[jclough]

Hi all,

Does anybody know what the shape of a [P4] dianion is? Is it the same as the P4 tetrahedron, but perhaps with a double bond somewhere...? Or perhaps does it adopt a new shape, such as a square? I also know that P tends to favour forming sigma bonds, as opposed to pi ones, but without changing the formula (ie. P4) I can't think of a way of incorporating further sigma bonds. I have also been fiddling about with orbital hybridisation...

It's probably quite simple, but any suggestions would be very welcome!

[sjb]

By analogy with cyclobutene, I can't see it being a square (which has 4 identical sides). What it may form, though is a tetrahedron (like the uncharged species), but with a slightly shorter bond length - not quite as short as an isolated P=P bond which can be delocalised. There are 2 pi electrons here, which could indicate an aromatic system. Is it described or prepared anywhere?

S

[jclough]

Thanks for your reply! That was the conclusion that my tutor came to... although he didn't really know for sure either...

I'm not sure if it's actually prepared as such- it was actually from an exam question I was doing as practice...

[sjb]

Piqued by this, I actually had a quick literature search, and it seems that the structure is, partially at least, dependent on the counter-ion. Do you have access to the literature? Perhaps see http://dx.doi.org/10.1021/ic0514445 or http://dx.doi.org/10.1002/chem.200500414 ? (modified to use dois)