Archive for the ‘Hypervalency’ Category
Saturday, November 23rd, 2013
Mercury (IV) tetrafluoride attracted much interest when it was reported in 2007[1] as the first instance of the metal being induced to act as a proper transition element (utilising d-electrons for bonding) rather than a post-transition main group metal (utilising just s-electrons) for which the HgF2 dihalide would be more normal (“Is mercury now a transition element?”[2]). Perhaps this is the modern equivalent of transmutation! Well, now we have new speculation about how to induce the same sort of behaviour for caesium; might it form CsF3 (at high pressures) rather than the CsF we would be more familiar with.[3] Here I report some further calculations inspired by this report.
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References
- X. Wang, L. Andrews, S. Riedel, and M. Kaupp, "Mercury Is a Transition Metal: The First Experimental Evidence for HgF<sub>4</sub>", Angewandte Chemie International Edition, vol. 46, pp. 8371-8375, 2007. https://doi.org/10.1002/anie.200703710
- M. Miao, "Caesium in high oxidation states and as a p-block element", Nature Chemistry, vol. 5, pp. 846-852, 2013. https://doi.org/10.1038/nchem.1754
Tags:animation, energy, free energy barrier, free energy change, metal, pence, post-transition main group metal, potential energy surface
Posted in Hypervalency, Interesting chemistry | 13 Comments »
Monday, July 8th, 2013
A feature of a blog which is quite different from a journal article is how rapidly a topic might evolve. Thus I started a few days ago with the theme of dicarbon (C2), identifying a metal carbide that showed C2 as a ligand, but which also entrapped a single carbon in hexa-coordinated mode. A comment was posted bringing attention to the origins of the discovery of hexacoordinated carbon, and we moved on to exploring the valency in one such species (CLi6). Here I ask if hydrogen itself might exhibit such coordination.
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Tags:chemical shift, metal atoms, metal carbide
Posted in Hypervalency, Interesting chemistry | 2 Comments »
Friday, July 5th, 2013
A comment made on the previous post on the topic of hexa-coordinate carbon cited an article entitled “Observation of hypervalent CLi6 by Knudsen-effusion mass spectrometry“[1] by Kudo as a amongst the earliest of evidence that such species can exist (in the gas phase). It was a spectacular vindication of the earlier theoretical prediction[2],[3] that such 6-coordinate species are stable with respect to dissociation to CLi4 and Li2.
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References
- H. Kudo, "Observation of hypervalent CLi6 by Knudsen-effusion mass spectrometry", Nature, vol. 355, pp. 432-434, 1992. https://doi.org/10.1038/355432a0
- E.D. Jemmis, J. Chandrasekhar, E.U. Wuerthwein, P.V.R. Schleyer, J.W. Chinn, F.J. Landro, R.J. Lagow, B. Luke, and J.A. Pople, "Lithiated carbocations. The generation, structure, and stability of CLi5+", Journal of the American Chemical Society, vol. 104, pp. 4275-4276, 1982. https://doi.org/10.1021/ja00379a051
- P.V.R. Schleyer, E.U. Wuerthwein, E. Kaufmann, T. Clark, and J.A. Pople, "Effectively hypervalent molecules. 2. Lithium carbide (CLi5), lithium carbide (CLi6), and the related effectively hypervalent first row molecules, CLi5-nHn and CLi6-nHn", Journal of the American Chemical Society, vol. 105, pp. 5930-5932, 1983. https://doi.org/10.1021/ja00356a045
Tags:energy, gas phase, Knudsen, low energy 2s/2p carbon, metal-metal bonding, pence
Posted in Hypervalency, Interesting chemistry | 7 Comments »
Wednesday, May 15th, 2013
In the preceding post, I introduced Dewar’s π-complex theory for alkene-metal compounds, outlining the molecular orbital analysis he presented, in which the filled π-MO of the alkene donates into a Ag+ empty metal orbital and back-donation occurs from a filled metal orbital into the alkene π* MO. Here I play a little “what if” game with this scenario to see what one can learn from doing so.
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Tags:African Union, alkene-metal compounds, empty metal orbital, energy, filled metal orbital, free energy, Historical, lower energy form, metal
Posted in Hypervalency, Interesting chemistry | 1 Comment »
Saturday, March 16th, 2013
Functionalisation of a (hetero)aromatic ring by selectively (directedly) removing protons using the metal lithium is a relative mechanistic newcomer, compared to the pantheon of knowledge on aromatic electrophilic substitution. Investigating the mechanism using quantum calculations poses some interesting challenges, ones I have not previously discussed on this blog.
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Tags:carbon-metal bond, lithiation, metal, metal alkyls, metal lithium, pericyclic, Reaction Mechanism, Tutorial material
Posted in Hypervalency, Interesting chemistry | 2 Comments »
Saturday, January 21st, 2012
Chemistry rarely makes it to the cover of popular science magazines. Thus when this week, the New Scientist ran the headline “Forbidden chemistry. Reactions they said could never happen“, I was naturally intrigued. The examples included Woodward and Hoffmann’s “symmetry-forbidden” reactions, which have been the subject of several posts here already. But in the section on nobel gas chemistry, the same Hoffmann is reported as having been shocked to hear of a compound of xenon and gold, both of which in their time were thought of as solidly inert, and therefore even more unlikely to form a union.
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Tags:New Scientist, nobel gas chemistry, scientist, the New Scientist
Posted in Hypervalency, Interesting chemistry | No Comments »
Wednesday, August 3rd, 2011
Unusual bonds are always intriguing, and the Xe-Xe bond is no exception. It was first reported (10.1002/anie.199702731) for the species Xe2+. Sb4F21– and its length (3.09Å) was claimed as “unsurpassed in length in main group chemistry by any other element -element bond”. Krapp and Frenking then creatively tweaked the bond (in a computer). The counterion was replaced by C60, and the two xenon atoms placed inside! Buckyballs have a fascinating ability to absorb electrons, up to six in fact, from whatever is placed inside the cavity, and so this assembly acts as a rather intriguing ion-pair. So the issue reduces to how many electrons does C60 manage to scavenge from two Xenon atoms, and what is the nature of any resulting bonding formed between these two atoms?
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Tags:endohedral complexes, Extreme chemical intimacy, ultimate chemical bond
Posted in Hypervalency, Interesting chemistry | 1 Comment »
Sunday, June 26th, 2011
A little while ago, I speculated (blogs are good for that sort of thing) about hexavalent carbon, and noted how one often needs to make (retrospectively) obvious connections between two different areas of chemistry. That post has attracted a number of comments in the two years its been up, along the lines: what about carboranes? So here I have decided to explore that portal into boron chemistry. The starting point is the reported crystal structure of a molecule containing a CH12B11– anion (DOI: 10.1021/ja00201a073). This differs from the molecule I previously reported in having not so much 5C-C + 1C-H bonds around a single carbon, but instead 5B-C + 1C-H bonds. The basic cluster is much in fashion (as B12Cl122-) for its properties as a non-coordinating counterion.
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Tags:ELF, QTAIM
Posted in Hypervalency | 1 Comment »