Metal ions radius

Fig. 19. The variation in logK for alkali metal ions with crown ethers 12-crown-4 (3), 15-crown-5 (O), 18-crown-6 ( ) and dibenzo-30-crown-10 (C) as a function of metal ion radius. Metal ion radii in A from Ref. (20). Formation constants in methanol from Refs. (49 and 50).

The electron-rich oxygen anions exhibit basic electron donor capacity. Basic metal oxides are commonly used for neutralizing or scrubbing acidic gases. Alkaline earth metal oxides have been used for the removal of NOx. The surfaces of cubic alkaline metal oxide such as MgO, CaO, and BaO are dominated by the Lewis basicity of surface oxide anions. The basicity increases down the alkaline earth family as the metal ion radii become larger and the chaige on the metal ion becomes more positive. 

Molecular motion of chemically modified wood is influenced by binding metal ions. One factors is valency, as mentioned previously. In general, however, there is not only valency but also other factors related to mobility [45-47]. Eisenberg reported that the mobility of polymers binding metal ions relates to three factors charge, amount of metal ion, and metal ion radii [48]. The mobility of molecules of carboxymethylated wood, especially that of... 

All complexes mentioned above were highly effective single-component catalysts for the ROPs of e-caprolactone (Scheme 8) and rac-lactide (Scheme 14) without the need of an activator. The metal radius was influential to the catalytic activity. Both polymerization catalysis rates decreased in the trend of 96 >99 >98 >97, in agreement with the decrease in metal ion radii (La > Nd > Sm > Y). The investigation of polymer end group showed that the polymer chain growth was initiated by allyl transfer to monomer [77]. 

LanthaDide(III) and yttriimi(III) ions have been reported to promote 2 + 2 condensation of 2,6-diformyl-4-methylphenol and a rigid 2,6-diaminopyridine ligson [68], Decreasing the metal ion radii of the lanthanide(III) cations diminishes the yield of the final product, whereas their potential ability to act as a template remains intact. 

As it can be seen, the difference between these radii is about 0.002 nm, which indicates that the interionic interactions lead to a shortening of bond lengths and if the oxygen ion radius is assumed to be 0.14 nm, the metal ion radii should be smaller by about 0.002 nm. On the other hand, if we assume oxygen ion radius for coordination number 4 as 0.138 nm, i.e., the value proposed by Shannon and Prewitt (Shannon Prewitt, 1969, 1970), then metal ion radii do not differ much from the table values. 

Thus, this is an alternative method for the estimation of the mean ion radius in mixed-valence oxides or in non-stoichiometric oxides, using values of metal ion radii in various oxides of the same metal. The above method allows for the prediction of a mean ionic radius in oxides having so much deformed structure that it is difficult to determine the coordination number of metal ions or this number changes with the oxidation state. 

The size of the ionic radii and the character of their interactions, dependent on the metal type, is reflected in the space packing density. Knowing the values of ionic radii one can calculate the p>acking density of ions in individual oxides. The relation between the packing fraction of ions and the metal ion radius is presented in Fig.lO. The relative metal ion radii were used and the oxygen ion radius was assumed to be 0.14 nm. The packing fraction was calculated as the ratio of the volume occupied by ions (Vai) to the volume of the unit cell calculated from lattice parameters (Vx). 

Using experimental relations for alkali metal oxides, alkaline earth metal oxides and MO2/-electron metal oxides with Cap2 structure, the effective metal ion radii relative to constant oxygen ion radius equal 0.140 nm may be determined for oxides with compact... 

The coordination polyhedron for the 3,3-dimethylthietane-l-oxide adduct of Eu(DPM)3 (Wing et al., 1973) and for the 3-methylpyridine adduct of Lu(DPM)3 (Wasson et al., 1973) can both be described as capped trigonal prisms. Of particular interest is the adoption of essentially the same polyhedron by complexes in which the metal ion radii are substantially different. Moreover, Erasmus and Boeyens (1970) had previously concluded from their study of Pr2(DPM)6 that seven-coordination would be impossible if the metal-oxygen distances were less than 2.27 A. In the europium complex the europium-DPM oxygen distances... 

Figure 20. Removal of Cu(II), Zn(II) and Cd(II) in the ion flotation process with p-CD polymer and nonylphenol polyoxyethyl glycol ether as a function of hydrated metal ion radii...

The Universal Force Field, UFF, is one of the so-called whole periodic table force fields. It was developed by A. Rappe, W Goddard III, and others. It is a set of simple functional forms and parameters used to model the structure, movement, and interaction of molecules containing any combination of elements in the periodic table. The parameters are defined empirically or by combining atomic parameters based on certain rules. Force constants and geometry parameters depend on hybridization considerations rather than individual values for every combination of atoms in a bond, angle, or dihedral. The equilibrium bond lengths were derived from a combination of atomic radii. The parameters [22, 23], including metal ions [24], were published in several papers. 

Shannon and Prewitt base their effective ionic radii on the assumption that the ionic radius of (CN 6) is 140 pm and that of (CN 6) is 133 pm. Also taken into consideration is the coordination number (CN) and electronic spin state (HS and LS, high spin and low spin) of first-row transition metal ions. These radii are empirical and include effects of covalence in specific metal-oxygen or metal-fiuorine bonds. Older crystal ionic radii were based on the radius of (CN 6) equal to 119 pm these radii are 14-18 percent larger than the effective ionic radii. 

The axial O-An bonds are clearly very strong. They cannot be protonated and are nearly always shorter than the equatorial bonds. In the case of U02 ", for instance, it is likely that the U 0 bond order is even greater than 2, since the U-O distance is only about 180 pm in spite of the difference in the ionic radii of the metal ions (U = 73 pm. Os " = 54.5 pm), this is close to that of the 0s=0 double bond found in the isostructural, osmyl group (175 pm, see p. 1085). It is usually assumed that combinations... 

It is important to note that the number of different compounds found in such systems increases significantly when moving along the sequence of alkali metals, from lithium to cesium, as does their thermal stability. This phenomenon is related to the systematic increase of both ionic radii and polarity of alkali metals ions when moving from lithium to cesium. 

Accommodation of metal atoms of widely differing ionic radii into the same overall structure creates interesting possibilities for the doping of metal ions into a common matrix for spectroscopic examination under nearly constant crystal field effects. 

Coordination Numbers and Radii. In the transition metal ions, the interaction of the ligand orbitals with the d orbitals of the metal ions generally determines the coordination number and geometry of the oordination sphere about the metal. The... 

The uncertainty of the proper coordination number of any particular plutonium species in solution leads to a corresponding uncertainty in the correct cationic radius. Shannon has evaluated much of the available data and obtained sets of "effective ionic radii" for metal ions in different oxidation states and coordination numbers (6). Unfortunately, the data for plutonium is quite sparse. By using Shannon s radii for other actinides (e.g., Th(iv), U(Vl)) and for Ln(III) ions, the values listed in Table I have been obtained for plutonium. These radii are estimated to have an uncertainty of 0.02 X ... 

Can we rationalize these observations in terms of ligand-field or other effects The data that we have presented in Fig. 8-14 refers to the log Ki values for each ligand with the high spin divalent metal ions. The sequence reflects a number of simple properties of the cations. Firstly, the trend closely parallels the ionic radii... 

Bond length differences between HS and LS isomers have been determined for a number of iron(II), iron(III) and cobalt(II) complexes on the basis of multiple temperature X-ray diffraction structure studies [6]. The available results have been collected in Table 17. Average values for the bond length changes characteristic for a particular transition-metal ion have been extracted from these data and are obtained as AR 0.17 A for iron(II) complexes, AR 0.13 A for iron(III) complexes, and AR = 0.06 A for cobalt(II) complexes. These values may be compared with the differences of ionic radii between the HS and LS forms of iron(II), iron(III) and cobalt(II) which were estimated some time ago [184] as 0.16, 0.095, and 0.085 A, respectively. 

In Table 3 are also shown the hydrated radii (r ) which are evaluated with n and r by Eq. (25). A good correlation of with the Stokes radius [60] (r ) has been observed for hydrated cations (alkali and alkaline earth metal ions) [46] ... 

The 15 trivalent lanthanide, or/ -block, ions La3+, Ce3+, Pr3+, Nd3+, Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, and Lu3+, which may be collectively denoted Ln3+, represent the most extended series of chemically similar metal ions. The progressive filling of the 4/orbitals from La3 + to Lu3 + is accompanied by a smooth decrease in rM with increase in atomic number as a consequence of the increasingly strong nuclear attraction for the electrons in the diffuse / orbitals (the lanthanide contraction). Thus, the nine-coordinate rM decrease from 121.6 to 103.2 pm from La3+ to Lu3+, and the eight-coordinate ionic radii decrease from 116.0 to 97.7 pm from La3+ to Lu3+ (2). Ligand field effects are small by comparison with those observed for the first-... 

Another interesting plot is given in Figure 5. Here the radii of the metallic ions M2+ are correlated with the M-O and M-N distances. Again, the two dependences are in opposite direction (at least in the series Zn-Fe-Mn-Ca) with the exception of the barium compound. 

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