Complexes with FeIII2(μ-O)(μ-OH), FeIII2(μ-O)2, and [FeIII3(μ2-O)3] Cores: Structures, Spectroscopy, and Core Interconversions

We have synthesized the first complexes with bis(μ-oxo)diiron(III) and (μ-oxo)(μ-hydroxo)diiron(III) cores (1 and 2, L = TPA (a), 5-Et3-TPA (b), 6-Me3-TPA (c), 4,6-Me6-TPA (d), BQPA (e), BPEEN (f), and BPMEN (g)) and found them to have novel structural properties. In particular, the presence of two single-atom bridges in these complexes constrains the Fe−Fe distances to 2.7−3.0 A and the Fe−μ-O−Fe angles to 100° or smaller. The significantly acute Fe−O−Fe angles (e.g., 92.5(2)° for 1c and 100.2(2)° for 2f) enforced by the Fe2O2(H) core endow these complexes with UV−vis, Raman, and magnetic properties quite distinct from those of other (μ-oxo)diiron(III) complexes. Complex 1c exhibits visible absorption bands at 470 (e = 560 M-1 cm-1) and 760 nm (e = 80 M-1 cm-1), while complexes 2 show features at ca. 550 (e ≈ 800 M-1 cm-1) and ca. 800 nm (e ≈ 70 M-1 cm-1), all of which are red shifted compared to those of other (μ-oxo)diiron(III) complexes. These complexes also exhibit distinct νFe-O-Fe vibrations at ca....