A series of cocrystals involving theophylline and fluorobenzoic acids highlights the difficulty of predicting supramolecular interactions in molecular crystals.MKC and DKB gratefully acknowledge financial support from the UCL Faculty of Mathematical and Physical Sciences. DKB and WJ thank the Royal Society for a Newton International Fellowship and the Isaac Newton Trust (Trinity College, University of Cambridge) for funding. MA thanks the EPSRC for a studentship, while SAS acknowledges funding through the EPSRC CASE scheme with Pfizer. We are grateful for computational support from the UK national high performance computing service, ARCHER, for which access was obtained via the UKCP consortium and funded by EPSRC grant (EP/K013564/1).This is the final version of the article. It first appeared from the Royal Society of Chemistry via https://doi.org//10.1039/C6CE00293
