Caffeine (0.01 mol)and maleic acid

Caffeine (0.01 mol)and maleic acid (0.07 mol) were added to 30 mL of acetone at 25
C and stirred for 5 min to dissolve the majority of the solid and create a mixture having the overall composition (4.51% caffeine, 22.99% maleic acid, 72.50% acetone) lying in region 4 of the ternary diagram (Figure 5). The stirring was stopped and after 1 h needle-like crystals of suitable size for single-crystal XRD were obtained. The unit cell parameters were found to be a= 6.7565(2), b= 12.4860(3), c= 15.7929(5) A˚ , R= 90.00, β= 93.998(3), γ= 90.00, volume = 1329.07 A˚ 3,which agreed well with those reported previously by Trask et al.for the 1:1 cocrystal. Powder samples could also be prepared in this way, but in addition were made by both dry and solvent drop grinding. Dry grinding of maleic acid (1 mmol) and