Polymorphism in molecular crystals

1 Introduction and historical background; 1.1 Introduction; 1.2 Definitions; 1.2.1 Polymorphism; 1.2.2 Pseudopolymorphism, solvates, and hydrates; 1.2.3 Conventions for naming polymorphs; 1.3 Is this material polymorphic?; 1.3.1 Occurrence of polymorphism; 1.3.2 Literature sources of polymorphic compounds; 1.3.3 Polymorphic compounds in the Cambridge Structural Database; 1.3.4 Powder Diffraction File; 1.3.5 Patent literature; 1.3.6 Polymorphism of elements and inorganic compounds; 1.3.7 Polymorphism in macromolecular crystals; 1.4 Historical perspective 1.5 Commercial/industrial importance of polymorphism-some additional comments2 Fundamentals; 2.1 Introduction; 2.2 Thermodynamics of polymorphic molecular crystals; 2.2.1 The Phase Rule; 2.2.2 Thermodynamic relations in polymorphs; 2.2.3 Energy vs temperature diagrams-the Gibbs free energy; 2.2.4 Enantiotropism and monotropism; 2.2.5 Phase diagrams in terms of pressure and temperature; 2.2.6 Heat-of-transition rule; 2.2.7 Heat-of-fusion rule; 2.2.8 Entropy-of-fusion rule; 2.2.9 Heat-capacity rule; 2.2.10 Density rule; 2.2.11 Infrared rule 2.3 Kinetic factors determining the formation of polymorphic modifications2.4 Structural fundamentals; 2.4.1 Form vs habit; 2.4.2 Structural characterization and comparison of polymorphic systems; 2.4.3 Presentation of polymorphic structures for comparison; 3 Controlling the polymorphic form obtained; 3.1 General considerations; 3.2 Aggregation and nucleation; 3.3 Thermodynamic vs kinetic crystallization conditions; 3.4 Monotropism, enantiotropism, and crystallization strategy; 3.5 Concomitant polymorphs; 3.5.1 Crystallization methods and conditions 3.5.2 Examples of different classes of compounds3.5.3 The structural approach; 3.6 Disappearing polymorphs; 3.7 Control of polymorphic crystallization by design; 4 Analytical techniques for studying and characterizing polymorphs; 4.1 Introduction; 4.2 Optical/hot stage microscopy; 4.3 Thermal methods; 4.4 X-ray crystallography; 4.5 Infrared spectroscopy; 4.6 Raman spectroscopy; 4.7 Solid state nuclear magnetic resonance (SSNMR) spectroscopy; 4.8 Scanning electron microscopy; 4.9 Atomic force microscopy (AFM) and scanning tunnelling microscopy (STM); 4.10 Density measurements 4.11 New technologies and 'hyphenated techniques'4.12 Are two samples polymorphs of the same compound?; 4.13 Concluding remarks; 5 Conformational polymorphism: intra- and intermolecular energetics; 5.1 Introduction; 5.2 Molecular shape and energetics; 5.3 Intermolecular interactions and energetics; 5.4 The search for examples of conformational polymorphism; 5.5 Presenting and comparing conformational polymorphs; 5.6 Some examples of conformational polymorphism; 5.7 What are conformational polymorphs good for?; 5.8 Computational studies of the energetics of polymorphic systems