Further investigations of the crystal-to-crystal phase transition of a [2]pseudorotaxane composed of ferrocene-terminated dialkylammonium and dibenzo[24]crown-8-ether

Abstract

[2]Pseudorotaxane, [(FcCH₂NH₂CH₂C₆H₄-4-Me)(DB24C8)][PF₆] ([1][PF₆]; Fc = ferrocenyl and DB24C8 = dibenzo[24]crown-8-ether), undergoes crystalline phase transition at 128 °C upon heating and at 106 °C upon cooling (α-phase at low temperature; β-phase at high temperature), as shown in our previous reports. This paper presents new results from the detailed studies on the crystal phase transition of pseudorotaxane, the dielectric constant of the crystal, and the formation of a gel from a PhCl solution. The crystalline phase transition has been revealed to accompany the partial rotation of the DB24C8 molecule while maintaining the hydrogen bonds between the axle and macrocyclic component molecules. The ultrasonication of a PhCl suspension of a mixture of the axle and cyclic molecules forms a gel, which is composed of microcrystalline [1][PF₆] with a new crystal form (α′-phase). The pseudorotaxane crystals with mixed counter anions, [1][PF₆]_1−x[Y]_x (Y = AsF₆ and SbF₆), exist in the α- or β-phase, depending on the anion composition. Further, [1][PF₆]_0.28[AsF₆]_0.72 and [1][PF₆]_0.76[SbF₆]_0.24 are obtained in the α-phase, while [1][PF₆]_0.65[SbF₆]_0.35 crystallises in the β-phase. The phase transition temperature of the pseudorotaxane with PF₆⁻ and SbF₆⁻ counter anions is investigated using differential scanning calorimetry (DSC).