Synthesis, structures, and photoluminescence properties of lanthanide dicyanoaurates containing dimeric aurophilic interactions

The synthesis of a series of lanthanide dicyanoaurates containing the ancillary ligand 2,2′:6′,2″-terpyridine (terpy) have been carried out by reaction of Ln3+ nitrate salts with terpy and potassium dicyanoaurate. The resultant compounds, [Ln(C15H11N3)(H2O)(NO3)2Au(CN)2] (Ln = Eu, Tb, Dy, Ho, Er, Yb), form an isostructural series as established by single-crystal X-ray diffraction studies. These studies reveal the existence of two important non-covalent interactions in these compounds. Dimeric aurophilic interactions and terpyridine π-stacking are both present with distances of ∼3.5 Å for each. Photoluminescence measurements illustrate that the Eu3+ and Tb3+ compounds display enhanced Ln-based emission due to intramolecular energy transfer from the coordinated terpy ligands. Additionally, a [Au(CN)2−]2 dimeric excimer produces a broad, green emission band in this class of compounds, albeit reduced in intensity in several of the compounds where a reasonable energy match exists with Ln3+ excitation bands.