PUB - Publikationen an der Universität Bielefeld

The mu-oxo-bridged diferric complex [(susan(Pr)){(FeCl)-Cl-III(mu-O)(FeCl)-Cl-III}](ClO4)(2) was synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR, UV/Vis/NIR, and Mossbauer spectroscopies as well as magnetic and electrochemical measurements. The properties are compared to the corresponding values for the complex [(susan){(FeCl)-Cl-III(mu-O)(FeCl)-Cl-III}](ClO4)(2), which exhibits a central ethylene spacer, whereas [(susan(Pr)){(FeCl)-Cl-III(mu-O)(FeCl)-Cl-III}](ClO4)(2) has a propylene spacer. Both complexes exhibit a trans configuration of the two terminal chloride ligands. This configuration induces more steric demand in the case of the propylene spacer, which results in a rotation of the two octahedral units along the Fe-(mu-O)-Fe axis and a tilting of the Fe-N bonds of the diamine spacer. The iron bond lengths are only slightly elongated by the steric demand of the propylene spacer, which is reflected by almost no change in the Mossbauer spectrum. However, the UV/Vis/NIR spectra show a stronger ligand field for [(susan(Pr)){(FeCl)-Cl-III(mu-O)(FeCl)-Cl-III}](ClO4)(2). The slightly longer iron bond lengths result in less electron donation, which is reflected by an anodic shift of 120 mV for the oxidation of the complex. This comparison provides more information on the variation of the properties of the diferric complexes by slight changes in the second coordination sphere.