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 (λmax = 330−405 and 417−458 nm, respectively, εmax = (3−6) × 103 dm3 mol−1 cm−1) are assigned as dπ(RuII) → 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 λmax = 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(Me3Tacn)]+ has also been determined, and the Ru···Ru distance has been found to be 3.1842(6) Å.