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 [Fe(3)O((t)BuCO(2))(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 [Fe(3)(mu(3)-O)](7+) subunits that are related by an inversion centre and linked at two of their apices, each via one mu-hydroxide and two mu-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/vertical bar D vertical bar = 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.