Carborane

Some tiny things look like little cages.

These cages are made of small bits. They use bits called boron and carbon. They also use hydrogen.

These cages can be many shapes. Some are small. Some are large. They can have 5 to 14 bits in the frame.

Most of these cages have two carbon bits. They can be closed shapes. Some are open shapes.

These tiny shapes can help doctors. They might help treat sick people. Do you like tiny shapes?

Carboranes are tiny clusters of atoms. They are made of boron, carbon, and hydrogen.

Most carboranes form a cage shape. These cages are three-dimensional. This is different from many other organic compounds. Most organic compounds form long chains or rings. Carborane cages can have 5 to 14 atoms in their frame. Most of these cages have two carbon atoms.

These clusters can be many shapes. Some are closed shapes called closo- clusters. Others are open shapes. We call these nido- or arachno- clusters.

Scientists use special rules to understand them. These are called the Wade–Mingos rules. These rules explain how the atoms bond together. The bonds in these cages are special. They are called electron-delocalized bonds. This means the power of the bonds is shared among many atoms.

Carboranes can be used in science. Some can help remove waste from radiowastes. Other types might help doctors treat sick people. They can provide boron for a type of medical care.

Carboranes are fascinating tiny clusters of atoms. They are made of boron, carbon, and hydrogen.

These clusters are called heteroboranes because they use different kinds of atoms. Most carboranes have two carbon atoms in their framework. The size of these clusters can change quite a bit. They can have as few as 5 atoms. Some can have as many as 14 atoms in their cage. These shapes are very important to how they work.

Most carboranes form a three-dimensional cage shape. This is very different from many organic compounds. Most organic compounds form long chains or simple rings. Carborane cages are clusters that look like solid shapes.

These cages can be complete shapes called closo- clusters. Some are missing parts of their shape. We call these open shapes nido-, arachno-, hypho-, or even megalo-. The way the atoms bond is also special. They use electron-delocalized bonding. This means the bonding power is shared across many atoms.

Scientists use special rules to understand these shapes. These are the Wade–Mingos rules. Kenneth Wade first stated these rules in 1971. Michael Mingos expanded on them in 1972. These rules help explain how the atoms bond together. They focus on how the boron, carbon, and hydrogen atoms interact. The rules show how the bonding is shared among the atoms. This helps scientists predict what the clusters will look like.

There are many ways to make these clusters. Most people make them by adding alkynyl reagents to boron hydride clusters. This process usually creates clusters with two carbon atoms.

Some clusters are made by adding one-carbon reagents. These reagents can include things like formaldehyde or cyanide. Scientists can also make smaller clusters by breaking down larger ones. For example, heating ortho-carborane can turn it into meta-carborane. This requires a very high temperature of 700 °C.

Carboranes can be used for many important jobs. Some carboranes are used as superacids. A superacid is a very strong acid.

Some special carborane complexes can even help remove waste from radiowastes. This is done using a substance called bis(dicarbollide). Doctors are also looking at carboranes for medical uses. They can provide boron for boron neutron capture therapy. This could help doctors treat sick people in the future.

Carboranes are unique chemical clusters made of boron, carbon, and hydrogen atoms. They belong to a group called heteroboranes, which are clusters containing different types of atoms. Unlike many organic compounds that form simple chains or rings, carboranes build three-dimensional cage structures. These cages are held together by electron-delocalized bonding. This means the electrons are shared across the entire cluster rather than being stuck between just two atoms.

This shared bonding allows the atoms to form complex, stable polyhedra.

To understand these shapes, scientists use the Wade–Mingos rules. Kenneth Wade first proposed these rules in 1971, and Michael Mingos expanded them in 1972. These rules explain how the multi-centered bonding works between boron, carbon, and hydrogen. The rules help predict the geometry of the cluster based on how many electrons are available. The clusters are categorized by how complete their polyhedral shapes are. A complete shape is called a closo- cluster. If the shape is missing vertices, it receives different names. For example, a nido- cluster is missing one vertex, while an arachno- cluster is missing two. Other types include hypho-, hypercloso-, iso-, klado-, conjuncto-, and megalo- clusters.

Carboranes vary significantly in size. The cage framework can contain as few as 5 atoms or as many as 14 atoms. Most carboranes feature two carbon atoms within the cage. These are often called dicarbaboranes. Some clusters, known as monocarboranes, contain only one carbon atom. These are often made by adding one-carbon reagents like formaldehyde, cyanide, or isocyanides to boron hydride clusters. For instance, monocarbadodecaborate is produced using decaborane and formaldehyde, followed by the addition of borane dimethylsulfide.

There are different ways to prepare these clusters depending on their size. Smaller carboranes are usually built up from smaller parts. For example, pentaborane can react with acetylene to create nido-1,2-carborane. Larger, intermediate-sized clusters are often made by degrading larger clusters into smaller ones. One method involves the chromate oxidation of 11-vertex clusters. This process causes deboronation, which removes a boron atom. The resulting species can then be manipulated through heating, or thermolysis, to create new clusters.

Isomerism is a key feature of carborane structure. Geometrical isomers occur based on where the carbon atoms are located in the cage. In the 12-vertex closo-dicarbadodecaborane family, three specific isomers exist: 1,2-, 1,7-, and 1,12-. These are often called ortho-, meta-, and para-carborane. The 1,2- isomer, or ortho-carborane, is usually the first to form when decaborane reacts with acetylene. If you heat ortho-carborane to 700 °C in an inert atmosphere, it converts into meta-carborane. This process typically has a yield of about 25%. Generally, isomers where the carbon atoms are not next to each other are more thermally stable.

Carboranes also interact with metals to form new structures. Through a process called metalation, carboranes can react with iron carbonyl sources. Base-induced degradation can also create anionic nido-derivatives. These can act as ligands, which are molecules that attach to metals. This creates metallacarboranes, which contain transition metals or main group metals within the cage framework. The most famous of these are dicarbollide complexes.

Research into carboranes has led to several significant applications. In environmental science, bis(dicarbollide) has been used as a precipitant to help remove radiowastes. In medicine, carboranes are being explored for boron neutron capture therapy. This uses the boron within the carborane to help treat certain conditions. Additionally, carborane acid is a powerful superacid. It is strong enough to protonate fullerene. This makes carboranes a vital subject in the study of both highly reactive acids and specialized medical technologies.