Cation size

However, solubility, depending as it does on the rather small difference between solvation energy and lattice energy (both large quantities which themselves increase as cation size decreases) and on entropy effects, cannot be simply related to cation radius. No consistent trends are apparent in aqueous, or for that matter nonaqueous, solutions but an empirical distinction can often be made between the lighter cerium lanthanides and the heavier yttrium lanthanides. Thus oxalates, double sulfates and double nitrates of the former are rather less soluble and basic nitrates more soluble than those of the latter. The differences are by no means sharp, but classical separation procedures depended on them. 

The size of the cation in the chloroaluminate ionic liquids also appears to have an impact on the viscosity. For ionic liquids with the same anion(s) and compositions, the trend is for greater viscosity with larger cation size (Table 3.2-2). An additional contributing factor to the effect of the cation on viscosity is the asymmetry of the alkyl substitution. Highly asymmetric substitution has been identified as important for obtaining low viscosities [17]. 

In the binary haloaluminate ionic liquids, an increase in the mole percent of the imidazolium salt decreases the density of the liquid (see Table 3.2-2). The bromo-aluminate ionic liquids are substantially denser than their chloroaluminate counterparts, being between 0.57 g cm and 0.83 g cm denser than the analogous chloroaluminate ionic liquids (see Table 3.2-2). Variation of the substituents on the imidazolium cation in the chloroaluminate ionic liquids has been shown to affect the density on the basis of the cation size [17]. 

Cation size can affect bond lengths in OsCl6 Os—Cl is 2.284 A and 2.303 A in the Ph4P and Bu4N salts, respectively. Oxidation, however, has a more significant effect, so that Os-Cl in (Ph4P)2OsCl6 is 2.332 A. 

Chatterjee S., Bohidar H.B. 2005. Effect of cationic size on gelation temperature and properties of gelatin hydrogels. International Journal of Biological Macromolecules 35, 81-88. 

Our work described in this section clearly illustrates the importance of the nature of the cations (size, charges, electronegativities), electronegativity differences, electronic factors, and matrix effects in the structural preferences of polar intermetallics. Interplay of these crucial factors lead to important structural adaptations and deformations. We anticipate exploratory synthesis studies along the ZintI border will further result in the discovery of novel crystal structures and unique chemical bonding descriptions. 

The fourth lifetime components, r4, have values in the range of 2.7 - 5.0 ns (shown in Table 1 and 2), which, using equation (1), gives 0.34 - 0.47 nm for radii of the holes that are listed in Table 3 and 4. These lifetimes have also lower intensities than r3, suggesting the presence of the larger voids already in the initial phase of zeolite formation, but in a smaller extent. Here the correlation to the influence of cation sizes cannot be established. 

Calorimetric studies indicate that the enthalpies of complexation tend to show related trends to the observed stability constants and display selectivity peaks, although there is not necessarily a coincidence between the two sets of peaks. Complexation is characterized by the entropy becoming progressively less positive (less favourable) as the cation size decreases. This is illustrated in Figure 6.5 for the complexation of 2.2.1 with the alkali metals. 

The dissociation rates for a number of alkali metal cryptates have been obtained in methanol and the values combined with measured stability constants to yield the corresponding formation rates. The latter increase monotonically with increasing cation size (with cryptand selectivity for these ions being reflected entirely in the dissociation rates - see later) (Cox, Schneider Stroka, 1978). 

Cation Size. In their early studies, Hlnsberg (1) and Arcus (3) found that dissolution rates of resists decreased as the size of the cation of the base Increased. Our results support their conclusion. In Figure 5, the dissolution rates of a PMPS(10X)/p-N02-PHMP film 1n different alkali solutions clearly show a decreasing trend with increasing cation size. In fact, the rate 1s Inversely proportional to the cross-sectional area of the unhydrated cation (Figure 6). It is known 1n the diffusion of small molecules 1n polymers, the diffusion constant is Inversely related to the size of the molecule (IS). The observed dependence of dissolution rate on cation size 1s therefore suggestive of cation diffusion as a crucial step. It is... 

Both Tg and the activation energy below Tg Increase with cation size (Table VI). The activation energy values for p-Cl-PHMP compare favorably with the results of 1on conductivity measurements 1n cellulose acetate (16.18). shown 1n Figure 8. This relationship speaks strongly for cation diffusion as being Involved in the rate determining step. 

As in the case of rosin sizing, the first step is to retain the emulsified size particle in the wet web. The mechanism of retention is probably by heterocoagulation of the cationic size particles to the negatively charged fibre surface. The charge characteristics of the stabilising polymer become important as demonstrated by the effect of pH on the retention of AKD emulsion particles stabilised with a tertiary cationic starch (Figure 7.17). 

Moeller and Vicentini (48) have reported the complexes of DMA with lanthanide perchlorates in which the number of DMA molecules per metal ion decreases from eight for La(III)—Nd(III) to six for Tm(III)—Lu(III).apparently due to the decrease in the cationic size. The complexes of the intermediate metal ions have seven molecules of DMA in their composition. Complexes of lanthanide chlorides with DMA (49, 50) exhibit a decrease in L M from 4 1 to 3 1 through 3.5 1. These complexes probably have bridging DMA molecules. The corresponding complexes with lanthanide iodides (51), isothiocyanates (52), hexafluorophosphates (57), nitrates (54, 55), and perrhenates (49, 56) also show decreasing L M with decreasing size of the lanthanide ion. However, complexes of DMA with lanthanide bromides (55) do not show such a trend. Krishnamurthy and Soundararajan (41) have reported the complexes of DPF with lanthanide perchlorates of the composition [Ln(DPF)6]... 

Complexes of TSO with lanthanide perchlorates which have the formula Ln(TS0)9(C104)3 have been reported by Edwards et al. (266) (Ln = Ce or Y). Later, Vicentini and Perrier (267) have prepared the whole series of complexes of TSO with lanthanide perchlorates and have shown that the L M in these complexes gradually decreases from 9 1 to 7 1 as the cationic size decreases. These authors could not prepare Y(TS0)g(C104)3 reported by Edwards et al. (266). Instead, they obtained the complex of the composition Y(TS0)7(C104)3. Two series of complexes of TSO with lanthanide hexafluorophosphates are known (268, 269). While the L M in one of the series is 7.5 1, in the other series it is found to be 8 1. The change in the stoichiometry of the two series of compounds is attributed to the preparative procedures adopted. In both the series of complexes, the PFg ion remains ionic. Lanthanide nitrates (270), chlorides (270), and isothiocyanates (271) also yield complexes with TSO. In all these complexes, changes in the stoichiometry could be observed when the lanthanide series was traversed. In all these complexes the anions are coordinated to the metal ion. 

As one traverses through the lanthanide series, there is a reduction in the cation size as the atomic number increases. This results in small differences in the strength of interactions of the ligand with the lanthanide ions. These trends are reflected in the IR spectra of these complexes in a few cases. Cousins and Hart (203) have observed an increase in Pp Q with decreasing lanthanide ion radius for the complexes of TPPO with lanthanide nitrates. This observation has been attributed to an increase in the Ln—O bond strength with an increase in the atomic number of the lanthanide ion. 

The molar conductance values of the complex Ln(DPSO)6 I3 in acetonitrile are slightly higher than those suggested for 1 1 electrolytes, due to the displacement of some coordinated iodide by the solvent (250). The conductance values observed for the complexes, however, approach more closely the values reported for 1 1 electrolytes as the ionic size of the lanthanide ion decreases. This may be due to the increasing strength of the metal-anion bond with decreasing cation size. 

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