Metal hydrides
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chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, properties ...

chemistry
, a hydride is formally the
anion An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be po ...
of
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the chemical ...

hydrogen
( H). The term is applied loosely. At one extreme, all compounds containing covalently bound H
atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, l ...

atom
s are called hydrides:
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

water
(H2O) is a hydride of
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
,
ammonia Ammonia is an inorganic chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a dis ...

ammonia
is a hydride of
nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the pnictogens. It is a common element in the ...

nitrogen
, etc. For inorganic chemists, hydrides refer to compounds and
ion An ion () is an atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has n ...
s in which hydrogen is covalently attached to a less
electronegative Electronegativity, symbolized as ''Chi (letter), χ'', is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its ato ...

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. Almost all of the elements form binary compounds with hydrogen, the exceptions being
He
He
,
Ne
Ne
,
Ar
Ar
,
Kr
Kr
,
Pm
Pm
,
Os
Os
,
Ir
Ir
,
Rn
Rn
,
Fr
Fr
, and
Ra
Ra
. Exotic molecules such as
positronium hydride Positronium hydride, or hydrogen positride is an exotic molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisf ...
have also been made.


Bonds

Bonds between hydrogen and the other elements range from highly to somewhat covalent. Some hydrides, e.g.
boron hydrides Boranes is the name given to compounds with the formula BxHy and related anions. Many such boranes are known. Most common are those with 1 to 12 boron atoms. Although they have few practical applications, the boranes exhibit structures and bond ...
, do not conform to classical electron-counting rules and the bonding is described in terms of multi-centered bonds, whereas the interstitial hydrides often involve
metallic bond Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be describ ...
ing. Hydrides can be discrete
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

molecule
s,
oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomer, monomers.Quote: ''Oligomer molecule: A molecule of intermediate ...
s or
polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules called macromolecules, composed of many Repeat unit, repeating subunits. Due to t ...

polymer
s, ionic solids, monolayers, bulk metals (interstitial), or other materials. While hydrides traditionally react as
Lewis base A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty Non-bonding orbital, orbital which is capable of accepting an electron pair from a Lewis Base (chemistry), base to form a Lewis a ...
s or
reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...
s, some metal hydrides behave as hydrogen-atom donors and act as acids.


Applications

200px, Tris(trimethylsilyl)silane is an example of a hydride with a weak bond to H. It is used as a source of hydrogen atoms. *Hydrides such as
sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that ...

sodium borohydride
,
lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula lithium, Lialuminium, Alhydride, H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a re ...

lithium aluminium hydride
,
diisobutylaluminium hydride Diisobutylaluminium hydride (DIBALH, DIBAL, DIBAL-H or DIBAH) is a reducing agent with the chemical formula, formula (''i''-Bu2AlH)2, where ''i''-Bu represents isobutyl (-CH2CH(CH3)2). This Organoaluminum, organoaluminium compound is a reagent in o ...
(DIBAL) and super hydride, are commonly used as
reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...
s in
chemical synthesis As a topic of chemistry, chemical synthesis (or combination) is the artificial execution of chemical reactions to obtain one or several product (chemistry), products. This occurs by physics, physical and chemical manipulations usually involving o ...
. The hydride adds to an electrophilic center, typically unsaturated carbon. *Hydrides such as
sodium hydride Sodium hydride is the chemical compound with the empirical formula NaH. This alkali metal hydride is primarily used as a strong yet combustible base (chemistry), base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and ...
and
potassium hydride Potassium hydride, KH, is the inorganic compound of potassium and hydrogen. It is an alkali metal hydride. It is a white solid, although commercial samples appear gray. It is a powerful superbase that is useful in organic synthesis. It is sold com ...
are used as strong bases in
organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic chemistry, Organic molecules are often more complex than Inorganic chemistry, inorganic compounds, and t ...

organic synthesis
. The hydride reacts with the weak Bronsted acid releasing H2. *Hydrides such as
calcium hydride Calcium hydride is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) containing atoms from more than one chemical element held together by chemical ...
are used as
desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that Absorption (chemistry), a ...
s, i.e. drying agents, to remove trace water from organic solvents. The hydride reacts with water forming
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the chemical ...

hydrogen
and
hydroxide Hydroxide is a polyatomic ion, 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 Self-ionization ...
salt. The dry solvent can then be distilled or vacuum transferred from the "solvent pot". *Hydrides are important in storage battery technologies such as nickel-metal hydride battery. Various metal hydrides have been examined for use as a means of hydrogen storage for
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

fuel cell
-powered electric cars and other purposed aspects of a
hydrogen economy The hydrogen economy is using hydrogen fuel, hydrogen to Low-carbon economy, decarbonize economic sectors which are hard to Electrification, electrify, essentially, the "hard-to-abate" sectors such as cement, steel, long-haul transport etc. In ord ...
. * Hydride complexes are catalysts and catalytic intermediates in a variety of homogeneous and heterogeneous catalytic cycles. Important examples include
hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions e ...

hydrogenation
,
hydroformylation Hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of a formyl group (CHO) and a hydrogen atom to a carbon-carbon do ...

hydroformylation
,
hydrosilylation Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds."Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 2009 ...

hydrosilylation
,
hydrodesulfurization Hydrodesulfurization (HDS) is a catalytic chemical process widely used to desulfurization, remove sulfur (S) from natural gas and from oil refinery, refined petroleum products, such as gasoline, gasoline or petrol, jet fuel, kerosene, diesel fue ...
catalysts. Even certain enzymes, the
hydrogenase A hydrogenase is an enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substra ...
, operate via hydride intermediates. The energy carrier
nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide (NAD) is a Cofactor (biochemistry), coenzyme central to metabolism. Found in all living cell (biology), cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphat ...
reacts as a hydride donor or hydride equivalent.


Hydride ion

Free hydride anions exist only under extreme conditions and are not invoked for homogeneous solution. Instead, many compounds have hydrogen centres with hydridic character. Aside from
electride An electride is an ionic compound in which an electron is the anion. Solutions of alkali metals in ammonia are electride salts. In the case of sodium, these blue solutions consist of a(NH3)6sup>+ and solvated electrons: :Na + 6 NH3 → ...
, the hydride ion is the simplest possible
anion An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be po ...
, consisting of two
electron The electron ( or ) is a subatomic particle with a negative one elementary charge, elementary electric charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are generally thought t ...

electron
s and a
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

proton
. Hydrogen has a relatively low
electron affinity The electron affinity (''E''ea) of an atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety ...
, 72.77 kJ/mol and reacts exothermically with protons as a powerful
Lewis base A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty Non-bonding orbital, orbital which is capable of accepting an electron pair from a Lewis Base (chemistry), base to form a Lewis a ...
. :H- + H+ -> H2 The low electron affinity of hydrogen and the strength of the H–H bond () means that the hydride ion would also be a strong
reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...
:H2 + 2e- <=> 2H-


Types of hydrides

According to the general definition, every element of the
periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an Cultural i ...

periodic table
(except some
noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under Standard conditions for temperature and pressure, standard conditions, they are all odorle ...
es) forms one or more hydrides. These substances have been classified into three main types according to the nature of their bonding: *''Ionic hydrides'', which have significant
ionic bonding Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compou ...

ionic bonding
character. *''Covalent hydrides'', which include the hydrocarbons and many other compounds which covalently bond to hydrogen atoms. *''Interstitial hydrides'', which may be described as having
metallic bonding Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be describ ...

metallic bonding
. While these divisions have not been used universally, they are still useful to understand differences in hydrides.


Ionic hydrides

These are stoichiometric compounds of hydrogen. Ionic or saline hydrides are composed of hydride bound to an electropositive metal, generally an
alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
or
alkaline earth metal The alkaline earth metals are six chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that spec ...
. The divalent
lanthanide The lanthanide () or lanthanoid () series of chemical elements comprises the 15 Metal, metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium a ...
s such as
europium Europium is a chemical element with the Symbol (chemistry), symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is al ...

europium
and
ytterbium Ytterbium is a chemical element with the Symbol (chemistry), symbol Yb and atomic number 70. It is a metal, the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. Ho ...

ytterbium
form compounds similar to those of heavier alkaline earth metals. In these materials the hydride is viewed as a
pseudohalide Pseudohalogens are polyatomic analogues of halogens The halogens () are a group (periodic table), group in the periodic table consisting of five or six chemically related chemical element, elements: fluorine (F), chlorine (Cl), bromine (Br), i ...
. Saline hydrides are insoluble in conventional solvents, reflecting their non-molecular structures. Ionic hydrides are used as bases and, occasionally, as reducing
reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
s in
organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic chemistry, Organic molecules are often more complex than Inorganic chemistry, inorganic compounds, and t ...

organic synthesis
. :\overset + \overset -> C6H5C(O)CH2K + H2 Typical solvents for such reactions are
ethers In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that ...
.
Water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

Water
and other
protic solvent In chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, struct ...
s cannot serve as a medium for ionic hydrides because the hydride ion is a stronger base than
hydroxide Hydroxide is a polyatomic ion, 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 Self-ionization ...
and most
hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom Chemical bond, covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or ...

hydroxyl
anions. Hydrogen gas is liberated in a typical acid-base reaction. :NaH + H2O -> H2_ + NaOH :Δ''H'' = −83.6 kJ/mol, Δ''G'' = −109.0 kJ/mol Often alkali metal hydrides react with metal halides.
Lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula lithium, Lialuminium, Alhydride, H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a re ...

Lithium aluminium hydride
(often abbreviated as LAH) arises from reactions of
lithium hydride Lithium hydride is an inorganic compound with the formula Lithium, LiHydride, H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a Hydride#Ionic hydrides, salt-like (ionic) hydride, it has a ...

lithium hydride
with
aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often conta ...

aluminium chloride
. :\overset + AlCl3 -> LiAlH4 + 3 LiCl


Covalent hydrides

According to some definitions, covalent hydrides cover all other compounds containing hydrogen. Some definitions limit hydrides to hydrogen centres that formally react as hydrides, i.e. are nucleophilic, and hydrogen atoms bound to metal centers. These hydrides are formed by all the true non-metals (except zero group elements) and the elements like Al, Ga, Sn, Pb, Bi, Po, etc., which are normally metallic in nature, i.e., this class includes the hydrides of p-block elements. In these substances the hydride bond is formally a
covalent bond A covalent bond is a chemical bond A chemical bond is a lasting attraction between atoms or ions that enables the formation of Molecule, molecules and crystals. The bond may result from the Coulomb's law, electrostatic force between oppos ...
much like the bond made by a proton in a
weak acid Acid strength is the tendency of an acid An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis a ...

weak acid
. This category includes hydrides that exist as discrete molecules, polymers or oligomers, and hydrogen that has been chem-adsorbed to a surface. A particularly important segment of covalent hydrides are complex metal hydrides, powerful soluble hydrides commonly used in synthetic procedures. Molecular hydrides often involve additional ligands; for example,
diisobutylaluminium hydride Diisobutylaluminium hydride (DIBALH, DIBAL, DIBAL-H or DIBAH) is a reducing agent with the chemical formula, formula (''i''-Bu2AlH)2, where ''i''-Bu represents isobutyl (-CH2CH(CH3)2). This Organoaluminum, organoaluminium compound is a reagent in o ...
(DIBAL) consists of two aluminum centers bridged by hydride ligands. Hydrides that are soluble in common solvents are widely used in organic synthesis. Particularly common are
sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that ...

sodium borohydride
() and
lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula lithium, Lialuminium, Alhydride, H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a re ...

lithium aluminium hydride
and hindered reagents such as DIBAL.


Interstitial hydrides or metallic hydrides

Interstitial hydrides most commonly exist within metals or alloys. They are traditionally termed "compounds" even though they do not strictly conform to the definition of a compound, more closely resembling common alloys such as steel. In such hydrides, hydrogen can exist as either atomic or diatomic entities. Mechanical or thermal processing, such as bending, striking, or annealing, may cause the hydrogen to precipitate out of solution by degassing. Their bonding is generally considered . Such bulk transition metals form interstitial binary hydrides when exposed to hydrogen. These systems are usually
non-stoichiometric In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having chemical element, elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empir ...
, with variable amounts of hydrogen atoms in the lattice. In materials engineering, the phenomenon of
hydrogen embrittlement Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen Hydrogen is the chemical element with the Symbol (chemistry), sy ...

hydrogen embrittlement
results from the formation of interstitial hydrides. Hydrides of this type form according to either one of two main mechanisms. The first mechanism involves the adsorption of dihydrogen, succeeded by the cleaving of the H-H bond, the delocalisation of the hydrogen's electrons, and finally the diffusion of the protons into the metal lattice. The other main mechanism involves the electrolytic reduction of ionised hydrogen on the surface of the metal lattice, also followed by the diffusion of the protons into the lattice. The second mechanism is responsible for the observed temporary volume expansion of certain electrodes used in electrolytic experiments.
Palladium Palladium is a chemical element with the Symbol (chemistry), symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the 2 Pallas, asteroid ...

Palladium
absorbs up to 900 times its own volume of hydrogen at room temperatures, forming
palladium hydride Palladium hydride is metallic palladium that contains a substantial quantity of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and ...
. This material has been discussed as a means to carry hydrogen for vehicular
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

fuel cell
s. Interstitial hydrides show certain promise as a way for safe
hydrogen storage Hydrogen storage can be accomplished by several existing methods of holding hydrogen for later use. These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H2 upon demand ...
. Neutron diffraction studies have shown that hydrogen atoms randomly occupy the octahedral interstices in the metal lattice (in an fcc lattice there is one octahedral hole per metal atom). The limit of absorption at normal pressures is PdH0.7, indicating that approximately 70% of the octahedral holes are occupied. Many interstitial hydrides have been developed that readily absorb and discharge hydrogen at room temperature and atmospheric pressure. They are usually based on
intermetallic An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic bonding, metallic alloy that forms an ordered solid-state Chemical compound, compoun ...
compounds and solid-solution alloys. However, their application is still limited, as they are capable of storing only about 2 weight percent of hydrogen, insufficient for automotive applications.


Transition metal hydride complexes

Transition metal hydrides include compounds that can be classified as ''covalent hydrides''. Some are even classified as interstitial hydrides and other bridging hydrides. Classical transition metal hydride feature a single bond between the hydrogen centre and the transition metal. Some transition metal hydrides are acidic, e.g., and . The anions potassium nonahydridorhenate and are examples from the growing collection of known molecular homoleptic metal hydrides.A. Dedieu (Editor) Transition Metal Hydrides 1991, Wiley-VCH, Weinheim. As
pseudohalide Pseudohalogens are polyatomic analogues of halogens The halogens () are a group (periodic table), group in the periodic table consisting of five or six chemically related chemical element, elements: fluorine (F), chlorine (Cl), bromine (Br), i ...
s, hydride ligands are capable of bonding with positively polarized hydrogen centres. This interaction, called dihydrogen bonding, is similar to
hydrogen bonding In chemistry, a hydrogen bond (or H-bond) is a primarily Electrostatics, electrostatic force of attraction between a hydrogen (H) atom which is Covalent bond, covalently bound to a more electronegativity, electronegative "donor" atom or group ( ...
, which exists between positively polarized protons and electronegative atoms with open lone pairs.


Protides

Hydrides containing protium are known as ''protides''.


Deuterides

Hydrides containing
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...

deuterium
are known as ''deuterides''. Some deuterides, such as LiD, are important fusion fuels in thermonuclear weapons and useful moderators in nuclear reactors.


Tritides

Hydrides containing tritium are known as ''tritides.''


Mixed anion compounds

Mixed anion compounds exist that contain hydride with other anions. These include boride hydrides, carbohydrides, hydridonitrides, oxyhydrides and others.


Appendix on nomenclature

''Protide'', ''deuteride'' and ''tritide'' are used to describe ions or compounds that contain isotopic enrichment, enriched hydrogen-1,
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...

deuterium
or tritium, respectively. In the classic meaning, hydride refers to any Chemical compound, compound hydrogen forms with other elements, ranging over Periodic table group, groups 1–16 (the binary compounds of hydrogen). The following is a list of the nomenclature for the hydride derivatives of main group compounds according to this definition: *alkali metal, alkali and alkaline earth metal, alkaline earth metals: metal hydride *boron: borane, BH3 *aluminium: aluminium hydride, alumane, AlH3 *gallium: gallane, GaH3 *indium: indigane, InH3 *thallium: thallane, TlH3 *carbon: alkanes, alkenes, alkynes, and all hydrocarbons *silicon: silane *germanium: germane *tin: stannane *lead: plumbane *
nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the pnictogens. It is a common element in the ...

nitrogen
:
ammonia Ammonia is an inorganic chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a dis ...

ammonia
("azane" when substituent, substituted), hydrazine *phosphorus: phosphine (note "phosphane" is the IUPAC nomenclature of inorganic chemistry 2005, IUPAC recommended name) *arsenic: arsine (note "arsane" is the IUPAC nomenclature of inorganic chemistry 2005, IUPAC recommended name) *antimony: stibine (note "stibane" is the IUPAC nomenclature of inorganic chemistry 2005, IUPAC recommended name) *bismuth: bismuthine (note "bismuthane" is the IUPAC nomenclature of inorganic chemistry 2005, IUPAC recommended name) *helium: Helium hydride ion, helium hydride (only exists as an ion) According to the convention above, the following are "hydrogen compounds" and not "hydrides": *
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
: Properties of water, water ("oxidane" when substituted; synonym: hydrogen oxide), hydrogen peroxide *sulfur: hydrogen sulfide ("sulfane" when substituted) *selenium: hydrogen selenide ("selane" when substituted) *tellurium: hydrogen telluride ("tellane" when substituted) *polonium: hydrogen polonide ("polane" when substituted) *halogens: hydrogen halides Examples: *nickel hydride: used in NiMH battery, NiMH batteries *
palladium hydride Palladium hydride is metallic palladium that contains a substantial quantity of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and ...
: electrodes in cold fusion experiments *
lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula lithium, Lialuminium, Alhydride, H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a re ...

lithium aluminium hydride
: a powerful reducing agent used in organic chemistry *
sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that ...

sodium borohydride
: selective specialty reducing agent, hydrogen storage in direct borohydride fuel cell, fuel cells *
sodium hydride Sodium hydride is the chemical compound with the empirical formula NaH. This alkali metal hydride is primarily used as a strong yet combustible base (chemistry), base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and ...
: a powerful base used in organic chemistry *diborane: reducing agent, rocket fuel, semiconductor dopant, catalyst, used in organic synthesis; also borane, pentaborane and decaborane *arsine: used for Doping (semiconductor), doping semiconductors *stibine: used in semiconductor industry *phosphine: used for fumigation *silane: many industrial uses, e.g. manufacture of composite materials and water repellents *
ammonia Ammonia is an inorganic chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a dis ...

ammonia
: coolant, fuel, fertilizer, many other industrial uses *hydrogen sulfide: component of natural gas, important source of sulfur *Chemically, even
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

water
and hydrocarbons could be considered hydrides. All metalloid hydrides are highly flammable. All solid non-metallic hydrides except ice are highly flammable. But when hydrogen combines with halogens it produces acids rather than hydrides, and they are not flammable.


Precedence convention

According to IUPAC inorganic nomenclature, IUPAC convention, by precedence (stylized electronegativity), hydrogen falls between nitrogen group, group 15 and chalcogen, group 16 elements. Therefore, we have NH3, "nitrogen hydride" (ammonia), versus H2O, "hydrogen oxide" (water). This convention is sometimes broken for polonium, which on the grounds of polonium's metallicity is often referred to as "polonium hydride" instead of the expected "hydrogen polonide".


See also

*Parent hydride *Hydron (chemistry), Hydron (hydrogen cation) *Hydronium *Proton *Hydrogen ion *Hydride compressor *Superhydrides


References


Bibliography

W. M. Mueller, J. P. Blackledge, G. G. Libowitz, ''Metal Hydrides'', Academic Press, N.Y. and London, (1968)


External links

* {{Authority control Hydrides, Anions Hydrogen storage Functional groups