Ferrous
In chemistry, iron refers to the element iron in its +2 oxidation state. The adjective ferrous or the prefix ferro- is often used to specify such compounds, as in ferrous chloride for iron chloride. The adjective ferric is used instead for iron salts, containing the cation Fe3+. The word ferrous is derived from the Latin word, meaning "iron".
In ionic compounds, such an atom may occur as a separate cation abbreviated as Fe2+, although more precise descriptions include other ligands such as water and halides. Iron centres occur in coordination complexes, such as in the anion ferrocyanide,, where six cyanide ligands are bound the metal centre; or, in organometallic compounds, such as the ferrocene, where two cyclopentadienyl anions are bound to the FeII centre.
Ferrous ions in biology
All known forms of life require iron. Many proteins in living beings contain iron centers. Examples of such metalloproteins include hemoglobin, ferredoxin, and the cytochromes. In many of these proteins, Fe converts reversibly to Fe.Insufficient iron in the human diet causes anemia. Animals and humans can obtain the necessary iron from foods that contain it in assimilable form, such as meat. Other organisms must obtain their iron from the environment. However, iron tends to form highly insoluble iron oxides/hydroxides in aerobic environment, especially in calcareous soils. Bacteria and grasses can thrive in such environments by secreting compounds called siderophores that form soluble complexes with iron, that can be reabsorbed into the cell. to the more soluble ironIn contrast to iron aquo complexes, iron aquo complexes are soluble in water near neutral pH. Ferrous iron is, however, oxidized by the oxygen in air, converting to iron.
Ferrous salts and complexes
Typically iron salts, like the "chloride" are aquo complexes with the formulas, as found in Mohr's salt.The aquo ligands on iron complexes are labile. It reacts with 1,10-phenanthroline to give the blue iron derivative:
When metallic iron is placed in a solution of hydrochloric acid, iron chloride is formed, with release of hydrogen gas, by the reaction
Iron is oxidized by hydrogen peroxide to iron, forming a hydroxyl radical and a hydroxide ion in the process. This is the Fenton reaction. Iron is then reduced back to iron by another molecule of hydrogen peroxide, forming a hydroperoxyl radical and a proton. The net effect is a disproportionation of hydrogen peroxide to create two different oxygen-radical species, with water as a byproduct.
The free radicals generated by this process engage in secondary reactions, which can degrade many organic and biochemical compounds.File:Fe3 redox.svg|thumb|360px|center|Redox reaction of 2+.