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 [Fe6IIIO2(OH)2{(C4N2H2SMe)2C(OH)O}2(tBuCO2)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.

[Fe6O2(OH)2{C4N2H2SMe}2C(OH)O}2(tBuCO2)10] consists of two co-planar [Fe3(μ3-O)]7+ triangles, a structural type which gives rise to a well isolated S = 5 spin ground state. HF-EPR reveals a substantial negative zero-field splitting but also a high rhombicity (E/|D| = 0.27), explaining the absence of SMM behaviour in this class of complex.Figure optionsDownload as PowerPoint slide