1,4-Bis(carboxylatoethynyl)bicyclo[2.2.2]octane : un rotor ultra-rapide dans un cristal de sel dilué est freiné au sein d’un métal multifonctionnel

1,4-Bis(carboxylatoethynyl)bicyclo[2.2.2]octane : un rotor ultra-rapide dans un sel dilué est freiné au sein d’un métal multifonctionnel1 L’objectif de ce travail est la conception de systèmes dans lesquels les propriétés dynamiques d’une machine moléculaire seraient corrélées aux propriétés électroniques que l’on rencontre habituellement dans les matériaux conçus au laboratoire par la technique d’électrocristallisation. Pour cela un sel dilué de formulation [nBu4N+]2[BABCO][BABCO–]2 a été préparé à partir du 1,4-di(ethynyl)bicyclo[2.2.2]octane synthétisé en neuf étapes2. Des expériences de temps de relaxation spin-réseau du 1H sur cristal statique montrent que deux environnements différents des rotors sont associés à des énergies d’activation et des fréquences de rotation différentes. Ce sel a été engagé dans un processus d’électrocristallisation avec le donneur d’électrons de type π EDT-TTF-CONH2 pour donner un nouveau métal organique cristallin : (EDT-TTF-CONH2)2[BABCO–], pour la première fois avec une fonctionnalité dynamique. Une seule position d’équilibre est observée pour le rotor dont on observe que l’énergie d’activation est grandement augmentée : ceci pourrait être attribué à des contraintes à la rotation accrues, expression d’un réseau dense d’interactions non covalentes (liaisons hydrogènes et interactions dihydrogène attractives3).  Ce matériau organique métallique ouvre la voie à d’autres systèmes multifonctionnels amphidynamiques. 1C. Lemouchi, C. Mézière, L. Zorina, E. Canadell, P. Wzietek, P. Auban-Senzier, C. Pasquier, P. Batail, soumis 2C. Lemouchi, C. Vogelsberg, S. Simonov, L. Zorina, P. Batail, S. Brown, M. A. Garcia-Garibay, J. Am. Chem. Soc., 133, 6371-6379 (2011). 3J. Echeverrıa, G. Aullon, D. Danovich, S. Shaik, S. Alvarez, Nature Chem., 2011, DOI: 10.1038/nchem.100

Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo 2.2.2 octane with Distinct Gigahertz Rotation at Two Sites

As a point of entry to investigate the potential of halogen-bonding interactions in the construction of functional materials and crystalline molecular machines, samples of 1,4-bis(iodoethynyl)bicyclo[2.2.2] octane (BIBCO) were synthesized and crystallized. Knowing that halogen-bonding interactions are common between electron-rich acetylenic carbons and electron-deficient iodines, it was expected that the BIBCO rotors would be an ideal platform to investigate the formation of a crystalline array of molecular rotors. Variable temperature single crystal X-ray crystallography established the presence of a halogen-bonded network, characterized by lamellarly ordered layers of crystallographically unique BIBCO rotors, which undergo a reversible monoclinic-to-triclinic phase transition at 110 K. In order to elucidate the rotational frequencies and the activation parameters of the BIBCO molecular rotors, variable-temperature H-1 wide-line and C-13 cross-polarization/magic-angle spinning solid-state NMR experiments were performed at temperatures between 27 and 290 K. Analysis of the H-1 spin-lattice relaxation and second moment as a function of temperature revealed two dynamic processes simultaneously present over the entire temperature range studied, with temperature-dependent rotational rates of k(rot) = 5.21 x 10(10) s(-1).exp(-1.48 kcal.mol(-1)/RT) and k(rot) = 8.00 x 10(10) s(-1).exp(-2.75 kcal.mol(-1)/RT). Impressively, these correspond to room temperature rotational rates of 4.3 and 0.8 GHz, respectively. Notably, the high-temperature plastic crystalline phase I of bicyclo[2.2.2]octane has a reported activation energy of 1.84 kcal.mol(-1) for rotation about the 1,4 axis, which is 24% larger than E-a = 1.48 kcal.mol(-1) for the same rotational motion of the fastest BIBCO rotor; yet, the BIBCO rotor has three fewer degrees of translational freedom and two fewer degrees of rotational freedom! Even more so, these rates represent some of the fastest engineered molecular machines, to date. The results of this study highlight the potential of halogen bonding as a valuable construction tool for the design and the synthesis of amphidynamic artificial molecular machines and suggest the potential of modulating properties that depend on the dielectric behavior of crystalline media

Second Harmonic Generation in molecular crystals with helical rotors

Date du colloque&nbsp;: 10/2011</p

Static Modulation Wave of Arrays of Halogen Interactions Transduced to a Hierarchy of Nanoscale Change Stimuli of Crystalline Rotors Dynamics

Here we present a study where what can be seen as a static modulation wave encompassing four successive arrays of interacting iodine atoms in cryst. 1,​4-​Bis((4\u27-​(iodoethynyl)​phenyl) ethynyl)​bicyclo[2,​2,​2]​octane rotors changes the structure from one-​half mol. to three-​and-​a-​half mols. in the asym. unit below a phase transition at 105 K.  The remarkable finding is that the total 1H spin-​lattice relaxation rate, T1-​1, of unprecedented complexity to date in mol. rotors, is the weighted sum of the relaxation rates of the four contributing rotors relaxation rates, each with distinguishable exchange frequencies reflecting Arrhenius parameters with different activation barriers (Ea) and attempt frequencies (τo-​1)​.  This allows us to show in tandem with rotor-​environment interaction energy calcns. how the dynamics of mol. rotors are able to decode structural information from their surroundings with remarkable nanoscale precision

Amino acid derivatives of perylenediimide and their N-H center dot center dot center dot O peptide bond dipoles-templated solid state assembly into stacks

A methodology is proposed to provide direct access in good yields to peptide residues-appended perylenediimides PDI-(Cl-4)-[Gly-Ala(OEt)](2), 2a, PDI-(Cl-4)-[Gly-Val(OEt)](2), 2b and PDI-(Cl-4)-[Gly-Gly(OEt)](2), 2c from a generic perylenediimide (PDI) platform symmetrically functionalized with carboxylic acids at the imide sites, PDI-(Cl-4)-[Gly(OH)](2), 1. The latter is obtained in good purity by a non classical two-steps route avoiding the many, notoriously cumbersome successive chromatography steps typical of PDI chemistry, and including a single final purification allowing to crystallize the water soluble pure diacid 1, of great interest in its own right for further developments in a variety of fields. Then, the synthesis, crystallization and analysis of the crystal structures of 2a and 2b reveal a common pattern of self-assembly of the outer peptide residues based on collections of parallel N-H center dot center dot center dot O peptidic hydrogen bonds running alongside stacks where the constraints imposed upon on the inner PDI skeletons by long range interaction of these parallel electric dipoles reduce the dihedral angles around the bay regions by as much as 11% down to 32 degrees

Changing gears to neutral in a polymorph of one-dimensional arrays of cogwheel-like pairs of molecular rotors

We report on a polymorph (2) of an amphidynamic crystal of molecular rods with two helical 1,4-bis(ethynyl)bicyclo[2.2.2]octane rotators where half of the rod-like molecules appear to be shifted with respect to their closest neighbours. This translation takes cogwheel-like pairs of rotators apart in the lattice in such a way that their motion becomes uncorrelated. This property is to be contrasted with the highly correlated motion found to govern the rotators in a recently-published polymorph 1 of the same material. As with polymorph 1, this motion is shown to take place independently of mutations in the handedness of the rotators and of the ‘mutamer’-induced second harmonic generation

A Crystalline Hybrid of Paddlewheel Copper(II) Dimers and Molecular Rotors: Singlet-triplet Dynamics Revealed by Variable-temperature Proton Spin-lattice Relaxation

10.1002/zaac.20130062

Reversible Control of Crystalline Rotors by Squeezing Their Hydrogen Bond Cloud Across a Halogen Bond-Mediated Phase Transition

  We report on a crystalline rotor that undergoes a reversible phase transition at 145 K. Variable-temperature X-ray and 1H spin −lattice relaxation experiments, and calculations of rotational barriers, provide a description (i) of the way in which the rotators’ dynamics changes back and forth at the onset of the phase transition and (ii) of the mechanism responsible for the abrupt switching of the crystalline rotors from a very low-energy 4-fold degenerate equilibrium state, in which the rotation is ultrafast (9.6 GHz at 145 K), to a single higher-energy state associated with a slower motion (2.3 GHz at 145 K). Our results provide evidence that the reversible change observed in the rotational barriers at the transition is due to a cooperative modulation of the C −Hrotator···Istator hydrogen bond cloud across a C −I stator···Istator−C halogen bond-mediated phase transition. In addition, we report evidence for second-harmonic generation from this material, thereby confirming with a second example the benefit of using polarized light to probe the torsional degree of freedom of chiral helix blades, as well as symmetry and dimensionality of large collections of chiral rotors in the solid state.