Mercury polycations
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Mercury polycations are polyatomic cations that contain only mercury atoms. The best known example is the Hg2+
2 ion, found in mercury(I) (mercurous) compounds. The existence of the metal–metal bond in Hg(I) compounds was established using X-ray studies in 1927[2][page needed] and Raman spectroscopy in 1934[3] making it one of the earliest, if not the first, metal–metal covalent bonds to be characterised.
Other mercury polycations are the linear Hg2+
3 and Hg2+
4 ions,[3] and the triangular Hg4+
3 ion [4] and a number of chain[5] and layer polycations.[6]