The Crystal Structure of Anhydrous β-Caffeine as Determined from X-ray Powder-Diffraction Data

The crystal structure of the low‐temperature form of anhydrous caffeine has been determined by using X‐ray powder‐diffraction data with a combined simulated‐annealing/Rietveld method. Anhydrous caffeine crystallises with five crystallographically independent molecules in a monoclinic C‐centred unit cell with dimensions of a=43.0390(17), b=15.0676(6) and c=6.95314(14) Å and a β angle of 99.027(2)°. Caffeine crystals: A further piece in the jigsaw puzzle of the solid‐state behaviour and crystal forms of caffeine has been put into place. The complexity of the crystal structure of anhydrous caffeine (see figure) is a hint at why all earlier attempts to elucidate this structure failed.