Exchange Multidentate

Ligand Exchange Multidentate.—Kinetic studies of exchange of amino-carboxylate ligands at metal cations are listed in Table 13. Further studies of carbonate exchange at cis- and at // anj-[Co(en)(NH3)a(C03)]+ in basic solution confirm earlier postulations of parallel reaction by bimolecular 

Mechanisms of ligand exchange for complexes of multidentate ligands 

Zirconium tetrakistetrahydroborate, Zr(BH4)4, is effectively a twelve-co-ordinate complex of zirconium(iv), for there are twelve hydrogens, three 

The complex [Eu(N03)3(LL)a], with LL = 4,4 -di-n-butyl-2,2 -bipyridyl, appears to contain ten-co-ordinate europium(iii). The rate of exchange of the substituted bipyridyl with the complex is, in chloroform solution, independent of the concentration of added bipyridyl, indicating a dissociative mechanism. The activation parameters for the exchange are -5.7 kcal mol and AS = — 40 cal deg mol. This surprisingly negative value for the activation entropy is explained by solvation effects.  

Ligand Exchange Multidentate.— Exchange of acac with [Co(acac)3] takes place just sufficiently faster than decomposition of the complex for the kinetics of acac exchange to be monitored. The rate law is 

Kinetics of exchange of edta with two of its rare-earth complexes have been described - for La + and for Lu +. In the former case, catalysis by hydroxide ion was observed. Rates and mechanisms of ligand exchange for pdta and eddda complexes of Cd +, Zn +, and Pb + have been derived from n.m.r. line-broadening observations. On the basis of these ligand-exchange results and earlier kinetic data it is possible to establish the mechanisms of complex formation for these and related complexes.  

The rate law for ligand exchange at [Nd(tren)2] + in acetonitrile solution, established by n.m.r. line-broadening techniques, is 

Sulphate exchange with the i -sulphato-dichromium complexes (39) and (40) has been monitored by S labelling. Rates depend on pH  

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Another possible source of a phosphorus pendant group was [(2-dihydro grarsinoylphenylamino)methyl]phosphonic acid, which was used to modify the Amberlite XAD-16 polymeric matrix. Subramanian et al. also modified the polystyrene-divinylbenzene copolymer beads (Amberlite XAD-16) by anchoring 6,6,6-trifluoro-2,5-dioxo-4-(thiophene-2-carbonyl)he yl-phosphinic acid in its matrix in order to obtain a new chelating ion-exchange multidentate grafted polymer (Scheme 11.9). ... 

In this chapter, we will focus only on the latest reports, first dealing with a ligand-free system and later with multidentate N,N- and N,0-ligand systems. As a general rule of thumb, non-heme iron catalysts work best if they have exchangeable ligands [28]. 

As discussed above, the ligands that have been typically utilized for the preparation of chromium nitrides are multidentate. Consequently, ligand exchange reactions of such complexes are difficult and rare. Wieghardt and co-workers have reported such a process, however, for the synthesis of a nitrido chromium cyanide complex 43 (Eq. (13)) [18]. Thus, treatment of CrN(salen) 42 with excess sodium cyanide and tetramethyl ammonium chloride results in the formation of a six-coordinate penta-cyano chromium nitride [21]. 

In these reactions M and M represent metal ions or oxoions L and L represent ligands which, for reactions (2) and (3), are usually multidentate. (Other reactions, such as single ligand exchange between two metal ions, will not be as important in the internal environment, and will not be considered here). 

All three oxidation states of vanadium found in living systems form stable complexes with a wide variety of mono- and multidentate ligands. Ions of these three oxidation states form complexes rapidly they are therefore labile. As mentioned on page 142, bimolecular complex formation rate constants for monomeric vanadate species are approximately 104 M V1. Water exchange rate constants are 280s 1 for V3+, and 500s 1 for V02+ at 25 °C52. ... 

ANKB-33 resin is an iminodiacetic acid exchanger this multidentate chelating functionality is capable of forming metal coordination complexes with different stabilities [10,31]. 

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