Archive for the ‘Hypervalency’ Category

Never mind main group “hypervalency”, what about transition metal “hypervalency”?

Sunday, March 18th, 2018
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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. So the following molecule (drawn in three possible valence bond representations) first made in 1992 intrigues.[1]

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References

  1. R. Ahlrichs, D. Fenske, H. Oesen, and U. Schneider, "Synthesis and Structure of[Ni(PtBu6)] and[Ni5(PtBu)6(CO)5] and Calculations on the Electronic Structure of[Ni(PtBu)6] and(PR)6, R=tBu,Me", Angewandte Chemie International Edition in English, vol. 31, pp. 323-326, 1992. http://dx.doi.org/10.1002/anie.199203231

Hypervalent or not? A fluxional triselenide.

Saturday, February 24th, 2018
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Another post inspired by a comment on an earlier one; I had been discussing compounds of the type I.In (n=4,6) as possible candidates for hypervalency. The comment suggests the below as a similar analogue, deriving from observations made in 1989.[1]

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References

  1. Y. Mazaki, and K. Kobayashi, "Structure and intramolecular dynamics of bis(diisobutylselenocarbamoyl) triselenide as identified in solution by the 77Se-NMR spectroscopy", Tetrahedron Letters, vol. 30, pp. 2813-2816, 1989. http://dx.doi.org/10.1016/S0040-4039(00)99132-9

Hypervalent Helium – not!

Friday, February 16th, 2018
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Last year, this article[1] attracted a lot of attention as the first example of molecular helium in the form of Na2He. 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. The helium is neither valent, nor indeed hypervalent (the meanings are in fact equivalent for this element). In a separate blog posted in 2013, I noted a cobalt carbonyl complex containing a hexacoordinate hydrogen in the form of hydride, H. A comment appended to this blog insightfully asked about the isoelectronic complex containing He instead of H. Here, rather belatedly, I respond to this comment!

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References

  1. X. Dong, A.R. Oganov, A.F. Goncharov, E. Stavrou, S. Lobanov, G. Saleh, G. Qian, Q. Zhu, C. Gatti, V.L. Deringer, R. Dronskowski, X. Zhou, V.B. Prakapenka, Z. Konôpková, I.A. Popov, A.I. Boldyrev, and H. Wang, "A stable compound of helium and sodium at high pressure", Nature Chemistry, vol. 9, pp. 440-445, 2017. http://dx.doi.org/10.1038/nchem.2716

Hypervalent hydrogen?

Saturday, January 13th, 2018
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I discussed the molecule the molecule CH3F2- a while back. It was a very rare computed example of a system where the added two electrons populate the higher valence shells known as Rydberg orbitals as an alternative to populating the C-F antibonding σ-orbital to produce CH3 and F. The net result was the creation of a weak C-F “hyperbond”, in which the C-F region has an inner conventional bond, with an outer “sheath” encircling the first bond. But this system very easily dissociates to CH3 and F and is hardly a viable candidate for experimental detection.  In an effort to “tune” this effect to see if a better candidate for such detection might be found, I tried CMe3F2-. Here is its story.

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Are diazomethanes hypervalent molecules? An attempt into more insight by more “tuning” with substituents.

Tuesday, December 26th, 2017
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Recollect the suggestion that diazomethane has hypervalent character[1]. 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.

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References

  1. M.C. Durrant, "A quantitative definition of hypervalency", Chemical Science, vol. 6, pp. 6614-6623, 2015. http://dx.doi.org/10.1039/C5SC02076J

Can any hypervalence in diazomethanes be amplified?

Saturday, December 23rd, 2017
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In the previous post, I referred to a recently published review on hypervalency[1] 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. Here I explore the effect of substituting diazomethane with cyano and nitro groups.

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References

  1. M.C. Durrant, "A quantitative definition of hypervalency", Chemical Science, vol. 6, pp. 6614-6623, 2015. http://dx.doi.org/10.1039/C5SC02076J

Are diazomethanes hypervalent molecules? Probably, but in an unexpected way!

Saturday, December 23rd, 2017
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A recently published review on hypervalency[1] 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.

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References

  1. M.C. Durrant, "A quantitative definition of hypervalency", Chemical Science, vol. 6, pp. 6614-6623, 2015. http://dx.doi.org/10.1039/C5SC02076J

Ammonide: an alkalide formed from ammonia and resembling an electride.

Sunday, December 17th, 2017
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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! So here I take a look at this intriguingly simple little molecule.

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Identification of a simplest hypervalent hydrogen fluoride anion.

Friday, December 8th, 2017
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An article with the title shown above in part recently appeared.[1] Given the apparent similarity of HF1- to CH3F1- and CH3F2-, the latter of which I introduced on this blog previously, I thought it of interest to apply my analysis to HF1-.

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References

  1. M. Liu, H. Chen, C. Chin, T. Huang, Y. Chen, and Y. Wu, "Identification of a Simplest Hypervalent Hydrogen Fluoride Anion in Solid Argon", Scientific Reports, vol. 7, 2017. http://dx.doi.org/10.1038/s41598-017-02687-z

Octet expansion and hypervalence in dimethylidyne-λ6-sulfane.

Tuesday, November 28th, 2017
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I started this story by looking at octet expansion and hypervalence in non-polar hypercoordinate species such as S(-CH3)6, then moved on to S(=CH2)3. Finally now its the turn of S(≡CH)2.

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