Preparation, structures and properties of oxalate-bridged binuclear iron(III) complex: [(acac)(2)Fe(mu-ox)Fe(acac)(2)] and [(acac)(2)Fe(mu-ox)Fe(acac)(2)]center dot CH2CICH2Cl

摘要

An oxalate-bridged binuclear iron(III) complex, [(acac)(2)Fe(mu-ox)Fe(acac)(2)], (acac(-) = acetylacetonate anion and ox(2-) = oxalate anion) was prepared. The complex crystallized as two types of crystals under different conditions: one had 1,2-dichloroethane as a solvent molecule of crystallization 2, the other did not 1. Both compounds have been characterized by X-ray crystallography, infrared spectroscopy, and thermogravimetric analysis. Compound 1 has also been characterized by UN-Vis and H-1 NMR spectroscopies, mass spectrometry, and electrochemistry. In both crystals, each iron(III) is coordinated in an octahedral arrangement by the oxygen atoms of an oxalate-bridging ligand and four oxygen atoms belonging to peripheral acac ligands in an octahedral arrangement. The intermetallic distance of (FeFe)-Fe-... is 5.4368(9) Angstrom in 1 and 5.438(2) Angstrom in 2. Two iron(III) ions in each crystal are bridged by the oxalate and both lie in the oxalate-plane. The results of thermal analyses imply that the thermal stability of 2 is lower than that of 1. Cyclic voltammograms of 1 in acetonitrile and dichloromethane at low temperature showed two consecutive, quasi-Nernstian, one-electron reduction steps corresponding to the reduction of Fw(III)-Fe-III to Fe-III-Fe-II followed by the reduction of Fe-III-Fe-II to Fe-II-Fe-II. The electrochemical comproportionation constants (K-c) of the equilibrium (Fe-III-Fe-III) + (Fe-II-Fe-II) = 2(Fe-III-Fe-II) are 10(8.9) in acetonitrile medium and 10(8.5) in dichloromethane, respectively. The considerably large K-c values indicate that the main factor contributing to the stabilization of the Fe-III-Fe-II mixed-valence state is electronic delocalization through the oxalate-bridge. (C) 2003 Elsevier B.V. All rights reserved. [References: 68]