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The nuclide 54 Fe theoretically can undergo double electron capture to 54 Cr, but the process has never been observed and only a lower limit on the half-life of 4.4×10 20 years has been established. [22] 60 Fe is an extinct radionuclide of long half-life (2.6 million years). [23]
Iron(II) complexes are less stable than iron(III) complexes but the preference for O-donor ligands is less marked, so that for example [Fe(NH 3) 6] 2+ is known while [Fe(NH 3) 6] 3+ is not. They have a tendency to be oxidized to iron(III) but this can be moderated by low pH and the specific ligands used. [18]
Thus ferrocyanide ([Fe(CN) 6] 4− has no unpaired electrons, meaning it is a low-spin complex. With so-called "weak field ligands" such as water, four of the six electrons are unpaired, meaning it is a high-spin complex. Thus aquo complex [Fe(H 2 O) 6] 2+ is paramagnetic. With chloride, iron(II) forms tetrahedral complexes, e.g. [FeCl 4] 2− ...
Although often abbreviated as Fe 3+, 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 anion ferrioxalate, [Fe(C 2 O 4) 3] 3−, with three bidentate oxalate ions
Traces of iron-60 have been found in lunar samples. In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60 Ni, the granddaughter isotope of 60 Fe, and the abundance of the stable iron isotopes could be found, which is evidence for the existence of 60 Fe at the
The rarer isotopes nickel-62 and iron-58, which both have higher binding energies, are not shown. Iron-56 (56 Fe) is the most common isotope of iron. About 91.754% of all iron is iron-56. Of all nuclides, iron-56 has the lowest mass per nucleon. With 8.8 MeV binding energy per nucleon, iron-56 is one of the most tightly bound nuclei. [1]
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Species with a single charge are univalent (monovalent). For example, the Cs + cation is a univalent or monovalent cation, whereas the Ca 2+ cation is a divalent cation, and the Fe 3+ cation is a trivalent cation. Unlike Cs and Ca, Fe can also exist in other charge states, notably 2+ and 4+, and is thus known as a multivalent (polyvalent) ion. [15]