Octahedrons of 1,10-phenanthroline and 4′‑chloro-2,2′:6′,2″-terpyridine induced by protonation of nitrogen atoms: Synthesis and analysis

Two new octahedral compounds, [(phenH)(phen)]PF6 (phen = 1,10-phenanthroline) and [(ClterpyH2)(Clterpy)(H2O)](PF6)2 (Clterpy = 4′‑chloro-2,2′:6′,2″-terpyridine) were synthesized. Their light emission properties were investigated by experimental measurements and theoretical calculations, and the relationship between the emission and structure of the protonated compounds was studied. Time-dependent density functional theory calculations revealed that [(phenH)(phen)]PF6 and [(ClterpyH2)(Clterpy)(H2O)](PF6)2 exhibit hydrogen-bonded octahedrons, even in the excited states. In [(phenH)(phen)]PF6, an octahedron was formed by three hydrogen bonds and the dihedral angle between phenH+ and phen was 78° In [(ClterpyH2)(Clterpy)(H2O)](PF6)2, four hydrogen bonds were detected forming an octahedron with the angle between ClterpyH22+ and Clterpy being nearly 90° [(ClterpyH2)(Clterpy)(H2O)](PF6)2 also exhibited a unique configuration attributed to the attachment of a proton to the nitrogen, which causes an intense emission (Φ = 0.290). NMR analyses revealed that the presence of phenH+, phen, ClterpyH22+, and Clterpy did not present any additional peaks to the spectra, indicating that the H signals were averaged.