The effects of loading up lots of dispersion attractions (between t-butyl groups) into a compact molecule has the interesting consequence of allowing two “non-bonded” hydrogen atoms to approach to ~1.5Å of each other, thus creating the appearance of a “bond” where one normally would not be found. Can such an effect be injected into other combinations of two atoms, say H and F? Here I briefly explore this notion.

About 18 months ago, there was much discussion on this blog about a system reported by Bob Pascal and co-workers containing a short H…H contact of ~1.5Å[cite]10.1021/ja407398w[/cite]. In this system, the hydrogens were both attached to Si as Si-H…H-Si and compressed together by rings.

Both the cyclopropenium cation and the cyclopentadienide anion are well-known 4n+2-type aromatic ions, but could the two together form an ion-pair? A search of the Cambridge structure database reveals 52 instances of the cyclopropenium cation with a variety of counter-anions, 77 cyclopentadienide anions with a variety of counter-cations and one (SOWMOG, private communication to CSD) where the two sub-structures are common.

In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an “isolated” symmetrical cation is +ve, which means it is a true minimum and not a transition state for a [1,2] shift.

Occasionally one comes across a web site that manages to combine being unusual, interesting and also useful. Thus www.molinsight.net is I think a unique chemistry resource for blind and visually impaired students. If you think perhaps that it might be a little too specialised to be useful for you, go visit it first.

A few years back I followed a train of thought here which ended with hexacoordinate carbon, then a hypothesis rather than a demonstrated reality. That reality was recently confirmed via a crystal structure, DOI:10.5517/CCDC.CSD.CC1M71QM[cite]10.1002/anie.201608795[/cite]. Here is a similar proposal for penta-coordinate nitrogen. First, a search of the CSD (Cambridge structure database) for such nitrogen.

The Wikipedia entry on peroxydisulfate is quite short (as of today). But I suspect this article may change things.[cite]10.1038/s41559-017-0083[/cite]. A search of the Cambridge structure database reveals around 18 high quality crystal structures containing this species are known, many as metal salts.

This is another of those posts that has morphed from an earlier one noting the death of the great chemist George Olah.

George Olah passed away on March 8th. He was part of the generation of scientists in the post-war 1950s who had access to chemical instrumentation that truly revolutionised chemistry.

The thread thus far. The post about Na ₂ He introduced the electride anionic counter-ion to Na ⁺ as corresponding topologically to a rare feature known as a non-nuclear attractor. This prompted speculation about other systems with such a feature, and the focus shifted to a tetrahedral arrangement of four hydrogen atoms as a dication, sharing a total of two valence electrons. The story now continues here.