Cadmium: Inorganic Chemistry

This article provides an overview on the inorganic chemistry of cadmium. Cadmium is a bluish-white metal, the 67th most abundant element in the Earth's crust, and found in some minerals. The structure of the stable form at room temperature ( form) is hexagonal. Occurrence, production, and applications have been surveyed. CdII forms relatively few minerals: the most important are two sulfides, greenockite, and hawleyite. CdII, however, gives isomorphous replacement in several Zn minerals. For this reason, sphalerite (ZnS) is the main industrial source of cadmium. The metal is mainly obtained as a by-product of the metallurgy of Zn. Cadmium and its compounds find applications in several industrial materials: electrode materials in Ni–Cd batteries and solar cells; pigments in ceramics, glasses, paper, plastics, artist colors; coatings on steel, aluminum, and other nonferrous metals; specialized alloys; polymer stabilizers, and in nuclear industry and lab applications. 111Cd and 113Cd NMR spectroscopy can be used to study complexes, both in solid state and in solution, mostly to investigate the binding site of the metal ion in different metalloproteins. Toxicological and environmental risks are associated with its use. Cadmium compounds are highly toxic, and human exposure to this metal is known to be involved in cancer and other diseases. The targets are the body's cardiovascular, renal, gastrointestinal, neurological, reproductive, and respiratory systems. Cadmium does not seem to play any important role in higher organisms. The usual oxidation state of cadmium is 2+ and its chemistry closely resembles that of zinc and, to a lesser extend, mercury. Few compounds of CdI have been prepared and identified. CdII within zeolites is easily reduced by exposure to metal vapors to form cationic clusters containing Cd0 and CdI. The versatile coordination ability of CdII allows a wide variety of structures. The main compounds, ordered by metal oxidation state and bound anion, have been examined for their properties and structural aspects, both in solution and in the solid state. Several technologies have been developed to obtain cadmium compounds as nanocrystals or nanostructures. Cadmium glasses can find applications for their nonlinear optical properties.