Chemical compounds containing only hydrogen and one other chemical element
Binary compounds of hydrogen are
binarychemical compounds containing just
hydrogen and one other
chemical element. By convention all binary hydrogen compounds are called
hydrides even when the hydrogen atom in it is not an
anion.[1][2][3][4] These hydrogen compounds can be grouped into several types.
Overview
Binary hydrogen compounds in
group 1 are the ionic hydrides (also called saline hydrides) wherein hydrogen is bound electrostatically. Because hydrogen is located somewhat centrally in an electronegative sense, it is necessary for the counterion to be exceptionally electropositive for the hydride to possibly be accurately described as truly behaving ionic. Therefore, this category of hydrides contains only a few members.
Hydrides in
group 2 are polymeric covalent hydrides. In these, hydrogen forms bridging covalent bonds, usually possessing mediocre degrees of ionic character, which make them difficult to be accurately described as either covalent or ionic. The one exception is
beryllium hydride, which has definitively covalent properties.
Hydrides in the
transition metals and
lanthanides are also typically polymeric covalent hydrides. However, they usually possess only weak degrees of ionic character. Usually, these hydrides rapidly decompose into their component elements at ambient conditions. The results consist of metallic matrices with dissolved, often stoichiometric or near so, concentrations of hydrogen, ranging from negligible to substantial. Such a solid can be thought of as a
solid solution and is alternately termed a metallic- or interstitial hydride. These decomposed solids are identifiable by their ability to conduct electricity and their magnetic properties (the presence of hydrogen is coupled with the delocalisation of the valence electrons of the metal), and their lowered density compared to the metal. Both the saline hydrides and the polymeric covalent hydrides typically react strongly with water and air.
It is possible to produce a metallic hydride without requiring decomposition as a necessary step. If a sample of bulk metal is subjected to any one of numerous hydrogen absorption techniques, the characteristics, such as luster and hardness of the metal is often retained to a large degree. Bulk
actinoid hydrides are only known in this form. The affinity for hydrogen for most of the
d-block elements are low. Therefore, elements in this block do not form hydrides (the hydride gap) under
standard temperature and pressure with the notable exception of
palladium.[5] Palladium can absorb up to 900 times its own volume of hydrogen and is therefore actively researched in the field
hydrogen storage.
Due to the total number of possible binary saturated compounds with
carbon of the type CnH2n+2 being very large, there are many
group 14 hydrides. Going down the group the number of binary
silicon compounds (
silanes) is small (straight or branched but rarely cyclic) for example
disilane and
trisilane. For
germanium only 5 linear chain binary compounds are known as gases or volatile liquids. Examples are n-pentagermane, isopentagermane and neopentagermane. Of tin only the distannane is known.
Plumbane is an unstable gas.
Non-classical hydrides are those in which extra hydrogen molecules are coordinated as a ligand on the central atoms. These are very unstable but some have been shown to exist.
Polyhydrides or superhydrides are compounds in which the number of hydrogen atoms exceed the valency of the combining atom. These may only be stable under extreme pressure, but may be
high temperature superconductors, such as H3S, superconducting at up to 203 K. Polyhydrides are actively studied with the hope of discovering a
room temperature superconductor.
The isolation of
monomeric molecular hydrides usually require extremely mild conditions, which are partial pressure and cryogenic temperature. The reason for this is threefold - firstly, most molecular hydrides are thermodynamically unstable toward decomposition into their elements; secondly, many molecular hydrides are also thermodynamically unstable toward polymerisation; and thirdly, most molecular hydrides are also kinetically unstable toward these types of reactions due to low
activation energy barriers.
Instability toward decomposition is generally attributable to poor contribution from the orbitals of the heavier elements to the molecular bonding orbitals. Instability toward polymerisation is a consequence of the electron-deficiency of the monomers relative to the polymers. Relativistic effects play an important role in determining the energy levels of molecular orbitals formed by the heavier elements. As a consequence, these molecular hydrides are commonly less electron-deficient than otherwise expected. For example, based on its position in the 12th column of the periodic table alone, mercury(II) hydride would be expected to be rather deficient. However, it is in fact satiated, with the monomeric form being much more energetically favourable than any oligomeric form.
The table below shows the monomeric hydride for each element that is closest to, but not surpassing its heuristic valence. A heuristic valence is the valence of an element that strictly obeys the octet, duodectet, and sexdectet valence rules. Elements may be prevented from reaching their heuristic valence by various steric and electronic effects. In the case of chromium, for example, stearic hindrance ensures that both the octahedral and trigonal prismatic molecular geometries for CrH 6 are thermodynamically unstable to rearranging to a
Kubas complex structural isomer.
Where available, both the enthalpy of formation for each monomer and the enthalpy of formation for the hydride in its standard state is shown (in brackets) to give a rough indication of which monomers tend to undergo aggregation to lower enthalpic states. For example, monomeric lithium hydride has an enthalpy of formation of 139 kJ mol−1, whereas solid lithium hydride has an enthalpy of −91 kJ mol−1. This means that it is energetically favourable for a mole of monomeric LiH to aggregate into the ionic solid, losing 230 kJ as a consequence. Aggregation can occur as a chemical association, such as polymerisation, or it can occur as an electrostatic association, such as the formation of hydrogen-bonding in water.
This table includes the thermally unstable dihydrogen complexes for the sake of completeness. As with the above table, only the complexes with the most complete valence is shown, to the negligence of the most stable complex.
Non-classical covalent hydrides
A molecular hydride may be able to bind to hydrogen molecules acting as a ligand. The complexes are termed non-classical covalent hydrides. These complexes contain more hydrogen than the classical covalent hydrides, but are only stable at very low temperatures. They may be isolated in inert gas matrix, or as a cryogenic gas. Others have only been predicted using
computational chemistry.
Hydrogen has a highly variable solubility in the elements. When the continuous phase of the solution is a metal, it is called a metallic hydride or interstitial hydride, on account of the position of the hydrogen within the crystal structure of the metal. In solution, hydrogen can occur in either the atomic or molecular form. For some elements, when hydrogen content exceeds its solubility, the excess precipitates out as a stoichiometric compound. The table below shows the solubility of hydrogen in each element as a molar ratio at 25 °C (77 °F) and 100 kPa.
^Data in KJ/mole gas-phase source: Modern Inorganic Chemistry W.L. Jolly
^
abWang, Xuefeng; Andrews, Lester (12 July 2007). "Infrared spectra and theoretical calculations of lithium hydride clusters in solid hydrogen, neon, and argon". The Journal of Physical Chemistry A. 111 (27): 6008–6019.
Bibcode:
2007JPCA..111.6008W.
doi:
10.1021/jp071251y.
PMID17547379.
^Tague Jr., Thomas J.; Andrews, Lester (December 1993). "Reactions of beryllium atoms with hydrogen. Matrix infrared spectra of novel product molecules". Journal of the American Chemical Society (PDF). 115 (25): 12111–12116.
doi:
10.1021/ja00078a057.
^Tague Jr., Thomas J.; Andrews, Lester (June 1994). "Reactions of pulsed-laser evaporated boron atoms with hydrogen. Infrared spectra of boron hydride intermediate species in solid argon". Journal of the American Chemical Society. 116 (11): 4970–4976.
doi:
10.1021/ja00090a048.
^Wang, Xuefeng; Andrews, Lester (2 August 2007). "Sodium hydride clusters in solid hydrogen and neon: infrared spectra and theoretical calculations". The Journal of Physical Chemistry A. 111 (30): 7098–7104.
Bibcode:
2007JPCA..111.7098W.
doi:
10.1021/jp0727852.
PMID17602543.
^Chertihin, George V.; Andrews, Lester (October 1993). "Reactions of pulsed-laser ablated aluminum atoms with hydrogen: Infrared spectra of aluminum hydride (AlH, AlH2, AlH3, and Al2H2) species". The Journal of Physical Chemistry. 97 (40): 10295–10300.
doi:
10.1021/j100142a007.
^
abcdeWang, Xuefeng; Andrews, Lester (15 December 2011). "Tetrahydrometalate Species VH 2(H 2), NbH 4, and TaH 4: Matrix Infrared Spectra and Quantum Chemical Calculations". The Journal of Physical Chemistry A. 115 (49): 14175–14183.
Bibcode:
2011JPCA..11514175W.
doi:
10.1021/jp2076148.
^Wang, Xuefeng; Andrews, Lester (1 January 2003). "Chromium hydrides and dihydrogen complexes in solid neon, argon, and hydrogen: Matrix infrared spectra and quantum chemical calculations". The Journal of Physical Chemistry A. 107 (4): 570–578.
Bibcode:
2003JPCA..107..570W.
doi:
10.1021/jp026930h.
^
abWang, Xuefeng; Andrews, Lester (30 April 2003). "Matrix infrared spectra and density functional theory calculations of manganese and rhenium hydrides". The Journal of Physical Chemistry A. 107 (20): 4081–4091.
Bibcode:
2003JPCA..107.4081W.
doi:
10.1021/jp034392i.
^
abWang, Xuefeng; Andrews, Lester (18 December 2008). "Infrared Spectra and Theoretical Calculations for Fe, Ru, and Os Metal Hydrides and Dihydrogen Complexes". The Journal of Physical Chemistry A. 113 (3): 551–563.
Bibcode:
2009JPCA..113..551W.
doi:
10.1021/jp806845h.
PMID19099441.
^Billups, W. E.; Chang, Sou-Chan; Hauge, Robert H.; Margrave, John L. (February 1995). "Low-Temperature Reactions of Atomic Cobalt with CH 2N 2, CH 4, CH 3D, CH 2D 2, CHD 3, CD 4, H 2, D 2, and HD". Journal of the American Chemical Society. 117 (4): 1387–1392.
doi:
10.1021/ja00109a024.
^Li, S.; van Zee, R. J.; Weltner Jr., W.; Cory, M. G.; Zerner, M. C. (8 February 1997). "Magneto-Infrared Spectra of Matrix-Isolated NiH and NiH 2 Molecules and Theoretical Calculations of the Lowest Electronic States of NiH 2". The Journal of Chemical Physics. 106 (6): 2055–2059.
Bibcode:
1997JChPh.106.2055L.
doi:
10.1063/1.473342.
^
abcWang, Xuefeng; Andrews, Lester (13 September 2003). "Infrared spectra and DFT calculations for the coinage metal hydrides MH, {{Chem|(H|2|)MH}}, MH 2, M 2H, M 2H− , and (H 2)CuHCu in solid argon, neon, and hydrogen". The Journal of Physical Chemistry A. 107 (41): 8492–8505.
Bibcode:
2003JPCA..107.8492W.
doi:
10.1021/jp0354346.
^
abGreene, Tim M.; Brown, Wendy; Andrews, Lester; Downs, Anthony J.; Chertihin, George V.; Runeberg , Nino; Pyykko, Pekka (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 (2 December 2003). "Infrared spectra of gallium hydrides in solid hydrogen: {{Chem|Ga|H|1,2,3}}, Ga 2H 2,4,6, and the GaH− 2,4 anions". The Journal of Physical Chemistry A. 107 (51): 11371–11379.
Bibcode:
2003JPCA..10711371W.
doi:
10.1021/jp035393d.
^Wang, Xuefeng; Andrews, Lester (17 September 2005). "Matrix infrared spectra and density functional theory calculations of molybdenum hydrides". The Journal of Physical Chemistry A. 109 (40): 9021–9027.
Bibcode:
2005JPCA..109.9021W.
doi:
10.1021/jp053591u.
PMID16332007.
^Wang, Xuefeng; Andrews, Lester (19 March 2002). "Infrared spectra of rhodium hydrides in solid argon, neon, and deuterium with supporting density functional calculations". The Journal of Physical Chemistry A. 106 (15): 3706–3713.
Bibcode:
2002JPCA..106.3706W.
doi:
10.1021/jp013624f.
^Andrews, Lester; Wang, Xuefeng; Alikhani, Mohammad Esmaïl; Manceron, Laurent (6 March 2001). "Observed and calculated infrared spectra of {{Chem|Pd(H|2|)|1,2,3}} complexes and palladium hydrides in solid argon and neon". The Journal of Physical Chemistry A. 15 (13): 3052–3063.
Bibcode:
2001JPCA..105.3052A.
doi:
10.1021/jp003721t.
^Wang, Xuefeng; Andrews, Lester (24 April 2004). "Infrared spectra of indium hydrides in solid hydrogen and neon". The Journal of Physical Chemistry A. 108 (20): 4440–4448.
Bibcode:
2004JPCA..108.4440W.
doi:
10.1021/jp037942l.
^Wang, Xuefeng; Andrews, Lester (29 June 2002). "Neon Matrix Infrared Spectra and DFT Calculations of Tungsten Hydrides WH x (x = 1−4, 6)". The Journal of Physical Chemistry A. 106 (29): 6720–6729.
Bibcode:
2002JPCA..106.6720W.
doi:
10.1021/jp025920d.
^Andrews, Lester; Wang, Xeufeng; Manceron, Laurent (22 January 2001). "Infrared Spectra and Density Functional Calculations of Platinum Hydrides". The Journal of Chemical Physics. 114 (4): 1559.
Bibcode:
2001JChPh.114.1559A.
doi:
10.1063/1.1333020.
^Wang, Xuefeng; Andrews, Lester (19 March 2004). "Infrared Spectra of Thallium Hydrides in Solid Neon, Hydrogen, and Argon". The Journal of Physical Chemistry A. 108 (16): 3396–3402.
Bibcode:
2004JPCA..108.3396W.
doi:
10.1021/jp0498973.
^Matsuoka, T.; Fujihisa, H.; Hirao, N.; Ohishi, Y.; Mitsui, T.; Masuda, R.; Seto, M.; Yoda, Y.; Shimizu, K.; Machida, A.; Aoki, K. (5 July 2011). "Structural and valence changes of europium hydride induced by application of high-pressure H 2". Physical Review Letters. 107 (2): 025501.
Bibcode:
2011PhRvL.107b5501M.
doi:
10.1103/PhysRevLett.107.025501.
PMID21797616.
^Ma, Buyong; Collins, Charlene L.; Schaefer, Henry F. (January 1996). "Periodic Trends for Transition Metal Dihydrides MH , Dihydride Dihydrogen Complexes MH 2 ·H2 , and Tetrahydrides MH4 (M = Ti, V, and Cr)". Journal of the American Chemical Society. 118 (4): 870–879.
doi:
10.1021/ja951376t.
^Wang, Xuefeng; Andrews, Lester (January 2003). "Chromium Hydrides and Dihydrogen Complexes in Solid Neon, Argon, and Hydrogen: Matrix Infrared Spectra and Quantum Chemical Calculations". The Journal of Physical Chemistry A. 107 (4): 570–578.
Bibcode:
2003JPCA..107..570W.
doi:
10.1021/jp026930h.
^Wang, Xuefeng; Andrews, Lester (18 December 2008). "Infrared spectra and theoretical calculations for Fe, Ru, and Os metal hydrides and dihydrogen complexes". The Journal of Physical Chemistry A. 113 (3): 551–563.
Bibcode:
2009JPCA..113..551W.
doi:
10.1021/jp806845h.
PMID19099441.
^Wang, Xuefeng; Andrews, Lester (13 August 2008). "Infrared spectrum of the RuH 2(H 2) 4 complex in solid hydrogen". Organometallics. 27 (17): 4273–4276.
doi:
10.1021/om800507u.
^Wang, Xuefeng; Andrews, Lester (May 2004). "Infrared Spectra of Indium Hydrides in Solid Hydrogen and Neon". The Journal of Physical Chemistry A. 108 (20): 4440–4448.
Bibcode:
2004JPCA..108.4440W.
doi:
10.1021/jp037942l.
^Songster, J.; Pélton, A. D. (1 June 1993). "The H-Li (Hydrogen-Lithium) System". Journal of Phase Equilibria. 14 (3): 373–381.
doi:
10.1007/BF02668238.
^San-Martin, A.; Manchester, F. D. (1 June 1990). "The H-Na (Hydrogen-Sodium) System". Bulletin of Alloy Phase Diagrams. 11 (3): 287–294.
doi:
10.1007/BF03029300.
^San-Martin, A.; Manchester, F. D. (1 October 1987). "The H−Mg (Hydrogen-Magnesium) System". Journal of Phase Equilibria. 8 (5): 431–437.
doi:
10.1007/BF02893152.
^Qiu, Caian; Olson, Gregory B.; Opalka, Susanne M.; Anton, Donald L. (1 November 2004). "Thermodynamic evaluation of the Al-H system". Journal of Phase Equilibria and Diffusion. 25 (6): 520–527.
doi:
10.1007/s11669-004-0065-1.
ISSN1863-7345.
^Sangster, J.; Pelton, A. D. (1 August 1997). "The H-K (Hydrogen-Potassium) System". Journal of Phase Equilibria. 18 (4): 387–389.
doi:
10.1007/s11669-997-0066-y.
^Predel, B. (1993). "Ca-H (Calcium-Hydrogen)". In Madelung, O. (ed.). Ca-Cd – Co-Zr. Landolt-Börnstein - Group IV Physical Chemistry. Springer Berlin Heidelberg. pp. 1–3.
doi:
10.1007/10086082_696.
ISBN978-3-540-47411-1.
^Manchester, F. D.; Pitre, J. M. (1 April 1997). "The H-Sc (Hydrogen-Scandium) System". Journal of Phase Equilibria. 18 (2): 194–205.
doi:
10.1007/BF02665706.
^San-Martin, A.; Manchester, F. D. (1 February 1987). "The H−Ti (Hydrogen-Titanium) System". Bulletin of Alloy Phase Diagrams. 8 (1): 30–42.
doi:
10.1007/BF02868888.
^Predel, B. (1996). "H-V (Hydrogen-Vanadium)". In Madelung, O. (ed.). Ga-Gd – Hf-Zr. Landolt-Börnstein - Group IV Physical Chemistry. Springer Berlin Heidelberg. pp. 1–5.
doi:
10.1007/10501684_1565.
ISBN978-3-540-44996-6.
^San-Martin, A.; Manchester, F. D. (1 June 1995). "The H-Mn (Hydrogen-Manganese) System". Journal of Phase Equilibria. 16 (3): 255–262.
doi:
10.1007/BF02667311.
^San-Martin, A.; Manchester, F. D. (1 April 1990). "The Fe-H (Iron-Hydrogen) System". Bulletin of Alloy Phase Diagrams. 11 (2): 173–184.
doi:
10.1007/BF02841704.
^Wayman, M. L.; Weatherly, G. C. (1 October 1989). "The H−Ni (Hydrogen-Nickel) System". Bulletin of Alloy Phase Diagrams. 10 (5): 569–580.
doi:
10.1007/BF02882416.
^Predel, B. (1994). "Cu-H (Copper-Hydrogen)". In Madelung, O. (ed.). Cr-Cs – Cu-Zr. Springer Berlin Heidelberg. pp. 1–3.
ISBN978-3-540-47417-3.
^San-Martin, A.; Manchester, F. D. (1 December 1989). "The H-Zn (Hydrogen-Zinc) System". Bulletin of Alloy Phase Diagrams. 10 (6): 664–666.
doi:
10.1007/BF02877640.
^Sangster, J.; Pelton, A. D. (1 February 1994). "The H-Rb (Hydrogen-Rubidium) System". Journal of Phase Equilibria. 15 (1): 87–89.
doi:
10.1007/BF02667687.
^Khatamian, D.; Manchester, F. D. (1 June 1988). "The H−Y (Hydrogen-Yttrium) System". Bulletin of Alloy Phase Diagrams. 9 (3): 252–260.
doi:
10.1007/BF02881276.
^Zuzek, E.; Abriata, J. P.; San-Martin, A.; Manchester, F. D. (1 August 1990). "The H-Zr (Hydrogen-Zirconium) System". Bulletin of Alloy Phase Diagrams. 11 (4): 385–395.
doi:
10.1007/BF02843318.
^Okamoto, H. (1 April 2013). "H-Nb (Hydrogen-Niobium)". Journal of Phase Equilibria and Diffusion. 34 (2): 163–164.
doi:
10.1007/s11669-012-0165-2.
^
abMaterials Science International Team (2006). "Au-H-Pd (Gold - Hydrogen - Palladium)". In Effenberg, G.; Ilyenko, S. (eds.). Noble Metal Systems. Selected Systems from Ag-Al-Zn to Rh-Ru-Sc. Landolt-Börnstein - Group IV Physical Chemistry. Vol. 11B. Berlin: Springer Berlin Heidelberg. pp. 1–8.
doi:
10.1007/10916070_26.
ISBN978-3-540-46994-0.
^Subramanian, P.R (1 December 1991). "The Ag-H (Silver-Hydrogen) System". Journal of Phase Equilibria. 12 (6): 649–651.
doi:
10.1007/BF02645164.
^Songster, J.; Pelton, A. D. (1 February 1994). "The H-Cs (Hydrogen-Cesium) System". Journal of Phase Equilibria. 15 (1): 84–86.
doi:
10.1007/BF02667686.
^San-Martin, A.; Manchester, F. D. (1 June 1991). "The H-Ta (Hydrogen-Tantalum) System". Journal of Phase Equilibria. 12 (3): 332–343.
doi:
10.1007/BF02649922.
^Guminski, C. (1 October 2002). "The H-Hg (Hydrogen-Mercury) System". Journal of Phase Equilibria. 23 (5): 448–450.
doi:
10.1361/105497102770331460.
^Khatamian, D.; Manchester, F. D. (1 February 1990). "The H-La (Hydrogen-Lanthanum) System". Bulletin of Alloy Phase Diagrams. 11 (1): 90–99.
doi:
10.1007/BF02841589.
^Manchester, F. D.; Pitre, J. M. (1 February 1997). "The Ce-H (Cerium-Hydrogen) system". Journal of Phase Equilibria. 18 (1): 63–77.
doi:
10.1007/BF02646759.
^Zinkevich, M.; Mattern, N.; Handstein, A.; Gutfleisch, O. (13 June 2002). "Thermodynamics of Fe–Sm, Fe–H, and H–Sm Systems and its Application to the Hydrogen–Disproportionation–Desorption–Recombination (HDDR) Process for the System Fe 17Sm 2–H 2". Journal of Alloys and Compounds. 339 (1–2): 118–139.
doi:
10.1016/S0925-8388(01)01990-9.
^Manchester, F. D.; San-Martin, A. (1 June 1995). "The H-U (Hydrogen-Uranium) System". Journal of Phase Equilibria. 16 (3): 263–275.
doi:
10.1007/BF02667312.