Substituent effects on iron diimine complexes II. Correlations with thermodynamic and spectral properties in acetonitrile

• Published in: Inorganica Chimica Acta Vol. 37; pp. 113 - 119
• Main Authors: Chum, Helena Li, Rock, Monica
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1979
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(00)95527-0

The electrochemical oxidation of nineteen iron(II) complexes, FeL 2+ 3, with aliphatic diimine ligands, L = H 3CNC(R)C(R′)NCH 3, where R, R′ = H, H; H, CH 3; CH 3, CH 3; CH 3, C 2H 5; CH 2CH 2CH 2CH 2; CH 2CH(CH 3)CH 2CH 2; H, C 6H 5; CH 3, C 6H 5, and mixed diimine ligands, L = C 5H 4NC(R 1)N(R 2), where R 1, R 2 = H, CH 3; H, C 2H 5; CH 3, CH 3; CH 3, C 2H 5; CH 3, C 6H 5; CH 3, m- or p-NH 2C 6H 4; C 6H 5; CH 3, m- or p-NH 2C 6H 4; C 6H 5, C 6H 5; C 6H 5, m- or p-NH 2C 6H 4 was studied by means of cyclic voltammetry in acetonitrile, 0.2 M tetra-ethylammonium perchlorate at 25.0 °C. Except for compounds R, R′ = H, C 6H 5; CH 3, C 6H 5, and for the compounds with free amino groups, reversible one-electron oxidation processes were found. For the amino containing compounds the electrochemical oxidation is more complex due to concurrent oxidation of the amino group. For the phenyl derivatives of the aliphatic series, chemical and electrochemical steps follow the primary reversible one-electron reaction. For the compounds which exhibit reversible electrochemical oxidation, the half-wave potentials are identical to the standard electrode potentials. These potentials can be correlated with the sum of the polar Taft parameters for the substituents. Substituents presenting large steric or mesomeric effects do not fit this correlation, since these effects are excluded from the polar Taft parameters. A better correlation can be obtained by including steric effects. The frequencies of the intense absorption band in the visible region, assigned to an inverse charge transfer, are correlated with the half-wave potentials of the reversible oxidation processes. A correlation between the square-foot of the molar absorpivities at the absorbance maximum of the inverse charge transfer band with the sum of the polar Taft parameters of the substituents is also obtained.