Iron(II) chloride

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions. Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions. Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with hydrochloric acid. Such solutions are designated 'spent acid,' especially when the hydrochloric acid is not completely consumed: The spent acid requires treatment before its disposal. It is also a byproduct from titanium production, since some titanium ores contain iron. Ferrous chloride is prepared by addition of iron powder to a solution of hydrochloric acid in methanol. This reaction gives the methanol solvate of the dichloride, which upon heating in a vacuum at about 160 °C converts to anhydrous FeCl2. The net reaction is shown: FeBr2 and FeI2 can be prepared analogously. An alternative synthesis of anhydrous ferrous chloride is the reduction of FeCl3 with chlorobenzene: In one of two classic syntheses of ferrocene, Wilkinson generated FeCl2 in situ by conproportionation of FeCl3 with iron powder in THF. Ferric chloride decomposes to ferrous chloride at high temperatures. The dihydrate, FeCl2(H2O)2, crystallizes from concentrated hydrochloric acid. The dihydrate is a coordination polymer. Each Fe center is coordinated to four doubly bridging chloride ligands. The octahedron is completed by a pair of mutually trans aquo ligands. FeCl2 and its hydrates form complexes with many ligands. For example, solutions of the hydrates react with two molar equivalents of Cl to give the salt 2.