Why do nickel complexes form complexes with EDTA

Experiment: copper-glycine complex

In the case of the chelate complexes, individual ligands are connected to the central particle at two or more points. They too align in a symmetrical shape.

They are often complexes with bidentate ligands, such as ethylenediamine for short en:

For example, three lay down en-Molecules octahedral around a nickel (II) ion and form the tris (ethylenediamine) nickel (II) complex [Ni (en)3]2+:

Another example is dimethylglyoxime, for short H2dmg:

Two such ligands form a square-planar complex with a nickel (II) ion, each bound to the two nitrogen atoms, the bis (dimethylglyoximato) nickel (II) [Ni (hdmg)2]2+.

But there are also ligands with six binding sites, the complexes of which are particularly stable. Ethylenediaminetetraacetic acid, in short, is particularly effective edta.

An edta molecule forms especially with divalent metal ions in the complex [Ca (edta)]2- an octahedral structure.

The calcium edta complex

The amino acids are also good chelating ligands. This applies, for example, to the simplest amino acid, glycine.

Two glycine molecules form a deep blue complex with a copper (II) ion (-> experiment).

2 Gly + Cu2+ [Cu (gly)2] + 2H+

This has the following structure.

Colored chelates play an important role in analysis, especially in complexometry. This is used to determine the concentrations of metal ions by titration. Examples: Eriochrome black T for water hardness determination and heavy metal determination with Murexide.

The formation of colored chelates is also the basis for fixing dye molecules on the fibers (stain dyeing).

Further texts on the subject of complex compounds