Cadmium hydride (systematically named cadmium dihydride) is an inorganic compound with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

(also written as or ). It is a solid, known only as a thermally unstable, insoluble white powder.

Nomenclature

The systematic name ''cadmium dihydride'', a valid

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name, is constructed according to the compositional nomenclature. ''Cadmium dihydride'' is also used to refer to the related molecular compound ''dihydridocadmium'' and its oligomers. Care should be taken to avoid confusing the two compounds. ''Cadmium hydride'' is also used as a compositional IUPAC name for the compound with the chemical formula CdH.

History

In 1950 a research group led by Glenn D. Barbaras, synthesized cadmium hydride for the first time. This reaction sequence consisted of

demethylation Demethylation is the chemical process resulting in the removal of a methyl group (CH3) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen at ...

of dimethylcadmium in

diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...

at −78 °C, to cadmium hydride.

Chemical properties

Solid cadmium hydride, on the basis of its infrared spectrum, is believed to contain hydrogen-bridge bonds. Other lower metal hydrides polymerize in a similar fashion. Unless cooled below , cadmium hydride rapidly decomposes to produce

cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...

and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

: : → ''n'' Cd + ''n''

Dihydridocadmium

Dihydridocadmium is the monomeric, molecular form with the chemical formula (also written ). It is a colorless gas that does not persist undiluted. Dihydridocadmium has a low activation barrier toward autopolymerisation into the standard form of cadmium hydride and would rapidly do so in undiluted concentrations. Since the activation barrier for the reverse reaction is much greater than that of the decomposition reaction, autopolymerisation of dihydridocadmium may be considered as irreversible for most intents and purposes. It was produced by the gas phase reaction of excited cadmium atoms with

dihydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, a ...

, H₂, and the structure determined high-resolution infrared emission spectra. The molecule is linear, with a bond length of 168.3 pm.

Chemical properties

The two-coordinate hydridocadmium group (-CdH) in hydridocadmiums such as dihydridocadmium can accept an electron-pair donating ligand into the molecule by adduction: :] + L → Because of this acceptance of the electron-pair donating

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...

(L), dihydridocadmium has Lewis-acidic character. Dihydridocadmium can accept two electron-pairs from ligands, as in the case of the tetrahydridocadmate(2−) anion (). The compound, Cs₃CdH₅, prepared by the reaction of caesium hydride, CsH, and cadmium metal powder at high temperature contains the ion, along with caesium cations, Cs⁺, and hydride anions, H⁻. The tetrahedral anion is an example of an ionic complex of CdH₂. The average Cd-H bond length in is 182pm. In gaseous dihydridocadmium, the molecules form groups ( trimers), being connected by

van der Waals force In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...

s. The dissociation enthalpy of the dimer is estimated at 8.8 kJ mol⁻¹.

References

Cadmium compounds Metal hydrides {{Inorganic-compound-stub