Chemistry:Zinc hydride
| Names | |
|---|---|
| IUPAC name
Zinc(II) hydride
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| Systematic IUPAC name
Zinc dihydride | |
| Other names
Zinc hydride
Zincane | |
| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
PubChem CID
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| Properties | |
| ZnH 2 | |
| Molar mass | 67.425 g/mol |
| Appearance | White crystals |
| Structure | |
| linear at Zn | |
| linear | |
| 0 D | |
| Related compounds | |
Related compounds
|
Mercury(II) hydride Cadmium(II) hydride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
 verify (what is   ?)
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| Infobox references | |
Zinc hydride is an inorganic compound with the chemical formula ZnH
2. It is a white, odourless solid which slowly decomposes into its elements at room temperature; despite this it is the most stable of the binary first row transition metal hydrides. A variety of coordination compounds containing Zn–H bonds are used as reducing agents,[1] however ZnH
2 itself has no common applications.
Discovery and synthesis
Zinc(II) hydride was first synthesised in 1947 by Hermann Schlesinger, via a reaction between dimethylzinc Zn(CH
3)
2 and lithium aluminium hydride Li[AlH
4];[2] a process which was somewhat hazardous due to the pyrophoric nature of Zn(CH
3)
2.
- Zn(CH
3)
2 + 2 Li[AlH
4] → ZnH
2 + 2 Li[AlH
3CH
3]
Later methods were predominantly salt metathesis reactions between zinc halides and alkali metal hydrides, which are significantly safer.[3][4] Examples include:
Small quantities of gaseous zinc(II) hydride have also been produced by laser ablation of zinc under a hydrogen atmosphere[5][6] and other high energy techniques. These methods have been used to assess its gas phase properties.
Chemical properties
Structure
New evidence suggests that in zinc(II) hydride, elements form a one-dimensional network (polymer), being connected by covalent bonds.[7] Other lower metal hydrides polymerise in a similar fashion (c.f. aluminium hydride). Solid zinc(II) hydride is the irreversible autopolymerisation product of the molecular form, and the molecular form cannot be isolated in concentration. Solubilising zinc(II) hydride in non-aqueous solvents, involve adducts with molecular zinc(II) hydride, such as ZnH
2 · H
2 in liquid hydrogen.
Stability
Zinc(II) hydride slowly decomposes to metallic zinc and hydrogen gas at room temperature, with decomposition becoming rapid if it is heated above 90°C.[8]
- ZnH
2 → Zn + H
2
It is readily oxidised and is sensitive to both air and moisture; being hydrolysed slowly by water but violently by aqueous acids,[3] which indicates possible passivation via the formation of a surface layer of ZnO. Despite this older samples may be pyrophoric.[3] Zinc hydride can therefore be considered metastable at best, however it is still the most stable of all the binary first row transition metal hydrides (c.f. titanium(IV) hydride).
Molecular form
Molecular zinc(II) hydride, ZnH
2, has been identified as a volatile product of the acidified reduction of zinc ions with sodium borohydride.[citation needed] This reaction is similar to the acidified reduction with lithium aluminium hydride, however a greater fraction of the generated zinc(II) hydride is in the molecular form. This can be attributed to a slower reaction rate, which prevents a polymerising concentration of building over the progression of the reaction. This follows earlier experiments in direct synthesis from the elements. The reaction of excited zinc atoms with molecular hydrogen in the gas phase was studied by Breckenridge et al using laserpump-probe techniques.[citation needed] Owing to its relative thermal stability, molecular zinc(II) hydride is included in the short list of molecular metal hydrides, which have been successfully identified in the gas phase (that is, not limited to matrix isolation).
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.[citation needed] Therefore, the overall reaction is nearly ergoneutral.
- Zn(g) + H
2(g) → ZnH
2(g)
Molecular zinc hydride in the gas phase was found to be linear with a Zn–H bond length of 153.5 pm.[9]
The molecule can be found a singlet ground state of 1Σg+.
Quantum chemical calculations predict the molecular form to exist in a doubly hydrogen-bridged, dimeric groundstate, with little or no formational energy barrier.[citation needed] The dimer can be described as di-μ-hydrido-bis(hydridozinc), according to IUPAC additive nomenclature.
References
- ↑ Enthaler, Stephan (1 February 2013). "Rise of the Zinc Age in Homogeneous Catalysis?". ACS Catalysis 3 (2): 150–158. doi:10.1021/cs300685q.
- ↑ A. E. Finholt, A. C. Bond, Jr., H. I. Schlesinger; Bond; 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.
- ↑ 3.0 3.1 3.2 Herrmann, Wolfgang A. (1997). Synthetic Methods of Organometallic and Inorganic Chemistry. Georg Thieme Verlag. ISBN 978-3-13-103061-0.
- ↑ Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN:0-12-352651-5
- ↑ Greene, Tim M.; Brown, Wendy; Andrews, Lester; Downs, Anthony J.; Chertihin, George V.; Runeberg, Nino; Pyykko, Pekka (1 May 1995). "Matrix Infrared Spectroscopic and ab Initio Studies of ZnH2, CdH2, and Related Metal Hydride Species". The Journal of Physical Chemistry 99 (20): 7925–7934. doi:10.1021/j100020a014.
- ↑ Wang, Xuefeng; Andrews, Lester (2004). "Infrared Spectra of Zn and Cd Hydride Molecules and Solids". The Journal of Physical Chemistry A 108 (50): 11006–11013. doi:10.1021/jp046414m. ISSN 1089-5639. Bibcode: 2004JPCA..10811006W.
- ↑ Grochala, Wojciech; Edwards, Peter P. (18 February 2004). "Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen". Chemical Reviews 104 (3): 1283–1316. doi:10.1021/cr030691s. PMID 15008624.
- ↑ W. A. Herrmann, ed (1999). Synthetic methods of organometallic and inorganic chemistry. Stuttgart: Thieme. p. 115. ISBN 9783131030610.
- ↑ Shayesteh, Alireza; 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.
| Alkali metal (Group 1) hydrides |  Lithium hydride, LiH ionic metal hydride   Beryllium hydride Left (gas phase): BeH2 covalent metal hydride Right: (BeH2)n (solid phase) polymeric metal hydride   Borane and diborane Left: BH3 (special conditions), covalent metalloid hydride Right: B2H6 (standard conditions), dimeric metalloid hydride  Methane, CH4 covalent nonmetal hydride  Ammonia, NH3 covalent nonmetal hydride  Water, H2O covalent nonmetal hydride  Hydrogen fluoride, HF covalent nonmetal hydride | ||||||||||||||||||
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| Alkaline (Group 2) earth hydrides |
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| Group 13 hydrides |
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| Group 14 hydrides |
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| Pnictogen (Group 15) hydrides |
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| Hydrogen chalcogenides (Group 16 hydrides) |
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| Hydrogen halides (Group 17 hydrides) | |||||||||||||||||||
| Transition metal hydrides | |||||||||||||||||||
| Lanthanide hydrides |
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| Actinide hydrides |
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