Oxygen complexing ability

The yield of the tricyclic IV/108 increases in the presence of Li+ instead of Na+ while that of the 2-phenylketone, IV/107, decreases (see Scheme IV/17 for the cyclohexanone reaction). Because of its better oxygen complexing ability the... 

As a result of this reaction, we isolated a violet product with a peak at 1284.3 by fast atomic bombardment mass spectrometry (FABMS). The mass of the molecular ion indicated the incorporation of three cobalt atoms. This result was confirmed by elemental analysis. We tried examining the oxygen-complexing ability of our salen-type complex 71, but... 

Tannin chemistry is complex and tannin blends (composed of singletree species tannins mixed together) offer a number of useful water treatment functions. Apart from oxygen-scavenging abilities, they act as passivating agents, film-formers, sequestrants, and polymeric sludge dispersants (for more details, see Section 10.3). 

Changes in the electron density of crown ether oxygen atoms greatly affect the stability constants for cation complexation. The electron density on phenol ether oxygens is less than that on alkyl ether oxygens consequently dibenzo[18]crown-6 (2) shows weaker complexing ability than [18]crown-6 (1) and hexabenzo[18]crown-6 does not complex cations at all (80APO(17)279). 

The enthalpy and entropy of complex formation between Zn11 and picolinate and dipicolinate anions in aqueous solution have been determined by calorimetry and from formation constant data. The greater stability of the dipicolinate complex compared to the picolinate complex reflects an entropy effect, and Ais actually less favourable. These anions are well known to have a low basicity to H+ compared to their complexing ability to metals. In the present case, this probably reflects the coplanarity of the carboxylate anions and the pyridine ring, so that the oxygen atoms are in a favourable position to coordinate.800... 

All of these examples illustrate the complexing ability of an ax-eq-ax sequence of oxygen atoms on a six-membered or of a cis-cis sequence on a five-membered ring. Attempts have been made to find other complexing sites on sugar molecules but with little success. The 0-3, 0-5, and 0-6 arrangement of hexofuranoses, which allows the ready formation of tri-dentate periodate (IS), and orthoformate esters (19), does not form stable complexes with metal ions. In solution the side-chain of 1,2-0-isopropylidene-a-D-glucofuranose (13) is in the extended zig-zag form... 

The complexing ability of the multi-armed polyethers diminishes when (a) the arms are shortened so as to possess only two oxygens per arm and (b) the number of arms are successively reduced. This is illustrated with formula (l)-(4) (a) and (b). 

The thiosulfate ion, S2 O2- "3, is a structural analogue of the sulfate ion where one oxygen atom is replaced by one sulfur atom. The two sulfur atoms of thiosulfate thus are not equivalent. Indeed, the unique chemistry of the thiosulfate ion is dominated by the sulfide-like sulfur atom which is responsible for both the reducing properties and complexing abilities. The ability of thiosulfates to dissolve silver halides through complex formation is the basis for their commercial application in photography (qv). 

By replacement of just one oxygen atom in 5 by a methylene group, affinity of the corresponding cryptand 15 to NH4+ decreases by a factor of ca. 100 (NH4+ c 15 log /Ca = 4.3). The macrobicycle 16 has almost completely lost the complexation ability and the selectivity of 5 (NH4+ c 16 log /Ca = 1.7). This dramatic effect results from the removal of one bridge of 5, i.e., from a decrease in cyclic order from the tricyclic to the bicyclic ring system, demonstrating the importance of the spherical macrotricyclic structure for the binding properties of 5. 

In the group of ethers of intermediate complexing ability, Chlorex [(bis-cy chloroethyl) ether] is preferred because of easy availability and low cost. Presence of electron negative chlorine atoms in the Chlorex molecule reduces the electronreleasing capacity of the oxygen atom and in turn reduces thp bond strength with TEA. 

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