Ever since the concept of a shared two-electron bond was conjured by Gilbert N. Lewis in 1916,[cite]10.1021/ja02261a002[/cite] chemists have been fascinated by the related concept of a bond order (the number of such bonds that two atoms can participate in, however a bond is defined) and pushing it ever higher for pairs of like-atoms.
I have posted often on the chemical phenomenon known as hypervalency, being careful to state that as defined it applies just to “octet excess” in main group elements. But what about the next valence shell, occurring in transition metals and known as the “18-electron rule”? You rarely hear the term hypervalency being applied to such molecules, defined presumably by the 18-electron valence shell count being exceeded.
Another post inspired by a comment on an earlier one; I had been discussing compounds of the type I.I n (n=4,6) as possible candidates for hypervalency.
Last year, this article[cite]10.1038/nchem.2716[/cite] attracted a lot of attention as the first example of molecular helium in the form of Na 2 He. In fact, the helium in this species has a calculated ‡ bond index of only 0.15 and it is better classified as a sodium electride with the ionisation induced by pressure and the presence of helium atoms.
I discussed the molecule the molecule CH3F2- a while back.
Recollect the suggestion that diazomethane has hypervalent character[cite]10.1039/C5SC02076J[/cite]. When I looked into this, I came to the conclusion that it probably was mildly hypervalent, but on carbon and not nitrogen. Here I try some variations with substituents to see what light if any this casts.
In the previous post, I referred to a recently published review on hypervalency[cite]10.1039/C5SC02076J[/cite] which introduced a very simple way (the valence electron equivalent γ) of quantifying the effect. Diazomethane was cited as one example of a small molecule exhibiting hypervalency (on nitrogen) by this measure.
A recently published review on hypervalency[cite]10.1039/C5SC02076J[/cite] introduced a very simple way of quantifying the effect. One of the molecules which was suggested to be hypervalent using this method was diazomethane. Here I take a closer look.
Alkalides are anionic alkali compounds containing e.g. sodide (Na–), kalide (K–), rubidide (Rb–) or caeside (Cs–). Around 90 examples can be found in the Cambridge structure database (see DOI: 10.14469/hpc/3453 for the search query and results). So what about the ammonium analogue, ammonide (NH4–)? A quick search of Scifinder drew a blank!
An article with the title shown above in part recently appeared.[cite]10.1038/s41598-017-02687-z[/cite] Given the apparent similarity of HF 1- to CH 3 F 1- and CH 3 F 2- , the latter of which I introduced on this blog previously, I thought it of interest to apply my analysis to HF 1- . The authors[cite]10.1038/s41598-017-02687-z[/cite] conclude that “ the F atom of HF −