What is "pentaborane"

n. (context inorganic compound English) Either of two boranes containing five boron atoms, but especially the stable compound B₅H₉ once proposed as a rocket fuel

Pentaborane, also called pentaborane(9) to distinguish it from pentaborane(11) (BH), is an inorganic compound with the formula BH. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity toward oxygen, it was once evaluated as rocket or jet fuel. Like many of the smaller boron hydrides, pentaborane is colourless, diamagnetic, and volatile.

Pentaborane(11) is inorganic compound with the chemical formula BH. It is a colorless liquid at room temperature with a boiling point of 63 °C.