Fac-Re(CO)₃ complexes of 2,6-bis(4-substituted-1,2,3-triazol-1- ylmethyl)pyridine "click" ligands: Synthesis, characterisation and photophysical properties

The syntheses of the 4-n-propyl and 4-phenyl substituted fac-Re(CO) ₃ complexes of the tridentate "click" ligand (2,6-bis(4-substituted-1,2,3-triazol-1-ylmethyl)pyridine) are described. The complexes were obtained by refluxing methanol solutions of [Re(CO) ₅Cl], AgPF₆ and either the 4-propyl or 4-phenyl substituted ligand for 16 h. The ligands and the two rhenium(i) complexes were characterised by elemental analysis, HR-ESMS, ATR-IR, ¹H and ¹³C NMR spectroscopy and the molecular structures of both complexes were confirmed by X-ray crystallography. The electronic structure of the fac-Re(CO)₃ "click" complexes was probed using UV-Vis, Raman and emission spectroscopy, cyclic voltammetry and DFT calculations. Altering the electronic nature of the ligand's substituent, from aromatic to alkyl, had little effect on the absorption/emission maxima and electrochemical properties of the complexes indicating that the 1,2,3-triazole unit may insulate the metal centre from the electronic modification at the ligands' periphery. Both Re(i) complexes were found to be weakly emitting with short excited state lifetimes. The electrochemistry of the complexes is defined by quasi-reversible Re oxidation and irreversible triazole-based ligand reduction processes.