Pentaborane, also known as B5H9, is a chemical compound composed of five boron (B) atoms and nine hydrogen (H) atoms. It is a member of the boranes family, which consists of boron-hydrogen compounds. Pentaborane is a highly reactive and pyrophoric liquid, which means it ignites spontaneously upon exposure to air.

Here are some important points about pentaborane:

1. Structure: Pentaborane has a three-dimensional cluster structure with five boron atoms and nine hydrogen atoms. It is a complex and unstable molecule.
2. Pyrophoric: Pentaborane is highly reactive with air and moisture. Upon exposure to air, it ignites spontaneously, releasing heat and burning with a green flame.
3. Rocket Propellant: Pentaborane has been considered as a potential rocket propellant due to its high energy content. However, its extreme reactivity and hazards associated with storage and handling have limited its practical use.
4. Research Reagent: Pentaborane has been used in research laboratories as a source of boron atoms in various chemical reactions.
5. Safety Concerns: Due to its pyrophoric nature, pentaborane poses significant safety challenges and must be handled with extreme caution in a controlled environment with specialized equipment.

It is important to note that pentaborane is considered extremely hazardous and is not used in most laboratory or industrial settings due to its extreme reactivity and potential for accidents. Proper safety protocols and protective equipment are essential when working with pentaborane or any other pyrophoric substance.