Crystallographic evidence of side-arm lariat effect in the series of chiral ortho- and para-methoxyphenoxymethyl-15-crown-5 complexes with sodium perchlorate

Structural aspects of partial solid solution formation: two crystalline modifications of a chiral derivative of 1,5-dihydro-2H-pyrrol-2-one under consideration

“…Although the number of symmetry-independent molecules does not relate to the enthalpy or entropy of a solid phase directly, in all probability, Z′ > 1 provides more flexibility to accommodate the packing, which could contribute to or contradict the best crystal formative motif. 23,[28][29][30] Moreover, the presence of a second and more "extra" symmetrically independent molecule in crystals is often accompanied by the pseudosymmetry phenomenon, 31 which we exemplified earlier in glycerol derivatives 20,21 and a pair of mucochloric acid polymorphs.…”

“…It is worth noting that the choice of the space group P2 1 rather than P2 1 /n was clear for the experiment at 150 K but was more ambiguous for the room temperature data. The E-statistics suggest a centrosymmetric space group but this behavior can be explained, especially at 293 K, by the pseudosymmetry of the crystal structure, 21,23,45 which increases with heating. The data measured at 150 K include 137 unique h0l (<I/σ(I)> = 3.9), h + l odd reflections, 41 of which have I > 3σ(I) and 15 have I > 10σ(I).…”

Intricate Phase Behavior and Crystal Structure Features of Chiral para-Methoxyphenyl Glycerol Ether Forming Continuous and Partial Solid Solutions

“…Furthermore, the molecules of one site are supposed to have geometry similar to an antipode of molecules from the other site. Only the molecules located on the particular strained site (in practice they show chiral mimicry described above and conformational disorder ,, ) are substituted, while the molecules of the other site are not affected. Such substitution results in a molecular compound.…”

“…If this does not lead to a significant loss in the enthalpy, the entropy factor could make a significant contribution to the free energy of crystal formation and even provides thermodynamic preference of the structure with high disordering. Most obviously the above-described effect is manifested in the cases of exotic and poorly studied continuous − and partial − mixed crystals, or, in other words, solid solutions. Behavior of a solid solution could be additionally complicated owing to transition into ordered phase (phase layering) at low temperatures.…”

Solubility- and melting-based approaches to evaluate the inner-crystal enantiophobia and enantiophilia undergoing a structural change within a homologous series, exemplified by chiral glycerol ethers

“…1,3,13,14 They are also interested in other rare ways of crystallising chiral matter. [15][16][17][18][19][20][21][22][23][24][25][26][27][28] However, it is possible that the reasons for chiral discrimination lie precisely in trivial heterochiral crystallisation, which is much more common than homochiral crystallisation, and understanding these reasons may lead to insights into the relationship sought. In particular, it is possible to systematically change the structure of a chemical compound, analysing how this affects the manner it crystallises.…”