The trimeric clusters [Fe(III)3(X-Sal-AHA)3(μ3-OCH3)](-), where X-Sal-AHA is a tetradentate chelate incorporating an α-hydroxy acid moiety (AHA) and a salicylidene moiety (X-Sal with X being 5-NO2, 3,5-diCl, all-H, 3-OCH3, or 3,5-di-t-Bu substituents on the phenolate ring), undergo a photochemical reaction resulting in reduction of two Fe(III) to Fe(II) for each AHA group that is oxidatively cleaved. However, photolysis of structurally analogous mixed Fe/Ga clusters demonstrate that a similar photolysis reaction will occur with only a single Fe(III) in the cluster. Quantum yields of iron reduction for the series of [Fe(III)3(X-Sal-AHA)3(μ3-OCH3)](-) complexes measured by monitoring Fe(II) production are twice those for ligand oxidation, measured by loss of the CD signal for the complex due to cleavage of the chiral AHA group.The quantum yields, 2-13% in the UVA and UVB ranges, are higher for complexes with electron-withdrawing X groups than for those with electron-donating X groups [corrected]. The observed final photolysis product of the chelate is different if irradiation is done in the air than if it is done under Ar. The first observed photochemical product is the aldehyde resulting from decarboxylation of the AHA. This is the final product under anaerobic conditions. In air, this is followed by an Fe- and O2-dependent reaction oxidizing the aldehyde to the corresponding carboxylate, then a second Fe- and light-dependent decarboxylation reaction giving a product that is two carbons smaller than the initial ligand. These reactivity studies have important biological implications for the photoactive marine siderophores. They suggest that different types of photochemical products for different siderophore structure types do not result from different initial photochemical steps, but rather from different susceptibility of the initial photochemical product to air oxidation.

The structures and stability of the analogous [M(III) 3 (3,5-diCl-Sal-AHA) 3 (-OCH 3)]complexes with Fe and Ga are compared. The Fe(III) 3 O 4 cubane has an S = ½ ground state based on the EPR spectra. The clusters are stable to metal or chelate exchange, while the  3-methoxy bridge can be exchanged with hydroxide.

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This report describes a laboratory experiment for an undergraduate-level inorganic chemistry or biochemistry course involving the study of the kinetics of the catecholase activity of a synthetic nickel(II)−oximate complex. A model substrate, 3,5-ditert-butylcatechol (DBC), undergoes aerobic oxidation to 3,5-di-tert-butylbenzoquinone (DBQ) in the reaction. Students determine the initial rates of production of DBQ, measured by the increase of the absorption in the UV−vis spectrum at 400 nm; this was performed for solutions containing five separate substrate-to-catalyst ratios. Saturation kinetics was observed at high substrate-to-catalyst ratios, and the Michaelis−Menten model of enzymatic kinetics was applied to determine the kinetic parameters for the catalyst (k cat , V max , and K m ). Students explored the ability of two antioxidants, L-glutathione and αtocopherol, to inhibit the oxidation reaction. The experiment has been employed at a small, four-year college in the Inorganic Chemistry course for three semesters. The experiment successfully provided students with a hands-on experience of using spectroscopy to monitor the kinetics of an enzyme-like system, including producing relevant plots and data analysis of Michaelis−Menten kinetic parameters. Students also examined the effects and roles of antioxidants in biochemical systems.

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