Marie-France Charlot

Efficient electron transfer through a triazole link in ruthenium(II) polypyridine type complexes

Spectroscopic, electrochemical and theoretical characterisations of photoactive systems readily assembled via click-chemistry show an efficient bi-directional charge shift through the triazole link.

Electron paramagnetic resonance study of the S=1/2 ground state of a radiolysis-generated manganese(III)-trimanganese(IV) form of [Mn-IV;O-4(6)(bipy)(6)](4+) (bipy=2,2'-bipyridine). Comparison with the photosynthetic Oxygen Evolving Complex

gamma-Ray irradiation at liquid nitrogen temperature of a dimethylformamide solution of the tetranuclear complex [(Mn4O6)-O-IV(bipy)(6)](4+) (bipy = 2,2-bipyridine) allowed the generation of the first mixed-valence tetranuclear system containing Mn-III and Mn-IV ions and exhibiting a S = 1/2 ground state. The X-band EPR spectrum of this tetranuclear system has been obtained. Simulations have been undertaken and the Mn hyperfine coupling tensors determined clearly show a (MnMn3IV)-Mn-III, composition for the EPR active species. A general approach for the analysis of the isotropic components of the Mn hyperfine tensors is presented in detail. This allowed the determination of the spin projection value for each Mn site. A three J coupling scheme assuming that the linear topology of the starting compound remains is able to reproduce these spin projection values if and only if the Mn-III ion is located at a terminal position in a N4O2 environment. The EPR signal of this [Mn4O6(bipy)(6)](3+) species is compared with the multiline signal observed in the S-2 state of the photosynthetic Oxygen Evolving Complex.

Synthesis, Structure, Electronic, Redox, and Magnetic Properties of a New Mixed‐Valent Mn‐Oxo Cluster: [Mn2III,IVO2(N,Nbispicen)2]3+ (N,Nbispicen = N,N‐bis(2‐pyridylmethyl)‐1,2‐diaminoethane)

The synthesis and structural characterization of the novel [MnIII,IV2O2(N,Nbispicen)2](ClO4)3·CH3CN complex employing the tetradentate ligand N,Nbispicen = N,N-bis(2-pyridylmethyl)-1,2-diaminoethane are reported. Magnetic properties were determined and show that the ground state is a spin doublet. This can be quantitatively interpreted by antiferromagnetic coupling between a Mn(III) high spin and a Mn(IV) (J = −316 cm−1). The 16 line solution EPR spectrum exhibits an unusual splitting in the low field resonances. The following rhombic tensors were needed to simulate the EPR spectrum: |A1x|= 160 10−4 cm−1, |A1y| = 144 10−4 cm−1, |A1z|= 109 10−4 cm−1, |A2x|= 69 10−4 cm−1, |A2y| = 72 10−4 cm−1, |A2z| = 75 10−4 cm−1, gx = 2.001, gy = 1.996, gz = 1.984. The classical ligand field theory of local [gIII] and [gIV] tensors implemented with the first order perturbation theory to describe the properties of the pair does not result in a satisfying description of the [g1/2] tensor unless a large reduction in the spin-orbit constant is invoked. A simplified version of second-order perturbation theory leads to effects in qualitative agreement with experiment but weak as expected from the large |J| value. The magnitude of these effects depends, however, on the anisotropy effects on each Mn ion. It is suggested that determination of the anisotropy of the magnetic properties of the monomeric Mn(III) and Mn(IV) moieties would be a valuable goal for a future study of these mixed valent dimanganese-di-μ-oxo complexes. The complex exhibits two quasi-reversible waves in the cyclic voltammogram, one at E1/2 = 0.18 V vs SCE for the III/IV █ III/III couple and the other at E1/2 = 0.98 V vs SCE for the III/IV █ IV/IV couple. The UV-Vis spectra of the three redox states have been recorded spectroelectrochemically.