Thermal Properties and Crystal Structures of Ionic Liquids from Ruthenium Sandwich Complexes with Trialkoxybenzene Ligands: Effects of Substituent Positions and Alkyl Chain Lengths

2015-04-13T00:00:00Z (GMT) by Takahiro Ueda Tomoyuki Mochida
A series of ionic liquids containing [Ru­(C<sub>5</sub>H<sub>5</sub>)­(arene)]<sup>+</sup>, where the arene ligands are 1,2,3-C<sub>6</sub>H<sub>3</sub>(OC<sub><i>n</i></sub>H<sub>2<i>n</i>+1</sub>)<sub>3</sub> and 1,3,5-C<sub>6</sub>H<sub>3</sub>(OC<sub><i>n</i></sub>H<sub>2<i>n</i>+1</sub>)<sub>3</sub> (<i>n</i> = 6, 12, and 18), were synthesized. The counteranions were PF<sub>6</sub> and FSA (bis­(fluorosulfonyl)­amide). The melting points of the PF<sub>6</sub> and FSA salts were 33–93 °C and −18–62 °C, respectively. In the PF<sub>6</sub> salts, the melting points of the 1,3,5-derivatives were lower than those of the 1,2,3-derivatives by 28–55 °C, whereas no such tendency was observed in the FSA salts. X-ray crystallography showed the formation of lamellar structures in the PF<sub>6</sub> salts of the 1,2,3-derivatives in the solid state. In these crystals, cation–anion pairs via C<sub>Cp</sub>H···F H-bond-like interactions were commonly observed. Several 1,3,5-derivatives showed metastable phases with lower melting points than the stable phases. The salts of the 1,2,3-derivative (<i>n</i> = 2) were also synthesized and characterized.