Zintl phase
Encyclopedia
In chemistry
a Zintl phase is the product of a reaction between
Zintl phases were named for the German chemist Eduard Zintl
who investigated them in the 1930s. The term "Zintl Phases was first used by Laves
in 1941.
Zintl phases are a subgroup of brittle
, high melting point intermetallic compounds which are diamagnetic
or exhibit temperature-independent paramagnetism
, are poor conductors or semiconductor
s. Zintl noted that there was an atomic volume contraction when these compounds were formed and realised this could indicate cation formation. He suggested that the structures of Zintl phases were ionic, where there was complete electron transfer from the more electropositive metal. The structure of the anion
(nowadays called the Zintl ion) should then be considered on the basis of the resulting electronic state. These ideas were further developed to become the Zintl rule or Zintl Klemm concept, where the polyanion structure should be similar to an isoelectronic element.
Examples of Zintl phases:
, which contrasts to group 14 and above that tend to form salts with polymer
ic anions. It is now recognised that some Zintl phases contain Zintl clusters
and that this accounts for the variable stoichiometries. The bonding in many of these clusters cannot be accounted for by classical octet rule
involving covalent, 2-centre, 2-electron bonds, as implied by the Zintl rule. The reaction of Ge, Sn or Pb and Na in liquid NH3 in the presence of ethylene diamine
(en) gives the Zintl cluster Na4en7Sn9.
calculations have shown that the anion is (In11)7− and that the extra electron is distributed over the cations and, possibly, the anion antibonding orbitals.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
a Zintl phase is the product of a reaction between
- group 1 (alkali metalAlkali metalThe alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
s) or group 2 (alkaline earths) and - post transition metalMetalA metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s or metalloidMetalloidMetalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...
s from group 13, 14, 15 or 16.
Zintl phases were named for the German chemist Eduard Zintl
Eduard Zintl
Eduard Zintl was a German chemist.After his family moved from Weiden and Bayreuth to Munich and after he had finished school he was drafted for military service during World War I. At the age of 21 he started studying at the University of Munich with Otto Hönigschmid. He got his PhD at the age of...
who investigated them in the 1930s. The term "Zintl Phases was first used by Laves
Fritz Laves
-References:...
in 1941.
Zintl phases are a subgroup of brittle
Brittle
A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...
, high melting point intermetallic compounds which are diamagnetic
Diamagnetism
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the...
or exhibit temperature-independent paramagnetism
Paramagnetism
Paramagnetism is a form of magnetism whereby the paramagnetic material is only attracted when in the presence of an externally applied magnetic field. In contrast with this, diamagnetic materials are repulsive when placed in a magnetic field...
, are poor conductors or semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s. Zintl noted that there was an atomic volume contraction when these compounds were formed and realised this could indicate cation formation. He suggested that the structures of Zintl phases were ionic, where there was complete electron transfer from the more electropositive metal. The structure of the anion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
(nowadays called the Zintl ion) should then be considered on the basis of the resulting electronic state. These ideas were further developed to become the Zintl rule or Zintl Klemm concept, where the polyanion structure should be similar to an isoelectronic element.
Examples of Zintl phases:
- NaTl, where it is now known that the structure consists of a polymeric anion (-Tl
− -)n with a covalent diamond structure with Na+ ions fitted into the anionic lattice. - NaSi where the polyanion is tetrahedralTetrahedronIn geometry, a tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids...
(Si4)4− similar to phosphorusPhosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
moleculeMoleculeA molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
P4. - Na2Tl which the polyanion is tetrahedral (Tl4)8
− similar to phosphorus molecule P4.
Zintl line
The Zintl line is a hypothetical boundary drawn between group 13 and group 14, to highlight the tendency for group 13 metals to form phases with a variety of stoichiometriesStoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
, which contrasts to group 14 and above that tend to form salts with polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic anions. It is now recognised that some Zintl phases contain Zintl clusters
Cluster chemistry
In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...
and that this accounts for the variable stoichiometries. The bonding in many of these clusters cannot be accounted for by classical octet rule
Octet rule
The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low (The octet rule is a chemical rule of thumb that states that atoms of low (...
involving covalent, 2-centre, 2-electron bonds, as implied by the Zintl rule. The reaction of Ge, Sn or Pb and Na in liquid NH3 in the presence of ethylene diamine
Ethylene diamine
Ethylenediamine is the organic compound with the formula C2H42. This colorless liquid with an ammonia-like odor is a strongly basic amine. The liquid fumes upon contact with humid air...
(en) gives the Zintl cluster Na4en7Sn9.
Exceptions
There are examples of a new class of compounds that, on the basis of their chemical formulae, would appear to be Zintl phases, e.g., K8In11, which is metallic and paramagnetic. Molecular orbitalMolecular orbital
In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The term "orbital" was first...
calculations have shown that the anion is (In11)7