Clathrate compound

Some tiny things act like little cages.

These cages trap other small things inside. They are like tiny houses for molecules.

Some cages are made of water. They can hold gas deep under the ocean. Some cages are made of other materials. Inside these cages, the small things can rattle. This rattling helps keep heat away. We can use these cages to store gas. They can even help make batteries work.

Imagine a tiny cage made of atoms. This cage traps a smaller molecule inside. We call this a clathrate. The word comes from a Latin word meaning "with bars."

Clathrates have two main types. The first type is called a clathrate hydrate. These cages are made of water. They can trap methane gas. This gas stays frozen under the ocean or in frozen ground.

The second type is an inorganic clathrate. These cages are made of different atoms. They are often very strong. In these cages, the guest atom can "rattle" around. This rattling helps stop heat from moving through the material.

Scientists use these cages for many things. They help store gases. They can also help make better batteries. Some clathrates can even act as superconductors. This means they can carry electricity very well. People study them to make new tools for power and energy.

A clathrate is a special kind of chemical substance. It is made of a lattice that traps small molecules inside. The word clathrate comes from a Latin word. That word means "with bars" or "latticed."

You can think of it like a tiny cage. The cage is the host. The molecule inside is called the guest. This structure is very important in science. It helps us understand how atoms can hold onto each other.

There are two main ways these cages work. The first way is through clathrate hydrates. In these, water forms a cage using hydrogen bonds. These cages can trap methane gas. This methane stays frozen in permafrost or under the ocean sea-bed.

The second way is through inorganic clathrates. These have a framework made of inorganic atoms. These atoms are held together by strong covalent bonds. This makes the cages smaller than the water cages. The guest atoms in these cages often rattle around inside.

Scientists study these materials to find new uses. They look at how the guest atoms move. When a guest atom rattles, it scatters phonons. Phonons are things that transport heat. This movement leads to low thermal conductivity. This means heat does not move through the material easily. This is very helpful for making thermoelectric devices. These devices can turn heat into power. Researchers use a design called the phonon glass electron crystal concept.

Many different substances can form these structures. For example, Hofmann clathrates use a formula like Ni(CN)4·Ni(NH3)2(arene). These are used to separate certain hydrocarbons. Other examples include calixarenes and cyclodextrins. Even zeolites can act as hosts. Some inorganic clathrates, like Ba8Si46, can be superconductors. This means they carry electricity very well. Other clathrates use metals like sodium in a silicon framework. One specific formula studied is A8B16X30. In this, A is an alkaline earth metal. B is a group III element. X is an element from group IV.

Clathrates connect to many things we use every day. They can be used for gas storage and gas production. They also help with gas separation and desalination. Some scientists use them to study batteries. They might even be used in photovoltaics to catch sunlight. These tiny cages help us solve big problems with energy. They show how small movements can change how a material works. Even a tiny rattle can help us build better tools for the world.

A clathrate is a unique chemical substance defined by its structure. It consists of a lattice that traps or contains other molecules. The name comes from the Latin word "clathrum," which means "with bars" or "latticed."

This structure is often described as a host-guest system. The host is the large framework that forms the cage. The guest is the smaller molecule trapped inside that cage. According to IUPAC, these are inclusion compounds where a guest molecule resides within a cage. These cages can be formed by a single host molecule or a large lattice of host molecules.

There are two primary categories of clathrates: clathrate hydrates and inorganic clathrates. Each type relies on a specific framework to hold its guests. In clathrate hydrates, the framework is built from water molecules. These water molecules are held together by hydrogen bonds.

Methane clathrates are a famous example of this type. In these, methane molecules are trapped within the water framework. These can be found naturally in permafrost or under the ocean sea-bed. Other hydrogen-bonded networks can be formed using substances like urea, thiourea, or hydroquinone.

Inorganic clathrates work differently than hydrates. Instead of hydrogen bonds, they use a covalently bonded framework of inorganic atoms. This covalent bonding is much stronger than the bonds in hydrates. Because of this strength, the cages in inorganic clathrates are often smaller. The guest atoms in these structures are usually alkali or alkaline earth metals. These guest atoms interact with the host through ionic or covalent bonds. To keep the overall charge of the compound conserved, the substitution of guest atoms follows Zintl rules.

Scientists use different methods to create inorganic clathrates. One common way is through direct reaction using ball milling. This process requires high temperatures or high pressures to work. Another method is crystallization from a melt. Because the host and guest species can vary so much, inorganic clathrates are chemically diverse. They can possess a wide range of physical properties. For instance, some inorganic clathrates can act as insulators. Others, such as Ba8Si46, can function as superconductors.

One of the most interesting properties of inorganic clathrates is low thermal conductivity. This means they do not conduct heat very well. This happens because of the way the guest atoms move inside the cages. The guest atoms can "rattle" within the host framework. This freedom of movement allows the atoms to scatter phonons. Phonons are the particles or waves that transport heat through a material.

By scattering these phonons, the guest atoms effectively slow down the flow of heat.

This ability to control heat and electricity is useful for thermoelectric devices. Researchers use a design strategy called the phonon glass electron crystal concept. In this concept, scientists want a material to behave like a glass for phonons and a crystal for electrons. They aim for low thermal conductivity and high electrical conductivity. This combination is necessary to produce the Seebeck Effect. To achieve this, the guest and host framework must be appropriately tuned. Some clathrates used for this purpose have the formula A8B16X30. In this formula, A is an alkaline earth metal, B is a group III element, and X is a group IV element.

Clathrates are also used for many practical industrial applications. They are explored for gas storage, gas production, and gas separation. They can also be used in desalination, batteries, and photovoltaics. Hofmann clathrates are a notable example used in industry. These are coordination polymers with the formula Ni(CN)4·Ni(NH3)2(arene). They can crystallize with small aromatic guests like benzene or certain xylenes. This specific selectivity allows them to be used commercially for the separation of these hydrocarbons.

Even metal organic frameworks, known as MOFs, can form clathrates.