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. 2018 Jan 31;3(1):1293-1297.
doi: 10.1021/acsomega.7b01580. Epub 2018 Jan 30.

Asymmetric Choreography in Pairs of Orthogonal Rotors

Antonio Rodríguez-Fortea  1 , Jiří Kaleta  2 , Cécile Mézière  3 , Magali Allain  3 , Enric Canadell  4 , Pawel Wzietek  5 , Josef Michl  2   6 , Patrick Batail  3
Affiliations

Asymmetric Choreography in Pairs of Orthogonal Rotors

Antonio Rodríguez-Fortea et al. ACS Omega. .

Abstract

An asymmetric mechanism for correlated motion occurring in noninteracting pairs of adjacent orthogonal 1,4-bis(carboxyethynyl)bicyclo[1.1.1]pentane (BCP) rotators 1 in the solid state is unraveled and shown to play an important role in understanding the dynamics in the crystalline rotor, Bu4N+[1-]·H2O. Single crystal X-ray diffraction and calculation of rotor-rotor interaction energies combined with variable-temperature, variable-field 1H spin-lattice relaxation experiments led to the identification and microscopic rationalization of two distinct relaxation processes.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(A) A pair of layers of strings of hydrogen-bonded anions 1 that stack on top of each other along c in Bu4N+[1–]·H2O (Bu4N+ omitted for clarity). Hydrogen-bonded water molecules impose the orthogonal configuration of the two layers within a pair; (B) C–H···H–C (blue dotted lines) and C–H···O (red dotted lines) hydrogen bonds, which determine rotor–rotor and rotor–carboxylate interactions, respectively. Both the majority (0.71) and minority (0.29) occupancy positions (darker and lighter atoms and lines, respectively) of the BCP rotators in dynamic equilibrium in the lattice are represented.
Figure 2
Figure 2
Variable-temperature 1H spin–lattice relaxation time, T1–1, at 57 and 209 MHz for a static crystalline sample of Bu4N+[1–]·H2O. The red and blue solid lines represent the fit of the data to the Kubo–Tomita formula, τc = τ0 exp(Ea/kT), yielding Ea1 = 823 K (1.63 kcal mol–1) and Ea2 = 990 K (1.97 kcal mol–1), respectively, and the attempt correlation times of τ1 = 5.6 × 10–13 s and τ2 = 4.4 × 10–13 s, respectively.
Figure 3
Figure 3
Majority−majority (ma−ma), majority−minority (ma−mi), and minority−minority (mi−mi) configurations given by the crystal structure (Figure 1).
Scheme 1
Scheme 1
Figure 4
Figure 4
(A) Two protocols for the geometry optimization: Either (i) θ1 is given a set value and the geometry of the three blades of each rotor is optimized or (ii) θ1 and θ2 are given set values to impose a motion of both rotors (see text), and the geometry is optimized. The computed energy profiles for the ma–ma (B) and ma–mi (C) pairs of BCP rotators (see the text for a detailed explanation).
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