Ammines structures

Isomerism in Metal-Ammines—Structure Isomerism—Ionisation Isomerism— Hydrate Isomerism—Polymerism—Stereo-isomerism. 

No structural studies have been reported on these complexes, but detailed study of their vibrational spectra permits the assignments shown in Table 2.13. Like the rhodium analogues, iridium ammines are photoactive therefore, on excitation of ligand-field bands, solutions of [Ir(NH3)6]3+ or [Ir(NH3)5Cl]+ afford [Ir(NH3)5(H20)]3+. 

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). 

The soft Au+ forms relatively few complexes compared with those of phosphines. Complexes with ammines, nitriles and diazoles like Au(NH3)2 and Au(RCN)2 are known but little studied. In linear Au(NH3)2, Au-N is 2.01-2.03 A [70a], [Au(NCPh)2]+ has been used as a labile source of other gold complexes [70b]. AuCl(piperidine) is a monomer with weak tetra-meric association in contrast AuX(py) (X = Cl, Br, I) are [Aupy2]+[AuX2] with a chain structure in the solid state (and Au-Au interactions), suggesting a close balance between factors for molecular and ionic structures [70c] (note also the tetrahydrothiophene complexes in section 4.10.6). 

Tri-tert-butoxidesilanethiolate forms complexes with both Co11 and Co111. Reaction of the thiol with a Co11 ammine in water yields a dimer which undergoes oxidation in an ammonia-saturated atmosphere to form octahedral [Co(SSi(0-t-Bu)3)2(NH3)4]+, the first silanethiolate characterized structurally.1044... 

The affinity of platinum(II) for N-donor ligands is well established. There are numerous examples in the literature of mono-, di-, and trinuclear platinum(II)-ammine and alkylamine complexes, most of which are structural analogues of the anticancer agent, mplatin (cis- PtCl2(NH3)2]), and the corresponding trans isomer. Selected novel complexes and synthetic methods are presented below. 

Stein and co-workers have reported the structure of an unusual tetranuclear platinum(II) complex possessing both ammine and carbonato ligands.325 During a study of the reaction of cisplatin with Ag+, followed by the addition of 2 -deoxyuridine to afford platinum blue -like products from aqueous solution (pH < 2), a colorless minor product was isolated from the reaction mixture. X-ray crystallography confirmed that the product was a cyclo tetra-cation... 

The chemistry of zinc ammine complexes is well known. There are X-ray structural examples of both the tetrahedral tetra-ammine and octahedral hexa-ammine.90,91 Four- and five-coordinate mixed ligand complexes are common and participation in coordination networks as terminal ligands is observed.92,93... 

Figure 4.33 displays optimized structures of the amminated coordination complexes Fh WCNFE), n = 1 — 3. Table 4.23 summarizes the metal atomic charges (Qw) and energies (AE ) of successive coordination reactions in (4.73),... 

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. 

Figure 4.52 The leading donor-acceptor (nN->-szn ) interaction between the donor ammine lone pair and the acceptor 4s metal orbital in 22e [Zn(NH3)6]2+ (of. Fig. 4.51). (Note that the inner nodal structure of the Zn 4s orbital is absent in the effective-core-potential representation of the metal atom.)...

Polynuclear anion-hridged complexes. The structure of [(NH3)3(H20)Co-(p-OH)2Co(H20XNH3)3](N03), 2H20 has been reported, although it was not possible to distinguish between the ammine and aquo ligands. When [Co(acac)2] in methanol, containing KOAc, is treated with H2O at 25°C for 1 h, [(acac)2Co(p-OH)2Co(acac)2] is formed. The structure of rac-... 

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