Iron Complexes of New Pentadentate Ligands Containing the 1,4,7-Triazacyclononane-1,4-diacetate Motif. Spectroscopic, Electro-, and Photochemical Studies

Three new pentadentate, pendent arm macrocycles containing the 1,4,7-triazacyclononane-1,4-diacetate motif have
been synthesized, and their coordination chemistry with Fe(III) has been investigated. Eight new octahedral Fe(III)
complexes containing chloro, azido, or μ-oxo ligands have been synthesized, five of which have been characterized
by X-ray crystallography. Spectroscopic characterization of these octahedral Fe(III) complexes by UV−vis, IR,
electrochemistry, EPR, magnetic susceptibility, and zero-field Mössbauer measurements firmly establishes the high-spin state of the iron in all complexes. Electrochemistry studies of the azido−Fe(III) complexes show that they can
be reversibly oxidized to the corresponding Fe(IV) species at −20 °C, and Fe(II), Fe(III), and Fe(IV) species show
characteristic IR and UV−vis profiles. Photolysis of one of the azido complexes was studied as a function of
temperature (room temperature vs 77 K) and wavelength (480, 419, and 330 nm). Photoreduction to a high-spin
Fe(II) species occurs under all conditions, which is proposed to be the dominant photochemical pathway generally
available to high-spin ferric azido complexes.