Stuck in Our Teeth? Crystal Structure of a New Copper Amalgam, Cu3Hg

We have synthesized a new Cu amalgam, the Cu-rich phase Cu3Hg. It crystallizes with the Ni3Sn structure type with a hexagonal unit cell (space group P63/mmc , a = 5.408(4) Å, c = 4.390(3) Å) and shows some mixed occupancy of Cu on the Hg site, resulting in a refined composition of Cu3.11Hg0.89. This is the first example of an amalgam with the Ni3Sn structure type where Hg is located mainly on the Sn site. Cu3Hg might be one of the phases constituting dental amalgams and therefore has major relevance, as well as the only Cu amalgam phase described so far, Cu7Hg6 with the γ-brass structure. It occurs as a biphase in our samples. Thermal decomposition of Cu amalgam samples in a dynamic vacuum yields nanostructured copper networks, possibly suitable for catalytic applications.