Molecular polygons and tubes

Molecular structure of the nickel wheel. The bridging pyridone and terminal THF ligands point alternately above and below the mean plane of the twelve nickel atoms. From A. J. Blake, C. M. Grant, S. Parsons, J. M. Rawson and R. E. P. Winpenny. Chem. Commun., 2363—4 (1994). 

The two independent tpst ligands are each bound to four silver atoms but in different coordination modes three pyridyl N plus one thioether S, or three pyridyl N plus one triazine N. The silver atoms exhibit two kinds of coordination modes normal linear AgN2 and a very unusual AgN2S2 mode of distorted square-planar geometry. 

Structure of a square molecular tube in M[N(CN)2]2(apym) (M=Co, Ni). From P. Jensen, S. R. Batten, B. Moubaraki and K. S. Murray, Chem. Commun., 

---