Wikipedia:Reference desk/Archives/Science/2018 December 10

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December 10

What's the largest (smallest sphere containing van der Waals surface) molecule that's single bonds in a hub-and-spoke shape?

Tetrahedral protactinium tetratantalide? Mononeptunium heptatantalide?

And what's the largest diatomic molecule? Francium astatide? Francium tantalide? Francium ceside? Difrancium gas? Sagittarian Milky Way (talk) 02:31, 10 December 2018 (UTC)

I was thinking you could get the longest bond length out of a noble gas (taking care not to make it infinite!) so something like tetraxenonogold(II) might be a step in the right direction, though that's an ion, so it won't count any more than dixenon cation. No idea if anyone has ever been nuts enough to make tetraradonogold. This "source" [1] claims that "The longest known bond length occurs in the Noble gas compound Xe2Sb2F11. The Xe-Xe single bond in this compound is 3.0871 Å." I haven't tried to run that down, since it's also not within the criteria. Wnt (talk) 14:27, 10 December 2018 (UTC)

For diatomic see dihelium. Graeme Bartlett (talk) 20:58, 10 December 2018 (UTC)

Just to highlight a key detail from that article, the He–He distance in that compound is 52 Å (!). It's a Van der Waals molecule, however, so it's possibly not surprising that the bond is so much longer than in a normal covalent situation. DMacks (talk) 10:21, 11 December 2018 (UTC)

That's about the length of this: Sagittarian Milky Way (talk) 17:21, 11 December 2018 (UTC)

Yeah, but the OP said "within a Van der Waals radius", so any Van der Waals molecule automatically fails. Wnt (talk) 02:21, 12 December 2018 (UTC)

So what's the largest ionic molecule that Cesium (rather than Francium) bonds with? 67.175.224.138 (talk) 12:12, 16 December 2018 (UTC).