Crystal structure of the meta-stable intermediate in the photomechanical, crystal-to-crystal reaction of 9-tert-butyl anthracene ester

Abstract

The photodimerization of 9-tert-butyl-anthracene ester in molecular crystal nanorods can cause expansions of up to 15%. This expansion results from the formation of a metastable crystalline intermediate, the solid-state reacted dimer (SSRD). In this paper, a combination of powder X-ray diffraction, solid-state nuclear magnetic resonance, and computational modeling is used to determine the crystal structure of the SSRD intermediate. An ensemble of six possible structures is obtained, which differ only in small packing details that lead to different crystal space groups. The structure with the best overall agreement with the experimental data belongs to the Pccn space group and, like the other members of the ensemble, retains a packing motif close to that of the monomer crystal. This crystal structure allows us to conclude that the SSRD crystal density is slightly greater than that of the monomer crystal and that gross changes in the volume or unit cell parameters of the SSRD are not responsible for the photoinduced expansion. CrystEngCommThis journal is

Measuring and Modeling Highly Accurate 15N Chemical Shift Tensors in a Peptide.

“…TwoF IREMAT spectra were acquired at spinning speeds of 1282 and 261 Hz. [47] Spectra were acquired at 14.1 T( 600.01 MHz 1 H, 150.87 MHz 13 C) on aB ruker AV600 spectrometer equipped with a4mm double resonance MAS probe with samples spinning at 1.1 kHz;c ross-polarization was implemented using spin locking fields of 40 kHz on 1 H and 38 kHz (linearly ramped AE 25 %) on 13 Cw ith a2ms contact time;o ther RF powers were 83 kHz 1 H( excitation and SPINAL-64 decoupling) and 50 kHz 13 C( p and p/2 pulses). Data obtained at 1281 Hz had evolution and acquisition dimension spectral widths of 5.128 and 19.231 kHz, respectively.F our evolution increments of 12 288 transients each were acquired with a5sr ecycle time for at otal analysis time of 2.8 days.…”

“…Cross-polarization was implemented using as pin lock field of 41 kHz on 13 Ca nd ar amped field of 33-44 kHz on 1 H, with a2ms contact time;o ther RF powers were 83 kHz 1 H( excitation and decoupling) and 50 kHz 13 C( p and p/2 pulses). [47] Indirect evolution and acquisition spectral widths were 100 and 41.6 kHz, respectively,w ith at otal of 128 (real) and 2048 (complex) time points each, resulting in the acquisition of 4r otor periods in the indirect dimension. [47] Indirect evolution and acquisition spectral widths were 100 and 41.6 kHz, respectively,w ith at otal of 128 (real) and 2048 (complex) time points each, resulting in the acquisition of 4r otor periods in the indirect dimension.…”

“…[63] TOSS-t 1 -deTOSS experiments were performed using am odified version of the original sequence [46] as previously described. [47] Spectra were acquired at 14.1 T( 600.01 MHz 1 H, 150.87 MHz 13 C) on aB ruker AV600 spectrometer equipped with a4mm double resonance MAS probe with samples spinning at 1.1 kHz;c ross-polarization was implemented using spin locking fields of 40 kHz on 1 H and 38 kHz (linearly ramped AE 25 %) on 13 Cw ith a2ms contact time;o ther RF powers were 83 kHz 1 H( excitation and SPINAL-64 decoupling) and 50 kHz 13 C( p and p/2 pulses). Indirect evolution and acquisition spectral widths were 4.098 and 50 kHz, respectively,w ith at otal of 64 and 2048 complex time points each.…”

“…The xCSA experiment was modified for extended detection in the indirect dimension as described previously. [47] Indirect evolution and acquisition spectral widths were 100 and 41.6 kHz, respectively,w ith at otal of 128 (real) and 2048 (complex) time points each, resulting in the acquisition of 4r otor periods in the indirect dimension. 16 transients were acquired at each time point, with ar ecycle time of 60 sf or at otal experiment time of 34 h. 13 Cs pectra were indirectly referenced to neat TMS by setting the higher frequency resonance of adamantane to 38.48 ppm.…”

TensorView: A software tool for displaying NMR tensors

“…Visualizing nuclear magnetic resonance (NMR) tensors as surfaces on molecular models is an information‐rich presentation that highlights the geometric relationship between tensor principal components and essential aspects of the underlying molecular and electronic structure . These relationships are particularly important in applications of “NMR‐assisted crystallography,” which often combine solid‐state NMR with computational methods to build and test atomic‐resolution models of structure and dynamics . Enabling these computationally‐aided approaches has been the remarkable success of first‐principles computational chemistry at modeling solid‐state structure and calculating—with high accuracy—the corresponding NMR properties such as chemical shielding/shift, and dipole–dipole, J , and quadrupolar couplings .…”