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Analytical Chemistry

Triangulene, By Force

The molecule on the right is triangulene, and it’s an odd one. You’d think at first that you could fill everything in with alternating double bonds, like a small piece of graphite or a bigger relative of anthracene, but when you try, you find that the geometry won’t let you. You’re either going to end up with a “Texas carbon” (five bonds), or you’re going to have electrons left that aren’t involved in a bond at all (as shown). The molecule has been kicking around for decades on fume sashes and chalkboards/whiteboards, but no one has ever been able to synthesize it. It’s theoretically stable (for some values of “stable”) but should be extremely reactive.

So non-chemical synthesis has stepped in. In a new paper, a team at IBM’s Zürich facility has used their expertise with the scanning tunneling microscope to make single molecules of triangulene by the most direct route imaginable. They start from the dihydro form (prepared at the University of Warwick), with CH2 groups on the side, and then step in on an individual molecule with an STM/AFM tip to rip off two hydrogens like picking apples off a tree branch. The molecule that’s left sitting on the surface is indeed triangulene – it’s perfectly flat, and its EPR behavior is what you would expect from the triplet diradical. As long as you keep it at low temperature, it seems stable – one of the molecules they made hung around for days on a copper surface.

Press coverage of this work has mentioned that triangulene might be useful in quantum computing, and while that’s not wrong, I wouldn’t, uh, spin it that way. This is a molecule that we’ve known for a long time could exist, but no chemist had ever seen it or been able to make it. Now we can reach in and tug on individual atoms, though, and that does the trick – just the thought of direct mechanical synthesis being the way to make an elusive species like this is enough for me.


30 comments on “Triangulene, By Force”

  1. luysii says:

    How in the world could they be mass produced to produce the qubits for a quantum computer, never mind shielded, addressed individually etc. etc.

    1. anon says:

      Certainly not with this attitude. The technology in the future may allow us to synthesize it on larger scales. You have to start from somewhere.

    2. RM says:

      It sort of depends on how you imagine quantum computers being assembled. If you’re thinking along the lines of current integrated circuits, where you do something like bulk lithography, washing the surface with bulk amounts of chemicals (most of which wash off) then, yes, this sort of synthesis is probably not going to cut it.

      Another approach to hypothetical future quantum computers is nano-assembly, where you carefully assemble individual molecules into precise positions, using some sort of as-yet-to-be-developed AFM robot farm. If you’re thinking along those lines, this sort of synthesis might slot in nicely.

      1. loupgarous says:

        We’re already working with graphene at the industrial level, through a variety of methods, the best one depending on the specific use you have in mind for it. Graphene’s basically a sheet of carbon atoms in a hexagonal lattice (the ur-aromatic), one atom thick.

        It’s worth investigating what can be made along the same lines as fabricating triangulene but with graphene as a starting material. It’s possible all sorts of interesting structures could be made that way. Some may even be both interesting as building blocks in quantum technology and stable enough to fabricate and use industrially.

  2. myma says:

    what color is that thing?

    1. Erebus says:

      Who knows? They only made a couple of individual molecules, and those are too small to be resolved optically. (Smaller than the wavelength of visual light.)

      “What color is it” is a question that would take a hell of a long time, and a lot of work, to figure out.

      1. David Borhani says:

        QM calcs of band gap, no?

      2. Staus says:

        “Resolved” =/= “Detected”

        The size of the thing has no bearing on whether or not it can be detected. Single-molecule spectroscopy has been a field for nearly 20 years, which started with absorbance measurements on individual (cold) organic molecules. No reason you couldn’t do the same with this to figure out what wavelengths it absorbs. I would think with all of that free electron density it would have quite the extinction coefficient, too.

        Also, resolution only matters if you are trying to separate signals from different objects. If you’ve got one molecule absorbing or emitting on a surface, then there’s no need to resolve anything. Of course the image you generate will be blurred by the point spread function of the system, but assuming you could hit this with the right wavelength of light without it falling apart, generating that image should be routine.

        1. Erebus says:

          I stand corrected. Fascinating stuff!

        2. David says:

          I think the key there might be “without it falling apart” since it somehow continues to exist as a split -2 ion. I’d imagine hitting it with much anything would cause it to react with something?

          1. c says:

            Split -2 ion? This is a neutral diradical. Hydrogen atoms (electron included) are being ripped off, not protons.

  3. Argon says:

    It’s informal name is ‘Q-bert-ene’.

  4. Jack Straw from Wichita says:

    i am amazed they could “find” a single molecule on the surface. it can be a long effort to rastor the surface enough to find a bunch of 3D (ie surface bound organic molecules) structures growing up from a chip/wafer matrix. even then differentiating that “find” from noise can be challenging as well. i guess life AFM life is different with a CO tip.

    ….just the tip….just for a second to see how it feels

  5. Anon says:

    Pah, I’ve been synthesizing this compound for years. Generally on the surface of my barbecue pork chops.

  6. Jorgensen says:

    This would be trivial to make using Quinuclidine Abstraction Activation Mode(TM). We question whether it could be a persistent radical.

  7. Curious Wavefunction says:

    One of the many predictions from Feynman’s famous “There’s Plenty of Room at the Bottom” talk that was ahead of its time:

    “Ultimately, we can do chemical synthesis. A chemist comes to us and says, “Look, I want a molecule that has the atoms arranged thus and so; make me that molecule.” The chemist does a mysterious thing when he wants to make a molecule. He sees that it has got that ring, so he mixes this and that, and he shakes it, and he fiddles around. And, at the end of a difficult process, he usually does succeed in synthesizing what he wants. By the time I get my devices working, so that we can do it by physics, he will have figured out how to synthesize absolutely anything, so that this will really be useless.

    But it is interesting that it would be, in principle, possible (I think) for a physicist to synthesize any chemical substance that the chemist writes down. Give the orders and the physicist synthesizes it. How? Put the atoms down where the chemist says, and so you make the substance. The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed – a development which I think cannot be avoided.”

    1. What a time to be alive says:

      That exists already. Don’t you remember Drug Printer? The 3D printer that makes drugs atom by atom? Surely it was on this blog

    2. gippgig says:

      Reminds me of the first (as I recall) synthesis of perbromate – they synthesized selenate using a radioactive selenium isotope and let it decay to bromine.

      1. tangent says:

        That’s beautiful, and a different sort of brute force than AFM twiddling.

        I see the next perbromate synthesis involved XeF2, which is another kind of brute force too.

  8. Skeptick says:

    Is this really a molecule of triangulene, or is it a compound of copper and carbon? I.e., would it exist in free space or does it require being held together by a big block of copper?

  9. Anon says:

    This must be a world record for “lowest measurable yield”!

    1. anon electrochemist says:

      Hey now, it’s 100% pure!

  10. Barry says:

    wouldn’t the singlet diradical be EPR silent? So the triplet seen in EPR might be a rare minority contribution (or all or it, or anything in between)?

  11. Gaear Grimsrud says:

    ZZZZZZ, ZZZZZZzzzzzzz,zzzzzzz!

  12. loupgarous says:

    Actually, there MIGHT be a way to scale even this “brute force and crowbar the hydrogens off” synthesis of triangulene and similar molecules up – nanofabrication.

    Of course, nanofab is, itself, blue sky territory, mostly. But one could see how, using any of a number of newly-developed nanoengines to do the same thing as the electron microscope guys did, one could make the chemical in at least a modest, small-fraction-of-a-mole scale.

    What to do with it? I’m sure there’s a fellow at DARPA mulling that over as you read this.

  13. anonymous says:

    Waiting for “strangulatene ” from these laboratories!

  14. patently says:

    Wait for the flood of patent applications for previously unsynthesisable molecules citing this as their “sufficient” description of how to make it.

  15. Marya Lieberman says:

    In 1970, Ward and Pettit published paper (Chem Comm, 1970, p. 1419-1420) describing several amazingly stable low valent metal compounds of trimethylene methane (which is another ground state diradical, although one that can be synthesized in a frozen noble gas matrix). So my guess is that the copper is not “innocent”.

  16. Mike D. says:

    I guess that makes the STM the world’s most expensive enzyme?

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