Crystal polymorphism and crystalline-state photochromism of a rhodium dithionite complex with n-methoxypropyl moieties

A rhodium dinuclear complex having n-methoxypropyltetramethylcyclopentadienyl (CpMPro = η5-C5Me4n-C3H6OCH3) and photoresponsive dithionite (μ-O2SSO2) ligands, [(CpMProRh)2(μ-CH2)2(μ-O2SSO2] (1MPro), was found to form two polymorphic crystals (a previously reported brock-like α-crystal and a...

Luminescent polymorphic crystals: mechanoresponsive and multicolor-emissive properties

Mechanoresponsive luminescent organic crystals have recently attracted increasing interest owing to their potential applications in advanced optoelectronic devices, mechanosensors, security technologies, etc. In the past few years, an increasing number...

Growth of Acetaminophen Polymorphic Crystals and Solution-Mediated Phase Transition from Trihydrate to Form II in Agarose Gel

The growth of acetaminophen polymorphic crystals and the solution-mediated phase transition from trihydrate to form II in agarose gel were investigated. The form II crystals grown in gels, presumably because of the agarose content, dissolved less rapidly at high temperatures and were more stable than in water. The trihydrate crystals in the gel were also expected to be stabilized by containing agarose, but in fact the fine morphology resulted in reduced stability. The solution-mediated phase transition from trihydrate to form II via form II seeding took longer in the gel because the gel slowed down the dissolution of the trihydrate by hindering the dispersion of the form II seeds and delayed the growth of form II by reducing the diffusion rate of the molecules dissolved from the trihydrate. Delays in solution-mediated phase transition and changes in stability for crystals grown in gels indicate the effectiveness of gels in controlling polymorphisms in pharmaceutical compounds.

Multi-color mechanochromic luminescence of three polymorphic crystals of a donor–acceptor-type benzothiadiazole derivative

The past decade has witnessed rapid advances in the development of organic crystals that exhibit mechanochromic luminescence (MCL), i.e., the reversible color change of photoluminescence induced by mechanical force. However,...

Polymorphic crystals of oxacalix[4]arene with 1,3-alternate conformations of S 4 and C 2 symmetry

Calix[4]arene and oxacalix[4]arene derivatives have eight possible conformations in the up and down directions of their four aromatic rings from the mean plane of a bridged central ring, the conformations of which determine the functionality of the host frameworks. Despite being a known compound for five decades, oxacalix[4]arene, C24H16O4, has not been characterized previously by crystallographic methods. It crystallizes from hexane/CH2Cl2 solution to give two polymorphs, i.e. prismatic and block-shaped crystals as twisted 1,3-alternate structures with S 4 and C 2 symmetry, respectively. These were previously suggested as the prefered stable conformations by density functional theory (DFT) calculations.

Modelling of the Polymorph Nucleation based on Classical Nucleation Theory

To elucidate the relative nucleation rates of different polymorphs, a competitive kinetic model is developed based on classical nucleation theory to describe the time evolution of two different polymorphic cluster size distributions controlled by the association and dissociation of the solute molecules during polymorph nucleation. Although there is only one type of the solute molecules, the agglomerated solute clusters are divided into two types–A form and B form, which resemble the structures and morphologies of the different mature polymorphs and eventually lead to the formation of two polymorphic crystals. A dissociation kernel is incorporated into the proposed model to account for gradual dissolution of the solute clusters smaller than a critical nucleus size due to the thermodynamic instability. By fitting the experimental induction period data and the final measured weight fractions of eflucimibe polymorphs with the proposed model, the association and dissociation rate constants for two polymorphs are determined. The developed model is satisfactory to explain the competitive mechanism of polymorph nucleation for eflucimibe that B form dominates at higher supersaturation while A form dominates at lower supersaturation. The results also indicate that A form is more stable than B form with a transition energy of 3.1kJ/mole at 35°C.

Crystal Polymorphism of 1-Butyl-3-methylimidazolium Hexafluorophosphate: Phase Diagram, Structure, and Dynamics

The ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6), is one of the most representative ILs. Despite its relatively simple ion structure and popularity, [C4mim]PF6 shows complex and confusing thermal phase behaviours, which stem from crystal polymorphism associated with cation conformational change and large thermal hysteresis. To the best of our knowledge, [C4mim]PF6 is the most investigated IL in terms of phase diagram, whereas full understanding has not yet been achieved due to its complexity. Here we review the current status of understanding of the phase diagram and structure/dynamics of each crystalline phase. Presently, depending on temperature and pressure, five structurally different polymorphic crystals have been reported as α, β, γ, δ, and δ’ in addition to some unspecified phases implied by calorimetric studies. Particularly for the α, β and γ phases, the structure and dynamics are well investigated by Raman, NMR, and X-ray scattering techniques.