Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS5)Cl](PF6)

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS5)Cl](PF6), and a study of its properties utilizing single crystal X-ray diffraction, electronic spectroscopy, NMR spectroscopy, density functional theory calculations and cyclic voltammetry. The crystal structure shows a single [15]aneS5 macrocycle and a chloro ligand coordinated in a distorted octahedral fashion around the ruthenium(II) center. A significant shortening (0.15 Å) of the trans Ru–S bond length occurs in this complex compared to the related PPh3 complex (2.4458(10) to 2.283(1) Å) due to the differences in the trans influence of the two ligands. 13C NMR spectroscopy demonstrates that the structure of [Ru([15]aneS5)Cl]+ is retained in solution. As expected for a Ru(II) complex, the electronic absorption spectrum shows two d–d transitions at 402 and 331 nm. These are red-shifted compared to hexakis(thioether)ruthenium(II) complexes and consistent with the weaker ligand field effect of the chloro ligand. The electrochemical behavior of the complex in acetonitrile shows a single one-electron reversible oxidation–reduction at +0.722 V versus Fc/Fc+ which is assigned as the Ru(II)/Ru(III) couple. DFT calculations for [Ru([15]aneS5)Cl]+ show a HOMO with orbital contributions from a t2g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS5, and a p orbital of the chloro ligand while the LUMO consists of orbital contributions of d x 2 - y 2 orbital of the Ru center and p orbitals of the four equatorial S donors.