Electron-donor groups ligands

The term complexation refers to the reaction of a metal ion with an electron donor group (ligand), and entails the transformation of a solvated metal ion into a complex ion. In aqueous solutions of metal salts, the metal cations are surrounded by a sheath of aquo groups which are collectively called the primary hydration sphere. These solvated metal ions are not referred to as complex ions. Instead, a complex ion is formed if one or more of the solvent molecules within the primary hydration sphere of the metal ion is replaced either by ions, or by... 

DFT calculations confirmed the similarities with the alkyne/vinylidene transformation but have revealed that additional parameters were essential to achieve the isomerization [8, 20-23]. The hydride ligand on the 14-electron fragment RuHC1L2 opens up a pathway for the transformation similar to that obtained for the acetylene to vinylidene isomerization. However, thermodynamics is not in favor of the carbene isomer for unsubstituted olefins and the tautomerization is observed only when a re electron donor group is present on the alkene. Finally the nature of the X ligand on the RuHXL2+q (X = Cl, q=0 X = CO, q=l) 14-electron complex alters the relative energy of the various intermediates and enables to stop the reaction on route to carbene. 

Figure 10.1 Chelation of Cu2+ by glycinate anion ligands to form the glycinate chelate. Each electron donor group on the glycinate anion chelating agents is designated with an asterisk. In the chelate, the central copper(ll) metal ion is bonded in four places and the chelate has two rings composed of the five-atom sequence Cu-O-C-C-N.

In some complex-formation titrations, the endpoint is noted by the formation or disappearance of a solid phase. For example, in the titration of cyanide with silver ion, the solution remains clear, but the first excess of silver causes formation of a white solid that marks the endpoint. The electron-donor groups of most common ligands tend to combine not only with metallic ions but also with protons thus, the equivalence point in a complex-formation titration is often accompanied by a marked change in pH, which can be detected with an acid-base indicator. 

Few metal-metal-bonded metal carbonyl complexes contain three-electron donor group IVB ligands. Dimers containing allyl ligands are known [e.g., (C3H5NiCl)2], but these do not contain metal-metal bonds. These are prepared in high yield M = Pd will... 

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