An attempt to describe, at a molecular level, solid-solid transformations between copper-(II) oxinates of known structure is presented. On the basis of experimental data and by modeling the molecular movements, it is shown that the dehydration of the stable dihydrated form (β) takes place with the transmission of structural information from the parent to the daughter phase, so that a coherence is maintained. After the departure of water molecules through channels, the resulting unstable new anhydrous material (NAM) reorganizes rapidly toward one of the two closest energy minima: X′ or β′, depending on whether an adduct is present or not in the parent structure. Polymorphic transitions from the anhydrous metastable forms (β′, γ ′, X′) to the stable form (β′′) are described by a nucleation and growth mechanism, with a complete loss of the structural information contained in the parent phase. Both proposed mechanisms (continuous and cooperative processes for the dehydration, and nucleation and growth mechanism for the polymorphic transitions) are consistent with available experimental results: crystal structures, routes of preparation, evolution of the crystal size distribution (CSD), specific surfaces, SEM photographs, and DSC results. An extension of this study together with several other examples led to a unified model for the dehydration mechanism of molecular crystals being proposed. Four decisive topological, energetic, and physical criteria are proposed. The mechanisms are related to the possible filiation of structural information and fall into two categories: class I mechanisms are associated with the absence and class II mechanisms correspond to the presence of structural filiation. Each class is divided into several subclasses according to the process of release of water molecules (cooperative or destructive) and to the eventual process of reorganization (cooperative or through a nucleation and growth process).

This contribution focuses primarily on chiral discrimination in the solid state, i.e. the formationof conglomerates, how to detect them and the various benefits that can be retrieved from chiral recognitionin crystal lattices.The core of the work is devoted to phase diagrams (mainly binary and ternary). The stable and metastableheterogeneous equilibria are depicted and used to understand different variants of preferential crystallizationand how the entrainment effect proceeds. Seeded and auto-seeded processes are analyzed minutely. The seedingprocedure has a significant impact on the control of stereoselective secondary nucleation and crystalgrowth.The review ends with a systematic analysis of the reasons that can put, sometimes, severe limitationson the entrainment effect.

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The aim of the tutorial review is to show that any crystallization from solution is guided by stable or metastable equilibria and thus can be rationalized by using phase diagrams. Crystallization conducted by cooling, by evaporation and by anti-solvent addition is mainly considered. The driving force of crystallization is quantified and the occurrence of transient metastable states is logically explained by looking at the pathways of crystallization and the progressive segregation which might occur in a heterogeneous system.