Luminescent Indium Dicyanoaurate Coordination Polymers with Short Aurophilic Interactions

A series of coordination polymers were synthesized by combining In(OTf)₃ (OTf = trifluoromethanesulfonate), 2,2';6',2"-terpyridine (Terpy) or its substituted analogues 4'-amino-2,2';6',2"-terpyridine (NH₂-Terpy), 4'-chloro-2,2';6',2"-terpyridine (Cl-Terpy), and 4'-bromo-2,2';6',2"-terpyridine (Br-Terpy), with K[Au(CN)₂]. All compounds consist of 1D chains of hydroxy-bridged [In₂(OH)₂(X-Terpy)₂]⁴⁺ dimers connected to a 1D chain of [Au(CN)₂]^- units featuring very short aurophilic interactions (3.0106(3)-3.2155(4) Å). The distance of the aurophilic interaction is directly tunable through minor modifications of the ligand, with the Au(I)···Au(I) distance increasing as the size of the substituent on the Terpy ligand increases. The compounds display photoluminescence emission maxima ranging from 600 to 650 nm, which are significantly lower energy than for most [Au(CN)₂]^--based materials. The emission maxima shift to higher energy as the aurophilic interactions become longer. These results demonstrate the ability to tune the Au(I)···Au(I) distance, and in turn the luminescence, by varying the size of the substituent on the chelating ligand.