Catenated atoms and groups.

Chemists are as fond of records as any, although I doubt you will find many chemical ones in the Guinness world records list. Polytriangulanes chase how many cyclopropyl 3-rings can be joined via a vertex. Steve Bachrach on his blog reports some recent work by Peter Schreiner and colleagues[1] and the record for catenation of such rings appears to be 15. This led me to think about some other common atoms and groups. Here I have searched for crystal structures only; there may be examples of course for which no such data has been reported.

  1. For the halogens F and Cl it is 3. 
  2. But for Br, believe it or not it reaches the heady value of 24, doi: 10.5517/CC14K0PD[2]
  3. For iodine it is effectively infinite, as noted in my earlier post.
  4. For oxygen it is 3; there are none with four consecutive oxygens.
  5. For sulfur, a ring of twelve is known[3] and for Se ~11[4]
  6. For nitrogen it may surprise to learn it reaches 6 if the connecting bonds are all single. A typical example can be seen at doi: 10.5517/CCZCR35[5] It reaches 10 if any kind of  N-N bond is allowed. doi: 10.5517/CCYVNZD
  7. For phosphorus, 16 is not uncommon 10.5517/CC1JWTQY [6] but the record may be 21.
  8. The alkyne group C≡C, reaches 10 (20 carbon atoms), doi: 10.5517/CCSGR98 [7]
  9. The carbonyl group (C=O) can form a ring of six such groups 10.5517/CC9JR6R[8]

Such records are probably very uncompetitive; I doubt any researchers set out to extend the count. Most of the above are probably simply unexpected discoveries. My favourite is the bromine example; this element so often surprises.


  1. W.D. Allen, H. Quanz, and P.R. Schreiner, "Polytriangulane", Journal of Chemical Theory and Computation, vol. 12, pp. 4707-4716, 2016.
  2. J. Steidel, R. Steudel, and A. Kutoglu, "R�ntgenstrukturanalysen von Cyclododekaschwefel (S12) und Cyclododekaschwefel-1-Kohlendisulfid (S12 � CS2) [1]", Zeitschrift f�r anorganische und allgemeine Chemie, vol. 476, pp. 171-178, 1981.
  3. M.G. Kanatzidis, and S.P. Huang, "Unanticipated redox transformations in gold polyselenides. Isolation and characterization of diselenobis(tetraselenido)diaurate(2-) and undecaselenido(2-)", Inorganic Chemistry, vol. 28, pp. 4667-4669, 1989.

3 Responses to “
Catenated atoms and groups.

  1. Henry Rzepa says:

    The 3D structure for this [Cl8]2- species can be seen at doi: 10.5517/ccdc.csd.cc1kwp7c

  2. Henry Rzepa says:

    Almost as soon as I asserted that the record for a string of P atoms joined to each other was 21, an example with an infinite such chain is found. It is part of a double helix, see this post.

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