Ammine complexes Complex species that

Ammine complexes Complex species that contain ammonia molecules bonded to metal ions. 

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh . ... 

This, together with the known tendency of metal ions to form mixed hydroxy-am-mine complexes, snggested to them that two ammonia molecnles were involved in the first step and that the adsorbed species in Reaction (3.58) was a hy-droxy-ammine species, viz. Cd(OH)2(NH3)2. Decomposition of the hydroxide-ammine-thiourea complex was then assumed to occur by nucleophilic attack of an ammonia species on the S=C bond of the thiourea. 

The resulting estimates of <5r/c i for Cr(III)/Cr(II) aquo couples, ca. 0.1-0.3 A, are close to that extracted from temperature-dependence measurements and indicate that these strongly hydrated species follow marginally non-adiab-atic pathways even at the plane of closest approach [30]. Markedly larger values of 5rK°eU ca. 5 A, were obtained for similar ammine complexes, as from a related comparison involving unimolecular outer-sphere reactivities [21], This is consistent with the smaller hydrated radii of the ammines allowing a closer approach to the metal surface, whereupon a 1 [15a, 30]. 

The number of covalent bonds that a cation tends to form with electron donors is its coordination number. Typical values for coordination numbers are 2,4, and 6. The species formed as a result of coordination can be electrically positive, neutral, or negative. For example, copper(II), which has a coordination number of 4, forms a cationic ammine complex, Cu(NH3)4 a neutral complex with glycine, Cu(NH2CH2COO)2 and an anionic complex with chloride ion, CuClj. ... 

Many cations form hydrous oxide precipitates when the pH is raised to the level required for their successful titration with EDTA. When this problem is encountered, an auxiliary complexing agent is needed to keep the cation in solution. For example, zinc(II) is ordinarily titrated in a medium that has fairly high concentrations of ammonia and ammonium chloride. These species buffer the solution to a pH that ensures complete reaction between cation and titrant in addition, ammonia forms ammine complexes with zinc(II) and prevents formation of the sparingly soluble zinc hydroxide, particularly in the early stages of the titration. A somewhat more realistic description of the reaction is then... 

The Ag+ ion is reduced by [e ] and H to Ag = 360 nm) which undergoes successive reaction with Ag to form Ag, Agj and Ag species. Pulse radiolysis is used to study the reactions of Ag atonls especially as they serve as a pool for electrons in redox reactions and the reduction " of HjO. The mechanism of reduction of Ag(I)-ammine complexes is similar to that of Ag" ". 

The reversible 4e-/3H+ interconversion between NH3 and N3- in the coordination spheres of OsTp complexes has been described by Meyer et al 77 Electrochemical or chemical reduction of the nitrido complex [OsVI(Cl)2(Tp)N] gives Osn-ammine species that after air-oxidation transforms into [Osm(Cl)2(Tp)(NH3)], structurally characterized. The latter species can be reoxidized electrochemically to the starting nitrido complex by a stepwise mechanism involving the loss of both electrons and protons and sequential Os(III —> IV) and Os(IV —> V) oxidation. 

The reduction of ammines of the type [Ru(NH3)5L]3 + with Cr2+ and other reducing agents has been studied in detail.24 The reactions are similar to those of Co111 complexes except that the electron enters the t2g rather than the eg level and the resulting Ru11 complexes are diamagnetic. Bridged species are probably intermediates. 

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