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.

References

1. W.D. Allen, H. Quanz, and P.R. Schreiner, "Polytriangulane", Journal of Chemical Theory and Computation, vol. 12, pp. 4707-4716, 2016. http://dx.doi.org/10.1021/acs.jctc.6b00669
2. J. Steidel, R. Steudel, and A. Kutoglu, "Röntgenstrukturanalysen von Cyclododekaschwefel (S₁₂) und Cyclododekaschwefel‐1‐Kohlendisulfid (S₁₂ · CS₂) [1]", Zeitschrift für anorganische und allgemeine Chemie, vol. 476, pp. 171-178, 1981. http://dx.doi.org/10.1002/zaac.19814760520
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. http://dx.doi.org/10.1021/ic00325a026