Diethylformamide Research Articles

Redox kinetics of metal complexes in non-aqueous solutions. XII. Effect of non-bridging ligands on intramolecular electron transfer in the FeL 3+5/Fe(Me 4phen) 2+3 reaction in acetonitrile

In acetonitrile the reductions of a series of iron-(III) solvates, FeL 3+ 6 (L = TMP, DMF, DEF (= diethyl formamide), AA (= acetamide), and DMSO), by Fe(tmphen) 2+ 3 (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) proceed via formation of a kinetically-detectable intermediate. All evidence available suggests its form as L 5Fe(acetonitrile)Fe(tmphen) 5+ 3 wherein acetonitrile features a bridge between phenanthroline and FeL 3+ 5 in that the CN triple bond interacts with the π orbitals on the peripheries of the phenanthroline complex and the nitrile N coordinates to FeL 3+ 5. The decomposition rate constant of that intermediate, signifying the rate of the actual electron transfer, has been measured in dependence of ligands and temperature. For the series of related reactions the isokinetic relationship holds. As the donor number of the ligands increases, the activation energy is decreased according to the increase in electronic coupling, over the wide range of 50 kJ mol −1. At the same time the activation entropy shifts to more negative values, due to increased steric crowding in the successor complex, over an even wider range from −41 to the extremely negative value of −286 J K −1 mol −1. Consequently the decrease in ΔS≠ strongly overcompensates the favorable change in ΔH≠: The reaction series is entropy-controlled, as is recognized by an isokinetic temperature which is below the experimental temperature range T iso ∼ −70 °C.

Electron Spin Relaxation in Solvated Manganese(II) Ion Solutions

Electron spin resonance (ESR) spectra were obtained for solutions of manganese(II) perchlorate in dimethylformamide (DMF), diethylformamide (DEF), dimethylsulfoxide (DMSO), and water. Variation of line shape with solvent and temperature was obtained and interpreted at low temperatures in terms of a model in which solvent fluctuations about the solvated ion modulate the ligand field and relax the electron spin through spin—orbit interaction. Relaxation times for Δms=1 transitions of the S=52 system were calculated using a semiclassical density-matrix formalism. In DMF, DEF, and DMSO solutions another contribution to relaxation was observed at high temperatures which may be attributable to ligand exchange or to internal motion in the complex ion. The high-temperature process was not observed in aqueous manganese(II) solutions.

Solvent effects in N.M.R. spectra of amide solutions

The chemical shifts of the proton resonances in dimethyl formamide, diethyl formamide and dimethyl acetamide have been measured as a function of concentration in 31 solvents. The shifts extrapolated to infinite dilution are discussed in terms of complex formation between the amide and aromatic solvents.