Chelate, defined

X-ray crystal structures have been determined for a series of [/f(L10 lH)] chelates, defining nine-coordinate capped square antiprismatic (CSAP) or inverted capped square antiprismatic structures. The acetate arms of the L10 or DOTA ligand are arranged in a propeller-like fashion above the basal plane made up of the four N donor atoms, which encompass the... 

The next example (see Figure 13) is the tris(ethylenedia= mine)cobalt(III) complex. The site symmetry term is octahedral, six coordinate or OC-6, and the configuration number is 11. The nitrogen atoms are all equivalent, and the chelation defines a right-handed or A helix to give the complete notation 0C-6-11-A. I have indicated the primes on the chelating ligands in this structure to illustrate how to determine the... 

Vi. Dosage and method of administration for lead poisoning (adults and children). Note Administration of EDTA should never be a substitute for removal from lead exposure. In adults, the federal OSHA lead standard requires removal from occupational lead exposure of any worker with a single blood lead concentration in excess of 60 mcg/dL or an average of three successive values in excess of 50 mog/dL. (However, recent declines in background lead levels and concern over adverse health effects of lower-level exposure support removal at even lower levels). Prophylactic chelation, defined as the routine use of chelation to prevent elevated blood lead concentrations or to lower blood lead levels below the standard In asymptomatic workers, is not permitted. Consult the local or state health department or OSHA (see Table IV-3, p 525) for more detailed information. 

The sulfur atom of the thiocarbonyl group is a good nucleophile, and reaction between benzyl bromide and l-(2-thiazolyl)thiourea yields the isothiouronium salt (496). The sulfur atom may also be engaged in a chelate, as exemplified by the Cu chelate of 2-thioureido-4-methylthiazole (491). These chelates with metal ions were thoroughly studied in acidic, neutral, and alkaline media for 66 metal ions in order to define their analytical use. They are formed in the molar ratio of 1 2 for metal II compounds (498). 

On the basis of the values of AS° derived in this way it appears that the chelate effect is usually due to more favourable entropy changes associated with ring formation. However, the objection can be made that and /3l-l as just defined have different dimensions and so are not directly comparable. It has been suggested that to surmount this objection concentrations should be expressed in the dimensionless unit mole fraction instead of the more usual mol dm. Since the concentration of pure water at 25°C is approximately 55.5 moldm , the value of concentration expressed in mole fractions = cone in moldm /55.5 Thus, while is thereby increased by the factor (55.5), /3l-l is increased by the factor (55.5) so that the derived values of AG° and AS° will be quite different. The effect of this change in units is shown in Table 19.1 for the Cd complexes of L = methylamine and L-L = ethylenediamine. It appears that the entropy advantage of the chelate, and with it the chelate effect itself, virtually disappears when mole fractions replace moldm . ... 

Coordination numbers higher than 6 are rare and in some cases are known to involve chelating N03 ions which not only have a small bite but, may also be coordinated asymmetrically so that the coordination number is not well defined. 

Homoleptic lanthanide(III) tris(amidinates) and guanidinates are among the longest known lanthanide complexes containing these chelating ligands. In this area the carbodiimide insertion route is usually not applicable, as simple, well-defined lanthanide tris(alkyls) and tris(dialkylamides) are not readily available. A notable exception is the formation of homoleptic lanthanide guanidinates from... 

In 1994, Kiindig et al. described a related catalyst, in which both CO ligands have been replaced by a chiral F,f -chelate ligand providing evidence that structurally defined cationic Fe sandwich complexes are indeed efficient catalysts for Diels-Alder reactions [33]. 

C18-0042. Use your own words to define (a) buffer solution, (b) stoichiometric point, (c) common-ion effect, and (d) chelate. 

MandyPhos Initial attempts to synthesize defined chelating biphosphine complexes by reacting (1) with established Ruthenium(II) precursors such as [Ru(COD)Cl2]x, [Ru(benzene)Cl2]2, [Ru(p-cymene)Cl2]2, (COD)Ru(Methylallyl)2,... 

Use of the above conditions in conjunction with the enol tosylate 32, provided only low yields of 22, prompting an extensive screening of structurally diverse phosphine ligands/solvents and palladium sources to attempt to define suitable conditions. Quite quickly a number of conditions were found to be effective, with chelating diphosphines being superior to monodentate phosphines (Table 9.7). In... 

A permeable reactive barrier (PRB) is defined as an in situ method for remediating contaminated groundwater that combines a passive chemical or biological treatment zone with subsurface fluid flow management. Treatment media may include zero-valent iron, chelators, sorbents, and microbes to address a wide variety of groundwater contaminants, such as chlorinated solvents, other organics,... 

Ligands with S donors in addition to N and or O donors bound to Co11 are reasonably large in number. For example, the 4-amino-3-alkyl-l,2,4-triazole-5-thione can bind Co11 as a chelate employing the primary amine and thione substituents on the five-membered ring,510 whereas the trifluoromethyl ligand (afmt) forms [Co(afmt)2(H20)2](N03)2, defined as the A -irons isomer... 

Examples in organometallic systems are known. Reaction of thiuram disulfides, (R2NCS2)2, with Co(Cp)(CO)2 produces dithiocarbamato pseudo-octahedral cobalt(III) complexes Co(Cp)(dtc)2 with one chelated and one monodentate dtc, also accessible via Co(Cp)I(dtc).1050 Fluxional behavior, including monodentate chelate exchange, was observed for some complexes in temperature-dependent NMR studies. The Co(Cp)I(dtc) complex was defined in a crystal structure. 

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