Slow magnetic relaxation in Fe(II) m -terphenyl complexes.

Two-coordinate transition metal complexes are exciting candidates for single-molecule magnets (SMMs) because their highly axial coordination environments lead to sizeable magnetic anisotropy. We report a series of five structurally related two-coordinate Fe(II) m -terphenyl complexes (4-R-2,6-Xyl 2 C 6 H 2 ) 2 Fe [R = t Bu (1), SiMe 3 (2), H (3), Cl (4), CF 3 (5)] where, by changing the functionalisation of the para -substituent (R), we alter their magnetic function. All five complexes are field-induced single-molecule magnets, with relaxation rates that are well-described by a combination of direct and Raman mechanisms. By using more electron donating R groups we were able to slow the rate of magnetic relaxation. Our ab initio calculations predict a large crystal field splitting (>850 cm -1 ) and sizeable zero-field splitting parameters ( ca. -60 cm -1 , | E | < 0.2 cm -1 ) for 1-5. These favourable magnetic properties suggest that m -terphenyl ligands have untapped potential as chemically versatile ligands able to impose highly axial crystal fields.