Heterobimetallic Complexes with MIII-(μ-OH)-MIICores (MIII= Fe, Mn, Ga; MII= Ca, Sr, and Ba): Structural, Kinetic, and Redox Properties.
The effects of redox-inactive metal ions on dioxygen activation were explored using a new FeIIcomplex containing a tripodal ligand with 3 sulfonamido groups. This iron complex exhibited a faster initial rate for the reduction of O2than its MnIIanalog. Increases in initial rates were also observed in the presence of group 2 metal ions for both the FeIIand MnIIcomplexes, which followed the trend NMe4+< BaII< CaII= SrII. These studies led to the isolation of heterobimetallic complexes containing FeIII-(μ-OH)-MIIcores (MII= Ca, Sr, and Ba) and one with a [SrII(OH)MnIII]+motif. The analogous [CaII(OH)GaIII]+complex was also prepared and its solid state molecular structure is nearly identical to that of the [CaII(OH)FeIII]+system. Nuclear magnetic resonance studies indicated that the diamagnetic [CaII(OH)GaIII]+complex retained its structure in solution. Electrochemical measurements on the heterobimetallic systems revealed similar one-electron reduction potentials for the [CaII(OH)FeIII]+and [SrII(OH)FeIII]+complexes, which were more positive than the potential observed for [BaII(OH)FeIII]+. Similar results were obtained for the heterobimetallic MnIIcomplexes. These findings suggest that Lewis acidity is not the only factor to consider when evaluating the effects of group 2 ions on redox processes, including those within the oxygen-evolving complex of Photosystem II.
Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, CA, 92697-2025, USA. ; Tel: 949-824-1510.
Young Jun
YJ
Park
Sarah A
SA
Cook
Nathaniel S
NS
Sickerman
Yohei
Y
Sano
Joseph W
JW
Ziller
A S
AS
Borovik