Unusual six-connected self-catenated network with 5-fold interpenetrated CdSO4subnets: 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 CdII 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 Schafli 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.