An electride is an ionic compound in which an electron serves the role of the anion. [1] Solutions of alkali metals in ammonia are electride salts. [2] In the case of sodium, these blue solutions consist of [Na(NH3)6]+ and solvated electrons:
The cation [Na(NH3)6]+ is an octahedral coordination complex.
Addition of a complexant like crown ether or [2.2.2]-cryptand to a solution of [Na(NH3)6]+e− affords [Na (crown ether)]+e− or [Na(2,2,2-crypt)]+e−. Evaporation of these solutions yields a blue-black paramagnetic solid with the formula [Na(2,2,2-crypt)]+e−.
Most solid electride salts decompose above 240 K, although [Ca24Al28O64]4+(e−)4 is stable at room temperature. [3] In these salts, the electron is delocalized between the cations. Electrides are paramagnetic, and are Mott insulators. Properties of these salts have been analyzed. [4]
ThI2 and ThI3 have also been reported to be electride compounds. [5] Similarly, CeI
2, LaI
2, GdI
2, and PrI
2 are all electride salts with a tricationic metal ion. [6] [7]
Magnesium reduced nickel(II)-bipyridyl (bipy) complex have been labeled organic electrides. An example is [(THF)4Mg4(μ2-bipy)4]–, in which the electride ion is centered within a square formed by four Mg2+ centers within the larger complex. [8]
"Inorganic electrides" have also been described. [9]
Electride salts are powerful reducing agents, as demonstrated by their use in the Birch reduction. Evaporation of these blue solutions affords a mirror of Na metal. If not evaporated, such solutions slowly lose their colour as the electrons reduce ammonia:
This conversion is catalyzed by various metals. [10] An electride, [Na(NH3)6]+e−, is formed as a reaction intermediate.
Theoretical evidence supports electride behaviour in insulating high-pressure forms of potassium, sodium, and lithium. Here the isolated electron is stabilized by efficient packing, which reduces enthalpy under external pressure. The electride is identified by a maximum in both the electron localization function and the charge density distribution, [11] which distinguishes the electride from pressure-induced metallization. Electride phases are typically semiconducting or have very low conductivity, [12] [13] [14] usually with a complex optical response. [15] A sodium compound called disodium helide has been created under 113 gigapascals (1.12×106 atm) of pressure. [16]
The intrinsic polarization between atomic nucleus and the electron anion in these high pressure electrides will lead to unique properties, such as the splitting of the longitudinal and transverse acoustic modes (i.e., LA-TA splitting, an analogue to the LO-TO splitting in ionic compound), [17] the universal but robust gapless surface state in insulating electride that forming a de facto real space topological distribution of charge carriers, [18] and the colossal charge state of some impurities in them. [11]
Layered electrides or electrenes are single-layer materials consisting of alternating atomically thin two-dimensional layers of electrons and ionized atoms. [19] [20] The first example was Ca2N, in which the charge (+4) of two calcium ions is balanced by the charge of a nitride ion (-3) in the ion layer plus a charge (-1) in the electron layer. [19]
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. The corresponding electrically neutral compound HO• is the hydroxyl radical. The corresponding covalently bound group –OH of atoms is the hydroxy group. Both the hydroxide ion and hydroxy group are nucleophiles and can act as catalysts in organic chemistry.
Sodium is a chemical element; it has symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotope is 23Na. The free metal does not occur in nature and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and halite (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.
In chemistry, a salt or ionic compound is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a neutral compound with no net electric charge. The constituent ions are held together by electrostatic forces termed ionic bonds.
In chemistry, there are three definitions in common use of the word "base": Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century.
In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen atom with two electrons. The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are also called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. For inorganic chemists, hydrides refer to compounds and ions in which hydrogen is covalently attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.
Sodium azide is an inorganic compound with the formula NaN3. This colorless salt is the gas-forming component in some car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance, is highly soluble in water, and is acutely poisonous.
Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula NaBH4. It is a white crystalline solid, usually encountered as an aqueous basic solution. Sodium borohydride is a reducing agent that finds application in papermaking and dye industries. It is also used as a reagent in organic synthesis.
In organometallic chemistry, acetylide refers to chemical compounds with the chemical formulas MC≡CH and MC≡CM, where M is a metal. The term is used loosely and can refer to substituted acetylides having the general structure RC≡CM. Acetylides are reagents in organic synthesis. The calcium acetylide commonly called calcium carbide is a major compound of commerce.
In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a non-carbon radical anion is the superoxide anion, formed by transfer of one electron to an oxygen molecule. Radical anions are typically indicated by .
In the area of solid state chemistry. graphite intercalation compounds are materials prepared by intercalation of diverse guests into graphite. The materials have the formula (guest)Cn where n can range from 8 to 40's. The distance between the carbon layers increases significantly upon insertion of the guests. Common guests are reducing agents such as alkali metals. Strong oxidants, such as arsenic pentafluoride also intercalate into graphite. Intercalation involves electron transfer into or out of the host. The properties of these materials differ from those of the parent graphite.
A solvated electron is a free electron in a solution, in which it behaves like an anion. An electron's being solvated in a solution means it is bound by the solution. The notation for a solvated electron in formulas of chemical reactions is "e−". Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but solvated electrons also occur in water and many other solvents – in fact, in any solvent that mediates outer-sphere electron transfer. The solvated electron is responsible for a great deal of radiation chemistry.
Sodium atoms have 11 electrons, one more than the stable configuration of the noble gas neon. As a result, sodium usually forms ionic compounds involving the Na+ cation. Sodium is a reactive alkali metal and is much more stable in ionic compounds. It can also form intermetallic compounds and organosodium compounds. Sodium compounds are often soluble in water.
An alkalide is a chemical compound in which alkali metal atoms are anions with a charge or oxidation state of −1. Until the first discovery of alkalides in the 1970s, alkali metals were known to appear in salts only as cations with a charge or oxidation state of +1. These types of compounds are of theoretical interest due to their unusual stoichiometry and low ionization potentials. Alkalide compounds are chemically related to the electrides, salts in which trapped electrons are effectively the anions.
Lithium superoxide is an unstable inorganic salt with formula LiO2. A radical compound, it can be produced at low temperature in matrix isolation experiments, or in certain nonpolar, non-protic solvents. Lithium superoxide is also a transient species during the reduction of oxygen in a lithium–air galvanic cell, and serves as a main constraint on possible solvents for such a battery. For this reason, it has been investigated thoroughly using a variety of methods, both theoretical and spectroscopic.
Sodium perrhenate (also known as sodium rhenate(VII)) is the inorganic compound with the formula NaReO4. It is a white salt that is soluble in water. It is a common precursor to other rhenium compounds. Its structure resembles that of sodium perchlorate and sodium permanganate.
Potassium nonahydridorhenate(VII) is an inorganic compound having the formula K2[ReH9]. This colourless salt is soluble in water but only poorly soluble in most alcohols. This salt contains the nonahydridorhenate(VII) anion, [ReH9]2−, which is a rare example of a coordination complex bearing only hydride ligands.
Metal amides (systematic name metal azanides) are a class of coordination compounds composed of a metal center with amide ligands of the form NR2−. Amido complexes of the parent amido ligand NH2− are rare compared to complexes with diorganylamido ligand, such as dimethylamido. Amide ligands have two electron pairs available for bonding.
Pentaamine(nitrogen)ruthenium(II) chloride is an inorganic compound with the formula [Ru(NH3)5(N2)]Cl2. It is a nearly white solid, but its solutions are yellow. The cationic complex is of historic significance as the first compound with N2 bound to a metal center. [Ru(NH3)5(N2)]2+ adopts an octahedral structure with C4v symmetry.
Antimony phosphate, is a chemical compound of antimony and phosphate with formula SbPO4. Antimony is in the form Sb(III) with +3 oxidation state. Antimony atoms have a lone pair of electrons.
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