Archive for January, 2020

Molecules of the year 2019: Hexagonal planar crystal structures.

Thursday, January 23rd, 2020

Here is another selection from the Molecules-of-the-Year shortlist published by C&E News, in which hexagonal planar transition metal coordination is identified. This was a mode of metal coordination first mooted more than 100 years ago,[1] but with the first examples only being discovered recently. The C&E News example comprises a central palladium atom surrounded by three hydride and three magnesium atoms, all seven atoms being in the same plane.

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References

  1. M. Garçon, C. Bakewell, G.A. Sackman, A.J.P. White, R.I. Cooper, A.J. Edwards, and M.R. Crimmin, "A hexagonal planar transition-metal complex", Nature, vol. 574, pp. 390-393, 2019. http://dx.doi.org/10.1038/s41586-019-1616-2

Comment on “Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces”: The 7Σ heptet excited states for related molecules.

Thursday, January 2nd, 2020

I noted in an earlier blog, a potential (if difficult) experimental test of the properties of the singlet state of dicarbon, C2. Now, just a few days ago, a ChemRxiv article has been published suggesting another (probably much more realistic) test.[1] This looks at the so-called 7Σ open shell state of the molecule where three electrons from one σ and two π orbitals are excited into the corresponding σ* and π* unoccupied orbitals. The argument is presented that these states are not dissociative, showing a deep minimum and hence a latent quadruple bonding nature. They also note that the isoelectronic BN molecule IS dissociative. Thus to quote: “Hence, the proof of existence of a minimum in the 7Σu+ for C2 and the absence of such a minimum in the equivalent case for BN is likely to corroborate our findings on quadruple bonding in these two cases.

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References

  1. I. Bhattacharjee, D. Ghosh, and A. Paul, "Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective", 2019. http://dx.doi.org/10.26434/chemrxiv.11446224.v1