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Temperature-Dependent Phase Transitions in Two Crystalline Host–Guest Complexes Derived from Mandelic Acid

“…In the course of these studies we found a reversible phase transition of the crystalline inclusion compounds with dimethylformamide (DMF). (a), (/7) and (c) Weber et al (1996Weber et al ( , 1997a, respectively.…”

“…A new class of chiral crystalline host compounds derived from natural mandelic acid has been previously synthesized, see (I) (Weber et al, 1996(Weber et al, , 1998a. These compounds present two hydroxyl groups, one being attached to the chiral center of the molecule, and three aromatic groups, one derived from mandelic acid.…”

“…These compounds present two hydroxyl groups, one being attached to the chiral center of the molecule, and three aromatic groups, one derived from mandelic acid. These host compounds were tested (Weber et al, 1996(Weber et al, , 1998a with different solvents to obtain information on their inclusion behavior and on their possible usefulness in the separation of racemic mixtures by cocrystallization or vapor inclusion, as in the previously studied lactic acid derivatives (Weber et al, 1992). In order to improve the selectivity of the inclusion, the efficiency of the enantiomer separation and the crystallization properties, we systematically introduced substituents to the chiral mandelic acid precursor [see (I)].…”

“…The absolute configuration of the host in (1) was given by the commercial optically pure mandelic acid precursor. Compound (2) was obtained from a racemic precursor; so its absolute configuration was assigned according to a previous structure determination of the same host molecule in a 1:1 complex with DMSO (Weber et aL, 1998b). Final atomic coordinates for non-H atoms are given in Table 2.…”

“…obtained from a previous obtained from a previous determination (Weber et al,determination (Weber et al, 1998b) 1998b Computer (Altomare et al, 1994) 1994) 1994) 1994) Xtal CRYLSQ (Hall et al, Xtal CRYLSQ (Hall et al, Xtal CRYLSQ (Hall et aL, Xtal CRYLSQ (Hall et al, 1994) 1994) 1994) 1994) Xtal BONDLA CIFIO (HallXtal BONDLA CIFIO (HallXtal BONDLA CIFIO (HallXtal BONDLA CIFIO (Hall et al, 1994(Hall et al, ) et al, 1994(Hall et al, ) et al, 1994(Hall et al, ) et al, 1994 significant differences in terms of bond distances and angles, as shown by half normal probability plots (Nardelli, 1983); the main differences are due to the tert-butyl group conformation and the torsion angle of the C(21)-C(26) phenyl ring in molecule 2 of (2a). Apart from the twist of the phenyl rings at C(1), the observed geometries compare well with those of the previously reported analogous compounds [see (I) (Weber et aL, 1996(Weber et aL, , 1998a].…”