Selenides are compounds that contain a selenium anion, just like sulfur in the sulfide. Due to the low content of selenium in the Earth’s crust (0.05 ppm), it is treated as a trace element. Even so, it is present in many compartments of the nature like rocks, minerals, soils, volcanic matter, deposits of sulfur and sulfides, coal and coal ash, and dust. The chemical properties of selenides and sulfides are similar. Similar to sulfides, the selenide ions Se2- are prevalent only in very basic conditions in aqueous solutions. Hydrogen selenide ion HSe- is most common in neutral conditions. When under acidic conditions, hydrogen selenide, H2Se is formed. Some selenides are reactive to oxidation in air. Metal selenides are more readily decomposed into elements than sulfides due to the greater reducing power of selenides.
Material science: The co-polymer, which is made of selenium compounds via Kumada coupling reaction, exhibits moderate solubility in organic solvents, thermally stability, low molecular weight and PDI value. Polymer film, which is prepared via spray-casting process on the transparent ITO/glass surface, can give very stable electrochromic material with reversible electrochemical oxidation properties, low driving voltage, high coloration efficiency, high redox stability and especially a high contrast ratio in the NIR region. Due to high contrast change in the NIR region, the co-polymer may be one of the most important materials in the NIR application. On the other hand, the co-polymer may be one of the most important materials in opto-electronic application due to its excellent electrochemical and optical properties.
Biological chemistry: A synergistic effect is seen in the combination of selenium with vitamin E, which has immunostimulatory properties. Together, they can prevent damage to unsaturated fatty acids resulting from lipid peroxidation, which releases free radicals. Selenium compounds can trap free radicals, thereby converting them into stable compounds. For human beings, selenium is an essential element, that plays a major role in many physiological and biochemical processes. Selenium compounds are readily absorbed through the digestive tract and respiratory system, and selenyl chloride enters through the skin. The National Research Council (USA) recommended for a daily selenium intake of 50 to 200 µg for the first time. This range is established mainly on the basis of results obtained from animal experiments.