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The exotic properties of quantum spin liquids (QSLs) have continually been of interest since Anderson's 1973 ground-breaking idea. Geometrical frustration, quantum fluctuations, and low dimensionality are the most often evoked material's characteristics that favor the long-range fluctuating spin state without freezing into an ordered magnet or a spin glass at low temperatures. Among the few known QSL candidates, organic crystals have the advantage of having rich chemistry capable of finely tuning their microscopic parameters. Here, we demonstrate the emergence of a QSL state in [EDT-TTF-CONH2]+ 2 [BABCO] (EDT-BCO), where the EDT molecules with spin-1/2 on a triangular lattice form layers which are separated by a sublattice of BCO molecular rotors. By several magnetic measurements, we show that the subtle random potential of frozen BCO Brownian rotors suppresses magnetic order down to the lowest temperatures. Our study identifies the relevance of disorder in the stabilization of QSLs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Here we present a study where what can be seen as a static modulation wave encompassing four successive arrays of interacting iodine atoms in crystalline 1,4-Bis((4′-(iodoethynyl)phenyl) ethynyl)bicyclo[2,2,2]octane rotors changes the structure from one-half molecule to three-and-a-half molecules in the asymmetric 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 molecular 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 calculations how the dynamics of molecular rotors are able to decode structural information from their surroundings with remarkable nanoscale precision. [ABSTRACT FROM AUTHOR]

We report on a crystalline rotorthat undergoes a reversible phase transition at 145 K. Variable-temperatureX-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 andforth at the onset of the phase transition and (ii) of the mechanismresponsible for the abrupt switching of the crystalline rotors froma very low-energy 4-fold degenerate equilibrium state, in which therotation is ultrafast (9.6 GHz at 145 K), to a single higher-energystate associated with a slower motion (2.3 GHz at 145 K). Our resultsprovide evidence that the reversible change observed in the rotationalbarriers at the transition is due to a cooperative modulation of theC–Hrotator···Istatorhydrogenbond cloud across a C–Istator···Istator–C halogen bond-mediated phase transition. Inaddition, we report evidence for second-harmonic generation from thismaterial, thereby confirming with a second example the benefit ofusing polarized light to probe the torsional degree of freedom ofchiral helix blades, as well as symmetry and dimensionality of largecollections of chiral rotors in the solid state. [ABSTRACT FROM AUTHOR]

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 wide-line and 13C cross-polarization/magic-angle spinning solid-state NMR experiments were performed at temperatures between 27 and 290 K. Analysis of the 1H spin-lattice relaxation and second moment as a function of temperature revealed two dynamic processes simultaneously present over the entire temperature range studied, with 10 -1 / -I 10 -I temperature-dependent rotational rates of krot = 5.21 x 10 s exp-1.48 kcal mol /RT) and krot = 8.00 x 10 s exp- (-2.75 kcalmoF'/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' for rotation about the 1,4 axis, which is 24% larger than E, = 1.48 kcal mol' 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. [ABSTRACT FROM AUTHOR]

A correction to the article "Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of l,4 Bis(iodoethynyl)- bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites," that was published in the 2011 issue is presented.