Synthesis, structural characterization and C H activation property of a tetra-iron(III) cluster

A non-heme tetra-iron cluster, [Fe 4 III ( μ- O) 2 ( μ- OAc) 6 (2,2′-bpy) 2 (H 2 O) 2 ](NO 3 − )(OH − ) ( 1 ), [OAc = acetate; 2,2′-bpy = 2,2′-bipyridine] containing oxido- and acetato-bridges was synthesized and structurally characterized by different spectroscopic methods including single crystal X-ray diffraction studies. X-ray crystal structure analysis of 1 revealed that tetra-iron complex was crystallized in monoclinic system with C 2/ c space group. Each of the Fe centres in 1 was found to exist in octahedral geometry and interconnected by oxido- and acetato-bridges. Bond valence sum (BVS) calculation recommended the existence of iron centres in +3 oxidation state. Variable temperature magnetic measurement authenticated the dominating antiferromagnetic ordering among the iron centres in the solid state of 1. This tetra-iron cluster was also evaluated as an efficient catalytic system towards the oxidation of both linear & cyclic alkanes without production of primary C H bond oxidation products. Oxidation of secondary C H bonds attested the formation of both the corresponding alcohols & ketones in 27–900 TONs. The tetra-iron catalytic system with Alcohol/Ketone values 0.2–1.7 indicated the involvement of freely diffusing carbon-centered radicals rather than metal based oxidant.