Types of hydrides Hydride

1 types of hydrides

1.1 ionic hydrides
1.2 covalent hydrides
1.3 interstitial hydrides or metallic hydrides
1.4 transition metal hydride complexes
1.5 deuterides

types of hydrides

according general definition every element of periodic table (except noble gases) forms 1 or more hydrides. these substances have been classified 3 main types according nature of bonding:

ionic hydrides, have significant ionic bonding character.
covalent hydrides, include hydrocarbons , many other compounds covalently bond hydrogen atoms.
interstitial hydrides, may described having metallic bonding.

while these divisions have not been used universally, still useful understand differences in hydrides.

ionic hydrides

ionic or saline hydrides composed of hydride bound electropositive metal, alkali metal or alkaline earth metal. divalent lanthanides such europium , ytterbium form compounds similar of heavier alkali metal. in these materials hydride viewed pseudohalide. saline hydrides insoluble in conventional solvents, reflecting non-molecular structures. ionic hydrides used bases and, occasionally, reducing reagents in organic synthesis.

c6h5c(o)ch3 + kh → c6h5c(o)ch2k + h2

typical solvents such reactions ethers. water , other protic solvents cannot serve medium ionic hydrides because hydride ion stronger base hydroxide , hydroxyl anions. hydrogen gas liberated in typical acid-base reaction.

nah + h2o → h2 (g) + naoh  Δh = −83.6 kj/mol, Δg = −109.0 kj/mol

often alkali metal hydrides react metal halides. lithium aluminium hydride (often abbreviated lah) arises reactions of lithium hydride aluminium chloride.

4 lih + alcl3 → lialh4 + 3 licl

covalent hydrides

according definitions, covalent hydrides cover other compounds containing hydrogen. definitions limit hydrides hydrogen centres formally react hydrides, i.e. nucleophilic, , hydrogen atoms bound metal centers.these hydrides formed true non-metals (except 0 group elements) , elements al, ga, sn, pb, bi, po, etc., metallic in nature, i.e., class includes hydrides of p-block elements. in these substances hydride bond formally covalent bond bond made proton in weak acid. category includes hydrides exist discrete molecules, polymers or oligomers, , hydrogen has been chem-adsorbed surface. particularly important segment of covalent hydrides complex metal hydrides, powerful soluble hydrides commonly used in synthetic procedures.

molecular hydrides involve additional ligands such as, diisobutylaluminium hydride (dibal) consists of 2 aluminum centers bridged hydride ligands. hydrides soluble in common solvents used in organic synthesis. particularly common sodium borohydride (nabh4) , lithium aluminium hydride , hindered reagents such dibal.

interstitial hydrides or metallic hydrides

interstitial hydrides commonly exist within metals or alloys. traditionally termed compounds , though not strictly conform definition of compound; more closely resembling common alloys such steel. in such hydrides, hydrogen can exist either atomic, or diatomic entities. mechanical or thermal processing, such bending, striking, or annealing may cause hydrogen precipitate out of solution, degassing. bonding considered metallic. such bulk transition metals form interstitial binary hydrides when exposed hydrogen. these systems non-stoichiometric, variable amounts of hydrogen atoms in lattice. in materials engineering, phenomenon of hydrogen embrittlement results formation of interstitial hydrides. hydrides of type form according either 1 of 2 main mechanisms. first mechanism involves adsorption of dihydrogen, succeeded cleaving of h-h bond, delocalisation of hydrogen s electrons, , finally, diffusion of protons metal lattice. other main mechanism involves electrolytic reduction of ionised hydrogen on surface of metal lattice, followed diffusion of protons lattice. second mechanism responsible observed temporary volume expansion of electrodes used in electrolytic experiments.

palladium absorbs 900 times own volume of hydrogen @ room temperatures, forming palladium hydride. material has been discussed means carry hydrogen vehicular fuel cells. interstitial hydrides show promise way safe hydrogen storage. during last 25 years many interstitial hydrides developed readily absorb , discharge hydrogen @ room temperature , atmospheric pressure. based on intermetallic compounds , solid-solution alloys. however, application still limited, capable of storing 2 weight percent of hydrogen, insufficient automotive applications.

transition metal hydride complexes

transition metal hydrides include compounds can classified covalent hydrides. classified interstitial hydrides , other bridging hydrides. classical transition metal hydride feature single bond between hydrogen centre , transition metal. transition metal hydrides acidic, e.g., hco(co)4 , h2fe(co)4. anions [reh9] , [feh6] examples growing collection of known molecular homoleptic metal hydrides. pseudohalides, hydride ligands capable of bonding positively polarized hydrogen centres. interaction, called dihydrogen bond similar hydrogen bonding exists between positively polarized protons , electronegative atoms open lone pairs.

deuterides

hydrides containing deuterium known deuterides. deuterides, such lid, important fusion fuels in thermonuclear weapons, , useful moderators in nuclear reactors.