Crystal engineering
Encyclopedia
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
engineering are based on hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
ing and coordination complexation. These may be understood with key concepts such as the supramolecular synthon
Synthon
A synthon is a concept in retrosynthetic analysis. It is defined as a structural unit within a molecule which is related to a possible synthetic operation. The term was coined by E.J. Corey...
and the secondary building unit.
History of term
The term ‘crystal engineering’ was first used in 1971 by Schmidt in connection with photodimerisation reactions in crystalline cinnamic acidCinnamic acid
Cinnamic acid is a white crystalline organic acid, which is slightly soluble in water.It is obtained from oil of cinnamon, or from balsams such as storax. It is also found in shea butter and is the best indication of its environmental history and post-extraction conditions...
s. Since this initial use, the meaning of the term has broadened considerably to include many aspects of solid-state supramolecular chemistry
Supramolecular chemistry
Supramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components...
. A useful modern definition is that provided by Gautam Radhakrishna Desiraju
Gautam Radhakrishna Desiraju
Gautam Radhakrishna Desiraju is an Indian chemist who works in the Solid State and Structural Chemistry Unit of the Indian Institute of Science, Bangalore. He works in the area of supramolecular chemistry and crystal engineering. Desiraju has played a major role in the development of crystal...
, who in 1988 defined crystal engineering as "the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding in the design of new solids with desired physical and chemical properties." Since many of the bulk properties of molecular materials are dictated by the manner in which the molecules are ordered in the solid state, it is clear that an ability to control this ordering would afford control over these properties.
Non-covalent control of structure
Crystal engineering relies on noncovalent bondingNoncovalent bonding
A noncovalent bond is a type of chemical bond, typically between macromolecules, that does not involve the sharing of pairs of electrons, but rather involves more dispersed variations of electromagnetic interactions. The noncovalent bond is the dominant type of bond between supermolecules in...
to achieve the organization of molecules and ions in the solid state. Much of the initial work on purely organic
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
systems focused on the use of hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s, though with the more recent extension to inorganic systems, the coordination bond has also emerged as a powerful tool. Other intermolecular forces such as π…π, halogen…halogen, and Au…Au interactions have all been exploited in crystal engineering studies, and ionic
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...
interactions can also be important. However, the two most commonly used strategies in crystal engineering exploit hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s and coordination bonds.
Molecular self-assembly
Molecular self-assembly
Molecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly...
is at the heart of crystal engineering, and it typically involves an interaction between complementary hydrogen-bonding faces or a metal and a ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
. By analogy with the retrosynthetic
Retrosynthetic analysis
Retrosynthetic analysis is a technique for solving problems in the planning of organic syntheses. This is achieved by transforming a target molecule into simpler precursor structures without assumptions regarding starting materials. Each precursor material is examined using the same method. This...
approach to organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
, Desiraju coined the term “supramolecular synthon” to describe building blocks that are common to many structures and hence can be used to order specific groups in the solid state. The carboxylic acid dimer represents a simple supramolecular synthon, though in practice this is only observed in approximately 30% of crystal structures in which it is theoretically possible. The Cambridge Structural Database
Cambridge Structural Database
The Cambridge Structural Database , is a repository for small molecule crystal structures. Scientists use single-crystal x-ray crystallography to determine the crystal structure of a compound. Once the structure is solved, information about the structure is saved in a file and deposited in the CSD...
(CSD) provides an excellent tool for assessing the efficiency of particular synthons. The supramolecular synthon approach has been successfully applied in the synthesis of one-dimensional tapes, two-dimensional sheets and three-dimensional structures. The CSD today contains atomic positional parameters for nearly 300 000 crystal structure
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
s, and this forms the basis for heuristic or synthon-based or "experimental" crystal engineering.
In two dimensions
The study and formation of 2D architectures (i.e., molecularly thick architectures) has rapidly emerged as a branch of engineering with molecules . The formation (often referred as molecular self-assemblyMolecular self-assembly
Molecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly...
depending on its deposition process) of such architectures lies in the use of solid interfaces to create adsorbed monolayers. Such monolayers may feature spatial crystallinity in an investigated time-window, thus the terminology of 2D crystal engineering is well suited . However the dynamic and wide range of monolayer morphologies ranging from amorphous to network structures have made of the term (2D) supramolecular engineering a more accurate term. Specifically, supramolecular engineering refers to "(The) design (of) molecular units in such way that a predictable structure is obtained" or as "the design, synthesis and self-assembly of well-defined molecular modules into tailor-made supramolecular architectures".
Polymorphism
PolymorphismPolymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
is the phenomenon wherein the same chemical compound exists in different crystal forms. In the initial days of crystal engineering, polymorphism was not properly understood and incompletely studied. Today, it is one of the most exciting branches of the subject partly because polymorphic forms of drugs may be entitled to independent patent protection if they show new and improved properties over the known crystal forms. With the growing importance of generic drugs, the importance of crystal engineering to the pharmaceutical industry is expected to grow exponentially.
Specialized journals
Crystal engineering is a rapidly expanding discipline as revealed by the recent appearance of several international scientific journalScientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
s in which the topic plays a major role. These include CrystEngComm
CrystEngComm
CrystEngComm is a peer-reviewed online-only scientific journal publishing original research and review articles on all aspects of crystal engineering including properties, polymorphism, target materials and crystalline nanomaterials. CrystEngComm is published biweekly by the Royal Society of...
from the Royal Society of Chemistry
Royal Society of Chemistry
The Royal Society of Chemistry is a learned society in the United Kingdom with the goal of "advancing the chemical sciences." It was formed in 1980 from the merger of the Chemical Society, the Royal Institute of Chemistry, the Faraday Society and the Society for Analytical Chemistry with a new...
and Crystal Growth and Design from the American Chemical Society
American Chemical Society
The American Chemical Society is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 at New York University, the ACS currently has more than 161,000 members at all degree-levels and in all fields of chemistry, chemical...
.
See also
- Coordination polymersCoordination polymersA coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands, extending in an array. It can also be described as a polymer whose repeat units are coordination complexes...
- crystal nets (periodic graphs)Periodic graph (crystallography)In crystallography, a periodic graph or crystal net is a three dimensional periodic graph, i.e., a three-dimensional Euclidean graph whose vertices or nodes are points in three-dimensional Euclidean space, and whose edges are line segments connecting pairs of vertices, periodic in three linearly...
- CrystallographyCrystallographyCrystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
- Laser-heated pedestal growthLaser-heated pedestal growthLaser-heated pedestal growth is a crystal growth technique. The technique can be viewed as a miniature floating zone, where the heat source is replaced by a powerful CO2 or YAG laser...
- CrystEngCommCrystEngCommCrystEngComm is a peer-reviewed online-only scientific journal publishing original research and review articles on all aspects of crystal engineering including properties, polymorphism, target materials and crystalline nanomaterials. CrystEngComm is published biweekly by the Royal Society of...
- CrystEngCommunityCrystEngCommunityCrystEngCommunity is a virtual web community for people working in the field of crystal engineering. The website is owned by the Royal Society of Chemistry ....
- Hydrogen bondHydrogen bondA hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
- Molecular design softwareMolecular Design softwareMolecular design software is software for molecular modeling, that provides special support for developing molecular models de novo.In contrast to the usual molecular modeling programs such as the molecular dynamics and quantum chemistry programs, such software directly supports the aspects related...
- Supramolecular chemistrySupramolecular chemistrySupramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components...
- Self-assemblySelf-assemblySelf-assembly is a term used to describe processes in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction...
- Molecular self-assemblyMolecular self-assemblyMolecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly...