Manganese ionic radii

Ion Ionic radius, pm CoUoidal hydrous manganese dioxide, mol/mol Hydrated radius, pm 5-Mn02, )J.mol/g... 

Barium reacts with metal oxides and hydroxides in soil and is subsequently adsorbed onto soil particulates (Hem 1959 Rai et al. 1984). Adsorption onto metal oxides in soils and sediments probably acts as a control over the concentration of barium in natural waters (Bodek et al. 1988). Under typical environmental conditions, barium displaces other adsorbed alkaline earth metals from MnO2, SiO2, and TiO2 (Rai et al. 1984). However, barium is displaced from Al203 by other alkaline earth metals (Rai et al. 1984). The ionic radius of the barium ion in its typical valence state (Ba+) makes isomorphous substitution possible only with strontium and generally not with the other members of the alkaline earth elements (Kirkpatrick 1978). Among the other elements that occur with barium in nature, substitution is common only with potassium but not with the smaller ions of sodium, iron, manganese, aluminum, and silicon (Kirkpatrick 1978). 

Manganese(II) compounds are quite labile the metal shows distinct class (a) character 7 and its ionic radius (defined by the M—H20 distances in Table 1) is large compared with the other first row transition metals. These lead to distinct parallels with magnesium(II) rather than the latter, although there are also significant parallels with octahedral high spin nickel(II). 

Finally, there is the problem why iron smectite is selectively precipitated and not manganese smectite, as manganese has an ionic radius very similar to that of iron, and in most cases both ions can be diadochically exchanged in their compounds (Fe + = 0.67, Mn -" = 0.52). 

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). 

In addition to change of concentration by mixing processes, the relative concentrations of lanthanides may be changed by oxidation-reduction reactions followed by diflFerential mineral uptake (as for manganese nodules (4, JO), or phosphorites (4)), or by diflFerential solubility or ion-exchange processes aflFected by variations in ionic radius. The lanthanides are the group of elements for which such processes are known to be least effective only two, cerium and europium, are expected to exhibit stable ions other than trivalent, and as summarized by Moeller et aL (13), lanthanide complexes are typically weak, and show within the series, only modest variations in strength. 

Wang, R. Y., Q. Li, L. L. Cheng et al. 2014. Electrochemical properties of manganese ferrite-based supercapacitors in aqueous electrolyte The effect of ionic radius. Colloids and Surfaces A Physicochemical and Engineering Aspects 457 94-99. 

---