of zinc has much in common with that of magnesium. In other respects, there is little similarity with the late first-row transition metals. Zinc tends to form bonds with a greater degree of covalency and much more stable complexes with N- and S- donors. Complexes of zinc are mostly 4- or 6- coordinate, although 5-coordinate complexes are known. Zinc(I) compounds Zinc(I) compounds are very rare. The [Zn2]2+ ion is implicated by the formation of a yellow diamagnetic glass by dissolving metallic zinc in molten ZnCl2. The [Zn2]2+ core would be analogous to the [Hg2]2+ cation present in mercury(I) compounds. The diamagnetic nature of the ion confirms its dimeric structure. The first zinc(I) compound containing the Zn–Zn bond, (η5-C5Me5)2Zn2. Zinc(II) compounds Binary compounds of zinc are known for most of the metalloids and all the nonmetals except the noble gases. The oxide ZnO is a white powder that is nearly insoluble in neutral aqueous solutions, but is amphoteric, dissolving in both strong basic and acidic solutions. The other chalcogenides (ZnS, ZnSe, and ZnTe) have varied applications in electronics and optics. Pnictogenides (, , and ), the peroxide (), the hydride (), and the carbide () are also known. Of the four halides, has the most ionic character, while the others (, , and ) have relatively low melting points and are considered to have more covalent character. In weak basic solutions containing ions, the hydroxide forms as a white precipitate. In stronger alkaline solutions, this hydroxide is dissolved to form zincates (). The nitrate , chlorate , sulfate , phosphate , molybdate , cyanide , arsenite , arsenate and the chromate (one of the few colored zinc compounds) are a few examples of other common inorganic compounds of zinc. Organozinc compounds are those that contain zinc–carbon covalent bonds. Diethylzinc () is a reagent in synthetic chemistry. It was first reported in 1848 from the reaction of zinc and ethyl iodide, and was the first compound known to contain a metal–carbon sigma bond. Test for zinc Cobalticyanide paper (Rinnmann's test for Zn) can be used as a chemical indicator for zinc. 4 g of K3Co(CN)6 and 1 g of KClO3 is dissolved on 100 ml of water. Paper is dipped in the solution and dried at 100 °C. One drop of the sample is dropped onto the dry paper and heated. A green disc indicates the presence of zinc. History Ancient use