Boron trifluoride

Boron trifluoride is the inorganic compound with the formula BF3. This strong-smelling, colourless, and toxic gas forms white vapor in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.
Unlike the aluminium and gallium trihalides, the boron trihalides are all separate molecules that do not attach to each other. They undergo rapid halide exchange reactions.