Ahrland

Analogous to the classification of Lewis acids and bases in hard and soft species, Ahrland et al. have su ested a division of donors and acceptors into classes a and 6. See Ahrland, S. Chatt, J. Davies, N.R. Quart. Rev. 1958, 77, 265... 

S. Ahrland and co-workers, eds., Gmelin Handbook of Inorganic Chemistg, Thorium, Suppl Hoi D1, Properties of Thorium Ions in Solutions, 8th ed., Springer-Vedag, Berlin, 1988. 

It seems that, as suggested by Ahrland et alP in 1958, this distinction can be explained at least partly on the basis that class-a acceptors are the... 

I should like to take the opportunity to thank all those who have supplied information, answered questions or discussed points with me, including the late Sir Geoffrey Wilkinson Professors S. Ahrland, K.G. Caulton, F.A. Cotton, W.P. Griffith, D.M.P. Mingos, J.D. Woollins and R.K. Pomeroy and Drs A.J. Blake, P.R. Raithby, S.D. Robinson and P. Thornton. They are not, of course, responsible for the use I have made of the information. 

Thermodynamics of complex formation between hard and soft acceptors and donors. S. Ahrland, Struct. Bonding (Berlin), 1968, 5,118-149 (103). 

Ahrland, S. Larsson, R. Rosengren, K. Acta Chem. Scand. 

Ahrland, S. Liljenzin, J.O. Rydberg, J. "Solution Chemistry (of the Actinides)" Comprehensive Inorganic Chemistry. Vol. 

Aegerter MA (1996) Sol-Gel Chromogenic Materials and Devices. 85 149-194 Ahrland S (1966) Factors Contributing to (b)-behavior in Acceptors. 1 207-220 Ahrland S (1968) Thermodynamics of Complex Formation between Hard and Soft Acceptors and Donors. 5 118-149... 

Table 2.4. Classification of acceptor atoms in their normal valent states (Ahrland, Chatt Davies, 1958)... 

Ahrland, S., Chatt, J. Davies, N. R. (1958). The relative affinities of ligand atoms for acceptor molecules and ions. Quarterly Reviews, 12, 265-76. 

Ahrland, S. Thermodynamics of Complex Formation between Flard and Soft Acceptors and Donors. Vol. 5, pp. 118 149. 

Ahrland, S. Thermodynamics of the Stepwise Formation of Metal-Ion Complexes in Aqueous Solution. Vol. 15, pp. 167-188. 

Ahrland et al. (1958) classified a number of Lewis acids as of (a) or (b) type based on the relative affinities for various ions of the ligand atoms. The sequence of stability of complexes is different for classes (a) and (b). With acceptor metal ions of class (a), the affinities of the halide ions lie in the sequence F > Cl > Br > I , whereas with class (b), the sequence is F < Cl" < Br < I . Pearson (1963, 1968) classified acids and bases as hard (class (a)), soft (class (b)) and borderline (Table 1.23). Class (a) acids prefer to link with hard bases, whereas class (b) acids prefer soft bases. Yamada and Tanaka (1975) proposed a softness parameter of metal ions, on the basis of the parameters En (electron donor constant) and H (basicity constant) given by Edwards (1954) (Table 1.24). The softness parameter a is given by a/ a - - P), where a and p are constants characteristic of metal ions. 

They indicated that the softness parameter may reasonably be considered as a quantitative measure of the softness of metal ions and is consistent with the HSAB principle by Pearson (1963, 1968). Wood et al. (1987) have shown experimentally that the relative solubilities of the metals in H20-NaCl-C02 solutions from 200°C to 350°C are consistent with the HSAB principle in chloride-poor solutions, the soft ions Au" " and Ag+ prefer to combine with the soft bisulfide ligand the borderline ions Fe +, Zn +, Pb +, Sb + and Bi- + prefer water, hydroxyl, carbonate or bicarbonate ligands, and the extremely hard Mo + bonds only to the hard anions OH and. Tables 1.23 and 1.24 show the classification of metals and ligands according to the HSAB principle of Ahrland et al. (1958), Pearson (1963, 1968) (Table 1.23) and softness parameter of Yamada and Tanaka (1975) (Table 1.24). Compari.son of Table 1.22 with Tables 1.23 and 1.24 makes it evident that the metals associated with the gold-silver deposits have a relatively soft character, whereas those associated with the base-metal deposits have a relatively hard (or borderline) character. For example, metals that tend to form hard acids (Mn +, Ga +, In- +, Fe +, Sn " ", MoO +, WO " ", CO2) and borderline acids (Fe +, Zn +, Pb +, Sb +) are enriched in the base-metal deposits, whereas metals that tend to form soft acids... 

Present understanding of Lewis acidity and basicity is based mainly on the A and B type classification of metal ions of Ahrland, Chatt,... 

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