“Star of David” catenane. Two triply entwined rings composed of carbon, hydrogen, and nitrogen are linked together with bridging iron atoms via a complex chemical synthetic pathway to cross each other six times and form a hexagram (six-pointed star). The chemical structure is indicated on the left, where the two independent rings are colored blue and orange. On the right is the three-dimensional structure determined by x-ray crystallography with the carbon atoms of one ring in blue and the other light gray; irons are pink and nitrogens purple. In the center is a noncovalently bound, negatively charged phosphorus hexafluoride (cyan and green).

See D. A. Leigh, R. G. Pritchard, and A. J. Stephens, 2014, Nature Chem. 6:978–982.