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Carbohydrides (or carbide hydrides) are solid compounds in one phase composed of a metal with carbon and hydrogen in the form of carbide and hydride ions.[ citation needed ] The term carbohydride can also refer to a hydrocarbon. [1]
Many of the transition metal carbohydrides are non-stochiometric, particularly with respect to the hydrogen that can vary in proportion up to a theoretical balanced proportion. The hydrogen and carbon occupy holes in the metal crystalline lattice. The carbon takes up octahedral sites (surrounded by six metal atoms) and the hydrogen takes up tetrahedral sites in the metal lattice. The hydrogen atoms go to sites away from the carbon atoms, and away from each other, at least 2 Å apart, so there are no covalent bonds between the carbon or hydrogen atoms. Overall the lattice retains a high symmetry of the original metal. [2]
A carbodeuteride (or carbo-deuteride) is a compound where the hydrogen is of the isotope deuterium. [3] [4]
Metal carbide hydrides give off hydrogen when heated, and are in equilibrium with a partial pressure of hydrogen that depends on the temperature.
When Ca2LiC3H is heated with ammonium chloride, the gas C3H4 (methylacetylene-propadiene) is produced. [5]
There are also metal cluster molecules and ions that contain both carbon and hydrogen. Methylidyne complexes contain the CH group with three bonds to a metal e.g. NiCH+ or PtCH+.
Iron carbide hydrides do not appear to be stable at the conditions present in the Earth's inner core, even though carbon or hydrogen have been proposed as alloying light elements in the core. [6]
Carbohydrides are studied for their ability in hydrogen storage. [7] Carbohydrides may be made when carbides are manufactured by milling, using hydrocarbons as a carbon source. Since the carbohydride is not the desired outcome, other material like graphite is added to try to maximise carbide production. [8]
Transition metal carbohydrides can be produced by heating a metal carbide in hydrogen, for example at 2000 °C and 3 bars. This reaction is exothermic, and just needs to be ignited at a much lower temperature. [7] The process is called self-propagating high-temperature synthesis or SHS. [9] A hydrocarbide may be formed when the metal is milled in a hydrocarbon, for example in the manufacture of titanium carbide. [8]
Rare earth carbohydrides can be prepared by heating a metal hydride with graphite in a closed metal container, with a hydrogen atmosphere. [10]
Name | formula | form | space group | unit cell | appearance | density | structure | ref |
Lithium dicalcium tricarbide hydride | Ca2LiC3H | tetragonal | P4mbm | a=6.8236 c=3.7518 Z=2 | silver | 2.36 | has C34− | [5] |
Titanium carbo-deuteride | TiC0.48D0.60 | cubic | Fm3m | a=4.30963 | [7] | |||
Titanium carbo-deuteride | TiC0.48D0.60 | trigonal | Fm31 | a=3.08208 c=5.0405 | [7] | |||
Zirconium carbohydride | ZrC0.3H | [11] | ||||||
Hafnium carbohydride | Hf2CH2 | a=3.427 c=5.476 | [11] [12] | |||||
thorium carbohydride | ThCH2 | is cubic under 380°, and above is hexagonal. | [13] [14] | |||||
Th2CH2 | hexagonal | a=3.083 c=5.042 | [12] | |||||
Th3CH4 | monoclinic | [12] | ||||||
Niobium carbohydride | NbC0.76H0.18 | [15] | ||||||
Barium indium allenylide hydride | Ba12InC18H4 | cubic | Im3 | a=11.1447 | InBa12 icosahedrons | [16] | ||
Y5Si3C0.5H7.33 | [17] | |||||||
La2C3H1.5 | [18] | |||||||
La2CH4 | a=5.642 | [19] | ||||||
La2CH2 | monoclinic | C2/m | a = 7.206, b = 3.932, c = 6.739, β = 94.66 ° | [19] | ||||
La15(FeC6)4H | hexagonal | P6 | a=8.7764 c=10.7355 Z=1 V=720.42 | silver | [20] | |||
Ytterbium carbide hydride | Yb2CH2 | hexgonal | a=3.575 c=5.786 | [10] | ||||
Ytterbium dicarbide hydride | Yb2C2H | cubic | a=4.974 | fcc | [10] | |||
Pr3Fe27.5Ti1.5CxH | monoclinic | A2/m | [21] | |||||
Dy2Co17C0.2H2.8 | P63/mmc | a=8.418 c=8.165 V=501.1 | [22] | |||||
Dy2Ni17C0.4H2.7 | P63/mmc | a=8.3789 c=8.054 V=489.7 | [22] | |||||
Gd2ICH | P63/mmc | a = 3.8128 c = 14.844 | grey | 8.071 | [23] | |||
Gd2BrCH | P63/mmc | grey | [23] | |||||
Gd2ClCH | P63/mmc | grey | [23] | |||||
Tb2ICH | P63/mmc | grey | [23] | |||||
Tb2BrCH | P63/mmc | grey | [23] |
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
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.
Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li[AlH4] or LiAlH4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage.
In crystallography, the cubiccrystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
Tantalum carbides (TaC) form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaCx, where x usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metallic electrical conductivity. They appear as brown-gray powders, which are usually processed by sintering.
Lithium hydride is an inorganic compound with the formula LiH. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not soluble but reactive with all protic organic solvents. It is soluble and nonreactive with certain molten salts such as lithium fluoride, lithium borohydride, and sodium hydride. With a molar mass of 7.95 g/mol, it is the lightest ionic compound.
Zirconium hydride describes an alloy made by combining zirconium and hydrogen. Hydrogen acts as a hardening agent, preventing dislocations in the zirconium atom crystal lattice from sliding past one another. Varying the amount of hydrogen and the form of its presence in the zirconium hydride controls qualities such as the hardness, ductility, and tensile strength of the resulting zirconium hydride. Zirconium hydride with increased hydrogen content can be made harder and stronger than zirconium, but such zirconium hydride is also less ductile than zirconium.
Plutonium hydride is a non-stoichiometric chemical compound with the formula PuH2+x. It is one of two characterized hydrides of plutonium; the other is PuH3. PuH2+x is non-stoichiometric with a composition range of PuH2 – PuH2.7. Metastable stoichiometries with an excess of hydrogen (PuH2.7 – PuH3) can also be formed. PuH2 has a cubic structure. It is readily formed from the elements at 1 atmosphere at 100–200°C: When the stoichiometry is close to PuH2 it has a silver appearance, but gets blacker as the hydrogen content increases, additionally the color change is associated with a reduction in conductivity.
Titanium hydride normally refers to the inorganic compound TiH2 and related nonstoichiometric materials. It is commercially available as a stable grey/black powder, which is used as an additive in the production of Alnico sintered magnets, in the sintering of powdered metals, the production of metal foam, the production of powdered titanium metal and in pyrotechnics.
Thorium(IV) chloride describes a family of inorganic compounds with the formula ThCl4(H2O)n. Both the anhydrous and tetrahydrate (n = 4) forms are known. They are hygroscopic, water-soluble white salts.
Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.
Sodium aluminium hydride or sodium alumanuide is an inorganic compound with the chemical formula NaAlH4. It is a white pyrophoric solid that dissolves in tetrahydrofuran (THF), but not in diethyl ether or hydrocarbons. It has been evaluated as an agent for the reversible storage of hydrogen and it is used as a reagent for the chemical synthesis of organic compounds. Similar to lithium aluminium hydride, it is a salt consisting of separated sodium cations and tetrahedral AlH−
4 anions.
Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.
An iron hydride is a chemical system which contains iron and hydrogen in some associated form.
Magnesium nickel hydride is the chemical compound Mg2NiH4. It contains 3.6% by weight of hydrogen and has been studied as a potential hydrogen storage medium.
Chromium hydrides are compounds of chromium and hydrogen, and possibly other elements. Intermetallic compounds with not-quite-stoichometric quantities of hydrogen exist, as well as highly reactive molecules. When present at low concentrations, hydrogen and certain other elements alloyed with chromium act as softening agents that enables the movement of dislocations that otherwise not occur in the crystal lattices of chromium atoms.
In chemistry, a hydridonitride is a chemical compound that contains hydride and nitride ions in a single phase. These inorganic compounds are distinct from inorganic amides and imides as the hydrogen does not share a bond with nitrogen, and contain a larger proportion of metals.
The telluride oxides or oxytellurides are double salts that contain both telluride and oxide anions. They are in the class of mixed anion compounds.
Silicide carbides or carbide silicides are compounds containing anions composed of silicide (Si4−) and carbide (C4−) or clusters therof. They can be considered as mixed anion compounds or intermetallic compounds, as silicon could be considered as a semimetal.
Samarium compounds are compounds formed by the lanthanide metal samarium (Sm). In these compounds, samarium generally exhibits the +3 oxidation state, such as SmCl3, Sm(NO3)3 and Sm(C2O4)3. Compounds with samarium in the +2 oxidation state are also known, for example SmI2.
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