Supramolecular Construction of Cyanide-Bridged Re^I Diimine Multichromophores

The reactions of labile [Re­(diimine)­(CO)₃(H₂O)]⁺ precursors (diimine = 2,2′-bipyridine, bpy; 1,10-phenanthroline, phen) with dicyanoargentate anion produce the dirhenium cyanide-bridged compounds [{Re­(diimine)­(CO)₃}₂CN)]⁺ (1 and 2). Substitution of the axial carbonyl ligands in 2 for triphenylphosphine gives the derivative [{Re­(phen)­(CO)₂(PPh₃)}₂CN]⁺ (3), while the employment of a neutral metalloligand [Au­(PPh₃)­(CN)] affords heterobimetallic complex [{Re­(phen)­(CO)₃}­NCAu­(PPh₃)]⁺ (4). Furthermore, the utilization of [Au­(CN)₂]⁻, [Pt­(CN)₄]^2–, and [Fe­(CN)₆]^4–/3– cyanometallates leads to the higher nuclearity aggregates [{Re­(diimine)­(CO)₃NC}_xM]^m+ (M = Au, x = 2, 5 and 6; Pt, x = 4, 7 and 8; Fe, x = 6, 9 and 10). All novel compounds were characterized crystallographically. Assemblies 1–8 are phosphorescent both in solution and in the solid state; according to the DFT analysis, the optical properties are mainly associated with charge transfer from Re tricarbonyl motif to the diimine fragment. The energy of this process can be substantially modified by the properties of the ancillary ligands that allows to attain near-IR emission for 3 (λ_em = 737 nm in CH₂Cl₂). The Re–Fe^II/III complexes 9 and 10 are not luminescent but exhibit low energy absorptions, reaching 846 nm (10) due to Re^I → Fe^III transition.