Chelate effect-chelation?
Consider the two equilibria, in aqueous solution, between the copper(II) ion, Cu2+ and ethylenediamine (en) on the one hand and methylamine, MeNH2 on the other.
Cu2+ + en is in equilibrium with [Cu(en)]2+ (1)
Cu2+ + 2 MeNH2 is in equilibrium with [Cu(MeNH2)2]2+ (2)
In (1) the bidentate ligand ethylene diamine forms a chelate complex with the copper ion. Chelation results in the formation of a five–membered ring. In (2) the bidentate ligand is replaced by two monodentate methylamine ligands of approximately the same donor power, meaning that the enthalpy of formation of Cu—N bonds is approximately the same in the two reactions. Under conditions of equal copper concentrations and when the concentration of methylamine is twice the concentration of ethylenediamine, the concentration of the complex (1) will be greater than the concentration of the complex (2). The effect increases with the number of chelate rings so the concentration of the EDTA complex, which has six chelate rings, is much much higher than a corresponding complex with two monodentate nitrogen donor ligands and four monodentate carboxylate ligands. Thus, the phenomenon of the chelate effect is a firmly established empirical fact.
Can someone explain the meaning of the phrase starting from "Under conditions of~…..
Thanks
the phrase is ..
Under conditions of equal copper concentrations and when the concentration of methylamine is twice the concentration of ethylenediamine, the concentration of the complex (1) will be greater than the concentration of the complex (2).
put simply
There are two experiments:[1] and [2]
1] Cu2+ concentation =x mol/L, MeNH2 conc = 2y mol/L
2] Also Cu2+ concentation =x moles/L, en conc = y mol/L
Result, the conc of complex resulting in expt 2 is bigger than conc of complex in expt1.
Why?: what this is actually says, is that the bidentate ligand, with 2 coordinate bonds, bonds more strongly to the Cu2+, despite being present in a lower concentration in expt2. This means the equilibria is much more to the right in expt2 and the [Cu(en)]2+ complex is much more stable than the methylamine one.
Why is it confusing? NOT YOUR It is rather confusing what exactly is being referred to in each expt. I think it could have been worded and explained in an easier manner!
June 18th, 2009 at 10:10 pm
the phrase is ..
Under conditions of equal copper concentrations and when the concentration of methylamine is twice the concentration of ethylenediamine, the concentration of the complex (1) will be greater than the concentration of the complex (2).
put simply
There are two experiments:[1] and [2]
1] Cu2+ concentation =x mol/L, MeNH2 conc = 2y mol/L
2] Also Cu2+ concentation =x moles/L, en conc = y mol/L
Result, the conc of complex resulting in expt 2 is bigger than conc of complex in expt1.
Why?: what this is actually says, is that the bidentate ligand, with 2 coordinate bonds, bonds more strongly to the Cu2+, despite being present in a lower concentration in expt2. This means the equilibria is much more to the right in expt2 and the [Cu(en)]2+ complex is much more stable than the methylamine one.
Why is it confusing? NOT YOUR It is rather confusing what exactly is being referred to in each expt. I think it could have been worded and explained in an easier manner!
References :
retired Chemistry examiner