Acceptor 71-Acid Ligands

Ligands that reduce the activity of Hg(II) more than that of Hg(I) lead to disproportionation products when added to a solution containing Hg2 ions. Because the smaller Hg ion is a better electron-pair acceptor acid than the larger Hgj ion, the number of Hg(I) complexes may be limited, but many complexes of Hg(I) are formed by reactions of Hg, with ligands containing donor atoms from groups VB and VIB. Polyethers and polyesters are good solvents for these reactions, ... 

Ligand Preferences. The LVC s are electron rich and in order to exist in stable compounds they require ligands, such as CO, that are weak donors and good tt acceptors. On the other hand the HVC clusters are not attractive to such ligands nor do they require them for stability. In this respect, there is a direct parallel to mononuclear compounds where M° prefers CO, RNC or similarly ir-acidic ligands while the Mn+ (n = 2-4) ions do not generally form CO complexes. 

Phthalic acid, with trinuclear Os clusters, 6, 743 n-acceptor carbon ligands, in molybdenum carbonyls, 5, 455 Ti-allyl complexes, with molybdenum with cyclopentadienyl-supporting ligands, 5, 544 monomeric complexes, 5, 546 oxide surface binding, 5, 546... 

The bonding between the transition metal and the group 13 element has been studied extensively by computational methods. Because RM compounds have a valence electroitic structure consisting of a filled orbital of a symmetry and two unfilled orbitals of n symmetry, they are analogous to carbonyl ligands in that they can act as sigma donors and pi acceptors see tv-Acid Ligand). Such an electronic structure... 

If trans-subsituted carbene complexes containing ligands which have a greater (T-donor/n-acceptor ratio than CO (e.g., PRj, AsRj, SbRj or a Jt-aromatic ) are reacted with electron-pair acceptor acids, these ligands remain in the product complex. Only the heteroatom-containing substituent is removed from the carbene carbon and cationic carbyne complexes are formed ... 

It is possible to represent not only a ligand by the potential pharmacophores it possesses but also a protein target. In this case the pharmacophore points are identified by the positions where a ligand atom of a particular type (donor, acceptor, acid, base, hydrophobic, aro-... 

Al. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 2nd ed. Wiley, New York, 1966. Probably the best general introduction to organo-transition metal chemistry. See Chapter 27 (pp. 719-760) Complexes of w-acceptor (w-acid) ligands Chapter 28 (pp. 761-795) Organometallic compounds of transition metals. 

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