Themed collection Polymorphism

Welcome to this CrystEngComm themed issue on Polymorphism.

The development of rational crystallisation strategies in polymorphic systems requires the experimental manipulation of both kinetics and thermodynamics.

Sublimation of p-iso-propylcalix[4]arene (form I_P) under reduced pressure results in the concomitant formation of two new polymorphs (forms II_P and III_P).

Detailed analysis of the two polymorphic solid state forms of p-cresol are presented and possible transformation of the two forms are proposed.

Analysis of intermolecular interactions using purely geometric criteria can be misleading: glycine exhibits apparently ideal H-bonding geometry for dimers with repulsive interaction energies.

Pseudopolymorphs of binary cocrystals of the host and cyclododecene constitute ternary cocrystals.

Two cocrystals of piroxicam (PRX) and 2,5-dihydroxybenzoic acid (HBA) were found using a microfluidic cocrystal screening approach; one crystal contained an acetone (ACT) impurity.

The compound isonicotinic acid (E)-(1-phenylethylidene)hydrazide exists in 6 different structural forms isolated through complex manipulations on a Kofler hot stage.

In situ Raman surface mapping on a trihydrate sample provides evidence for the existence of a transient phase X on the route to its stable anhydrous polymorph I. The phase transformation events are observed in the order trihydrate → transient phase → form I.

The role of temperature in polymorphism and the isolation of configurational isomers of 2-fluoro-N′-(3-fluorophenyl)benzimidamide have been investigated.

Isotopomeric polymorphism is observed in complexes of isonicotinamide with oxalic acid, highly unusual here in that each isotopic complex is itself polymorphic, a situation of “double polymorphism”. The four polymorphic forms exhibit different degrees of hydron transfer.

Lattice energy, entropy and free energy differences for over 500 pairs of known polymorphs are computed and discussed.

The polytypic α₁ and α₂ polymorphs of piroxicam are described and it is shown that they can be crystallized controllably.

Solid form screen of anti-hyperammonemic drug carglumic acid (CGA) resulted in two polymorphs, Form-I and Form-II. The crystal structure of Form-I is sustained by an acid catemer synthon, whereas Form-II has an acid–amide heterosynthon. Slurry grinding, thermal stress, stability measurements, and DVS analysis confirm the thermodynamic stability of Form-I.

Evidence that theophylline forms aggregates in H-bond donor solvents, and the presence of these aggregates hinders the nucleation and phase transformation to form IV.

The descriptors were determined, which can be most efficiently applied to virtual screening in order to provide answers to the following questions: 1) what is the propensity to form a solid state hydrate of a pharmaceutical compound, and 2) which coformer would provide for the highest stability with respect to relative humidity conditions?

4-Hydroxypiperidine 1 exists in two crystal forms, tetragonal 1t with axial NH and orthorhombic 1o with equatorial NH.

¹⁴N solid-state NMR is useful for differentiating polymorphs and chemically distinct nitrogen-containing compounds. A case study of glycine is presented.

The solid-state identity of 2-hydroxynicotinic acid is unveiled to be its tautomer, 2-oxo-1,2-dihydro-3-pyridinecarboxylic acid (2-ODHPCA), by both experimental and computational means. Four distinctive crystal structures are discovered of the compound.

The robustness of supramolecular synthons in two lamivudine salts with hydrobromic and hydrofluoric acids and the role of the five-membered ring conformation in the assembly of a polymorph of lamivudine hydrochloride.

Cocrystals of boronic acids in combination with L-proline, nicotinamide and isonicotinamide have been structurally characterized.