Ruthenium(II) isocyanide complexes supported by triazacyclononane/ trithiacyclononane and aromatic diimine: Structural, spectroscopic, and theoretical studies

Ruthenium(II) - isocyanide complexes bearing cyclic tridentate amine/thioether (1,4,7-trimethyl-1,4,7-triazacyclononane, Me₃Tacn/1, 4,7-trithiacyclononane, [9]aneS3) and aromatic diimine (1,10-phenanthroline, phen/2,2′-bipyridine, bpy) have been prepared. The molecular structures of [(Me₃Tacn)(bpy)Ru(t-BuNC)]²⁺, [([9]aneS3)(phen)Ru(t-BuNC) ]²⁺, and the nitrile-ligated congener [(Me₃Tacn)(phen) Ru(CH₃CN)]²⁺ show that the Ru - C distances in the isocyanide complexes are sensitive to the electron richness of the metal center, and isocyanide has a stronger trans influence than nitrile. The lowest-energy dipole-allowed absorptions for the isocyanide and nitrile complexes (λ_max) 330-405 and 417-458 nm, respectively, ε_max) (3-6) × 10 ³ dm ³ mol ^-1 cm^-1) are assigned as d_π(Ru^II) → π ^*(diimine) metal-to-ligand charge transfer (MLCT) transitions. These complexes are emissive in glassy MeOH/EtOH at 77 K upon photoexcitation and give emission at λ_max) 477-601 nm. Density functional theory (DFT) calculations and charge decomposition analysis (CDA) have been used to compare the σ-donating and π-accepting abilities of nitrile and different organometallic ligands including isocyanide, methoxycarbene, and allenylidene. The molecular structure of the cofacial bioctahedral complex [(Me₃Tacn)Ru(μ-Cl)₃Ru(Me ₃Tacn)]⁺ has also been determined, and the Ru ··· Ru distance has been found to be 3.1842(6) Å.