Ammine complexes group

In a dissociative process the reaction rate is expected to decrease as the strength of the metal to leaving ligand bond increases. This trend is generally observed in Co(III) ammine complexes. As can be seen in Table 2, a partial leaving group order is... 

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... 

ZnxZryFz. A fluoro complex of zirconium, ZrF62, and an ammine complex of zinc, ZnfNFF), have been used to grow ZnxZryFz films on silicon. The Zn/Zr/F ratio was 0.08/1/0.32, and the films contained hydroxyl groups and physisorbed water.128... 

Sargeson and his coworkers have developed an area of cobalt(III) coordination chemistry which has enabled the synthesis of complicated multidentate ligands directly around the metal. The basis for all of this chemistry is the high stability of cobalt(III) ammine complexes towards dissociation. Consequently, a coordinated ammonia molecule can be deprotonated with base to produce a coordinated amine anion (or amide anion) which functions as a powerful nucleophile. Such a species can attack carbonyl groups, either in intramolecular or intermolecular processes. Similar reactions can be performed by coordinated primary or secondary amines after deprotonation. The resulting imines coordinated to cobalt(III) show unusually high stability towards hydrolysis, but are reactive towards carbon nucleophiles. While the cobalt(III) ion produces some iminium character, it occupies the normal site of protonation and is attached to the nitrogen atom by a kinetically inert bond, and thus resists hydrolysis. 

A peculiar complex is formed by if coordination of Os(II) ammine complex to one of the double bonds of benzene rings, rather than rf coordination, and the coordinated benzene rings show interesting reactivity [82]. For example, Os(II) coordinates regioselectively to the 2,3-double bond of anisole to form the complex 333, and hence localization of the remaining 7r-electrons occurs. As a result, at 20 °C an electrophile attacks easily at C(4) due to electron-donation of the methoxy group. The 4H-cationic intermediate 334 is stabilized by backdonation from the metal, and the monosubstitution product 334 is formed without deprotonation. The / ara-substituted anisole 335 is... 

Of the Group VIII systems which have been studied Co(III) complexes are the best understood photochemically and electronically. Generally, Co(III) - cyanide and Co(III) — ammine complexes have been most well-studied and the former are the most photosensitive 46 but the latter have recently been examined.47 With respect to photosubstitution though the quantum yields for reaction are very small (< 10-2) upon population of the LF excited states. The Oh Co(CN)6- complex undergoes reaction (10) with a quantum yield of 0.3 at either 254 or 313 nm, i.e., direct population of either the 1 Tig or the state yields substitution with the same quantum ef-... 

Figure 3 Dlustration of photoinduced ET (PET) in a Zn-substituted Candida krusei cytochrome c (ZnP-protein) that was substituted at histidine 33 by a Ru(III) ammine complex. Photoexcitation of the cytochrome s Zn-porphyrin (ZnP) group produced the ZnP triplet state (ZnP3) which reduced the bound Ru(III) complex thorough protein-mediated ET. Subsequently the thermal back-ET within the Ru-substituted protein re-formed the starting ZnP-protein-Ru(III) complex.

In co-ordination chemistry, a different approach is used for example, in the structure for hexaamminecobaltate complex, [Co(NH3)6] , there are several alternative approaches. The simplest way to express this structure is shown in Fig. 42.2. While this is useful, it does not convey the three-dimensional aspects of the molecule. Therefore, an alternative approach to expressing the visualization of this structure is possible (Fig. 42.3) the complex is an octahedron, i.e. a geometric figure with eight sides. Note that the octahedron has six points of attachment where the hgands, i.e. ammine (NH3) groups, are attached. 

The dissociation constants for ionizing a proton from one or more coordinated ammine groups have been determined fairly accurately in a number of cases. A representative sampling is shown in Table I. The field strength of the platinum (II) ion is too small to render its ammine complexes sufficiently acidic for the dissociation constant to be determined in aqueous solution. Likewise, the complex ions [Co(NH3)6] , [Co(en)3] ", [Ir(en)3] ", and [Rh(en)3] " all have pKa values less than 10-12 T j0 fQj. [Rh(NH3) has been estimated to be approximately... 

In 1995, Morgan et al. synthesized a layered aluminophosphate compound by using a chiral cobaltammine complex as the template for the first time.[61] Recently, the Jilin group has synthesized a number of 2-D layered and 3-D open-framework metal phosphates by using a racemic mixture or an optically pure chiral metal complex as the template, and has systematically studied the chirality transfer from the guest chiral complex templates to the host inorganic open frameworks.1901 Table 7.15 lists some metal phosphates and oxides with open-framework structures templated by optically pure or racemic cobalt ammine complexes. 

Hydroxides are often used for precipitation of traces with collectors [72-74]. With Fe(III), Al, or La as collector, traces of most analytical group I-III metals are separated by addition of excess of ammonia. Metals forming ammine-complexes, e.g., Ag, Cu, Ni, Co, Zn, and Cd remain in solution. When excess of NaOH is used for precipitation, amphoteric metals such as Al, Pb, Zn, Sn, and Cr remain unprecipitated. In this case, Fe(III), Ti, Mg, or La may be used as the collector. Lanthanum is especially convenient, since it usually does not have to be determined in the trace concentrate. It has no chromophoric properties and it does not interfere in most spectrophotometric methods. 

---