Ligands - Online Tutor, Practice Problems & Exam Prep

• Ligands are molecules or ions that act as Lewis bases by donating at least one lone pair to a metal cation, which acts as a Lewis acid.
• Ligands can be neutral (e.g., ammonia, water, carbon monoxide) or negatively charged (e.g., hydroxide ion, halide ions, cyanide ion, thiocyanate ion).
• Neutral ligands like ammonia and water have lone pairs that can be donated to metal cations.
• Negatively charged ligands, such as cyanide, have a negative charge typically located on an atom that donates a lone pair to the metal cation.
• In ligand reactions, the product formed by the interaction of a ligand (Lewis base) and a metal cation (Lewis acid) is called an adduct.
• The overall charge of an adduct is the sum of the charges of the metal cation and the ligand(s).
• An example of an adduct is the complex formed between a cadmium ion (Cd2+) and four water molecules, resulting in a 2+ overall charge.

Ligand Types

In this video, we're going to talk about the ligand types. Now ligands themselves represent molecules or ions that act as Lewis bases and donate at least one lone pair to a metal cation. Remember, a Lewis base is an electron paired donor. The metal cation will behave as a Lewis acid and accept that lone pair. When we talk about ligand types though, we're talking about neutral ones versus negatively charged ones or anionic ones.

Now cationic or cationic like ligands, those with positive charges do exist, but we don't talk about those types within Gen. Cam O for right now. Just realize that the ligands that we're going to observe are either going to be neutral or negatively charged. If we take a look here for our neutral ones we have ammonia. It's a ligand because we have this lone pair which we could donate to a metal cation. If we chose water, we could donate one of these.

Here We have carbon monoxide here in this structure. Overall it is neutral, but if you were to do formal charges of the carbon and the oxygen, carbon will be negative, oxygen will be positive, and it's the negatively charged end that would be donating its lone pair. Also remember that carbon ideally wants to make four bonds. So out of the two it's the one that wants to make a bond. It's only making three here O₂. Both of those oxygens are the same. Either one could donate a lone pair to our metal cation.

On the other side we have our aniotic ligands or ligands, those that have negative charge O. We have hydroxide ion. We have X^-. Remember X represents A halogen, those in Group 7A, so it could be fluorine, chlorine, bromine or iodine. We have our cyanide ion again the negative charges on the carbon here, so it's what will donate its loan payer. Then we have here a file signing ion. In this case we have lone pairs. In terms of this we could have the formal charge of negative on the nitrogen, so it could donate its lone pairs if it chooses to to our metal cation.

So for right now, remember ligands or ligands represent Lewis spaces where they can donate a lone pair. We can have them either be neutral or them be negatively charged. In either case, they will donate a lone pair to a metal cation.

Ligands Example

Here it says which of the following would represent a neutral ligand or ligand. So here we have bromide, hydrogen sulfide, ammonium ion, hydroxide ion and cyanide ion. First of all remember we said that the ligand types that we will focus on in Gen. chem are either neutral or negatively charged. Ammonium ion is positive so it's going to be out.

Next we have bromide. I'd means it has a negative charge -1, so that's out. Hydroxide eyed again, negative charge, that's out. Cyanide, CN CN-. That's out. The answer is B. Here, hydrogen sulfide represents H₂S. H₂S is similar to H₂O. Remember H₂O we saw as a common type of neutral ligand or ligand.

So hydrogen sulfide will fit the same bill, substituting out the oxygen for sulfur. It'll behave in the same way. So in this case, option D represents our neutral form of a ligand.

Ligand Reaction

Now, a ligand reaction kind of coincides with something we've seen before. Recall that the adduct equals the product of a Lewis base and acid reaction. So remember a ligand or ligand represents a Lewis base. It's donating a lone pair to a metal cation which represents our Lewis acid.

Now when we talk about adduct, we're adding them together. The overall charge of an adduct equals the sum of the metal cation plus ligand or ligand charge O. If we take a look here, we have our metal cation in the form of Cadmium ion. We have our ligands which is water here. This is a metal cation which can accept the lone pair, so it represents our Lewis acid, and we're going to say here that water can use one of its lone pairs and donate it to that metal cation. So this is our Lewis base.

Now it could be multiple waters attaching to this cadmium, not just necessarily one. Here we have our adduct, we have in fact 4 water molecules attaching themselves to 1 cadmium ion. So here because it's an ion, we put it in brackets and the charge is going to be on the outside. Cadmium has a 2 plus charge. The four water molecules that we're adding to it are all neutral. So their charge is 0.

So the overall charge would be the charge of the metal cation plus the charges of the ligands. So overall that's going to be two plus. So this would be the overall charge of our adduct product between our cadmium ion and four water molecules.

Ligands Example

Determine the add up product when a nickel 3 ion combines with two bromide ions. All right. So we have nickel 3 plus and it's going to combine with two bromide ions. It's going to be ionic in nature.

So we have the plus three from the nickel. Each bromide ion is -1 and there's two of them. So that's -2 we'd have left over for our overall charge, A + 1. So here this addict has a charge and because of that we have to place it within brackets.

So this represents our adapt product.

Determine the charge of the metal cation in the given adduct product below:

• A. +1
• B. 0
• C. –2
• D. +3
• E. +2

Determine the type of ligand connected to the calcium ion.

• A. Neutral
• B. Anionic
• C. Cationic
• D. Not enough information given.

Determine the overall charge of the adduct when the aluminum ion combines with 2 bromides and 1 chlorides.

• A. +1
• B. 0
• C. –2
• D. –1
• E. +2