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Crystal chemistry and photomechanical behavior of 3,4-dimethoxycinnamic acid: correlation between maximum yield in the solid-state topochemical reaction and cooperative molecular motion.

Mishra MK, Mukherjee A, Ramamurty U, Desiraju GR - IUCrJ (2015)

Bottom Line: Form I exhibits photosalient behavior but this effect is absent in form II.It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction.Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

View Article: PubMed Central - HTML - PubMed

Affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore 560 012, India.

ABSTRACT
A new monoclinic polymorph, form II (P21/c, Z = 4), has been isolated for 3,4-dimethoxycinnamic acid (DMCA). Its solid-state 2 + 2 photoreaction to the corresponding α-truxillic acid is different from that of the first polymorph, the triclinic form I ([Formula: see text], Z = 4) that was reported in 1984. The crystal structures of the two forms are rather different. The two polymorphs also exhibit different photomechanical properties. Form I exhibits photosalient behavior but this effect is absent in form II. These properties can be explained on the basis of the crystal packing in the two forms. The nanoindentation technique is used to shed further insights into these structure-property relationships. A faster photoreaction in form I and a higher yield in form II are rationalized on the basis of the mechanical properties of the individual crystal forms. It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction. Form I of DMCA is more plastic and seems to react under Kaupp-type conditions with maximum molecular movements. Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

No MeSH data available.


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Molecular packing of DMCA form I. Blue dotted lines in form I represent slip planes.
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fig7: Molecular packing of DMCA form I. Blue dotted lines in form I represent slip planes.

Mentions: The appearance of parallel cracks in the direction [011] towards the main elongation axis (b axis) of the crystal is also indicative of significant molecular movements within form I crystals upon photoirradiation (Figs. 4 ▸a–f). The build-up of strain due to such molecular movement is released through cleavage of molecular planes; this is in itself facilitated by the presence of slip planes in form I across which there is considerable space for molecular movement (Fig. 7 ▸). Cleavage leads to a sudden release of accumulated strain in the form of kinetic energy. All this results in the observed photosalient behavior (Medishetty et al., 2014 ▸, 2015 ▸; Nath et al., 2014 ▸; Kim et al., 2014 ▸). In contrast, the crystal structure of form II is interlocked and this restricts such movement of molecules (Fig. 2 ▸b). The observed jumping behavior in form I and absence of it in form II is indicative of faster reaction in form I during the initial stages when the integrity of the slip planes is maintained in the pristine reactant crystal.


Crystal chemistry and photomechanical behavior of 3,4-dimethoxycinnamic acid: correlation between maximum yield in the solid-state topochemical reaction and cooperative molecular motion.

Mishra MK, Mukherjee A, Ramamurty U, Desiraju GR - IUCrJ (2015)

Molecular packing of DMCA form I. Blue dotted lines in form I represent slip planes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645110&req=5

fig7: Molecular packing of DMCA form I. Blue dotted lines in form I represent slip planes.
Mentions: The appearance of parallel cracks in the direction [011] towards the main elongation axis (b axis) of the crystal is also indicative of significant molecular movements within form I crystals upon photoirradiation (Figs. 4 ▸a–f). The build-up of strain due to such molecular movement is released through cleavage of molecular planes; this is in itself facilitated by the presence of slip planes in form I across which there is considerable space for molecular movement (Fig. 7 ▸). Cleavage leads to a sudden release of accumulated strain in the form of kinetic energy. All this results in the observed photosalient behavior (Medishetty et al., 2014 ▸, 2015 ▸; Nath et al., 2014 ▸; Kim et al., 2014 ▸). In contrast, the crystal structure of form II is interlocked and this restricts such movement of molecules (Fig. 2 ▸b). The observed jumping behavior in form I and absence of it in form II is indicative of faster reaction in form I during the initial stages when the integrity of the slip planes is maintained in the pristine reactant crystal.

Bottom Line: Form I exhibits photosalient behavior but this effect is absent in form II.It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction.Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

View Article: PubMed Central - HTML - PubMed

Affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore 560 012, India.

ABSTRACT
A new monoclinic polymorph, form II (P21/c, Z = 4), has been isolated for 3,4-dimethoxycinnamic acid (DMCA). Its solid-state 2 + 2 photoreaction to the corresponding α-truxillic acid is different from that of the first polymorph, the triclinic form I ([Formula: see text], Z = 4) that was reported in 1984. The crystal structures of the two forms are rather different. The two polymorphs also exhibit different photomechanical properties. Form I exhibits photosalient behavior but this effect is absent in form II. These properties can be explained on the basis of the crystal packing in the two forms. The nanoindentation technique is used to shed further insights into these structure-property relationships. A faster photoreaction in form I and a higher yield in form II are rationalized on the basis of the mechanical properties of the individual crystal forms. It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction. Form I of DMCA is more plastic and seems to react under Kaupp-type conditions with maximum molecular movements. Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

No MeSH data available.


Related in: MedlinePlus