Abstract:
The phonon spectrum, crystal structure, and stability of the ruthenocene molecule at ambient and high pressures were studied. The crystal had an orthorhombic structure Pnma, $Z$ = 4, $a$ = 7.119 $\mathring{\mathrm{A}}$, $b$ = 8.9899 $\mathring{\mathrm{A}}$, $c$ = 12.8084 $\mathring{\mathrm{A}}$, and $V_0$ = 819.73$\mathring{\mathrm{A}}$. A change in the parameters at high pressure could be described by the Murnaghan equation of state $(V_0/V)^{B'}=1+\{P \cdot B'/B_0\}$ with $B_0$ = 9.68 GPa and $B'$ = 6.1 up to a pressure of 4 GPa, above which a drastic increase in the mosaic parameters was observed in the X-ray diffraction patterns. The pressure dependence of phonon frequencies under hydrostatic compression changed abruptly at $\sim4$, $\sim8$, and $\sim5$ GPa in the first, second, and third series of measurements, respectively. The results of all measurements for a decrease in the pressure differed from those for an increase in the pressure, the changes being irreversible. Under non-hydrostatic compression, the changes occurred gradually in the range of $\sim$4 to $\sim$10 GPa. The ruthenocene molecule was stable in the eclipsed conformation; however, jumps to the staggered conformation were possible under heating. The energy barrier between the conformations determined from the Arrhenius dependence of the bandwidth of intermolecular phonons on temperature was (273 $\pm$ 19) meV/molecule.
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