EPR and Mssbauer spectroscopies, SQUID magnetometry, and DFT, TD-DFT, and CAS calculations. 1 and 2 are best described as high-spin iron(II) complexes with antiferromagnetically coupled -diiminato radical ligands. A strong magnetic exchange coupling between the iron(II) ion and the ligand radical was confirmed in 1, with an estimated coupling constant J < -250 cm-1 (J = -657 cm-1, DFT). Calibrated CAS calculations revealed that the ground-state Fe(II)--diiminato radical configuration has significant ionic contributions, which are weighted specifically toward the Fe(I)-neutral -diimine species. Experimental data and theoretical calculations also suggest that 1 possesses an easy-axis anisotropy, with an axial zero-field splitting parameter D in the range from -4 to-1 cm-1. Finally, dynamic magnetic studies show that 1 exhibits slow magnetic relaxation behavior with an energy barrier close to the theoretical maximum, 2|D|. These results demonstrate that incorporating strongly coupled -diiminato radicals into mononuclear transition metal complexes can be an effective strategy to prepare SMMs.

published proceedings

  • Inorg Chem

altmetric score

  • 3.7

author list (cited authors)

  • Wang, P., Saber, M. R., VanNatta, P. E., Yap, G., Popescu, C. V., Scarborough, C. C., ... Riordan, C. G.

citation count

  • 2

complete list of authors

  • Wang, Peng||Saber, Mohamed R||VanNatta, Peter E||Yap, Glenn PA||Popescu, Codrina V||Scarborough, Christopher C||Kieber-Emmons, Matthew T||Dunbar, Kim R||Riordan, Charles G

publication date

  • May 2021