Potential ligands

This type of isomerism occurs when isomers produce different ions in solution, and is possible in compounds which consists of a complex ion with a counter ion which is itself a potential ligand. The pairs [Co(NH3)5(N03)]S04, [Co(NH3)5(S04)]N03 and [PtCl2(NH3)4]Br2, [PtBr2(NH3)4]Cl2, and the series [CoCl(en)2-(N02)]SCN, [CoCl(en)2(SCN)]N02, [Co(en)2-(N02)(SCN)]C1 are examples of ionization isomers. 

The bulky ruthenium TMP complex Ru(TMP) is very electron deficient in the absence of any coordinating ligand, and a tt-complex with benzene has been proposed. In fact, it readily coordinates dinitrogen, forming the mono- and bis-N adducts Ru(TMP)(N2)(THF) and Ru(TMP)(N2)2, - As a result, the use of the TMP ligand for careful stereochemical control of the chemistry at the metal center, which has been very successful for the isolation of elusive rhodium porphyrin complexes, is less useful for ruthenium (and osmium) because of the requirement to exclude all potential ligands, including even N2,... 

These results may be viewed in the wider context of interactions between potential ligands of multifunctional xenobiotics and metal cations in aquatic environments and the subtle effects of the oxidation level of cations such as Fe. The Fe status of a bacterial culture has an important influence on synthesis of the redox systems of the cell since many of the electron transport proteins contain Fe. This is not generally evaluated systematically, although the degradation of tetrachloromethane by a strain of Pseudomonas sp. under denitrifying conditions clearly illustrated the adverse effect of Fe on the biotransformation of the substrate (Lewis and Crawford 1993 Tatara et al. 1993). This possibility should therefore be taken into account in the application of such organisms to bioremediation programs. 

The oxoanions of these elements represent an extensive set of potential ligands, characterized by a dominant, but not exclusive, tendency towards O bonding. Practically every known oxoanion has been introduced into the Co coordination sphere during the last century. 

A great many metal complexes are prepared by reactions carried out in aqueous solutions. Consequently, solid complexes are frequently obtained as hydrates. Water is also a potential ligand so various possibilities exist for compounds to be prepared with water held in both ways. For example, [Cr(H20)4Cl2]Cl-2ff20 and [Cr(H20)5Cl]Cl2-ff20 have the same formula, but they are obviously different compounds. In the first case, two chloride ions are coordinated and one is present as an anion, whereas in the second case the numbers are reversed. Many other examples of hydrate isomerism are known. 

Many substitution reactions occur between metal carbonyls and other potential ligands. For example,... 

This means that addition of elemental E to alkali metal polychalcogenide fluxes (200-600°C) will promote the formation of longer chains as potential ligands, when such molten salts are employed as reaction media for the preparation of polychalcogenide complexes. Speciation analysis for polychalcogenides in solution has been performed by a variety of physical methods including UV/vis absorption spectroscopy, Raman spectroscopy, Se, Te and Te NMR, electron spin resonance and electrospray mass spectrometry. 

A potential ligand such as the nitrile present in a nitrile-butadiene copolymer may inhibit the catalytic hydrogenation cycle ... 

Singer, M. S., Oliveira, L., Vriend, G and Shepherd, G. M. (1995) Potential ligand-binding residues in rat olfactory receptors identified by correlated mutation analysis. Recept. Channels 3, 89-95. 

The reactions of bare metal ions will be separated into two sections. Simple addition reactions (Section III.A.l) will be discussed first followed by reactions in which the metal ion causes bond disruption in the potential ligand (Section III. A.2). 

There have been fewer studies of the reactions of M ions with potential ligand molecules. Laser ablation, which has been the major ionization source for the production of bare metal ions, produces very few negative ions. Electron impact with low-energy electrons (12 eV) of metal carbonyls has been used to produce [Co(CO)4]- and Fc( CO)4 from Co2(CO)8 and Fe(CO)5. Collision-induced dissociation of these two anions produced Co- and Fc, which could be isolated. Both Co- and Fe were reacted with H2S, aliphatic thiols, aromatic thiols, CS2, and disulfides (153). Reactions with H2S gave the metal monosulfide anion [MS]-, which reacted with H2S by two pathways. 

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