Cobalt ionic radii

Symbol Ni atomic number 28 atomic weight 58.693 a transition metal element in the first triad of Group VIll(Group 10) after iron and cobalt electron configuration [Ar]3d 4s2 valence states 0, -i-l, +2, and -f-3 most common oxidation state +2 the standard electrode potential, NF+ -1- 2e Ni -0.237 V atomic radius 1.24A ionic radius (NF+) 0.70A five natural isotopes Ni-58 (68.08%), Ni-60 (26.22%), Ni-61 (1.14%), Ni-62 (3.63%), Ni-64 (0.93%) nineteen radioactive isotopes are known in the mass range 51-57, 59, 63, 65-74 the longest-lived radioisotope Ni-59 has a half-life 7.6x10 years. 

In aluminosilicates each high-spin trivalent transition metal ion has a larger ionic radius than the host Al3+ ion. However, cations such as Cr3+ (-249.9 kJ/mole), V3+(-182.8 kJ/mole) and Mn3+ (-150.8 kJ/mole), which acquire particularly large CFSE s in octahedral coordination (table 2.5), are induced to enter [A106] octahedra, and not five-coordinated [A105] (andalusite, yoderite) or tetrahedral [AlOJ (silhmanite) sites, by the enhanced stabilization bestowed in octahedral crystal fields. Although Co3+ ions have not been positively identified in silicate minerals, the strong enrichment of cobalt in natural and syn-... 

On the basis of ionic radius, cobalt ion should be placed between copper and cadmium ions, and thus it has a higher affinity than expected. Perhaps it substitutes the iron(II) of crystal lattice since the two ionic radii are about the same (0.84 nm). 

At normal levels of iron intake, absorption requires uptake from the intestinal lumen by the mucosa and transfer from the mucosa to the portal blood. Both events are inversely affected by the state of body iron stores. In iron deficiency states, nonferrous metals such as cobalt and manganese, which have an ionic radius similar to that of iron and form octahedral complexes with six-coordinate covalent bonds, also are absorbed at an increased rate. Oral administration of a large dose of iron reduces (or temporarily inhibits) the absorption of a second dose of iron by the absorptive enterocytes even in the presence of systemic iron deficiency. The mechanism of mucosal block, which resists acquiring additional iron by the en-teroeytes with high amounts of intracellular iron, is not yet understood. It probably involves set points established in the enterocytes for iron recently consumed in the diet (dietary regulator). 

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