Syntheses, crystal structures, and photochemical reactions of tris(di-2-pyridylamine)Ru(II) complex and its photoproducts cis/trans-bis(acetonitrile)bis(di-2-pyridylamine)Ru(II) complexes

Ruthenium(II) polypyridyl complexes, particularly those incorporating 2,2’-bipyridine (bpy) ligands, are well-established in photochemical research. However, their counterparts featuring di-2-pyridylamine (Hdpa) remain underexplored, largely due to their comparatively weaker absorption in the visible spectrum. This study presents the synthesis and structural characterization of a homoleptic Ru(II)-Hdpa complex, [Ru(Hdpa) 3 ]X 2 ( 1 ·X 2 ; X⁻ = OTf⁻ or Cl⁻). Crystallographic analysis reveals steric effects between the ligands, with two Hdpa moieties adopting the common bent syn-NH conformation, while steric interactions constrain the third into a relatively planar conformation. This steric crowding triggers a photochemical reaction in acetonitrile (MeCN), leading to ligand dissociation and the formation of cis -[Ru(Hdpa) 2 (MeCN) 2 ](OTf) 2 ( 2 ·(OTf) 2 ), which subsequently undergoes photoisomerization to trans -[Ru(Hdpa)₂(MeCN) 2 ](OTf) 2 ( 3 ·(OTf) 2 ). The resultant photoproducts were characterized using elemental analysis, ¹H NMR spectroscopy, and X-ray crystallography. Computational investigations further validated the structural findings, with DFT-optimized geometries aligning well with experimental data. Additionally, time-dependent density functional theory-calculated absorption spectra closely matched the measured spectra in MeCN, though minor blue shifts were observed in metal-to-ligand charge transfer (MLCT) transitions for 2²⁺ and 3²⁺ . These results provide critical insights into the steric and electronic properties of Ru(II)-Hdpa complexes, paving the way for their advancement in photochemical applications. • A Ru(II) complex with di-2-pyridylamine (Hdpa) ([Ru(Hdpa) 3 ](OTf) 2 ) was synthesized. • Demonstrated cis/trans -isomerization of [Ru(Hdpa) 2 (MeCN) 2 ](OTf) 2 by photoirradiation of [Ru(Hdpa) 3 ](OTf) 2 in MeCN solution demonstrated. • Photodissociation was reversible but cis – trans photoisomerization was irreversible. • The trans -isomer was thermally and photochemically stabilized by interlocking Hdpa ligands. • Time-dependent density functional theory calculated absorption spectra coincided with the experimental absorption spectra of all complexes and provided valuable insights into the photochemical behavior of Ru(II)-Hdpa complexes.