Question

Which of the following ligands can be polydentate? If the ligand can be polydentate, give the maximum number of places on the ligand that can bind simultaneously to a single metal center: (a) chloride ion; (b) cyanide ion; (c) ethylenediaminetetraacetate; (d) \(\mathrm{N}\left(\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)_{3}\).

Short answer

Chloride and cyanide ions are monodentate. Ethylenediaminetetraacetate is hexadentate with six binding sites, and Triethylenetetramine is tetradentate with four binding sites.

Step-by-step solution

Define Polydentate Ligands

Polydentate ligands, also known as chelating ligands, are molecules or ions that can form multiple bonds to a single metal ion using different atoms within the same ligand. These atoms are referred to as donor atoms.

Analyze Chloride Ion

A chloride ion (Cl-) can only donate through one site as it has only one atom with lone pair of electrons that can be used to coordinate to a metal center, making it a monodentate ligand.

Analyze Cyanide Ion

A cyanide ion (CN-) also can only donate through one site as it has one carbon atom with a triple bond to nitrogen and one lone pair of electrons that can be used to coordinate to a metal center, making it a monodentate ligand.

Analyze Ethylenediaminetetraacetate

Ethylenediaminetetraacetate (EDTA) is a well-known hexadentate ligand. It has four oxygen atoms and two nitrogen atoms that can bind to a metal center simultaneously, giving it six potential binding sites.

Analyze Triethylenetetramine

Triethylenetetramine is denoted as \(\mathrm{N}\left(\mathrm{CH}_{2} \mathrm{CH}_{2}\mathrm{NH}_{2}\right)_{3}\). This ligand has three nitrogen atoms from the amine groups and one nitrogen atom from the central amine that can bind to the metal center, making it a tetradentate ligand with four potential binding sites.

Key concepts

Chelating Ligands

Ligands are like friends to metals; they love to stick around and hang out. Chelating ligands are special because they don't just hold on with one hand, they use multiple! Imagine having a friend who gives you a big bear hug – that's how chelating ligands bond with metal ions. They wrap around the metal using two or more 'hands' (which are actually donor atoms), making the connection much stronger. This kind of attachment isn't just for fun; it's super useful in many areas, like cleaning water and treating illnesses.

Let's put it into a real-world context. Think of EDTA, the molecule from our exercise – it's like an octopus with six arms to grab onto metals, making it a super strong chelator! This is why chelators are like the superheroes in the chemistry world – they form these super bonds that are tough to break!

Coordination Chemistry

Coordination chemistry is the reason metals can have such complex social lives. It's the study of compounds that form between metal ions and ligands. Picture a dance floor where metals are looking for partners to dance with. Ligands step in with their 'lone pair' of electrons like hands ready for a dance, and when they connect, boom, chemistry happens – literally!

In this dance, metals can have one dancing partner or even a lively group, depending on how many hands (donor atoms) the ligands extend. Some dances form simple moves with monodentate ligands, or more complicated routines with polydentate ligands that can make multiple connections. Who knew metals had such interesting social dances?

Monodentate Ligand

A monodentate ligand is like a pal who shakes your hand with just one hand. It's the simplest kind of ligand and attaches to metal ions at only one point. The handshake isn't as strong as a group hug, but it is still a friendly connection.

Remember chloride and cyanide ions from our exercise? They are like those friends with only one 'hand' to offer – straightforward but reliable. While these one-on-one connections are simple, they're also super important. They're the building blocks for understanding the larger and more complex buddies like EDTA, who come along with more 'hands' to connect.

Hexadentate Ligand

A hexadentate ligand is like a many-armed creature from a sci-fi show – it can attach to a metal ion in six places all at once! Just think of our friend EDTA from the exercise, which can use four oxygen atoms and two nitrogen atoms to create a powerful bond with the metal.

This spectacular bonding Ability isn't just cool, it's incredibly useful. Hexadentate ligands create such stable complexes with metals that they're used in medicine to capture rogue metals that could harm our bodies, as well as in industrial processes to purify metals. It's kind of like how a super cleaner can remove stains in a flash – very handy!

Tetradentate Ligand

Imagine you're playing a game where you need to connect dots, and you have a piece that can cover four dots at once – that's what a tetradentate ligand does in the world of chemistry. It can connect to a metal ion at four different places. In our exercise, the ligand with a mouthful of a name, triethylenetetramine, shows how one molecule can grab onto a metal ion and hold tight at four points.

These four-point connectors are like a safety harness that keeps a climber secure on all sides – it's a bond that gives metal ions a whole lot of stability. In fact, tetradentate ligands are so good at stabilizing metals that they're used everywhere from manufacturing to medicine!