Temperature-controlled Cd(II)–phosphonate coordination polymers: Syntheses, crystal structures, and luminescent properties

Two temperature-controlled Cd(II)–phosphonate coordination polymers have been synthesized successfully. Compound {[Cd2(H4tpmb)(H2O)3]}n (1; H8tpmb = 1,2,4,5-tetrakis(phosphorylmethyl)benzene) produced at 80 °C adopts a three-dimensional network with a Cd:H2O ratio of 2:3, while compound {[Cd(H6tpmb)(H2O)4]·4H2O}n (2) synthesized at room temperature displays a zigzag one-dimensional chain structure with a Cd:H2O ratio of 1:4. The phosphonate ligand is partially deprotonation, being a form of H4tpmb4− in 1 and H6tpmb2− in 2, where the former shows a μ8-bridging mode with a cis,trans,cis,trans conformation while the latter adopts a μ2-bridging mode with a trans,cis,trans,cis conformation. These results indicate that water molecules make higher competition in coordinating with the Cd(II) center of such materials at room temperature, while at 80 °C, the water molecules are more labile and the coordination of phosphonate to the Cd(II) center becomes dominant. This clearly illustrates a case of temperature-modulated complexation of phosphonate ligand and water molecule towards the Cd(II) center, which result in differences in ligand charges, ligand conformations, and coordination modes, leading to drastic variations of network topologies.

Graphical abstractTwo temperature-controlled Cd(II)–phosphonate coordination polymers which clearly illustrate the potential and significance in a self-assembly system. The phosphonate ligand in the two Cd-based MOFs shows different coordination modes and different ligand conformations, which can be attributed to the flexible binding of the phosphonate ligands. These results also indicate that water molecules make higher competition in coordinating with the Cd(II) center of such materials at room temperature, while at 80 °C, the water molecules are more labile and the coordination of phosphonate to the Cd(II) center becomes dominant.Figure optionsDownload full-size imageDownload as PowerPoint slide