U-Turn Compression to a New Isostructural Ferrocene Phase

Abstract

Ferrocene exhibits a most intriguing transformation reflected in highly anomalous compression of the crystal, involving a discontinuity in unit-cell parameter c and reversed sign of compression coefficient β b = 1/b•∂b/∂p. The origin of this unexpected property is connected to the rotational and vibrational states of bis(cyclopentadienyl)iron(II) molecules in the crystal environment transformed under the high-pressure conditions. At ambient pressure, the cyclopentadienyl rings are conformationally disordered in the double-well potential energy E p function in the structure of ferrocene phase I. Above 3.24 GPa, the single-well E p function prevails due to intermolecular interactions enhanced by pressure, which leads to the unprecedented isostructural phase transition to the ordered ferrocene phase I′. Combined laboratory and synchrotron diffraction as well as Raman spectroscopy have been applied for describing structural transformations associated with this unique phase transition.

Molecular dynamics study of ferrocene topology under various temperatures

“…This may explain the fact that the Fc crystalline exhibits monoclinic structures (staggered) at higher temperatures (T > 164 K), but triclinic structures (eclipsed) does so at lower temperatures (T < 164 K). [34,46] Triclinic structures are also known as the rhombohedrum system, which may be skewed or inclined to one side, making it oblique.…”

Influence of Solvent in Crystal Engineering: A Significant Change to the Order–Disorder Transition in Ferrocene

“…[4][5] Solid ferrocene exhibits dynamic disorder of the cyclopentadienyl (Cp) rings at ambient temperature but transforms to a more ordered structure with a semi-eclipsed conformation of the Cp rings below ca. 164 K. [6][7][8][9] A fully eclipsed form has been reported in recrystallization experiments below 100 K. 10 As one of the few air-stable metallocenes, ferrocene is an ideal component for fundamental studies in crystal engineering. The central idea behind our investigation of this and other binary adducts involving small aromatic molecules is that it is possible to use simple ideas of molecular electrostatics to explain observed crystal structures, and to predict novel structures.…”

Giant strain geared to transformable H-bonded network in compressed β-d-mannose

“…[17][18][19][20] However, in contrast to H 2 O ices, it is characteristic that high-pressure transitions of D-sucrose, at 4.8 GPa, and a-D-glucose, at 5.4 GPa, preserve their space-group symmetry and lattice translations, an occurrence encountered at high pressure for quite a few compounds. [21][22][23][24][25] Presently, we found that a much lower pressure induces an exceptionally strong transformation between Phases I and II of b-D-mannose. Such major microscopic changes may lead to notable macroscopic effects.…”