The angles of the bent M +II -O -M +II core are fairly similar: 127.0 • for copper, 139.4 • for nickel, and 142.5 • for iron, as illustrated in Figure . The mean Cu-O and Fe-O bond lengths are 1.86 Å each, whereas the Ni-O bond length is slightly shorter at 1.83 Å. The intermetallic distances are, in every instance, sufficiently large to render direct magnetic coupling paths negligible. The magnetic coupling is thus anticipated to be mediated primarily drals have a considerable impact on the total magnetic coupling strength in µ-oxo-bridged metal complexes because of the relative ligand sphere orientations. The twisting of these M -O -M -N dihedrals thus modifies the amount of antiferromagnetic coupling along the σ-pathway by changing the overlap of the magnetically active orbitals. Solomon's examination of dinuclear copper systems, for instance, revealed a dramatic transition from strong antiferromagnetic coupling (-321 cm -1 ) for collineary aligned magnetic orbitals, to strong ferromagnetic coupling (+325 cm -1 ) for almost orthogonal magnetic orbitals.