TM - substitution of ligands

what are the three monodentate ligands

Cl-, NH3 and H2O

which two are similar in size

NH3 and H2O

what happens when these ligands are exchanged

there is no change in co-ordination number

substitution may be incomplete

Co2+ and Cu2+ example

[Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4(H2O)2]2+ + 4H2O

Co2+ initially undergoes the normal deprotonation reaction with 2NH3

with four NH3 = all of ligands substituted as NH3 is better ligand

pale yellow solution formed

[Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 2OH- + 4H2O

is Cl- larger or smaller ligand

larger and charged

exchange of ligand for Cl- does?

change co-ordination number and charge of overall complex potentially

reactions

[CuCl4]2- formed, can also be done with Fe3+ or Co2+

which ligands are bidentate

H2NCH2CH2NH2 and (C2O4)2-

what ligand is multidentate

EDTA4-

why might there be no enthalpy change in substitution reaction

ligand-metal bonds have similar enthalpy to previous ligand-metal bond

same number of bonds broken and made

what is the haem complex

iron (II) complex w multidentate ligand

what does the haemoglobin do

oxygen forms co-ordinate bond with Fe(II) in the haemoglobin, enables oxygen to be transported around

what is the problem with CO2

carbon dioxide is a better ligand - binds more strongly to haemoglobin than oxygen does so is toxic

what is the chelate effect

the tendency of bidentate/multidentate ligands to replace monodentate ligands in complexes

why does this occur

enthalpy usually negligible as same number of same type of similar bonds being broken and formed

entropy increases/entropy change is positive as disorder increases due to more particles being formed than reactants

free-energy change is negative so reaction is more feasible