Complexes with Related Ligands

Less study has been made of complexes with polydentate ligands. Ag-N linkages have been studied in relation to polynucleotide bases and the Ag-DNA interaction could be important in the use of the silver-sulphadiazine complex in burn treatment. Ethylenediamine is a bridging ligand in AgenC104 (2-coordinate silver) but essentially planar 5-coordination... 

Synthesis of functional models of carbonic anhydrase has been attempted with the isolation of an initial mononuclear zinc hydroxide complex with the ligand hydrotris(3-t-butyl-5-methyl-pyrazolyl)borate. Vahrenkamp and co-workers demonstrate the functional as well as the structural analogy to the enzyme carbonic anhydrase. A reversible uptake of carbon dioxide was observed, although the unstable bicarbonate complex rapidly forms a dinuclear bridged complex. In addition, coordinated carbonate esters have been formed and hydrolyzed, and inhibition by small ions noted.462 A number of related complexes are discussed in the earlier Section 6.8.4. 

These considerations lead, for example, to the assignment of a predominantly outer sphere character to Cl, Br, F, CIO3, NO3, sulfonate, and trichloro-acetate complexes and an inner sphere character to F", IO3, SO, and acetate complexes of trivalent actinides and lanthanides. The variation in AH° and AS° of complexation of related ligands indicates that those whose pA), values are <2 form predominantly outer sphere complexes, while those for whom > 2 form predominantly inner sphere complexes with the trivalent lanthanides and actinides. As the pK increases above 2, increasing predominance of inner sphere complexation is expected for these metals. 

A multiple-path mechanism has been elaborated for dissociation of the mono- and binuclear tris(hydroxamato)-iron(III) complexes with dihydroxamate ligands in aqueous solution. " Iron removal by edta from mono-, bi-, and trinuclear complexes with model desferrioxamine-related siderophores containing one, two, or three tris-hydroxamate units generally follows first-order kinetics though biphasic kinetics were reported for iron removal from one of the binuclear complexes. The kinetic results were interpreted in terms of discrete intrastrand ferrioxamine-type structures for the di-iron and tri-iron complexes of (288). " Reactivities for dissociation, by dissociative activation mechanisms, of a selection of bidentate and hexadentate hydroxamates have been compared with those of oxinates and salicylates. ... 

Four-coordinate neutral complexes with anionic ligands derived from deprotonated amines, imines, oximes and related ligands... 

Complexes with related chelating thioketone ligands are reversibly formed on protonation of enethiolato complexes of iron.101... 

Another type of cyclic thioether is l,3,5-tris(alkylthia)cyclohexane (7), which is related to the open-chain multifunctional ligands mentioned above. With R = Me, the formation of weak Cu11 complexes with this ligand has been observed.17... 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

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