Synthesis, structural, magnetic and high frequency EPR studies on a hexametallic Fe(III) complex with a highly rhombic S = 5 ground state

The synthesis, crystal structure and magnetic properties of the hexametallic Fe(III) cluster [ Fe 6 III O 2 ( OH ) 2 { ( C 4 N 2 H 2 SMe ) 2 C ( OH ) O } 2 ( t BuCO 2 ) 10 ] (1) are reported. Compound 1 was prepared by reaction of mixed-valent [Fe3O(tBuCO2)6(py)3] with one equivalent of the new ligand di-2-(4-methylthio)pyrimidyl ketone (DTPK) in MeCN solution. Compound 1 consists of a planar array of six Fe(III) ions comprising two [Fe3(μ3-O)]7+ subunits that are related by an inversion centre and linked at two of their apices, each via one μ-hydroxide and two μ-carboxylate groups. Variable temperature magnetic susceptibility and low temperature magnetization measurements show a well isolated S = 5 electronic spin ground state. Variable temperature W-band EPR measurements on a polycrystalline sample give well resolved spectra and simulations confirm a negative zero-field splitting of D = −0.224 cm−1 but also reveal a very rhombic nature (E/|D| = 0.27). Although 1 has a well isolated S = 5 ground state with a negative magnetic anisotropy, it is not a SMM due to this large rhombicity.