Although often abbreviated as Fe, that naked ion does not exist except under extreme conditions. Iron(III) centres are found in many compounds and coordination complexes, where Fe(III) is bonded to several ligands. A molecular ferric complex is the anionferrioxalate, [Fe(C2O4)3], with three bidentateoxalate ions surrounding the Fe core. Relative to lower oxidation states, ferric is less common in organoiron chemistry, but the ferrocenium cation [Fe(C5H5)2] is well known.
An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for its growth. It may react negatively or even die in the presence of free oxygen. Anaerobic organisms do not use oxygen as a terminal electron acceptor in their respiration process to produce energy, but a less powerful oxidizing agent, such as nitrate, ferric ion, Mn(IV), sulfate or bicarbonate anions. In contrast, an aerobic organism (aerobe) is an organism that requires a sufficiently oxygenated environment to respire, produce its energy, and thrive. Because the anaerobic energy production was the first mechanism to be used by living microorganisms in their evolution and is much less efficient than the aerobic pathway, anaerobes are practically, de facto, always unicellular organisms (e.g. bacteria and archaea (prokaryotes), or protozoans (eukaryotes). However, a minuscule multicellular organism, with an exceptionally rare metabolism and surviving in a hypersaline brine pool in the darkness of the bottom of the Mediterranean Sea, has been recently discovered. Meanwhile, it remains a scientific curiosity, as the much higher energy requirements of most multicellular organisms cannot be met by anaerobic respiration. Most fungi (eukaryotes) are obligate aerobes, requiring oxygen to survive and grow; however, some species, such as the Chytridiomycota that reside in the rumen of cattle, are obligate anaerobes; for these species, anaerobic respiration is used because oxygen would disrupt their metabolism or kill them. The deep seafloor and its underlying unconsolidatedsediments ranks among the largest potential habitats for anaerobic microorganisms on Earth. Moreover, chemoautotroph microbes also thrive around hydrothermal vents, discharging hot water on the oceanseabed near mid-ocean ridges, where anaerobic conditions prevail. These microbes produce energy in the absence of sunlight or oxygen through a process called anaerobic respiration, whereby inorganic compounds and ions such as protons (H), elemental sulfur and its derivatives (SO2−4, S2O2−3), or ferric ions, are reduced to drive oxidative phosphorylation.
In chemistry, iron(II) refers to the elementiron 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(II) chloride (FeCl2). The adjective ferric is used instead for iron(III) salts, containing the cation Fe. The word ferrous is derived from the Latin word ferrum, meaning "iron".
In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) abbreviated as Fe, although more precise descriptions include other ligands such as water and halides. Iron(II) centres occur in coordination complexes, such as in the anionferrocyanide, [Fe(CN)6], where six cyanide ligands are bound the metal centre; or, in organometallic compounds, such as the ferrocene[Fe(C5H5)2], where two cyclopentadienyl anions are bound to the Fe centre.
Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops, its color comes from ferric compounds. Deeply weathered profiles are widespread on the continental landmasses between latitudes 35°N and 35°S.
Conditions for the formation of deeply weathered regolith include a topographically moderate relief flat enough to prevent erosion and to allow leaching of the products of chemical weathering. A second condition is long periods of tectonic stability; tectonic activity and climate change can cause erosion. The third condition is humid tropical to temperate climate.
Methemoglobinemia can be due to certain medications, chemicals, or food, or it can be inherited. Substances involved may include benzocaine, nitrites, or dapsone. The underlying mechanism involves some of the iron in hemoglobin being converted from the ferrous [Fe] to the ferric [Fe] form. The diagnosis is often suspected based on symptoms and a low blood oxygen that does not improve with oxygen therapy. Diagnosis is confirmed by a blood gas analysis.
