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 Mössbauer 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).