Dihydrogen bond: Difference between revisions

image and mention H---H distances
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(image and mention H---H distances)
In [[chemistry]], a '''dihydrogen bond''' is a kind of [[hydrogen bond]], an interaction between a [[metal hydride]] bond and an OH or NH group or anotherother [[proton]] donor. TheWith firsta examplevan der Waals radius of this1.2 phenomenonÅ, ishydrogen creditedatoms todo Brownnot andusually Heseltineapproach other hydrogen atoms closer than 2.4 Å. Close approaches near 1.8 Å, are however characteristic of dihydrogen bonding.<ref>{{Cite journalname=ChemRev/>
 
An early example of this phenomenon is credited to Brown and Heseltine.<ref>{{Cite journal
| issue = 23
| pages = 1551–1552
| date = 1996-01-01
| pmid = 19904922
}}</ref> In other words, the amine is a protic acid and the borane end is hydridic. The resulting B&minus;H<sup>...</sup>H&minus;N attractions stabilize the molecule as a solid. In contrast, the related substance [[ethane]], H<sub>3</sub>CCH<sub>3</sub>, is a gas with a boiling point 285 °C lower. Because two hydrogen atomscenters are involved, thisthe interaction is termed a dihydrogen bond.
 
[[File:DihydrogenBondingBH4-H2O.png|thumb|Dihydrogen bonding is evident in the close H---H contacts between water of crystallization and the borohydride anion in the salt NaBH<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>.<ref name=ChemRev/>]]
 
Formation of a dihydrogen bond is assumed to precede formation of H<sub>2</sub> from the reaction of a hydride and a protic acid. A very short dihydrogen bond is observed in NaBH<sub>4</sub>·2H<sub>2</sub>O with H&minus;H contacts of 1.79, 1.86, and 1.94 Å.<ref name=ChemRev>{{Cite journal
| doi = 10.1021/cr000021b
| volume = 101