Crystal chemistry
The Crystal Chemistry (κρύσταλλος (krystallos) = ice; χημεία (chemeia) = Chemie) is a branch of the crystallography and deals with the relationships between the chemical composition of crystalline materials and their structural composition , and the resulting physical properties. It is the link between the fields of crystallography and chemistry . A related subject is structural chemistry , which is a branch of physical chemistry , and solid-state chemistry (branch of chemistry).
“[The aim of crystal chemistry is] ... to determine regular relationships between the chemical composition and the physical properties of crystalline substances. In particular, it is the task of crystal chemistry in the narrower sense to find the way in which the crystal structure depends on the chemical composition. "
history
Crystal chemistry developed from mineralogy (around 300 BC Theophrastus : "About stones") and later from crystallography (1669 Nicolaus Steno : angle constancy on rock crystals). In the 19th century the development was driven by the invention of the reflection goniometer ( William Hyde Wollaston 1809), the discovery of isomorphism and polymorphism by Eilhard Mitscherlich (1819) and enantiomorphism by Louis Pasteur (1840).
At the beginning of the 20th century, the first X-ray diffraction experiments on crystals ( Walter Friedrich , Paul Knipping and Max von Laue 1912) were an important step towards systematic crystal structure analysis. From 1923 to 1926 Goldschmidt , who is considered a co-founder of crystal chemistry, set up his structural principles for simple compounds. The main rule of these structural principles, as stated in Geochemical Distribution Laws of the Elements, VII, page 9 , is: “The crystal structure of a substance is determined by the size and polarization properties of its components; components are atoms (or ions) and groups of atoms. "
Fundamentals of crystal chemistry
Goldschmidt and Fritz Laves set up the postulates of space fulfillment for the construction of stable crystal structures with the smallest possible lattice energy (the atoms / ions in these postulates are viewed purely geometrically as rigid spheres):
- Space principle: The atoms / ions are packed as closely as possible
- Symmetry principle: The crystal has the highest possible symmetry
- Interaction principle: Every atom / ion surrounds itself with as many neighbors as possible
The atomic or ionic radius (which can vary depending on the type of bond ) also plays a role. For example, the structure of the crystal structure of some chemical compounds (such as the mineral olivine (Mg, Fe) 2 [SiO 4 ]) can be explained by the fact that one type of atom forms a close packing of spheres and the other (smaller) types of atoms occupy the remaining gaps.
The type of chemical bond in a crystal can be homodesmic (one type of bond predominates) or heterodesmic (stable, isolated groups of atoms or complexes that are in turn embedded in a larger unit). The pyrite FeS 2 is an example of a heterodesmic compound (covalent between the sulfur atoms, ionic between sulfur and iron).
For crystals with predominantly ionic bonds ( ionic crystals ), Pauling's rules of linkage apply .
Investigation methods
The most important investigation methods of crystal chemistry are the structural analysis methods based on z. B. X-ray or neutron diffraction and methods of analytical chemistry (in particular instrumental analysis, which includes spectroscopy ) and physical chemistry (determination of phase diagrams and phase transformations ).
Systematics
Crystal chemistry divides crystalline compounds into structure types, which are classified according to the type of stoichiometric compound and the order in which they were discovered. This classification goes back to the structural report developed by Hermann and Ewald . The sequence of discovery is numbered (1,2, ...), the stoichiometry or type of bond is identified by a letter:
- A: elements (e.g. Au )
- B: AB connections (e.g. NaCl )
- C: AB 2 compounds (e.g. FeS 2 )
- D: A n B m compounds (e.g. Al 2 O 3 )
- E:> 2 elements without pronounced complex formation (e.g. CaTiO 3 )
- F: with two- or three-atom complexes (e.g. NaNO 2 )
- G: with four-atom complexes (e.g. Na 2 CO 3 )
- H: with five-atom complexes (e.g. Na 2 SO 4 )
- L: alloys (e.g. amalgams )
- M: mixed crystals (e.g. NaCl / AgCl )
- S: Silicates (e.g. Al 2 SiO 5 )
"C4", for example, is the " rutile type " (TiO 2 ), "E2" is the " ilmenite type " (FeTiO 3 ), which is derived from the α-Al 2 O 3 structure by alternately replacing the Al layers can be derived from Fe and Ti.
literature
- Robert C. Evans: Introduction to Crystal Chemistry . Gruyter, 1976, ISBN 978-3-11-003976-4 .
- Anthony R. West, Cameron West: Basic Solid State Chemistry . Wiley & Sons, 1999, ISBN 978-0-471-98756-7 .
- Heinz Krebs: Fundamentals of inorganic crystal chemistry . Enke, 1968.
- Will Kleber , Hans-Joachim Bautsch , Joachim Bohm : Introduction to crystallography . Oldenbourg, 1998, ISBN 978-3-341-01205-5 .
- Linus Pauling: The nature of chemical bonds . Verl. Chemie, 1968.
- Nathaniel Warren Alcock: Bonding and Structures: Structural Principles in Inorganic and Organic Chemistry . Ellis Horwood, 1990, ISBN 978-0-13-465253-5 .
- IUCR publication "50 Years of X-ray Diffraction" (especially Chapters 9 and 11)
- Structure type database of the University of Freiburg
Trade journals
Individual evidence
- ↑ Crystal Chemistry University Leipzig script (PDF; 6.0 MB).