Haiges et al. (2004)

Welcome to the exciting world of “Highly Energetic Materials” where molecules are just waiting to get back to nitrogen gas, and perhaps take a finger or hand with them.

How to study such oddities, well IR is the way to go. Sprinkle and season with some group theory (Wednesday) and by Friday you’ll be ready to tackle this one.

Wednesday will be our crash course into the wicked and wonderful world of infra-red spectra prediction.


16 Responses to “Haiges et al. (2004)”

  1. Tony Says:

    It is crazy that they are trying to “tame” such an unstable molecule like N5+. I am guessing the ultimate application of such compound is either rocket fuel or bombs. How useful can this molecule really be considering it explodes at room temperature and is extremely shock sensitive? What can they use as stabilizers?

    Upon reading up on the author it is curious that his goal is to make “green” energetic materials. I guess that considering that the byproduct is nitrogen gas which is as harmful as air (because it’s basically air) he’s on the right track.

    In a sense this paper is probably the closest we are going to get to my research topic considering it deals with green high energy sources just like my research does so it was great to see some inorganic self relevance.

    • profhurst Says:

      Ok, this is an excellent start. Now, let’s try to delve a little bit deeper into the chemistry specifics and the use of symmetry and group theory.

    • Daniel B Says:

      I took a look at the first paper that was cited in the article. And they say that because of how sensitive the N5+ is, HF was used as a stabilizer.

      “A final important point is the need for a reaction mediumthat offers good solubility at low temperatures, can act as a heat sink for the exothermic reaction, and can stabilize a product that is potentially very shock sensitive. For N5,anhydrous HF was chosen because of its high dipole moment,low meltin g point (ÿ 808C), and high volatility.”

    • Adam Settimo Says:

      Yes, I think I came across something related to this “Thomas Klapötke and Davin Piercey of the University of Munich were trying to make a green alternative primary explosive,” using a ten nitrogen chain. An alternative to lead azide.

  2. Porter Marsh Says:

    The paper says that the direct synthesis is restricted by the small number of [N2F]+ salts. The paper then goes on to address the practicality of other types of synthesis since the direct synthesis from [N2F]+ salts is impractical
    My question is about why the low number of [N2F]+ salts is a problem. They’ve shown it can work and there four choices for [N2F]+ salts. If it works when they only have 4 choices, how many different salts would be enough? What about there only being 4 choices is impractical?

    • profhurst Says:

      Because you can’t use different anions to try and stabilize the molecule. It’s also a justification to say well if only we had a new method, maybe we could get something stable.

  3. Daniel B Says:

    This paper BLEW my mind!

    On the other hand, it raised a couple questions for about the group theory. I noticed that this paper did not show any specific salt structures, I assumed N5+ had a linear structure. I had to go exploring other papers to find theoretical structures of N5+. I was surprised to see it had a bend shape, making it non-linear. Giving it 9 vibrational modes (by using the wonderful equation we’ve been given) instead of 10, if it were a linear structure. How much of a difference would it make if it was observed to be a linear structure instead?

    My second question deals with Table 1. While looking it over, I noticed that all the Ramen frequencies were relatively the same for each N5+ salt compared with their standard deviations. Do the counter ions ([SbF6]+, [PF6]+, [BF4]+, [SO3F]+) play a role as a variable to determine the Ramen frequencies for each N5+ salt? Or is their sole prupose to hold that salt together to assist in the identification of N5+?

  4. Hunter Burgin Says:

    I think it is safe to say that pentazenium is a very potent molecule with explosive capabilities making it ideal for use as rocket fuel or explosives. In regards to our discussion on Wednesday about group theory and vibrational modes for a given molecule, I wondered if these two factors attributed to multi-nitrogen containing molecule’s explosive nature. The cation N5+, when by itself, has a total of 9 possible vibrational modes (3×5-6) making me wonder if a high amount of vibrational modes could attribute to pentazenium’s temperamentally explosive nature and desire to return to its nitrogen gas state. Does the high amount of vibrational modes present in N5+ make the molecule more likely to break apart into its lower energy gas state?

    • profhurst Says:

      No, there is not really a link between vibrations and instability. Other molecules have similar geometry and are very stable.

      The sensitivity is a thermodynamic issue, not a spectroscopic one.

  5. Josh Ellsworth Says:

    Given that the article assigns C2v symmetry to the pentazenium ion, and that there are 9 predicted vibrations present in the IR spectra, what methodology led the authors to exclude the vibration that occurs at 2210ish? Since it of the same class (?) of vibration as the 8 other B2 vibrations, what methodology is used to exclude one vibration from the rest of the herd? Is it possible that it is a reported peak from the teflon tube as there are no assignments given to the counter-ion at that wavelength? (It doesn’t make sense that the peak would be included in the table if that was the case).

    I noticed the same trend occuring in the raman spectroscopy. There are reported peaks more or less common to the different counter-ions that are not given an assignment. Does the observed frequency allow for tossing a peak out of the running? For that matter, is it possible to predict the frequency of an IR peak for such a highly energetic species?, or do the authors rely on data from other related compounds, like sodium azide? It seems that although azide has a completely different point group that the frequency of its vibrations would be similar to pentazenium (One could live dangerously and take spectra of lead or copper azide to match the point group, assuming that one can take the whole coordination compounds’ geometry into account). Exactly what criteria is used to distinguish relevant peaks from the red herrings?

  6. Adam Settimo Says:

    Some quick reads for those who have an abundance of time:



    I guess I would have to keep things short. Since we are talking about group theory and therefore symmetry, I feel like I’m missing something here. I have to admit first being a little surprised by the bending of these long nitrogen chains and why they might do that. If they are indeed chains and have the option of being straight and keeping as much distance from each other, then what would cause the bends as a conformations. They should of course vibrate in this way, but not bend that way.

    Also, While there is mention of some of the chemical structure in this paper, and further for some into point groups, there are a lot of structures presented that do not give indication of their structure and therefore their symmetry.

    Finally, I know that this seems like a very simple and obvious question to answer, but towards the end of the paper there is talk of other compounds that also have formula weights of over 90% Nitrogen. Their formulas and weights are listed, but I’m assuming the higher the formula weight, the higher the kcal/mol? I ask because there isn’t any talk of their types of bonds and structure, which makes me wonder about bond angles and lengths, which makes me wonder about the energy in the bonds.

  7. Kevin Greenwood Says:

    My question is in the same vein as Daniel’s regarding counterions. In looking over table 1, I noticed that all of the Raman peaks showed up at approximately the same place. All except for the N5+ peaks as associated with two of the cations. The A2 and B1 vibrations are missing under the hexafluorophosphate salt, but are present for all the others but one. The hexafluoroantimonate salt also has a missing signal corresponding to the B1 vibration. What is it about these salts that would cause missing signals? Looking into it further I learned that both of these salts are valence isoelectronic, but as they are just the counterions, I don’t see how that would have much of an effect on vibrations in the pentazenium cation.

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