Zinc(II) hydride
| Zinc(II) hydride | |
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Zinc hydride |
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Other names
Zinc(II) hydride |
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| Identifiers | |
| CAS number | 14018-82-7  |
| PubChem | 22056524 |
| ChemSpider | 10806557  |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | ZnH2 |
| Molar mass | 67.425 g mol-1 |
| Appearance | Colourless crystals |
| Related compounds | |
| Related compounds | Mercury(II) hydride |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Zinc hydride is a chemical compound of zinc and hydrogen, ZnH2, which is used as a reducing agent in organic synthesis. First reported in 1947,[1] it is a white crystalline powder when freshly made which turns grey if left at room temperature for a few days, presumably due to the decompostion to metallic zinc.[2] It can be prepared in a number of ways:[2][3]
- 2LiH + ZnBr2 → ZnH2 + 2LiBr
- 2NaH + ZnI2 → ZnH2 + 2NaI
- ZnI2 + 2LiAlH4 → ZnH2 + AlH3 + 2LiI
- Zn(CH3)2 + LiAlH4 → ZnH2 + LiAlH3(CH3)
It decomposes at 90 °C into the elements.[2] It is sensitive to air and moisture, and is hydrolysed slowly by water but violently by aqueous acids.[2] Older samples may be pyrophoric.[2] The solid state structure is not known but is believed to involve covalent bonding[4]
Molecular zinc hydride [edit]
Meta stable, gaseous ZnH2 have been discovered in an emission source that combines an electrical discharge with a high-temperature furnace. High-resolution infrared emission spectra of ZnH2 have been recorded with a Fourier transform spectrometer. The reaction of excited zinc atoms with molecular hydrogen in the gas phase was studied by Breckenridge et al using laserpump-probe techniques. The only spectroscopic studies on the zinc dihydride molecule are the infrared spectra of ZnH2 trapped in argon and krypton matrices at 10-12 K.
The average Zn-H bond energy was recently calculated to be 51.24 kcal mol-1, while the H-H bond energy is 103.3 kcal mol-1. Therefore, the overall reaction is nearly ergoneutral.
- Zn(g) + H2(g) → ZnH2(g)
Molecular zinc hydride was found to be linear with a Zn-H bond length of 153.5 pm.[5]
The molecule can be found a singlet ground state of 1Σg+.
References [edit]
- ^ A. E. Finholt, A. C. Bond, Jr., H. I. Schlesinger (1947). "Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry". Journal of the American Chemical Society 69 (5): 1199–1203. doi:10.1021/ja01197a061.
- ^ a b c d e Herrmann, Wolfgang A. (1997). Synthetic Methods of Organometallic and Inorganic Chemistry. Georg Thieme Verlag. ISBN 3-13-103061-5.
- ^ Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
- ^ Mackay, Rosemary Ann; Henderson, W.; (2002). Introduction to Modern Inorganic Chemistry (6th ed.). CRC Press. ISBN 0-7487-6420-8.
- ^ Shayesteh, Alireza; Appadoo, Dominique R. T.; Gordon, Iouli E.; Bernath, Peter F.; Journal of the American Chemical Society (2004). "Vibration−Rotation Emission Spectra of Gaseous ZnH2 and ZnD2". Journal of the American Chemical Society 126 (44): 14356–14357. doi:10.1021/ja046050b. PMID 15521746.
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