Models for Unsymmetrical Active Sites in Metalloproteins: Structural, Redox, and Magnetic Properties of Bimetallic Complexes with MII-(μ-OH)-FIII Cores

Bimetallic complexes are important sites in metalloproteins but are often difficult to prepare synthetically. We have previously introduced an approach to form discrete bimetallic complexes with M-II-(mu-OH)-Fe-II (M-II= Mn, Fe) cores using the tripodal ligand ( ethane-2,1-diyl) tris (2,4,6-trim ethylb enzenesulfonamido) ([MST](3-)). This series is extended to include the rest of the late 3d transition metal ions (M-II= Co, Ni, Cu, Zn). All of the bimetallic complexes have similar spectroscopic and structural properties that reflect little change despite varying the Mil centers. Magnetic studies performed on the complexes in solution using electron paramagnetic resonance spectroscopy showed that the observed spin states varied incrementally from S = 0 through S = 5/2; these results are consistent with antiferromagnetic coupling between the high-spin M-II and Feu' centers. However, the difference in the Mn ion occupancy yielded only slight changes in the magnetic exchange coupling strength, and all complexes had J values ranging from +26(4) to +35(3) cm