New triply bridged diiron(III) complexes with [Fe₂(μ-O)(μ-X)₂]²⁺ cores [X = MeCO₂, PhCO₂ or (PhO)₂PO₂]

Abstract

A group of three diiron(III) complexes having [Fe₂(μ-O)(μ-X)₂]²⁺ cores (X = benzoate, acetate or diphenyl phosphate) has been synthesised with the use of unsymmetrical facially capping tridentate ligands (L¹ and L²), where L¹ and L² are [2-(2-pyridyl)ethyl](2-pyridylmethyl)amine and methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine respectively. The lability of the bridging acetate groups in [Fe(μ-O)(μ-MeCO₂)₂L²₂]²⁺ has been demonstrated by exchange with diphenyl phosphate and deuterioacetate as revealed by UV/VIS and ¹H NMR studies. These complexes exhibit infrared, electronic and Mossbauer spectral features very similar to those of μ-oxo-diiron(III) proteins as well as of μ-oxo-bis(μ-carboxylato) or μ-oxo-bis(μ-phosphato)diiron(III) complexes. The inequivalence in the chelate rings around each iron(III) might have caused the asymmetry in these compounds which is reflected in their distinctively strong antiferromagnetic coupling (J=-127, -125 and -108 cm^-1 for the benzoate-, acetate- and phosphate-bridged complexes respectively).