Multiple Phase Transition Behavior of Silver Thiophenolates with Rigid Aromatic Rings and Flexible Alkoxy Chains

Silver thiolate coordination polymers (CPs) exhibit diverse structures and physical properties, although thermal behavior of silver thiophenolate CPs has rarely been investigated. In this study, we investigated the effects of ligands containing rigid aromatic rings and flexible alkoxy chains on the thermal phase transitions of silver thiophenolate CPs. A series of para -alkoxy-substituted silver thiophenolate CPs (AgSAr-OCX, where X denotes the number of carbon atoms in the alkoxy chain) were prepared through ligand exchange reactions. Structural characterization revealed that all AgSAr-OCX derivatives formed layered crystal structures and that the conformational order of alkyl chains increased with increasing chain length. DSC analysis showed that the number and temperatures of the thermal transitions strongly depended on alkyl chain length, with longer-chain derivatives exhibiting multiple thermal events. Variable-temperature powder X-ray diffraction measurements revealed two successive lamellar-to-lamellar transitions followed by transformation into a hexagonal columnar phase for the longer-chain derivatives. Variable-temperature FT-IR measurements further indicated conformational disordering of the alkyl chains during the reversible low-temperature transition. These multiple phase transitions may arise from the combination of rigid aromatic rings that stabilize the layered structures and flexible alkoxy chains that provide thermal responsiveness through conformational changes.