Iron complexes arsine oxide

There are several examples of iron(I) complexes in which the +1 oxidation state is stabilized by coordination of carbon monoxide or arsine ligands. In an early paper217 Hieber and Lagally... 

Very few molecular complexes containing the oxidation state iron(IV) are known, the most familiar being with the ligand o-phenylene-bis-(dimethyl-arsine). Two of these complexes have been examined and show a large temperature-independent quadrupole splitting [37]. 

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