Question 1

What is the difference between denticity and coordination number?

Accepted Answer

Denticity is the number of donor atoms supplied by one ligand. Coordination number is the total number of donor atoms attached to the central metal atom or ion, so it is calculated by adding the donor contributions of all ligands.

Question 2

Why is ethylenediamine called a bidentate ligand?

Accepted Answer

Ethylenediamine, often written as en, can bind to the same metal ion through both of its nitrogen atoms. One en ligand therefore has denticity 2 and contributes two to the coordination number.

Question 3

What is a chelate ring?

Accepted Answer

A chelate ring forms when one ligand binds to a central metal atom or ion through two or more donor atoms. Ethylenediamine and the metal form a five-membered chelate ring represented as M-N-C-C-N.

Question 4

Do two NH3 ligands and one ethylenediamine ligand give the same coordination number?

Accepted Answer

Yes, if both NH3 molecules and both nitrogen atoms of one en ligand are attached, the coordination number is two. The ligand counts differ: there are two NH3 ligands but only one en ligand.

Question 5

Is oxalate a monodentate or bidentate ligand?

Accepted Answer

Oxalate, C2O4^2-, is bidentate because it can coordinate through two oxygen donor atoms. A single oxalate ligand can therefore contribute two donor atoms to the coordination number.

Ligand Bench: Denticity and Chelation in Coordination Compounds

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