Remarkable Aurophilicity and Photoluminescence Thermochromism in a Homoleptic Cyclic Trinuclear Gold(I) Imidazolate Complex

A new aurophilically-bonded cyclic trinuclear gold(I) complex, tris[μ2-(1-ethylimidazolato-N3,C2)gold(I)] ([Au3(EtIm)3], 1), has been synthesized and characterized by temperature-dependent crystallographic and photophysical investigations. The crystal packing of 1 reveals two independent molecules in the unit cell, signifying two distinct pairs of dimer-of-trimer units convened by pairwise intermolecular Au···Au interactions of 3.0662(3) and 3.1407(3) Å at 100 K, representing the shortest pairwise intermolecular aurophilic interactions among all cyclic trimetallic gold(I) complexes to date. Remarkably, crystals of 1 exhibit gigantic photoluminescence thermochromism of 10164 cm-1-from violet to red!-attributed to internal conversion between a higher-energy (T2 → S0; λmax ∼409 nm) and lower-energy (T1 → S0; λmax ∼700 nm) phosphorescent band below and above 200 K, respectively, likely representing an excited-state phase change.