Problem 17 - Chemistry Central Science

Question

(a) What is the difference between a monodentate ligand and a bidentate ligand? (b) How many bidentate ligands are necessary to fill the coordination sphere of a six-coordinate complex? (c) You are told that a certain molecule can serve as a tridentate ligand. Based on this statement, what do you know about the molecule?

Step-by-Step Solution

Answer

(a) A monodentate ligand forms a single bond to the central metal atom/ion, while a bidentate ligand forms two bonds with the central metal atom/ion, having two donor atoms that can form coordinate covalent bonds simultaneously. (b) To fill the coordination sphere of a six-coordinate complex with bidentate ligands, three bidentate ligands are necessary, as they form a total of six bonds. (c) A tridentate ligand has three donor atoms that can form coordinate bonds with the central metal ion/atom. This means it can occupy three coordination sites at once in a coordination complex.

Step 1: (a) Difference between Monodentate and Bidentate Ligands

A monodentate ligand is a ligand that forms a single bond to the central metal atom/ion in a coordination complex. Examples include Cl-, OH-, and NH3. In contrast, a bidentate ligand is a ligand that forms two bonds with the central metal atom/ion. These ligands have two donor atoms that can form coordinate covalent bonds simultaneously. Examples of bidentate ligands include ethylenediamine (en) with two nitrogen donor atoms and oxalate ion (O2C2O4^2-) with two oxygen donor atoms.

Step 2: (b) Bidentate Ligands in a Six-Coordinate Complex

In a six-coordinate complex, the central metal ion/atom is surrounded by six ligands. To fill the coordination sphere of a six-coordinate complex with bidentate ligands, three bidentate ligands are necessary. This is because each bidentate ligand forms two coordinate bonds with the central metal ion/atom, so three of them will form a total of six bonds.

Step 3: (c) Information about a Tridentate Ligand

If a molecule is said to be a tridentate ligand, it means that it has three donor atoms that can form coordinate bonds with the central metal ion/atom simultaneously. These ligands can occupy three coordination sites at once in a coordination complex. Examples of tridentate ligands include diethylenetriamine (dien) and tris(2-aminoethyl)amine (tren). Knowing that a molecule is a tridentate ligand gives us information about its ability to bond with a central metal ion/atom and the number of coordination sites it can occupy.