Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS 5)Cl](PF 6)

Abstract

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS 5)Cl](PF 6), 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]aneS 5 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 PPh 3 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]aneS 5)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]aneS 5)Cl] + show a HOMO with orbital contributions from a t 2 g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS 5, 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.