Borromean links and other non-conventional links in ‘polycatenated’ coordination polymers: re-examination of some puzzling networks

Abstract

A number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the ‘polycatenanes’ class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion.