Synthesis and crystal structures of μ-oxido- and μ-hydroxido-bridged dinuclear iron (III) complexes with an N₂O donor ligand - a theoretical study on the influence of weak forces on the Fe-O-Fe bridging angle

Abstract

The synthesis and crystal structures of three nonheme diiron (III) complexes with a tridentate N,N,O Schiff-baseligand, 2-({[2-(dimethylamino)ethyl]imino}methyl)phenol (HL), are reported. Complexes [Fe₂OL₂(NCO) ₂] (1a) and [Fe₂OL₂ (SAL) ₂]•H₂O [SAL = o-(CHO)C₆H₄O^–] (1b) are unsupported μ-oxido-bridged dimers and [Fe₂ (OH)L₂(HCOO) ₂(Cl)] (2) is a μ-hydroxido-bridged dimer supported by a formato bridging ligand. All complexes have been characterized by X-ray crystallography and spectroscopic analysis. Complex 1b has been reported previously; however, it has been reinvestigated to confirm the presence of a crucial water molecule in the solid state. Structural analyses show that in 1a the iron atoms are pentacoordinate with a bent Fe–O–Fe angle [142.7(2)°], whereas in 2 the metal centers are hexacoordinate with a normal Fe–OH–Fe bridging angle [137.9(2)°]. The Fe–O–Fe angles in complexes 1a and 1b differ significantly to those usually shown by (μ-oxido)Fe^III complexes. A theoretical study has been performed in order to rationalize this deviation. Moreover, the influence of the water molecule observed in the solid-state structure of 1b on the Fe–O–Fe angle is also analyzed theoretically.