Coordination to metal ions

The nitrogen donor commonly found coordinated to metal ions in biology is the imidazole group from histidine. It is found coordinated... 

Most analytical uses of tetrazolium salts utilize their reducibility. The ability of the resulting formazan to coordinate to metal ions, causing a characteristic shift in the spectrum, is often utilized to determine the metal ions or to enhance the sensitivity of the detection. 

Carbon dioxide is another weak ligand that is able to coordinate to metal ions. The [FeC02]+ ion has been prepared by the reaction of Fe+ with p-butyrolactonc (135). 

Triple-decker sandwiches that are capped at one or both ends by C2B3 rings are important synthons for the construction of larger stacks via coordination to metal ions (see the following subsection), and many of these have been synthesized and their reactivity investigated.75,78 Bent triple-deckers such as 6879,80 that resemble bent metallocene complexes have been prepared, structurally characterized, and shown to be amenable to the introduction of halo- and organosubsitutuents at boron.80... 

When coordinated to metal ions in their normal or higher oxidation states, an isocyanide is rendered susceptible to attack at the ligating carbon atom by nucleophilic reagents.1 When alcohols or amines are the nucleophiles, carbene complexes that may be prepared for a variety of metals and substituent groups are obtained. The first fully characterized compounds were of platinum(H),2 and general methods of their preparation, with particular examples, are given below. 

Not all clathrates are hydrates. Other well-known examples have host lattices formed from hydrogen bonded aggregates of hydroquinone, phenol, and similar organic compounds. Non-hydrogen bonded host structures are also known. One example is a cyclotriphosphazene. (C6H402PN). that traps molecules such as benzene in tunnels in the crystal.2 In addition, coordination polymers are formed by ambidentate ligands, such as CN and SCN, which coordinate to metal ions at both ends (Chapter 12). Perhaps the best known of this type of compound is the series of Ni(CN)2NHj M compounds, where M may be benzene, thiophene, furon. pyrrole, aniline, or phenol. 

Asymmetrically substituted secondary and tertiary amines (27) are configurationally stable when irreversibly coordinated to metal ions, where they may be considered to be formally analogous to ammonium ions. 

CO activation via coordination to metal ions in higher oxidation states is especially well illustrated by the work of Halpem and co-workers (94) on the catalyzed oxidation of CO to C02 by ferricyanide according to (31). 

As already concluded above, heterocyclic ligands with a ring size smaller than five or larger than six are rare, and few coordination compounds are known. In principle, however, ligands such as (31) and (32) could be expected to coordinate to metal ions in a chelating manner. 

Thus, for both the terminal diammonium and dicarboxylate substrates, selective binding by the appropriate receptors describes a linear recognition process based on length complementarity in a ditopic binding mode. Important biological species, such as polyamines, amino acid and peptide diamines, and dicarboxylates [4.18] may also be bound selectively. Recognition is achieved by multiple coordination to metal ions in dinuclear bis-macrocyclic coreceptors that complex selectively complementary bis-imidazole substrates of compatible length [4.21]. 

When a ligand becomes coordinated its properties are markedly changed one example already encountered (Sections 58.2.2.1 and 58.2.3. l(i)(a)) is the enhancement of the acidity of the phenolic hydroxyl groups in o-hydroxydiarylazo compounds coordinated to metal ions. o-Aminodiarylazo compounds apparently offer an even more dramatic example. 

Rare tautomeric forms of the neutral (or monoanionic) base may be stabilized by coordination to metal ions [13] [22-24], especially with metals in high oxidation states such as Ptm and PtIV, but also with Ptn [25],... 

When building simple chelate rings coordinated to metal ions problems can arise and these become more severe with tridentate or macrocyclic ligands. These problems are not unique to HyperChem and arise because of the mathematical complexity associated with building complicated ligands. Therefore, it is necessary to... 

Ethylenediamine (en) is coordinated to metal ions as a chelate. The values of AH should therefore be of about the same order of magnitude as AH%2 for ammonia, while dS should be some 8 e.u. higher than dSj %... 

Although C104 does not coordinate to metal ions strongly, numerous complexes are known in which it is a ligand. Describe ways in which C1C>4 could form coordinate bonds to metal ions. 

Predict the ways in which SO32- could coordinate to metal ions. If the other ligands are H20, which way would it probably coordinate to Co3+ How would it likely coordinate to Pt2+ ... 

In the 7] -(S)-coordinated thiophenes, the sulfur appears to be sp -hybridized the metal does not lie in the plane of the thiophene. They are all weakly coordinating compared to THT (a dialkyl sulfide type of molecule) consequently, such complexes can be isolated only in some special cases. The tendency to coordinate to metal ions in the 77-(S) mode generally increases in the order T < BT < DBT. (As per the normal convention, the unstarred symbols T, BT, and DBT refer to the unsubstituted heterocycles thiophene, benzo[. ]thiophene, and diben-zo[i, . thiophene, respectively, while a star indicates the inclusion of substituted thiophenes as well. Cp and Cp refer to the 77 - bound CsHs and CsMcs, respectively.)... 

Bidentate phosphorus ligands coordinated to metal ions may be more suitable for hydrogenation processes than for carbonylation processes the competition of CO as a ligand would then be excluded. 

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