New Single-Element Compound Discovered

We've had bucky balls, C60, for a long time. Why is B28 a compound and C60 is not?

An excellent question. Any chemists know?

Why should this discovery rewrite chemistry books, if other large single-element molecules - carbon buckyballs (C60) and other fullerenes - are known since 1985?
And why should either even be called "compound", if they are not compound in the classical sense?

My understanding is that C60 and other fullerenes are uniform molecules (ie: each atom in the molecule is the same) and this compound is made of two different ions of the same element. But, as usual, I am probably wrong.

"...reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B2 pairs and B12 clusters and the resultant charge transfer between them."

I'm a chemist. Boron is very tricky. Because of the extreme hybridization (recombining the atomic orbitals with various percentages of "s" and "p" character), this may be where they're going. So, the hybridization, combined importantly with the geometry of the small cluster (only 28 atoms) is probably where they're going. I'll read the paper, but there has been a lot of success out of Canada w/ making aluminum clusters that behave entirely differently from elemental aluminum.

I think the journalist misread the abstract..

Yes, I believe, we are just observing a new hoax in its status nascendi.

Instead of Boron Boride can we call this 2-borine?

Physorg - when the readers are smarter than the editors. Thank you guys (particulary CptSunbeam) for straightening this up.

CptSunbeam says: "You also claim that different behaviour is significant. It is not. Graphite and diamond are both the same element, with very different properties. Many substances undergo dramatic phase changes under different conditions without their chemical character being altered."

I'm NOT a chemist, so I have to ask: do you mean that different behavior of two different substances, made of the same element, isn't significant in the sense that they're chemically identical, and so their different behaviors doesn't make for significant chemical differences? Graphite and diamond certainly have different behaviors (and appearance) in other ways than their identical chemical composition, that many people would find significant.

CptSunbeam -

no, I was correct. I just saw his (the first author's) talk about a month and a half back. He's here, @ stony brook. I read the whole paper. The B_12 icosahedra and the B_2 dimers are, in fact, acting as cations and anions - in other words, the geometry of the boron hybridization is allowing for aliovalency. So, not only are the space groups of the two subsets different (the B_2 dimer has the rocksalt structure, for example), but the resultant spacegroup (Pnnm) is different from the subsets as well. Note that this is a very extreme example, as this is under extreme pressue (~89GPa). But they actually give a DOS (density of states) in figure 4 of both the theoretical and the empirical, which make the B_2 dimer a p-type semiconductor and the B_12 an n-type, respectively.

This is effectively a high-pressure analog of the Al_12 clusters discovered (as I alluded to in my first post) by Bergeron, et al. in 2005.

So, no, while the material may be monoelemental, the hybridization, coupled with the geometry of the crystalline unit cell, can, in fact produce behavior that is radically different from the element itself. I suggest you review the rules regarding spherical harmonics Y(l,m) and the role that the Legendre polynomials play. You can constructively add them, but they end up being n-rank tensors (w/ n being the number, as you probably recall, of principal axis systems involved in the molecule), which makes the math extremely challenging. The resultant supergroup of electron density would then, as in this case, behave with either covalency or ionicity or, properties of both.

btw, your reference to allotropes like diamond, graphite, coal, etc. is not analogous. Yes, their behavior is radically different, as the space groups of graphite and diamond are dramatically different - however, the carbon atoms in both examples are uniform and no superclusters of carbon atoms are formed. C60, as mentioned by another post is still an allotrope. The geometry of the ball is what makes it so interesting. condensed matter physicists love this thing, since you can put a single potassium atom on it, which donates its single electron and then the ball acts as a diode, depending on the E field applied. Put H2 inside the C60 ball and you can watch the 1H NMR spin vector couple to the angular momentum of of the rotating H2 molecule. The dielectric isolation of the cage also provides for some fascinating chemistry inside the ball, but the C60 so far (besides creating a new space group) hasn't demonstrated superatomic behavior...

CptSunbeam -

it's behaving like a different compound, it is not a new compound, per se. As I said before, the forms of carbon are allotropes. I did provide evidence: Bergeron et al., which you did not read.

As Bergeron note, typically, aluminum is a metal (usually 5 oxidation state), but superclusters of aluminum atoms behave like halogens (-1), physically impossible for aluminum, unless properties far more profound than simple geometry are employed. The same phenomena are exhibited here.

Can anyone name any other single element substance with ionic bonding? I cannot. I guess that's the key. The research paper mentioned that the new phase can be considered as "boron boride" because of the ionic bonding. C60 has covalent bonding. All metals have metalic bonding. B28 is the only one with ionic bonding if I read it correctly.

about the chemical elements for nanoscience

http://nanochemic...spot.com