843653-66-7Relevant academic research and scientific papers
Crystals and aggregates of a molecular tetrarotor with multiple trityl embraces derived from tetraphenyladamantane
Stopin, Antoine,Garcia-Garibay, Miguel A.
scheme or table, p. 3792 - 3798 (2012/10/18)
Samples of tetrakis-1,3,5,7-(4′-(3″,3″,3″- triphenylpropynyl)-phenylene)adamantane and its trityl-deuterated isotopologue were synthesized and their crystallization and packing properties were analyzed within the context of formation of 4- or 6-fold phenyl embraces. The tetrahedral shape of these molecules with four propeller-like triphenylmethyl moieties generates several edge-to-face intermolecular interactions in the solid state that result in the formation of infinite chains of molecules that are tightly interlocked. The formation of analogous edge-to-face intermolecular interactions leading to aggregation in solution was also suggested by NMR experiments carried out in different solvents as a function of concentration. The formation of interdigitated chains was also manifested in fibrils and thin needles, which were documented by scanning electron microscopy (SEM). Single crystal X-ray diffraction studies revealed the presence of multiple 4-fold phenyl embraces and edge-to-face interactions as the leading motifs behind the formation of tightly interlocked molecular chains.
Solid-state molecular rotors with perdeuterated stators: Mechanistic insights from biphenylene rotational dynamics in ordered and disordered crystal forms
Obrien, Zachary J.,Karlen, Steven D.,Khan, Saeed,Garcia-Garibay, Miguel A.
experimental part, p. 2482 - 2491 (2010/07/15)
Samples of 4,4′-bis(3,3,3-tri-d5-phenylpropynyl)biphenyl 2, 9,10-bis(3,3,3-tri-d5-phenylpropynyl)anthracene 3, 1,4-bis(3,3,3-tri-d5-phenylpropynyl)naphthalene 4, and 4,4′-bis(3,3,3-tri-d5-phenylpropynyl)-1,1′-binaphthyl 5 were prepared via a Sonogashira coupling of 3,3,3-tri-d5- phenylpropyne 7 and the appropriate aryl dibromide. Single crystal X-ray diffraction structures were obtained for an o-xylene clathrate of 2 and for solvent-free crystals of 3. All four molecular rotors were characterized by CPMAS 13C NMR experiments with varying contact times in order to determine whether the carbon signals of the central rotator group could be selectively enhanced and studied without interference or overlap of signals from the deuterated stator, which is insensitive to the {1H}- 13C cross-polarization method. It was shown that the 13C signals of the natural abundance rotator group can be selectively observed with short contact times (ca. 50 μs) without interference from other 13C signals in the molecule. Variable-temperature CPMAS 13C NMR studies with a crystalline o-xylene solvate of biphenylene rotor 2 suggested a 2-fold flipping process in the fast exchange regime, even at temperatures as low as 199 K (?74 °C). Indirect support for this was obtained by studies carried out with a disordered, solvent-free solid, obtained by fast precipitation from hexanes and dichloromethane, which displayed slower dynamics within the same temperature range with an activation energy of 8.7 kcal/mol and a pre-exponential factor of 4.9 - 109 s?1. Confirmation of an exchange process in the megahertz regime for the crystalline solvate was obtained by variable-temperature quadrupolar echo 2H NMR data acquired with samples prepared with a deuterated biphenylene rotator and a natural abundance stator. Although rotational exchange occurs in the solvated samples with a slightly lower barrier of 7.4 kcal/mol, the main difference with the precipitated solid comes from the pre-exponential factor, which is nearly 3 orders of magnitude greater with a value of 2.5 - 1012 s ?1. On the basis of these differences, we speculate that efficient rotational motion in the solvated crystals may take advantage of long-range lattice vibrations that couple with molecular modes and that the lack of long-range order may be responsible for the low pre-exponential factor observed in the disordered crystals.
Highlighting gyroscopic motion in crystals in 13C CPMAS spectra by specific isotopic substitution and restricted cross polarization
Karlen, Steven D.,Garcia-Garibay, Miguel A.
, p. 189 - 191 (2007/10/03)
The temperature-dependent exchange rate and signal coalescence in the 13C CPMAS NMR spectrum of a crystalline molecular gyroscope are exposed by specifically deuterating the overlapping static carbons.
