Ruthenium(II) compounds containing a novel strong π-accepting ligand, 5, 5′-dimethyl-2,2′-bi-1,3,4-thiadiazole (dbtd). Crystal structure of [Ru(bipy)2(dbtd)][PF6]2·Me2CO(bipy = 2,2′-bipyridine)

Abstract

A series of ruthenium(II) complexes with a novel strong π-accepting ligand, 5,5′-dimethyl-2,2′-bi-1,3,4-thiadiazole (dbtd), has been synthesised and characterised. The complex [Ru(bipy)₂(dbtd)][PF₆]₂·Me₂CO (bipy = 2,2′-bipyridine) crystallises in the orthorhombic space group Pbca with unit-cell parameters a= 13.513(3), b= 16.763(4), c= 33.057(5)Å and Z= 8. The two bipy ligands are oriented in a cis geometry and the bisthiadiazole ligand, co-ordinated via the N³ atoms, occupies the fifth and sixth positions. All bidentate ligands have bite angles of 77–79° and ruthenium–nitrogen distances of 1.99–2.06 Å. Electrochemical and resonance Raman measurements on the thiadiazole-containing compounds show that this ligand has a low-lying π* level and is, therefore, expected actively to participate in the emission process. The mixed-chelate compound [Ru(bipy)₂(dbtd)]²⁺ shows an unusual low-energy emission (760 nm at 300 K). The decreased emission intensity for the thiadiazole-containing complexes has been explained by the energy-gap law.