Ionic Conductivities Induced by the Partial Solvent Molecule Removal from Diruthenium(II,III) Adamantanecarboxylate Salts

Abstract

Ionic conductivities are observed in the BF4– salts of the Ru2(II,III) dinuclear paddlewheels with adamantyl carboxylates [RuII,III2(R-AdCOO)4(MeOH)2]BF4·MeOH (R-AdCOO– = 3-R-adamantanecarboxylate, 1, R = H; 2, R = F; and 3, R = OH), according to the partial removal of the solvent MeOH molecules. In the crystal structures of 1–3, disordered MeOH molecules and BF4– ions are found at the neighboring sites surrounded by the adamantyl groups. The packing structures of 1 and 2 are almost identical, whereas 3 crystallizes in a different structure from that of 1 and 2, accompanied by a hydrogen-bonding network between the 3-OH-adamantyl groups. In the electron density maps at 300 K, the globular adamantyl groups of 1 and 2 fluctuate severely, whereas no significant fluctuations of the 3-OH-adamantyl group are found in 3. The impedance data are collected for the freshly prepared crystals of 1–3 during heating, and the data are analyzed using an equivalent circuit containing a frequency-independent capacitance (εr1), a capacitance following a Debye-type relaxation (εr2), and a conductive component (σ4) in the range of 78–350 K. At approximately 200 K, the εr2 values increase and semicircles are observed in the complex permittivity plots, corresponding to the orientational polarization of the MeOH molecules enclosed in the disordered sites surrounded by the adamantyl groups. The εr2 values of 1 and 2 are much larger than those of 3 because of the fluctuations in the adamantyl units surrounding the MeOH solvent molecule. At approximately 300 K, the σ4 values are highly evolved and semicircles are found in the complex impedance plots. Gradual weight losses are observed in the thermogravimetries at approximately 300 K, and the ionic conductivities are probably induced by the partial removal of the MeOH molecules neighboring the BF4– ions. The σ4 values of 3 are much larger than those of 1 and 2, which could be attributed to the robust framework of the hydrogen bonds between the 3-OH-adamantyl groups. The activation energies estimated by the Arrhenius plots are in the typical range of solid-state ionic conductors with hopping ion diffusion.