Inclusion Compounds of Plant Growth Regulators in Cyclodextrins. Part VI. Study of the Inclusion Compound of MCPA in β-Cyclodextrin by X-Ray Crystallography

摘要

The structure of the 4-chloro-2-methylphenoxyacetic acid (MCPA) inclusion compound in β -Cyclodextrin (β -CD) has been investigated by X-ray crystallography. The inclusion complex crystallizes in the P2_1 space group with unit cell dimensions a = 15.860(2) ?, b = 24.275 (5) ?, c = 19.334(6) ? and β = 108.80(3)°. Its asymmetric unit contains two β -CD molecules which host two disordered MCPA guest molecules (2:2 host:guest stoichiometry) occupying overall five sites. It also contains 16.13 water molecules distributed over 36 sites. One water molecule is entrapped inside the dimeric cavity, forming a hydrogen bond with the chlorine atom of a guest. The two complexes of the asymmetric unit are located alongside and they form head-to-head dimers with the symmetry related complexes by the 2-fold screw axis (b -axis). The dimers form channels developed along the a -axis. Graphical Abstract