Ruthenium(III) complexes with N-(acetyl)-N′-(5-R-salicylidene)hydrazines: Syntheses,structures and properties |
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Authors: | Raji Raveendran Samudranil Pal |
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Institution: | School of Chemistry, University of Hyderabad, Hyderabad 500 046, India |
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Abstract: | The reactions of 1 mol equiv. each of Ru(PPh3)3Cl2] and N-(acetyl)-N′-(5-R-salicylidene)hydrazines (H2ahsR, R = H, OCH3, Cl, Br and NO2) in alcoholic media afford simultaneously two types of complexes having the general formulae Ru(HahsR)(PPh3)2Cl2] and Ru(ahsR)(PPh3)2Cl]. The complexes have been characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. Molecular structures of Ru(HahsH)(PPh3)2Cl2] and Ru(ahsH)(PPh3)2Cl] have been confirmed by X-ray crystallography. In both species, the PPh3 ligands are trans to each other. The bidentate HahsH− coordinates to the metal ion via the O atom of the deprotonated amide and the imine–N atom in Ru(HahsH)(PPh3)2Cl2]. In HahsH−, the phenolic OH is involved in a strong intramolecular hydrogen bond with the uncoordinated amide N atom forming a seven-membered ring. In Ru(ahsH)(PPh3)2Cl], the tridentate ahsH2− binds to the metal ion via the deprotonated amide O, the imine N and the phenolate O atoms. In the electronic spectra, the green Ru(HahsR)(PPh3)2Cl2] and brown Ru(ahsR)(PPh3)2Cl] complexes display several absorptions in the ranges 385–283 and 457–269 nm, respectively. Both complexes are low-spin and display rhombic EPR spectra in frozen solutions. Both types of complexes are redox active and display a quasi-reversible ruthenium(III) to ruthenium(II) reduction which is sensitive to the polar effect of the substituent on the chelating ligand. The reduction potentials are in the ranges −0.21 to −0.12 and −0.42 to −0.21 V (versus Ag/AgCl) for Ru(HahsR)(PPh3)2Cl2] and Ru(ahsR)(PPh3)2Cl], respectively. |
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Keywords: | Ruthenium(III) complexes Acetylhydrazones Crystal structures Intramolecular hydrogen bond Redox properties |
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