Synthesis and structural characterization of ruthenium(II) hydrido carbonyl triphenylphosphine α-diimine complexes with derivatives of 2,2'-bipyridine.

Abstract

The structural and emission properties of two ruthenium(II) polypyridyl complexes, namely, carbonyl(4,4'-di-tert-butyl-2,2'-bypyridine)hydridobis(triphenylphosphine)ruthenium(II) hexafluorophosphate, [RuH(C₁₈H₂₄N₂)(C₁₈H₁₅P)₂(CO)]PF₆ or [Ru(H)(CO)(dtbbpy)(PPh₃)₂]PF₆ (dtbbpy is 4,4'-di-tert-butyl-2,2'-bipyridine), and (2,2'-biquinoline)carbonylhydridobis(triphenylphosphine)ruthenium(II) hexafluorophosphate, [RuH(C₁₈H₁₂N₂)(C₁₈H₁₅P)₂(CO)]PF₆ or [Ru(H)(CO)(bq)(PPh₃)₂]PF₆ (bq is 2,2'-biquinoline), were characterized by spectroscopic analysis, X-ray diffraction and density functional theory (DFT) computational methods, and compared to the parent [Ru(H)(CO)(bpy)(PPh₃)₂]PF₆ complex (bpy is 2,2'-bipyridine). The X-ray analysis of these compounds showed a slightly distorted octahedral geometry of the Ru^II ion typical for this kind of complex. Classical hydrogen bonds are not observed in the crystals of the investigated complexes. Weak intermolecular C-H...F contacts and, as shown by the Hirshfeld surface analysis, H...H interactions have the dominant contributions in the molecular packing in both structures. In CH₂Cl₂ solution at 298 K, both complexes show a weak broad emission band attributed to S₀←^3*MLCT transitions. At 77 K in frozen methanol/ethanol glass, the complexes exhibit strong luminescence of MLCT origin. DFT calculations confirm that the optimized geometries are in good agreement with the experimental structures. In the excited state, changes are observed in the metal-ligand bond lengths, which are consistent with a metal-to-ligand charge transfer (MLCT) character.