Ligand polydentate

Aurophilic attraction has been almost synonymous with Au(I)-Au(I) attraction. However some complexes which contain short d10-d8 Au(I)-Au(III) and d8-d8 Au 

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Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

The Schiff basses derived from salicylaldehydes polydentate ligands ai e known to form very stable complexes with transition metal ions [1]. 

We detenuined the influence of oxy- and ketocarboxylic acids (succinate, fumarate, adipinate, a-ketoglutarate, isocitrate, tartrate, E-malate) on the luminescence intensity of the Eu-OxTc complex. These substances interact as polydentate ligands similarly to citrate with the formation of ternary complexes with Eu-OxTc. As to succinate, fumarate, adipinate and a-ketoglutarate this they cannot effectively coordinate with EiT+ and significant fluorescence enhancement was not observed. 

Another group of very effective ligands that have recently been employed to coordinate alkali metal cations are the macrobicyclic polydentate ligands that J.-M. Lehn has termed... 

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... 

Substitution reactions of square planar complexes involving polydentate ligands. R. J. Mureinik, Rev. Inorg. Chem., 1979,1,1-50 (123). 

The behaviour of polydentate ligands containing sulphinyl groups has received much less attention. Giesbrecht and Osorio203 have reported the coordination compounds of bivalent transition metal (Mn2+, Co2+, Ni2+, Cu2 +, Cu2+, Zn2+) perchlorates with 2,2 -sulphinyldiethanol (SDE). 

Complexes with coordination number 6 tend to be octahedral those with coordination number 4 are either tetrahedral or square planar. Polydentate ligands can form chelates. 

Charles s law The volume of a given sample of gas at constant pressure is directly proportional to its absolute temperature V T. chelate A complex containing at least one polydentate ligand that forms a ring of atoms including the central metal atom. Example [Co(en)3]3+. chemical analysis The determination of the chemical composition of a sample. See also qualitative, quantitative. 

Table 1-4. Some typical polydentate ligands and their complexes.

When two or more donor atoms from the same ligand are coordinated to a single metal centre, the ligand is said to be chelating. It is a general observation that chelated complexes of polydentate ligands are always more thermodynamically stable than those of the same metal with an equivalent number of comparable monodentate ligands. That is to say, the equilibrium... 

The Chelate Effect and Polydentate Ligands 147 Table 8-1. Stability constants for some nickel(ii) complexes of ammonia and 1,2-diaminoethane. 

There are more examples of a second type in which the chirality of the metal center is the result of the coordination of polydentate ligands. The easiest case is that of octahedral complexes with at least two achiral bidentate ligands coordinated to the metal ion. The prototype complex with chirality exclusively at the metal site is the octahedral tris-diimine ruthenium complex [Ru(diimine)3 with diimine = bipyridine or phenanthroline. As shown in Fig. 2 such a complex can exist in two enantiomeric forms named A and A [6,7]. The bidentate ligands are achiral and the stereoisomery results from the hehcal chirality of the coordination and the propeller shape of the complex. The absolute configuration is related to the handness of the hehx formed by the hgands when rotated... 

The synthesis of di- or tri-nudear pentafluorophenyl derivatives by the use of polydentate ligands with [AulCgFsjltht)] is quite a general procedure as shown in Table 3.4. Many of these complexes have been characterized by X-ray diffraction and show short Au Au contacts as in [(CgFsjAulSdppmSjAulCfiFs)] [88] of 3.163(1) Aor in the dinuclear complex [57] shown in Figure 3.8 of 3.4671(9) A. 

Polynuclear Au(I) pentafluorophenyl complexes can also be obtained by reaction of [AulCfiFsjItht)] with polydentate ligands or with gold complexes that still have different coordination sites or can be created before the subsequent reaction. The ligands or complexes that react with [Au(C6F5)(tht)] and the complexes obtained are listed in Table 3.6. 

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