Color-change metals

Carbon monoxide detectors and food-spoilage indicators could emerge from a chance discovery that modified metals react to different gases by changing color. Cathleen Crudden and colleagues at Queen's University in Kingston, Ontario, found that their rhodium compound, an N-hetereocyclic carbene complex, changes to yellow in the presence of nitrogen, deep blue in the presence of oxygen, and brown in the presence of carbon monoxide. Uniquely, the attachment of different gas molecules to the complex does not disrupt the crystal structure. The team is no investigating whether the much cheaper metal, cobalt, might also work as a color-change gas detector.