By pairing gold and copper, two Nevada chemists have created a new example of a vapochromic sensor in which a large change in luminescence occurs when volatile organic compounds trade places with ligands on the organometallic complex (J. Am. Chem. Soc., DOI: 10.1021/ja104585q). Christoph E. Strasser and Vincent J. Catalano of the University of Nevada, Reno, synthesized the colorless gold-dicopper complex by treating a gold N-heterocyclic carbene complex with two equivalents of a copper acetonitrile complex. When the solid is exposed to methanol vapor, one methanol molecule substitutes for two acetonitrile ligands per copper atom. This exchange prompts formation of gold-copper bonding interactions needed for the copper atoms to maintain their tetrahedral coordination geometry (shown). The result is a buckling of the complex's molecular structure and a luminescence change under ultraviolet light from blue to green. Exposing the green-emitting complex to acetonitrile reverses the process.