Metallic radii. 178-9 trends

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]. 

Many of the ionic fiuorides of M, M and M dissolve to give highly conducting solutions due to ready dissociation. Some typical values of the solubility of fiuorides in HF are in Table 17.11 the data show the expected trend towards greater solubility with increase in ionic radius within the alkali metals and alkaline earth metals, and the expected decrease in solubility with increase in ionic charge so that MF > MF2 > MF3. This is dramatically illustrated by AgF which is 155 times more soluble than AgF2 and TIF which is over 7000 times more soluble than TIF3. 

It is possible to explain these trends in terms of the electron configurations of the corresponding atoms. Consider first the increase in radius observed as we move down the table, let us say among the alkali metals (Group 1). All these elements have a single s electron outside a filled level or filled p sublevel. Electrons in these inner levels are much closer to the nucleus than the outer s electron and hence effectively shield it from the positive charge of the nucleus. To a first approximation, each inner electron cancels the charge of one pro-... 

The data for the 1,2-diaminoethane complexes now parallels the trends in ionic radius and LFSE rather closely, except for the iron case, to which we return shortly. What is happening Copper(ii) ions possess a configuration, and you will recall that we expect such a configuration to exhibit a Jahn-Teller distortion - the six metal-ligand bonds in octahedral copper(ii) complexes are not all of equal strength. The typical pattern of Jahn-Teller distortions observed in copper(ii) complexes involves the formation of four short and two long metal-ligand bonds. 

Fig. 3.44. Metallicities in gas-poor galaxies (open symbols) and oxygen abundances at a representative radius in gas-rich disk galaxies (filled symbols), as a function of galaxy luminosity in blue light. The dotted lines in each panel represent identical trends for [Fe/H] and [O/H] and the ordinate 0.0 represents solar composition. Adapted from Zaritsky, Kennicutt and Huchra (1994).

Ions, like atoms, have size. For ions, the term is ionic radii. For cations, the loss of electrons results in a decrease in size, since (for the representative metals) an entire energy level is usually lost. A sodium ion, Na+, is smaller than a sodium atom. The greater the number of electrons removed, the greater the decrease in radius. This applies to any element and its cations as illustrated by the trend in radii of Fe > Fe2+ > Fe3+. 

Contrary to the usual trend, the covalent radius of gallium is ca. 0.05 A smaller that that of aluminium, which is reflected in Ga—Ga distances which are ca. 0.1 A shorter than the Al—Al distances in metal-metal bonded compounds that carry the same substituents. 

---