Recently, researchers of the State Key Laboratory for Oxo Synthesis and Selective Oxidation (OSSO), Lanzhou Institute of Chemical Physics (LICP), CAS, have designed a bis(4-pyridylurea) receptor (L), and reported four coordination polymers built from L and metal salts: {[CdL2(H2O)2]Cl2.2H2O}n (1), {[CdL2(H2O)2](NO3)2}n (2), {[CoL2(H2O)2]Cl2.2H2O}n (3), and {[CoL2(H2O)2]SO4.6H2O}n (4). These polymeric systems, despite the different metal centers and counter anions, feature an unprecedented type of entangled structure, the simplest 1D /1D interpenetration, formed by parallel and collinear interpenetration of two ribbons of M2L2 rings.

In the past few decades, the design and self-assembly of entangled coordination polymers have attracted great attention not only for their various chemical and physical properties and possible applications in catalysis, ion exchange, photochemistry, and gas storage, etc. but also for their intriguing architectures and topologies. Interpenetrating coordination polymers are one of the most important subjects in the area of entangled systems; in particular, low-dimensional interpenetrating structures have stimulated much interest because of their promising potential applications as molecular devices. Under a strategy of ‘‘network approach’’, by judicious choice of the bridge ligand and metal ion, low-dimensional entangled coordination polymers may be constructed. Batten reviewed that 1D / 1D interpenetrated structures by the catenation of two, ribbons of rings or ladders would be one of the possible future topologies.

However, at present there are very limited examples of low-dimensionality interpenetrations compared to high-dimensionality ones, because supramolecular isomerism or polymorphism occurs very frequently during the self-assembling processes for desired low-dimensional structures. The 1D/1D interpenetration was first observed in the hydrogen-bonded molecular ladders, and only one known example of 1D parallel interpenetrated coordination polymer was authenticated in 2007. The construction of low-dimensional structures is still a challenge facing the synthetic chemist.

The above-mentioned work of the researchers of the OSSO was published in CrystEngComm (CrystEngComm, 2010, 12, 2001–2004).

 Abstract of the paper published in CrystEngComm