Insights into the crystallisation process from anhydrous, hydrated and solvated crystal forms of diatrizoic acid

Design, screening, and properties of novel solvates of azoxystrobin based on isomorphism

The molecular size of the solvent is important for the formation of isomorphic azoxystrobin solvates.

The diiodomethyl-sulfonyl moiety: an unexplored halogen bond-donor motif

The α-iodosulfone moiety acts as a new and effective halogen bond donor system in the solid state and in solution.

Navigating the Waters of Unconventional Crystalline Hydrates

Elucidating the crystal structures, transformations, and thermodynamics of the two zwitterionic hydrates (Hy2 and HyA) of 3-(4-dibenzo[b,f][1,4]oxepin-11-yl-piperazin-1-yl)-2,2-dimethylpropanoic acid (DB7) rationalizes the complex interplay of temperature, water activity, and pH on the solid form stability and transformation pathways to three neutral anhydrate polymorphs (Forms I, II°, and III). HyA contains 1.29 to 1.95 molecules of water per DB7 zwitterion (DB7^z). Removal of the essential water stabilizing HyA causes it to collapse to an amorphous phase, frequently concomitantly nucleating the stable anhydrate Forms I and II°. Hy2 is a stoichiometric dihydrate and the only known precursor to Form III, a high energy disordered anhydrate, with the level of disorder depending on the drying conditions. X-ray crystallography, solid state NMR, and H/D exchange experiments on highly crystalline phase pure samples obtained by exquisite control over crystallization, filtration, and drying conditions, along with computational modeling, provided a molecular level understanding of this system. The slow rates of many transformations and sensitivity of equilibria to exact conditions, arising from its varying static and dynamic disorder and water mobility in different phases, meant that characterizing DB7 hydration in terms of simplified hydrate classifications was inappropriate for developing this pharmaceutical.

Conserved hydrogen bonding in tetrahydrocarbazolone derivatives: influence of solution-state assembly on crystal form nucleation

Two tetrahydocarbazolone derivatives were found to show multiple unsolvated crystal forms. A persistent dimer motif was detected in solution by FTIR spectroscopy that is maintained in the kinetic crystal forms. Rationally introduced steric bulk induces the formation of a more stable catemeric form.