Boron's chemistry is largely governed by it only having 3 electrons in its outer shell. As a result it tends to form 3 covalent bonds leaving one p-orbital unoccupied which can accept lone pairs of electrons. What is unusual in diboranes is that whilst a covalently bound hydrogen has no lone pairs, two molecules containing boron hydrogen bonds can share hydrogens in a form known colloquially as banana bonding due to its shape. This was first proposed by Longuet-Higgins while still an undergraduate chemist at Balliol college Oxford.
More info about the International Year of the Periodic Table (IYPT) in crystals project:
This project (#IYPTCrystals) is part of the International Year of the Periodic Table celebration (#IYPT2019), read more about the project here. You can follow us on social media using #IYPTCrystals and learn more about the wonders of crystals by following the CCDC on Twitter @ccdc_cambridge on Facebook ccdc.cambridge, on Instagram ccdc_cambridge or on YouTube CCDCCambridge.
If you want to find out more about some of the terms and concepts we have a Frequently Asked Questions Page.