Ruthenium (III) complexes of tetradentate NSNO pyridylthioazophenolates: Synthesis, spectral studies, crystal structure and redox properties

A family of ruthenium (III) complexes of tetradentate monobasic NSNO donor chelators (HL) have been synthesized and isolated in their pure form. On chromatographic separation, trans-dichloro and cis-dichloro ruthenium (III) complexes of pyridylthioazophenolates are eluted using 19:1 and 7:3 (v/v) DCM–MeOH mixtures, respectively. Both cis and trans isomers of the dark brown colored ruthenium (III) complexes, having the general formula of [Ru(L)Cl2], have been characterized by elemental analyses, spectroscopic and other physico-chemical tools. The magnetic moments of both the cis-and trans-[Ru(L)Cl2] complexes are in the range of 1.71–1.79 BM. One of the complexes, trans-[Ru(L1)Cl2] (2a), has been subjected to single-crystal X-ray analysis which confirms that the chlorines are in mutually trans positions in the molecule. The EPR spectra of the cis-[Ru(L)Cl2] complexes (1) in DMF are consistent with the fact that the complexes are low-spin octahedral with one unpaired electron having three different g values (gx ≠ gy ≠ gz). The results show that the Ru(III) complexes are monomeric with an octahedral coordination sphere. The electrochemical studies of [Ru(L)Cl2] in DMF show a quasi-reversible voltammogram. The reduction potentials for the cis-isomers are comparatively lower than those of the corresponding trans isomers. On reaction with the bidentate bipyridyl ligand in the presence of AgNO3, the cis-[Ru(L)Cl2] complexes (1) produce a series of complexes with the general formula [Ru(L)(bpy)2](PF6)2 (3), which have also been characterized by elemental analyses, spectroscopic and other physico-chemical tools.

Graphical abstractA family of monomeric low-spin octahedral ruthenium (III) complexes of tetradentate monobasic NSNO donor chelators (HL) have been synthesized and isolated in their pure form. Dark brown colored trans-dichloro and cis-dichloro ruthenium (III) complexes of pyridylthioazophenolates, having the general formula [Ru(L)Cl2], were separated chromatographically. The structure of one of the complexes, trans-[Ru(L1)Cl2] (2a), has been confirmed by single-crystal X-ray analysis. The reactivity of the cis-[Ru(L)Cl2] complexes (1) with the bidentate bipyridyl ligand in the presence of AgNO3 produces [Ru(L)(bpy)2](PF6)2 (3).Figure optionsDownload full-size imageDownload as PowerPoint slide