Medium and pressure effects on the reactivity and spectra of iron(ii)-diimine complexes.

摘要

Solvation trends of ternary iron(II)-cyanide-diimine complexes in binary aqueous media are examined using spectroscopic and thermodynamic techniques. The observed trends are discussed in terms of the solvent-solute interactions present, and how the relative importance of these interactions varies with the technique and the complex. Crystallographic data for two of these structures are reported and show the effect of the solvate molecules on the structure. Pressure effects on MLCT frequencies are investigated, and the correlation between piezochromic and solvatochromic effects for mono- and binuclear iron(II) and iron(III)-diimine complexes is shown. Pressure and solvent modification of the rate of oxidation of a series of iron(II)-diimine complexes are interpreted and discussed in terms of the solvation changes that occur upon transition state formation. Complementary partial molar volume data for these complexes are also reported, and combined to form a volume profile for one reactant pair. The structure of a binuclear iron(II)-diimine complex is examined in the solid state and in solution. Solvation trends in binary aqueous media are reported for this binuclear cation, and comparisons are made with mononuclear iron(II) and cobalt(III), and with binuclear cobalt(III) complexes. Kinetics of base hydrolysis of several binuclear iron(II)-diimine complexes are discussed in terms of the structural differences between these complexes. The effects of added organic cosolvents on the rate constants for one of these binuclear complexes is also reported. Spectroscopic evidence for a ligand substituted intermediate is found. The structure of such intermediates is discussed with respect to existing data for mononuclear iron(II)-diimine complexes. Finally, a preliminary chemical and electrochemical redox investigation is made on the most suitable binuclear iron(II)-diimine complex in light of the base hydrolysis reactivity patterns established.