Unusual six-connected self-catenated network with 5-fold interpenetrated CdSO4 subnets: stepwise synthesis, topology analysis and fluorescence properties

Abstract

In this work, the rod-like ligand 4,4′-bis(imidazol-1-yl)-biphenyl (L) has been utilized as a long building block to perform an intensive study on the entanglement of metal–organic frameworks (MOFs). The room-temperature reaction of Cd(ClO₄)₂·6H₂O with ligand L in a glass-tube affords a new coordination polymer {[Cd(ClO₄)₂(L)₂]·(CH₃OH)·(H₂O}_∞ (1), which exhibits an inter-digitated (4,4) layer pierced by the ClO₄⁻ ion. Considering the weak coordination affinity of the ClO₄⁻ ion and that it could be easily replaced by other ions, complex 1 was employed as a precursor to react with NH₄Cl, resulting in a novel organic–inorganic hybrid material {[CdCl(L)₂](ClO₄)·(H₂O)_5.5·(CH₃OH)_0.5}_∞ (2). In complex 2, the heteroleptic octahedral Cd^II node is connected by the linear spacer L into a five-fold interpenetrated CdSO₄ framework. Then, the subnet is further linked together by the Cl⁻ ion to form an unusual self-catenated network with the Schäfli symbol of 4⁴·6¹⁰·8. Great structural diversities in 1 and 2 reveal that the counterion plays an important role in the self-assembly of MOFs. Furthermore, complexes 1 and 2 both exhibit solid-state fluorescence properties at room temperature.