Ferrous

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Iron(II) chloride tetrahydrate, FeCl2·4H2O.

In

iron(III) salts, containing the cation Fe3+. The word ferrous is derived from the Latin word ferrum
, meaning "iron".

In

organometallic compounds, such as the ferrocene [Fe(C2H5)2], where two cyclopentadienyl
anions are bound to the FeII centre.

Iron(III) in biology

All known forms of life require iron.[1] Many proteins in living beings contain iron(III) centers. Examples of such metalloproteins include hemoglobin, ferredoxin, and the cytochromes. In many of these proteins, Fe(II) converts reversibly to Fe(III) [2]

Insufficient iron in the human diet causes

grasses can thrive in such environments by secreting compounds called siderophores that form soluble complexes with iron(III), that can be reabsorbed into the cell. (The other plants instead encourage the growth around their roots of certain bacteria that reduce iron(III) to the more soluble iron(II).)[3]

In contrast to iron(III) aquo complexes, iron(II) aquo complexes are soluble in water near neutral pH. Ferrous is however oxidized by the oxygen in air, converting to iron(III).

Pourbaix diagram of aqueous iron

Iron(II) salts and complexes

Redox reaction of [Fe(bipyridine)3]2+.

Typically iron(II) salts, like the "

ferrous ammonium sulfate.[4]

The aquo ligands on iron(II) complexes are labile. It reacts with 1,10-phenanthroline to give the blue iron(II) derivative:

When metallic iron (oxidation state 0) is placed in a solution of hydrochloric acid, iron(II) chloride is formed, with release of hydrogen gas, by the reaction

Fe0 + 2 H+ → Fe2+ + H2

Iron(II) is oxidized by hydrogen peroxide to

Fenton reaction. Iron(III) is then reduced back to iron(II) 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 (H+ + OH) as a byproduct.[5]

Fe2+ + H2O2 → Fe3+ + HO + OH

 

 

 

 

(1)

Fe3+ + H2O2 → Fe2+ + HOO + H+

 

 

 

 

(2)

The

free radicals
generated by this process engage in secondary reactions, which can degrade many organic and biochemical compounds.

Iron(II) minerals and other solids

Iron(II) oxide (ferrous oxide), FeO, is a very complicated material that contains iron(II).

Iron(II) is found in many minerals and solids. Examples include the sulfide and oxide, FeS and FeO. These formulas are deceptively simple because these sulfides and oxides are often

nonstoichiometric. For example, "ferrous sulfide" can refer to the 1:1 species (mineral name troilite) or a host of Fe-deficient derivatives (pyrrhotite). The mineral magnetite
("lode stone") is a mixed-valence compound with both Fe(II) and Fe(III), Fe3O4.

Bonding

Iron(II) is a d6 center, meaning that the metal has six "valence" electrons in the 3d orbital shell. The number and type of ligands bound to iron(II) determine how these electrons arrange themselves. With so-called "strong field ligands" such as

aquo complex
([Fe(H2O)6]2+ is paramagnetic. It is high-spin. With chloride, iron(III) forms tetrahedral complexes, e.g. [FeCl4]2−. Tetrahedral complexes are high spin.

d-orbital splitting scheme for low- and high spin octahedral Fe(II) complexes.

Gallery

See also

  • Ferric – The element iron in its +3 oxidation state — [ Iron(III)] compounds
  • Ferromagnetism – Mechanism by which materials form into and are attracted to magnets
  • Ferrous metal recycling
     – Recyclable materials left over from manufactured products after their use
  • Iron(II) oxide – Inorganic compound with the formula FeO (ferrous oxide)
  • Iron(II) bromide – chemical compound (ferrous bromide)
  • Steelmaking – Process for producing steel from iron ore and scrap

References

  1. ^ "Iron integral to the development of life on Earth – and the possibility of life on other planets". University of Oxford. 7 December 2021. Retrieved 9 May 2022.
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