Inductive influence of 4′-terpyridyl substituents on redox and spin state properties of iron(II) and cobalt(II) bis-terpyridyl complexes |
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| Affiliation: | 1. School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK;2. Departament de Química Inorgànica and Institut de Química Teòrica i Computacional, Universitat de Barcelona, Marti i Franquès 1-11, 08028 Barcelona, Spain;1. Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi, India;2. Molecular and Human Genetics, Banaras Hindu University, Varanasi, India;1. College of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe Road 850#, Dalian City, 116029 PR China;2. College of Life Science, Liaoning Normal University, Dalian 11602, PR China;1. Université Grenoble Alpes/CNRS, Département de Chimie Moléculaire, UMR-5250, Laboratoire de Chimie Inorganique Redox, Institut de Chimie Moléculaire de Grenoble FR-CNRS-2607, BP-53, 38041 Grenoble Cedex 9, France;2. Ecole Normale supérieure de Cachan/CNRS, Laboratoire de Photophysique et Photochimie Supramoléculaire et Macromoléculaires, UMR-8531, 61 av. du Président Wilson, 94235 Cachan Cedex, France |
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| Abstract: | A series of iron and cobalt bis-terpyridine (terpy) complexes were prepared with the general formula [M(R-terpy)2](PF6)2, where M represents Co(II) and Fe(II), and R is the following terpyridine substituents in order of increasing electron-withdrawing behavior [(C4H8)N, (C4H9)NH, HO, CH3O, CH3-phenyl, H, Cl, CH3SO, CH3SO2]. The complexes were prepared to investigate the extent of redox and spin state control that is attainable by simply varying the electron donating/withdrawing influence using a single substituent site on the terpyridine ligand. Cyclic voltammetry was used to assess the substituents influence on the M(III/II) redox couple. A plot of the M(III/II) redox potential (E1/2) versus the electron donating/withdrawing nature of the substituents (Hammett constants), shows a strong linear trend for both metals; however, the substituents were observed to have a stronger influence on the Fe(III/II) couple. Solution magnetic susceptibility measurements at room temperature were carried out using standard NMR methodology (modified Evans method) where all of the Fe(II) complexes exhibited a diamagnetic, low spin (S = 0) behavior. In the cobalt series where R = H for [Co(R-terpy)2]2+, the complex is known to be near the spin cross-over where the room temperature effective magnetic moment (μeff) in solution is ≈3.1 Bohr magnetons; however, in this study the μeff is observed to vary between 2.7 and 4.1 Bohr magnetons depending on the R-substituent. |
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