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|Title:||Paramagnetic ruthenium(III) ortho-metallated complexes. Synthesis, spectroscopic and redox properties|
LAHIRI, GOUTAM KUMAR
|Citation:||Journal of Organometallic Chemistry 586(2), 176-183|
|Abstract:||The reaction of (CS)Cl(PPh3)2RuII (μ-Cl)2 RuII (PPh3)2Cl(CS), A with the phenolic Schiff base ligands o-(OH)C6H4C(H)=N-C6H4(R), (R=p-OMe, Me, H, Cl, NO2; H2L1–H2L5) in methanol under aerobic conditions afforded the complexes RuIII(HL)2(PPh3)Cl, 1 and RuIII(L)(PPh3)(CH3OH)Cl, 2. In complexes 1 both the ligands (HL−) are bound to the metal center at the deprotonated phenolic oxygen and azomethine nitrogen and in the complexes 2 the L2− is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom of the amine fragment of H2L. During the reaction the metal ion is oxidized from the starting RuII in A to RuIII in the products 1 and 2. The complexes (1 and 2) are nonconducting and behave as one-electron paramagnets. Complexes display rhombic EPR spectra that have been analyzed to furnish values of axial (∆) and rhombic (V) distortion parameters as well as energies of the two expected ligand field transitions (ν1 and ν2) within the t2 shell. One of the transitions (ν2) has been observed in the predicted region. The complexes exhibit moderately strong ligand-to-metal charge-transfer transition in the visible region and intraligand transitions in the UV region. The complexes are electroactive and show ruthenium (IV)–ruthenium(III) (E1/2, 0.75–0.88 V vs. Ag/AgCl) and ruthenium(III)–ruthenium(II) (E1/2, −0.42 to −0.59 V) couples. The E1/2 values vary linearly with the Hammett constant of the substituents R. The role of coordination of phenolato function in stabilizing the unusual paramagnetic ruthenium(III) oxidation state in the complexes 2 is noted.|
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