Ligands ammine

The platinum(IV) compound that has shown most promise is carboplatin (paraplatin), which received FDA approval in 1990. Features to note in its structure are the use of hydroxy and carboxylate groups to improve water solubility. As noted above, the ammine ligand has been found to need at least one hydrogen, possibly for hydrogen-bonding to phosphate groups in the DNA (Figure 3.116). 

Because ammine ligands are neutral molecules, the oxidation state of each metal is the same as the charge on the complex. Iron loses two of its eight valence electrons to reach the +2 oxidation state, leaving six electrons for the d orbitals. Likewise, cobalt in its +3 oxidation state has six d electrons. 

Further reduction and protonation of the imido group leads to the formation of a Mo(I) ammine complex (8b) in a mechanism similar to the fluoro system in the classic Chatt cycle. The Mo(I) ammine complex 8b is first reduced to the corresponding Mo(0) complex 8c at which stage the ammine ligand is exchanged with... 

To illustrate further aspects of the interplay between covalent and coordinate bonding, let us consider the successive coordinative additions of ammonia molecules (ammine ligands, NH3) to tungsten hydrides in the series H6 2n W(NH3) , n = 1-3,... 

As shown in the third column of Table 4.23, replacement of two IT radicals by a coordinative ammine ligand becomes successively more endothermic for increasing... 

As a simple example of non-d coordination, let us consider the hexaammine-zinc(II) cation [Zn(NH3)6]2+, whose optimized structure is shown in Fig. 4.51. Each ammine ligand serves as a formal two-electron sigma donor, and the total electron count atZn therefore corresponds to a 22e system, again violating the 18-electron rule. Each ammine ligand is bound to the Zn2+ cation by about 60.7 kcal mol-1, which is in part attributable to classical electrostatic interactions of ion-dipole type. 

However, significant stabilization is also contributed by nN—>-szn donor-acceptor interactions, each with estimated second-order interaction energy 49.4 kcal mol-1, as depicted in Fig. 4.52. Each ammine ligand thereby donates about 0.061 e to the zinc cation, primarily to the vacant 4s orbital which acquires about 0.371 e total occupancy. As before, the high formal hypervalency at the metal center is achieved within the limits of the duodectet rule, i.e., without significant involvement of extravalent metal p orbitals. 

The overall volume changes could be accounted for in terms of electro-striction effects centered around the ammine ligands on the ruthenium center. A number of possible explanations in terms of the effect of pressure on electronic and nuclear factors were offered to account for the asymmetrical nature of the volume profile (159). 

This yellow, diamagnetic complex provides one of the few examples of metal hydrido compounds which contain only saturated ammine ligands. Osmiuin(v).—Further Os -arylimido-complexes have been synthesized via the reaction of phosphinimines with [OsOCl3(PPh3)2] ... 

Acetone complexes are also prepared by the trans activation of the ammine ligands in [Osn(NH3)5(C-Mepy)]2 + to form (r[Pg.285]

The acidity of the Os(III) ammine complexes is enhanced considerably by replacement of an ammine ligand by N-heterocyclic, imine, or... 

During calcination the dissociation of the [Pt(NH3)4]2+ complexes in the [Pt(NH3)4](HC03)2 nano fibers starts at about 423 K with the removal of ammine ligands. Above 573 K the ammine ligands decompose to N2 and H2 [21]. The produced H2 induces the reduction of the Pt2+ ions and due to this autoreduction metallic Pt is formed even in oxygen atmosphere ... 

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