Unique Thermal Structural Phase Transitions Exhibited by Unsymmetrical Organometallic Gold(III)‐Dithiolene Complexes with Pentylthio and Hexylthio Groups

Abstract

AbstractUnsymmetrical gold(III)‐dithiolene complexes are potential candidates for molecular materials that exhibit thermal structural phase transitions. In this study, unsymmetrical ppy‐gold(III) (ppy−=C‐deprotonated‐2‐phenylpyridine(−)) complexes [AuC5] and [AuC6] coordinated by dithiolene ligands containing tetrathiafulvalene (TTF) skeletons with pentylthio (2‐{bis(pentylthio)‐1,3‐dithiol‐2‐ylidene}‐1,3‐dithiol‐4,5‐dithiolate(2−)) and hexylthio groups (2‐{bis(hexylthio)‐1,3‐dithiol‐2‐ylidene}‐1,3‐dithiol‐4,5‐dithiolate(2−)) were synthesized. Both complexes exhibited a large absorption band at approximately 508 nm, owing to intramolecular ligand‐to‐ligand charge transfer. One‐dimensional columnar structures with head‐to‐tail molecular arrangements around the metal ions were constructed in the crystals. The flexible alkylthio groups were intercalated into crystalline spaces between dithiolene ligands in the columns. [AuC5] exhibits a simple phase transition at 198 °C between crystalline and isotropic phases irreversibly. The crystalline phase of [AuC6] observed at 25 °C melted at 148 °C. Another crystalline phase grew above 148 °C with a very slow crystallization rate from the liquid phase and was completely transformed into an isotropic phase at 200 °C.