Question

Put Cu-acetate, Cu-citrate, Cu-oxalate, and CuCO3 in order of increasing stability constant, explain why you put them in that order.

Answer 1

Increasing order of stability constant is cu-acetate <CuCO3<Cu-citrate< cu-oxalate. As we saw in this trend the cu-oxalate have maximum stability constant then citrate followed by correspondingly co3 and then acetate. First of all we need to know stability constant which is an equilibrium constant for formation of complex. It is defined as due to interaction between two reagents correspondingly. The formation of complex is based on several factors such as steric, size and chelate effect according to which we differentiate between the complexes such as which among all is max stable and what's the order. The order as i given above in which oxalate complex has maximum stability constant because as oxalate contains two donor oxygen atoms, thus it is known as bidentate ligand, also as a ligand donates from two sites, such ligand are known as chelating ligands and this effect is known as chelation effect. This effect increases stability of complex. Thus as a chelating ligand binds from two donor atoms, it forms ring, more is the formation of rings by ligand more will be the stability of complex. Thus as oxalate complex form 5 membered ring which is highly stable ring, this this complex has maximum stability constant followed by citrate complex. The citrate complex also acts as chelating ligand- bidentate ligand, it forms 7/8 membered ring with the central metal atom which is less stable than 5 membered ring. Also other factor here comes more in picture that is bulky effect. As citrate is bulky ligand it has bulky group attached with donor oxygen ligand, thus there's repulsion between donor atom and bulky group which weakens the metal-ligand bond Thus Cu-citrate complex is less stable than oxalate. After that carbonato comes, whose cu complex is less stable than Cu-citrate because as it's also a bidentate ligand but it forms 4 membered ring with central metal ion which makes it less stable than citrate complex (7/8 membered ring). Also co3 complex is less stable than citrate complex because in the citrate complex there's only one citrate ligand that forms(7/8 membered rings) whereas in carbonate complex, the complex is formed by two carbonato ligands that formed 4 membered rings each. As in citrate only one ligand form complex it will be more stable than that formed by two ligands or more. Thus by similar reason we say that acetate complex is least stable among them because as it's a monodentate ligand also it's use four ligands to form complex. Thus as it's a monodentate ligand, it can't form chelate complex, thus it is least stable. Thus as how we explained the above order written.