Structure of adamantane, C₁₀H₁₆, in the disordered phase

Abstract

Single-crystal X-ray diffraction data have been collected for disordered adamantane at room temperature (T = 293 K). The crystal structure is face-centred cubic with a = 9.445 (4),/k, Z = 4 and space group Fm3m. On the assumption of a rigid molecular skeleton, two kinds of orientational disorder have been investigated: isotropic free rotation of molecules around their centre of mass and hindered reorientations between equally weighted orientations. The second model gives the best fit and good agreement is found between observed and calculated structure factors (R w = 14.0%, R = 11.0%). The molecular packing then shows tertiary carbon atoms aligned in the I 1111 directions.

A cubic harmonic analysis of the plastic crystal structures of adamantane, C10H16, and adamantanone, C10H14O, at room temperature

“…We therefore fixed the three preceding parameters A2o+, to zero (space group Fm3m) for the further II refinements, whose results are summarized in Table 1. The calculated structure factors obtained with the cubic harmonics up to the order 10 are listed in the paper dealing with the Frenkel model (Amoureux, Bee & Damien, 1980). may not be negligible.…”

“…The 90 experimental structure factors, the definition of R w, the method of refinement and the five parameters defining the molecule are those described in the preceding paper (Amoureux, Bee & Damien, 1980). We therefore fixed the three preceding parameters A2o+, to zero (space group Fm3m) for the further II refinements, whose results are summarized in Table 1.…”

“…The stereographic projection (Fig. 2) of CCT(r) shows quasi-isotropic librations and so justifies the isotropic Debye-Waller factor (Willis & Pawley, 1970) we used in the Frenkel structure of adamantane (previous paper, Amoureux , Bee & Damien, 1980). The results obtained in the previous paper concerning the equilibrium positions and the translational and librational displacements ((U2X>vrenkel 2 1/2 = 0.048 _+ 0.003/~2, (0tsotropic)Frenkel --9.0 +_ 0.2 °) are in very good agreement with those we present now.…”

“…The normal structure investigations of these two plastic crystals at room temperature have already been reported: C~0H~40 , C~0H~6 (Amoureux, Bee & Damien, 1980). In these Frenkel models we used two uncoupled isotropic Debye-WaUer factors; the first one for the librations and the second for the translations.…”

Emergence of glassy-like dynamics in an orientationally ordered phase

“…Adamantane derivatives display a rich polymorphism that has stimulated a large number of experimental and theoretical investigations in order to rationalize the dynamics of the high-temperature orientationally disordered (OD) phases and, to a lesser extent, the low-temperature OO phases. [28][29][30][31] 2A=O is a "rigid" pseudoglobular molecule of C 2v symmetry obtained from adamantane by means of the substitution of two hydrogen atoms by one oxygen atom linked to a carbon by a double bond. Although the substitution of the oxygen atom gives rise to a strong dipole moment (μ = 3.4 D) 32,33 along the twofold symmetry axis, this compound exhibits still an OD high-temperature phase with face-centered-cubic (F m3m) symmetry appearing below the melting point at 529 K. 23,[33][34][35] This OD phase I transforms to an OO phase II at about 180 K. Due to high hysteresis, the transition is found at 205 K on heating from the stable phase II.…”