Hydrogen ionic radius

Mossbauer spectra of calcined samples (Table 1). The Fe3+(3) and Fe3+(4) components are probably located in tetrahedral (framework) positions. The charge distribution around the Fe3+(3) is asymmetric (large QS), thus here the charge compensation is probably provided by Fl+, i.e. indicating the existence of Bronsted sites. The charge symmetry around Fe3+(4) is more symmetric, thus the counterion is probably Na+ or Fe(OFl)+. Fe2+ ions are probably located outside of the framework (due to their larger ionic radius). Thus, in the hydrogen a small part of Fe3+ is reduced to Fe2+, and is probable removed to extra-framework sites. 

The above speculation [21] may be extended to include the related quaternary ammonium compounds such as xylocholine (XXXIX). It is probable that the volumes of the guanidinium ion and the trimethylammonium group are similar. The ionic radius of the guanidinium ion (IX) is about 3A the ionic radius of the tetramethylammonium ion has been estimated [300] to be 3-4A, although rather smaller values have also been proposed [301-303]. Crystallographic analyses of muscarine iodide [304], choline chloride [305] and acetylcholine bromide [306] have revealed that the carbon to nitrogen distance is about l-SA, and that a hydrogen bond (C-H-0 distance 2-87-3 07A) exists in the crystals of these compounds. 

Where the lanthanide ionic radius and the macrocyclic cavity are incompatible, though in hydrous conditions the crown ether is likely to be displaced by water ligands, the crown may still be present in the structure of the crystal as a hydrogen-bonded adduct. This behaviour is seen in [Gd(N03)3(H20)3]-(18-crown-6).445 This type of compound is quite well known in the case of s block metals also, e.g. [Mg(H20)6]Cl2 (12-crown-4)454 and, a more subtle case, [Ca(nitrobenzoate)2(benzo-15-crown-5)]-3H20(benzo-15-crown-5)455 in which an apparent 2 1 complex has only half its crown ligand coordinated to Ca2+. 

These solvent effects can be explained in classical terms. The intrinsic (gas-phase) reactivity increases as the as the ionic radius falls. The reasons are simple as the anion becomes smaller, the surplus electron generates greater interelectronic repulsions and the reactivity rises. Dipolar aprotic solvents interact only weakly with the halides, so they do not appreciably affect this reactivity order. In protic solvents where hydrogen bonds play an important role, the smaller the ion, the more stabilized it becomes and the reactivity order is inverted. 

P0 and PE-parameters of free atoms were calculated based on equations (1, 2), the results of which are given in Table 1. For hydrogen atom the value of Bohr radius of hydrogen atom equaled to 0.529A and besides, for some cases - ionic radius (1.36A) were used as the main dimensional characteristics. 

Chemisorption or specific adsorption involves greater forces of attraction than physical adsorption. As hydrogen bonding or n rbital interactions are utilised, the adsorbed species lose their hydrated spheres and can approach the surface as close as the ionic radius. Whereas multilayer adsorption is possible in physical adsorption, chemisorption is necessarily limited to monolayer coverage. 

Values are quoted relative to the hydrogen ion for cations and to the chloride ion for anions. As shown, selectivity also increases with increasing degree of. cross-linking. At concentrations greater than 0.1 M selectivity for monovalent over polyvalent ions increases. Ionic properties which determine reSin affinity are complex involving hydration energy, polarizability and hydrated ionic radius. The last shows an approximately inverse relationship to the selectivity coefficient. 

---