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Mercury(II) hydride
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Mercury(II) hydride
Mercury(II) hydride (systematically named mercurane(2) and dihydridomercury) is an inorganic compound with the chemical formula HgH
2 (also written as [HgH
2]). It is both thermodynamically and kinetically unstable at ambient temperature, and as such, little is known about its bulk properties. However, it can also be a white, crystalline solid, which is kinetically stable at temperatures below −125 °C (−193 °F), which was synthesized for the first time in 1951.
Mercury(II) hydride is the second simplest mercury hydride (after the significantly less stable mercury(I) hydride). Due to its instability, it has no practical industrial uses. However, in analytical chemistry, mercury(II) hydride is fundamental to certain forms of spectrometric techniques used to determine mercury content. In addition, it is investigated for its effect on high sensitivity isotope-ratio mass spectrometry methods that involve mercury, such as MC-ICP-MS, when used to compare thallium to mercury.
In solid mercury(II) hydride, the HgH2 molecules are connected by mercurophilic bonds. Trimers and a lesser proportion of dimers are detected in the vapour. Unlike solid zinc(II), and cadmium(II) hydride, which are network solids, solid mercury(II) hydride is a covalently bound molecular solid. This is due to relativistic effects, which also accounts for the relatively low decomposition temperature of -125 °C.
The HgH2 molecule is linear and symmetric in the form H-Hg-H. The bond length is 1.646543 Å. The antisymmetric stretching frequency, ν3 of the bond is 1912.8 cm−1, 57.34473 THz for isotopes 202Hg and 1H. The energy needed to break the Hg-H bond in HgH2 is 70 kcal/mol. The second bond in the resulting HgH is much weaker only needing 8.6 kcal/mol to break. Reacting two hydrogen atoms releases 103.3 kcal/mol, and so HgH2 formation from hydrogen molecules and Hg gas is endothermic at 24.2 kcal/mol.
Alireza Shayesteh et al conjectured that bacteria containing the flavoprotein mercuric reductase, such as Escherichia coli, can in theory reduce soluble mercury compounds to volatile HgH2, which should have a transient existence in nature.
Mercury(II) hydride may be prepared by the reduction of mercury(II) chloride. In this process, mercury(II) chloride and a hydride salt equivalent react to produce mercury(II) hydride according to the following equations, which depend on the stoichiometry of the reaction:
Variations of this method exits where mercury(II) chloride is substituted for its heavier halide homologues.
Mercury(II) hydride can also be generated by direct synthesis from the elements in the gas phase or in cryogenic inert gas martices:
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Mercury(II) hydride
Mercury(II) hydride (systematically named mercurane(2) and dihydridomercury) is an inorganic compound with the chemical formula HgH
2 (also written as [HgH
2]). It is both thermodynamically and kinetically unstable at ambient temperature, and as such, little is known about its bulk properties. However, it can also be a white, crystalline solid, which is kinetically stable at temperatures below −125 °C (−193 °F), which was synthesized for the first time in 1951.
Mercury(II) hydride is the second simplest mercury hydride (after the significantly less stable mercury(I) hydride). Due to its instability, it has no practical industrial uses. However, in analytical chemistry, mercury(II) hydride is fundamental to certain forms of spectrometric techniques used to determine mercury content. In addition, it is investigated for its effect on high sensitivity isotope-ratio mass spectrometry methods that involve mercury, such as MC-ICP-MS, when used to compare thallium to mercury.
In solid mercury(II) hydride, the HgH2 molecules are connected by mercurophilic bonds. Trimers and a lesser proportion of dimers are detected in the vapour. Unlike solid zinc(II), and cadmium(II) hydride, which are network solids, solid mercury(II) hydride is a covalently bound molecular solid. This is due to relativistic effects, which also accounts for the relatively low decomposition temperature of -125 °C.
The HgH2 molecule is linear and symmetric in the form H-Hg-H. The bond length is 1.646543 Å. The antisymmetric stretching frequency, ν3 of the bond is 1912.8 cm−1, 57.34473 THz for isotopes 202Hg and 1H. The energy needed to break the Hg-H bond in HgH2 is 70 kcal/mol. The second bond in the resulting HgH is much weaker only needing 8.6 kcal/mol to break. Reacting two hydrogen atoms releases 103.3 kcal/mol, and so HgH2 formation from hydrogen molecules and Hg gas is endothermic at 24.2 kcal/mol.
Alireza Shayesteh et al conjectured that bacteria containing the flavoprotein mercuric reductase, such as Escherichia coli, can in theory reduce soluble mercury compounds to volatile HgH2, which should have a transient existence in nature.
Mercury(II) hydride may be prepared by the reduction of mercury(II) chloride. In this process, mercury(II) chloride and a hydride salt equivalent react to produce mercury(II) hydride according to the following equations, which depend on the stoichiometry of the reaction:
Variations of this method exits where mercury(II) chloride is substituted for its heavier halide homologues.
Mercury(II) hydride can also be generated by direct synthesis from the elements in the gas phase or in cryogenic inert gas martices:
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