Ruthenium(II) complexes with tetradentate pyridylthioazoimine [N,S,N,N] ligands: Synthesis, crystal structure and spectroscopy

The Ru(II) complexes cis-[Ru(L)Cl2] (C1-C3) of novel tetradentate NSNN ligands (L) {where L is C5H4N-CH 2-S-C6H4N=C(COCH3)-N=N-C 6H4X, and X is H (L1), CH3 (L2) and Br (L3)}, were synthesized and characterized by spectroscopy (IR, UV/vis and NMR), cyclic voltammetry and crystallography. The tetradentate ligands were isolated as the amidrazones H2L {where H2L is C5H 4N-CH2-S-C6H4NH-C(COCH 3)+N-NH-C6H4X and X is H (H2L1), CH3 (H2L2) and Br (H2L3)} as shown by crystallography of H2L1, but oxidize to azoimines during the formation of the Ru(II) complexes. A crystallographic analysis of C1 showed that the Ru(II) centre is in a distorted octahedral coordination sphere in which the tetradentate ligand occupies three equatorial sites and one axial site (two azoimine nitrogens and a thio sulfur in the equatorial plane and an axial pyridine nitrogen) and two chlorides occupying axial and equatorial coordination sites. The Ru(II) oxidation state is greatly stabilized by the novel tetradentate ligand, showing Ru(III/II) couples ranging from 1.43 to 1.51 V. The absorption spectrum of C1 in acetonitrile was modelled by time-dependent density functional theory