Group 14 hydride

Structure of methane, silane, germane, and stannane.

Group 14 hydrides are chemical compounds with a group 14 element directly bonded to hydrogen. The elements of group 14 are carbon, silicon, germanium, tin, and lead. ^[1] This article focuses on parent compounds with the formula EH_n^x, where x can reflect neutral members or anions and cations.

Charge-neutral hydrides

Monohydrides

Monohydrides are rare for the group 14 elements. Methylidyne (CH) has been observed in the interstellar medium. With one unpaired electron, it is paramagnetic. ^[2]

Dihydrides

While PbH₂ remains uncharacterized, organic derivatives have been examined by X-ray crystallography including (C₆H₃-2,6-(mesityl)₂)PbH dimer

Compound	Chemical formula	Molecular geometry	comment
Methylene	CH2	bent (134°)	triplet ground state [4]
Silylene	SiH2	bent (92°)	singlet ground state [5]
Germylene	GeH2	bent	singlet ground state
Stanylene	SnH2	bent	singlet ground state
Plumbylene	PbH2	unknown	unknown

Trihydrides

Compound	Chemical formula	Molecular geometry	comment
Methyl	CH3	pyramidal	doublet ground state
Silyl radical	SiH3	pyramidal	doublet ground state
Germyl	GeH3	pyramida	doublet ground state
Stanyl	SnH3	pyramidal	doublet ground state
Plumbyl	PbH3	unknown	unknown

Tetrahydrides

The tetrahydrides have the chemical formula XH₄, with X representing any of the carbon family. In the case of C, Si, Ge, and Sn, the tetrahydrides are tetrahedral monomers. PbH₄ has not been verified experimentally, but it is predicted to be tetrahedral also on the basis of quantum chemical calculations. ^[6]

Compound	Chemical formula	Molecular geometry	comment
Methane	CH4	tetrahedral, C-H distance is 108.7 pm	main component of natural gas
Silane	SiH4	ttetrahedral, Si-H distance is 147 pm [7]	precursor to silicon-based microelectronics
Germane	GeH4	tetrahedral, Ge-H distance is 152.5 pm	precursor to germanium-based microelectronics
Stannane	SnH4	tetrahedral, Sn-H distance is 171 pm	academic interest
Plumbane	PbH4	uncertain	structure has not been verified experimentally

Anionic and cationic hydrides

Fragment of the BaSiH₆ lattice. The [SiH₆] center is apparent as the turquoise sphere (Si) surrounded by six white spheres (H). The H atoms link also to Ba (red spheres).

Many anionic hydrides have been evaluated computationally but very few can be isolated. In organic chemistry, methyllithium is treated as the equivalent of the carbanion CH₃^-. Similarly, reagents such as trimethyloxonium tetrafluoroborate are treated as the equivalent of the carbocation CH₃⁺.

Well-characterized hydride anions are salts of [SiH₆]^2-, an octahedral anion. ^[9]

Catenated hydrides

Group 14 elements are renown for catenation, i.e. forming chains. The neutral hydrides are no exception. Hydrocarbons are a vast inventory of carbon hydrides. ^[10] Oligomeric and polymeric silanes (see polysilane) and germanes (see polygermane) are far less extensive but have been shown to exist.

References

1. Roy, Matthew M. D.; Omaña, Alvaro A.; Wilson, Andrew S. S.; Hill, Michael S.; Aldridge, Simon; Rivard, Eric (2021). "Molecular Main Group Metal Hydrides". Chemical Reviews. 121 (20): 12784–12965. doi:10.1021/acs.chemrev.1c00278. PMID   34450005.
2. Encyclopedia of Astrobiology, Volume 1 edited by Ricardo Amils, José Cernicharo Quintanilla, Henderson James Cleaves, William M. Irvine, Daniele Pinti, Michel Viso. 2011, Springer: Heidelberg
3. Queen, Joshua D.; Fettinger, James C.; Power, Philip P. (2019). "Two quasi-stable lead(II) hydrides at ambient temperature". Chemical Communications. 55 (69): 10285–10287. doi:10.1039/c9cc05106f. PMID   31396611.
4. Shavitt, Isaiah (1985). "Geometry and singlet-triplet energy gap in methylene: A critical review of experimental and theoretical determinations". Tetrahedron. 41 (8): 1531–1542. doi:10.1016/S0040-4020(01)96393-8.
5. Dubois, I. (1968). "The absorption spectrum of the free SiH₂ radical". Canadian Journal of Physics. 46 (22): 2485–2490. doi:10.1139/p68-608.
6. Wang, Xuefeng; Andrews, Lester (2003). "Infrared Spectra of Group 14 Hydrides in Solid Hydrogen: Experimental Observation of PbH₄, Pb₂H₂, and Pb₂H₄". Journal of the American Chemical Society. 125 (21): 6581–6587. doi:10.1021/ja029862l. PMID   12785799.
7. Ohno, Keiichi; Matsuura, Hiroatsu; Endo, Yasuki; Hirota, Eizi (1985). "The microwave spectra of deuterated silanes: SiH3D, SiH2D2, and SiHD3". Journal of Molecular Spectroscopy. 111: 73–82. doi:10.1016/0022-2852(85)90070-0.
8. Beyer, Doreen C.; Spektor, Kristina; Vekilova, Olga Yu; Grins, Jekabs; Barros Brant Carvalho, Paulo H.; Leinbach, Logan J.; Sannemo-Targama, Michael; Bhat, Shrikant; Baran, Volodymyr; Etter, Martin; Sano-Furukawa, Asami; Hattori, Takanori; Kohlmann, Holger; Simak, Sergei I.; Häussermann, Ulrich (2025). "Synthesis of BaSiH₆ Hydridosilicate at High Pressures─A Bridge to BaSiH₈ Polyhydride". ACS Omega. 10 (15): 15029–15035. doi: 10.1021/acsomega.4c10502 . PMC   12019724 . PMID   40290916.
9. Puhakainen, Kati; Benson, Daryn; Nylén, Johanna; Konar, Sumit; Stoyanov, Emil; Leinenweber, Kurt; Häussermann, Ulrich (2012). "Hypervalent Octahedral SiH₆²⁻Species from High-Pressure Synthesis". Angewandte Chemie International Edition. 51 (13): 3156–3160. doi:10.1002/anie.201108713. PMID   22323241.
10. Greenwood and Earnshaw, p. 301.

Bibliography

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN   978-0-08-037941-8.