Rare-earth squarate frameworks with scu topology.

As a typical planar 4-connected ligand that possesses D4h symmetry, the squarate ligand is expected to construct some interesting topologies. Here, we report that the assembly of the squarate ligand with rare-earth ions can produce a series of (4, 8)-connected frameworks with the "smallest" scu type topology. Among these compounds, the Tb based analogue not only possesses a good proton conductivity, but also exhibits luminescence responses toward MnO4- and Cr2O72-, making it a candidate for multifunctional materials.