Alkylcyclopentadienyl complexes of high-spin chromium(II) and iron(II) central ions and their oxidized analogues

The project aims at a synthesis of high-spin (HS) Fe(II) and Cr(II) complexes with bulky alkylcyclopentadienyl ligands (RCp), preparation of their oxidized analogues, and studies on their structure and magnetic properties by experimental and DFT methods. Pentaisopropylcyclopentadienide (5Cp) and 1,2,4-tri(tert-butyl)cyclopentadienide (Cp’’’) will be primarily employed. The HS configuration of the ions will provide each metal centre with four unpaired electrons (S=2), and these centres will be combined into dinuclear or higher-nuclearity complexes. The former case can be exemplified by complexes [5CpFe(µ-X)]2 with two Fe(II) bridged by X = Cl, Br, I, where unusual ferromagnetic coupling is expected and single-molecule magnet behaviour could occur. The latter case is illustrated by the square [RCpCr(µ-CN)]4 tetramer, whose oxidation might provide intriguing mixed-valence systems. Besides spectroscopic characterization and crystal structure determination, the complexes will be probed by local methods of Mössbauer and EPR spectroscopy and by magnetic measurements in DC and AC fields.