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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.


Related in: MedlinePlus

Crystal packing of form I of DMCA. Note that molecules 1 and 4 are in a γ-type environment, while molecules 2 and 3 (translationally related to 4) are in the α-type environment and potentially reactive upon irradiation.
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fig1: Crystal packing of form I of DMCA. Note that molecules 1 and 4 are in a γ-type environment, while molecules 2 and 3 (translationally related to 4) are in the α-type environment and potentially reactive upon irradiation.

Mentions: In 1984, Desiraju and coworkers reported a triclinic modification (, Z = 4), of DMCA that was obtained by crystallization from 1:1 MeOH–acetone (Desiraju, Kamala et al., 1984 ▸). The crystal structure is unusual for a cinnamic acid in that while one of the two symmetry independent molecules is situated in the α-type environment (the nearest neighbor is inversion related and within photoreactive distance), the other is in a γ-type environment (the nearest neighbor is pseudo-translated and beyond the 4 Å reacting threshold distance; Fig. 1 ▸). A better resolved crystal structure of this form was published in 1989 but the packing features are essentially the same as that reported previously (Desiraju et al., 1991 ▸). In effect, only half of the molecules in the crystal are potentially reactive in the solid state according to Schmidt’s criterion, and these are the ones that are related by the inversion center. The maximum yield in the photodimerization reaction of this triclinic form was observed to be around 40%, and this was taken to be a confirmation of the topochemical argument by Desiraju, Kamala et al. (1984 ▸). However, and as noted for the α-acids studied by Schmidt, the maximum yield is not 50%, which is what might have been expected under strictly topochemical conditions, but lower (Cohen et al., 1964 ▸). This original form is hereafter referred to as form I.


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)

Crystal packing of form I of DMCA. Note that molecules 1 and 4 are in a γ-type environment, while molecules 2 and 3 (translationally related to 4) are in the α-type environment and potentially reactive upon irradiation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Crystal packing of form I of DMCA. Note that molecules 1 and 4 are in a γ-type environment, while molecules 2 and 3 (translationally related to 4) are in the α-type environment and potentially reactive upon irradiation.
Mentions: In 1984, Desiraju and coworkers reported a triclinic modification (, Z = 4), of DMCA that was obtained by crystallization from 1:1 MeOH–acetone (Desiraju, Kamala et al., 1984 ▸). The crystal structure is unusual for a cinnamic acid in that while one of the two symmetry independent molecules is situated in the α-type environment (the nearest neighbor is inversion related and within photoreactive distance), the other is in a γ-type environment (the nearest neighbor is pseudo-translated and beyond the 4 Å reacting threshold distance; Fig. 1 ▸). A better resolved crystal structure of this form was published in 1989 but the packing features are essentially the same as that reported previously (Desiraju et al., 1991 ▸). In effect, only half of the molecules in the crystal are potentially reactive in the solid state according to Schmidt’s criterion, and these are the ones that are related by the inversion center. The maximum yield in the photodimerization reaction of this triclinic form was observed to be around 40%, and this was taken to be a confirmation of the topochemical argument by Desiraju, Kamala et al. (1984 ▸). However, and as noted for the α-acids studied by Schmidt, the maximum yield is not 50%, which is what might have been expected under strictly topochemical conditions, but lower (Cohen et al., 1964 ▸). This original form is hereafter referred to as form I.

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