A series of tetrairon μ4-fluoride clusters, [LFe3F(PhPz)3Fe][OTf]n (n=1-3), was synthesized using the previously reported 1,3,5-triarylbenzene framework, a multinucleating ligand containing pyridine and alkoxide donors, which bind three of the four metal centers. These three metal sites contain six-coordinate iron atoms. 3-phenyl-pyrazolate ligands (PhPz) bridge the triiron core to a four-coordinate, site-differentiated iron center. These clusters have notably different redox properties than the closely related μ4-oxo analogues, [LFe3O(PhPz)3Fe][OTf]n (n=0-3). While for [LFe3O(PhPz)3Fe][OTf]2 three reversible redox events are observed at -1.73 V (vs. Fc/Fc+), -0.72 V, and +0.02 V (FeII4 " FeIIFeIII3), only two redox events are observed for the fluoride-bridged cluster, [LFe3F(PhPz)3Fe][OTf], at -0.52 V (FeII4/FeII3FeIII) and +0.17 V, (FeII3FeIII/FeII2FeIII2). Each redox state of the fluoride-bridged clusters, [LFe3F(PhPz)3Fe][OTf]n (n=1-3), was isolated and further investigated through spectroscopy and X-ray diffraction. These studies reveal that all of the oxidation state changes occur exclusively at one of the six-coordinate iron sites in the triiron core. Treatment of the above complexes with nitric oxide (NO) results in clusters with νN-O (1823 and 1842 cm-1) higher than the corresponding oxo-bridged clusters of the same oxidation states. The effects of the interstitial atom on small molecule activation will be discussed.

Effects of the μ4-bridging atom in a tetranuclear iron cluster on the activation of nitric oxide

251st National Meeting (2016)

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