X-ray structural comparison of the modes of inclusion of meclofenamate sodium and diclofenac sodium by β-cyclodextrin

The X-ray structure of the 1 : 1 meclofenamate sodium-beta-cyclodextrin complex has been determined. It crystallises in the orthorhombic system, space group P2(1)2(1)2(1), D-x = 1.440 g.cm(-3), D-m = 1.44(1) g.cm(-3), a = 15.087(2) Angstrom, b = 17.967(2) Angstrom, c = 29.634(4) Angstrom and Z = 4. Refinement yielded a final R-value of 0.076 for 5349 observed reflections. The mode of inclusion of the nonsteroidal anti-inflammatory drug in beta-cyclodextrin is compared with that of its structural isomer diclofenac sodium, as determined in an earlier crystallographic study. The latter indicated a 1 : 1 diclofenac sodium-beta-cyclodextrin complex belonging to the hexagonal system, space group P6(1), with a = 15.956(8) Angstrom, c = 50.95(1) Angstrom and Z = 6. Gross features of the modes of inclusion of meclofenamate sodium and diclofenac sodium are similar, but there are several weak host-guest interactions in the complex with diclofenac sodium which are not observed in the other complex. The crystal packing arrangements are different, that of the diclofenac sodium complex being unique and having a layered appearance while that of the meclofenamate sodium complex resembles the arrangement observed in the majority of known heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin complexes.