Bringing a New Flexible Mercaptoacetic Acid Linker to the Design of Coordination Polymers

Two new 3D coordination polymers (CPs), formulated as [Zn(p-XBT)]_n (1H) and [Cd(p-XBT)]_n (2H), were assembled from a virtually unexplored p-xylylene-bis(2-mercaptoacetic) acid linker (p-XBTA) and characterized by infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), thermal analysis methods (TG-DSC, TG-FTIR), single-crystal X-ray diffraction, and topological analysis. Two different synthetic strategies were explored, namely the precipitation (P) and hydrothermal (H) methods, resulting in a Zn(II) derivative [Zn(p-XBT)·H₂O]_n (1P) and its dehydrated analogue [Zn(p-XBT)]_n (1H), respectively. In the Cd(II)-containing system, the same [Cd(p-XBT)]_n (2P = 2H) products were generated by both synthetic methods. Upon dehydration, 1P undergoes a "crystal-to-crystal" phase transition in the 170-185 °C temperature range, producing an anhydrous polycrystalline sample (1H). Both CPs 1H and 2H are isostructural and feature polymeric 3D metal-organic nets of the cds topological type, which are driven by the 4-linked metal and p-XBT^2- nodes. These compounds represent unique examples of coordination polymers derived from p-xylylene-bis(2-mercaptoacetic) acid, thus opening up the use of this flexible S,O-heterodonor building block in the design of polymeric metal-organic architectures.