Structural Transformations in Crystals Induced by Radiation and

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Structural transformations in crystals induced by radiation and pressure. Part 6. The reactivity of difluorocinnamic acids under ambient and high pressures - comparative studies Tomasz Galica, Julia B#kowicz, Krzysztof Konieczny, and Ilona Turowska-Tyrk Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01602 • Publication Date (Web): 16 Jan 2018 Downloaded from http://pubs.acs.org on January 22, 2018

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Crystal Growth & Design

Structural transformations in crystals induced by radiation and pressure. Part 6. The reactivity of difluorocinnamic acids under ambient and high pressures - comparative studies Tomasz Galica, Julia Bąkowicz, Krzysztof Konieczny and Ilona Turowska-Tyrk* Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland

Abstract

The influence of the molecular environment and the intramolecular features on the [2+2] photodimerization of 2,5-difluorocinnamic acid (1) and 3,5-difluorocinnamic acid (2) in crystals were analysed. The crystal structures of (1) were determined at pressures of 0.1 MPa, 0.3 GPa and 0.9 GPa before the [2+2] photodimerization as well as for several steps of the reaction. The determined structures revealed the influence of pressure on the reaction rate: the reaction was faster at 0.3 GPa than at 0.1 MPa, but there was not a significant difference between 0.3 GPa and 0.9 GPa. For (2), the crystal structure was determined before the photochemical reaction and the unit cell parameters were monitored along with the reaction progress at 0.1 MPa and 0.4 GPa, which showed higher reactivity of (2) at 0.4 GPa. Despite the similar orientation and the distance between two neighbouring monomers and the volume of free space in the studied compounds, (2) reacted noticeably worse than (1). The differences in the reactivity were rationalized in terms of the substituent effect of fluorine. The results were compared with our previous studies carried out for 2,6-difluorocinnamic acid (3).

Ilona Turowska-Tyrk Wybrzeże Wyspiańskiego 27 50-370 Wrocław, Poland Fax: +48 71 320 33 64 Email: [email protected]

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Structural transformations in crystals induced by radiation and pressure. Part 6. The reactivity of difluorocinnamic acids under ambient and high pressures - comparative studies Tomasz Galica, Julia Bąkowicz, Krzysztof Konieczny and Ilona Turowska-Tyrk* Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland

Abstract

The influence of the molecular environment and the intramolecular features on the [2+2] photodimerization of 2,5-difluorocinnamic acid (1) and 3,5-difluorocinnamic acid (2) in crystals were analysed. The crystal structures of (1) were determined at pressures of 0.1 MPa, 0.3 GPa and 0.9 GPa before the [2+2] photodimerization as well as for several steps of the reaction. The determined structures revealed the influence of pressure on the reaction rate: the reaction was faster at 0.3 GPa than at 0.1 MPa, but there was not a significant difference between 0.3 GPa and 0.9 GPa. For (2), the crystal structure was determined before the photochemical reaction and the unit cell parameters were monitored along with the reaction progress at 0.1 MPa and 0.4 GPa, which showed higher reactivity of (2) at 0.4 GPa. Despite the similar orientation and the distance between two neighbouring monomers and the volume of free space in the studied compounds,


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(2) reacted noticeably worse than (1). The differences in the reactivity were rationalized in terms of the substituent effect of fluorine. The results were compared with our previous studies carried out for 2,6-difluorocinnamic acid (3).

Introduction The X-ray structural studies of the [2+2] photodimerization in crystals were pioneered by Schmidt and co-workes1–3 who emphasized the importance of the topochemical postulate and the concept of a reaction cavity and started to analyse the geometrical demands for this reaction. The [2+2] photodimerization in crystals only occurs in suitable conditions connected with intermolecular geometry. These conditions were widely described in literature.4–8 In the popular method of describing the geometrical environment for this reaction, the following parameters are used: α, τ, φ, κ and D, where α is the C=C···C angle, τ is the C=C···C=C angle, φ is the angle between the planes of the C=C bonds, κ is the angle between the C=C bond and four atoms of the C=C bonds and D is the distance between the C atoms of the C=C bonds. The ideal values of these parameters are: D < 4.2, α, κ = 90 and τ, φ = 0. The parameters are shown on Scheme 1. Aside from the above five geometrical parameters, there is another one replacing them, but rarely used, namely SUM.4,9 It is defined by the equation: SUM = Lobe1 + Lobe2, where Lobe1 is the distance between the apices of the p atomic orbital lobes of the first pair of the reacting C atoms and Lobe2 is the distance between the apices of the p atomic orbital lobes of the second pair of the reacting C atoms.9 The shorter these distances, the better reactivity is expected. Although the advantage of SUM is replacing the five geometrical parameters with just one, the consequence of using SUM is a certain loss of information: it is not known exactly whether a


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high or low value of SUM is a result of the angular parameters or of the distance between molecules. The analysis of the above parameters is insufficient because it only takes into account the mutual position of two molecules. There are also other factors influencing the [2+2] photodimerization, however, they are seldom considered. These factors include the neighbourhood of a pair of molecules: the volume of free space, the number and kind of intermolecular interactions and finally the structure of the molecule itself, i.e. the types and positions of substituents. The important factor influencing molecular reactivity in crystals is the volume of free space10 between and around a pair of molecules. Its influence was analysed in one of our previous papers.11 The free space can have a different impact depending on initial intermolecular geometry of a reacting pair of monomers. If the arrangement of molecules is suitable for the [2+2] photodimerization, smaller free spaces are beneficial for the reaction because they help to maintain the suitable intermolecular geometry of other pairs of monomers (this geometry can be destroyed by the neighbouring, reacted pairs of molecules).11,12 In the case of the unsuitable arrangement, bigger free spaces may be desirable because molecules will be able to change their position to a greater degree and fit better to a crystal lattice. This is also valid when the initial organization of monomers is suitable for the reaction to proceed, but the shape of a dimer differs significantly from that of a pair of monomers. It is worth mentioning that significant differences between a shape of a pair of monomers and a dimer (and also between their lattices) can lead to the decrease of crystal quality during the photochemical reaction.12


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Intermolecular interactions, and amongst them hydrogen bonds, are another factor which can influence the photochemical reactivity in crystals.4,13–22 Hydrogen bonds were often used in the case of preorganization of C=C bonds for template-directed [2+2] dimerization.15,17–19,21 Coordination bonds20,22 and argentophilic interactions21 were also applied to preorientate molecules for photochemical reactions. Nevertheless, sometimes, hydrogen bonds were observed blocking molecular reactivity in crystals.4,16 Electron withdrawing/releasing effects may have an influence on the rate of the [2+2] photodimerization by changing electron density in the region of the reacting double bond.23 Such a change is dependent on the type and position of substituents at the benzene ring. The halogens show the inductive electron withdrawing effect and also behave as donors in the resonance effect.24 In the meta position they behave as σ-electron withdrawing groups, but in the para and ortho positions they also act as the π-electron donating substituents. The substituent effect was widely studied for reactions in a liquid state, but it is under studied for the [2+2] photodimerization in crystals. The photoreactivity is also influenced by temperature14,25,26 and pressure. The influence of temperature can be compared, to a certain degree, to the impact of pressure. When the temperature is lowered, molecules show smaller thermal motions, which is also a result of an increase of pressure. An increase of temperature has the opposite effect and can be compared to a decrease of pressure. Despite similarities between those two factors, it should be remembered that because of the differences between crystallographic experiments at low temperature and crystallographic experiments at high pressure, the observed effect on determined structures is not the same. For low temperatures it is possible to obtain a better quality of structures than for highpressure studies due to completeness of data.


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It is also worth mentioning that the above-described parameters are not independent of each other: the pressure changes the volume of free space and the different positions of substitutes cause different intermolecular interactions. Although it is often not achievable to measure the influence of every single factor, it is desirable to conduct as detailed research as possible. In this paper, we study photoreactivity of two compounds: 2,5-difluorocinnamic acid (1) and 3,5-difluorocinnamic acid (2) during the [2+2] photodimerization in crystals under ambient and high pressures. The equation of the reaction is presented in Scheme 2. The determined structures of the reactant, of the mixed crystals containing both the reactant and the product in various proportions and of the products allowed us to monitor the changes in the site occupancy and the intermolecular geometry during the phototransformation of crystals. The second aim of the studies is the assessment of the importance of the factors which influence the [2+2] photodimerization. Finally, our research will add to already existing knowledge on the reactivity of derivatives of cinnamic acid.27 For instance, some interesting studies were carried out by Fernandes and Levendis on the 100% two-stage [2+2] photodimerization in high temperature conditions.28 Our previous experiments revealed that the [2+2] photodimerization of 2,6difluorocinnamic (3) acid is faster at high pressure.11 Although the research concerning photochemical reactions in crystals under high pressure are not yet common,11,29 Boldyreva et al. conducted valuable indirect studies, which may help to understand the nature of compounds under high pressure conditions.30

Experimental UV irradiation and X-ray data collection


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Crystals of 2,5-difluorocinnamic acid (1) and 3,5-difluorocinnamic acid (2) were bought from Alfa Aesar. The [2+2] photodimerization in them was induced gradually. As the source of UV radiation a 100 W Hg lamp was used. To ensure that the reaction went in a homogenous fashion, a WG-320 glass filter cutting off wavelengths corresponding to the maximum and the highenergy tail of the absorption band of (1) and (2) was applied. The transmission of a WG-320 filter has the following characteristics: ca. 100% above 365 nm, 50% at 320 nm and 0% below 300 nm. The maximum of the absorption band was at 262 nm and 267 nm for (1) and (2), respectively. At ambient pressure, only one crystal of (1) was used and its irradiation was 0, 120 sec and 60 min. The crystal was rotated along the longest dimension and irradiated perpendicularly to that direction. Two other crystals of (1) were taken for the high-pressure studies with a BoehlerAlmax diamond anvil cell and two series of experiments, for 0.3 GPa and 0.9 GPa, were conducted. The total irradiation time for 0.3 GPa was 0 and 60 and 120 sec and for 0.9 GPa was 0, 120, 240, and 480 sec. The crystal at 0.3 GPa was irradiated along the middle dimension and the crystal at 0.9 GPa along the shortest dimension. Owing to this the path of the UV beam through the three studied crystals was similar. In order to maintain the pressure isotropic inside the diamond anvil cell (DAC), a glycerin:water mixture (vol. 3:2) was used. The value of the pressure was estimated by the unit cell parameters of quartz31 which was inserted in the DAC together with the crystal of the studied compound. For each step of the reaction, the X-ray diffraction experiments and crystal structures determinations were carried out.32 The structure for (1) after 120 sec of UV irradiation at 0.1 MPa was of good quality (R1 = 0.0464, wR2 = 0.0965, ∆ρmax = 0.171 and ∆ρmin = -0.147) and revealed only the monomer despite of UV irradiation. A part of the sample was ground into fine


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powder and afterwards irradiated for 6-hours, during which the powder was mixed every hour. The irradiated powder changed its colour to an intense yellow. After recrystallization from toluene, crystals of the photoproduct were obtainable. The X-ray diffraction conducted for (2) at ambient pressure did not reveal the occurrence of the [2+2] photodimerization during one hour of irradiation. The situation changed after that time, but the crystal started to crack making further research impossible. The second crystal was irradiated under pressure of 0.4 GPa in the following steps: 0, 30, 90, 150, 210, 390 and 1200 sec in total. Nevertheless, none of the determined structures revealed the dimer due to the low crystal diffraction power after UV irradiation, however, the monitored unit cell parameters indicated that the reaction started to proceed after 390 sec of irradiation. Even when the WG-320 glass filter was changed for a weaker WG-295 filter, i.e. transmitting shorter wavelengths, the reaction was not observed to occur significantly (the transmittance of WG-295 was ca. 0% below 275 nm, 50% at 295 nm and 100% above 355 nm.) As in the case of (1) some crystals were ground into powder and irradiated over 6 hours. The colour of the powder changed from white to pale yellow. The 1H NMR experiment indicated that ca 30% of the monomer reacted to the dimer after this time. The irradiated powder was recrystallized from toluene giving two different kinds of crystals: many small crystals of the reactant and a few big pale-yellow crystals of the dimer, the structure of which was determined. Structure determination The structures were solved and refined with the SHELX2014 software,33,34 but for those at high pressure the initial atomic coordinates were taken from the ambient data. During our experiments, there were two types of structures: pure reactant/product and of the mixed crystals,


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i.e. containing both the reactant and the product in different proportions. While the structures of the first type were simple to be refined, in the second case the disorder had to be modelled over two positions. The main crystallographic data and the content of the monomer/dimer in the crystals for the determined structures are presented in Tables 1 and 2. The complete data are given in the cif files. The crystal data of (2) at 0.4 GPa for 30, 90, 150 and 210 sec of UV irradiation were almost the same as for 0 sec of UV irradiation and were not given in the paper. The structures determined for the same crystal after 390 and 1200 sec of UV irradiation were not of satisfactory quality and were not presented in the paper. In the case of the pure reactant crystals of (1) and (2) at ambient and high pressures no restraints were used. For the product crystals of (1) and (2) containing disordered molecules of toluene on the symmetry centres the DANG, DFIX, FLAT and SIMU restraints were applied. The DANG and DFIX instructions restrained the bond lengths and valence angles to the target values and FLAT ensured the coplanarity of atoms, whereas SIMU restrained atomic displacement parameters. Owing to the reactant-product disorder, in the case of the structures of the partly reacted crystals the C7 and C8 atoms in the reactant molecule (the atoms labelled R) and in the product molecule (the atoms labelled P1 and P2) were refined with some restraints, i.e. DFIX, DANG, FLAT and SIMU, while the groups of other atoms (−COOH and −C6H3F2) were treated as rigid rotating fragments. The geometry of the reactant fragments was taken from the pure reactant crystals at the respective pressures and the geometry for the product fragments was taken from the structure of the pure product crystal at ambient pressure.


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For the structure of (1) after 120 sec of irradiation at 0.3 GPa and after 480 sec of irradiation at 0.9 GPa, the whole monomer and only the cyclobutane ring of the dimer were refined. This was because of the low crystal diffraction power and the small number of observed reflections after that time of irradiation. For the pure reactant and product crystals of (1) and (2) at ambient pressure, all nonhydrogen atoms were refined anisotropically. For the structure of (1) after 60 min of UV irradiation at ambient pressure, several non-hydrogen atoms of the major component were refined anisotropically and all atoms of the minor component were treated isotropically. For the pure reactant crystals of (1) at 0.3 GPa and 0.9 GPa, only fluorine atoms or fluorine and oxygen atoms were refined anisotropically, respectively. For the remaining structures all non-hydrogen atoms were refined isotropically. The determined structures of the partly reacted crystals of (1) and (2) have R-factors above 0.10 (see Tables 1 and 2). This is a consequence of the data collection at high-pressure (and the fraction of the unique reflections collected) and of the reactant-product disorder. Results and discussion Structural changes induced by pressure and radiation The changes in the unit cell parameters along with the progress of the [2+2] photodimerization of (1) for pressure 0.1 MPa, 0.3 GPa and 0.9 GPa are shown in Fig. 1. The unit cell of the pure reactant crystals shrunk under high pressure, however, the values of the cell parameters shortened anisotropically. En route from 0.1 MPa to 0.8 GPa, a decreased by 3.9% (0.15 Å), b by 4.2% (0.45 Å), c by 0.9% (0.18 Å) and the volume of the unit cell by 8.8% (71 Å3). The


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biggest change occurred for b, while the smallest change was for c. In general, such changes depend on the strength of intermolecular interactions and on the size and shape of molecules in the direction of cell axes. Usually, if no strong restraints are connected to the intermolecular interactions and molecular shape, the longer the period, the bigger the absolute change observed. The small change for the longest cell constant, c, indicates that the intermolecular interactions along this direction are strong and/or that the longest dimension of molecules is parallel to this axis. Significant changes in the unit cell dimensions of (1) were also observed during the progress of the [2+2] photodimerization. These occurred because of the differences in the geometry of one dimer molecule and one pair of monomer molecules. In our previous studies, it was observed that the changes induced by the same reaction can have different characteristics for different pressures.11 This effect was also observed for the a parameter of (1): under 0.1 MPa and 0.3 GPa its value was almost constant, but for 0.9 GPa it significantly decreased. For b and c, the character of the changes was the same for different values of pressure. In order to explain in detail the above observations, we studied the differences between the shape of one pair of monomers and one dimer molecule and the neighbourhood of molecules, namely, the voids and the intermolecular interactions. The molecules of the product are formed by addition of two double C=C bonds of the reactant. This causes the product molecule to have a butterfly-like shape. The example of the reactant molecules superimposed on the product molecule in the partly reacted crystal of (1) is presented in Fig. 2. As it is shown in Fig. 3, the voids in the crystal of (1) are located between the stacks of molecules and also form stacks along the a axis. At 0.1 MPa they have a lengthened shape along the c axis. As the pressure was increased, the voids shrunk and their shape became more spherical, which is also seen in Fig. 3.


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The volume of the voids en route from 0.1 MPa through 0.3 GPa to 0.9 GPa was: 47.36, 23.42 and 11.83 Å3 per one unit cell, respectively. It seems that at the lower pressure the voids can have some influence on the direction and the size of the changes in the unit cell parameters along the reaction progress owing to some possibilities of molecular shifts along the b and c directions. However, at the higher pressure their significance is smaller. We have also analysed intermolecular interactions in the crystal of (1). The strongest interactions are the O–H···O hydrogen bonds between the carboxyl groups forming the R ଶଶ(8) synton. These kinds of interactions are quite common in crystals of carboxylic acids.37 It is known that such interactions are strong and their energy is in the range of 25-30 kJ/mol.38 In the crystal of (1) the direction of these interactions is approximately parallel to the c axis. The second kind of interactions found along the same axis are the weaker C–H···F interactions. They also give the R ଶଶ(8) synton. These two types of interactions form the chains of molecules and may prevent the unit cell from stronger changes in this direction under the influence of pressure. The arrangement of molecules in the crystal of (1) is presented in Fig. 4. The above analysis can explain the changes in the unit cell parameters during the [2+2] photodimerization and also those differences when the high pressure was applied. As it was written in the Experimental section, the structure determination of (2) did not detect the dimer in a noticeable degree after the UV irradiation of the crystals. Nevertheless, some small changes in the unit cell parameters under the influence of UV irradiation at 0.4 GPa were observed indicating that the reaction started to undergo. Moreover, the structure obtained after the recrystallization of the irradiated powder of (2) clearly revealed the dimer and the same was valid for (1) and (3). The respective dimer molecules and their O–H···O bonds are presented in


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Fig. 5. As can be seen, the dimers of (1) and (2) form chains in the crystals, while the dimer of (3) interacts with only one molecule. Crystal lattice design It is known that halogen atoms can be used as steering groups in crystal engineering and that the position of such substitutes in molecules affects not only the geometry of a whole lattice but also the reactivity of a molecule owing to the resonance and/or inductive effects.13,39–42 In all three compounds (1) – (3) studied by us there are two fluorine substituents at the benzene ring. In (2) both fluorine atoms are at the meta positions and in (3) both fluorine atoms are at the ortho positions. (1) has one fluorine atom at the ortho and one fluorine atom at the meta position. In the crystals of all the studied compounds, molecules are stacked along the a axis. The above-mentioned chains in the crystal of (1) and shown in Fig. 4 are connected by the C–H···F interactions, which further give the three-dimensional lattice. Molecules belong to two families of the planes: (582) and (58ത2) with the angle between them of 57.4°. For (2), molecules are connected into dimers via O–H···O hydrogen bonds between the carboxyl groups and then into chains via C–H···F interactions, similarly as in the crystal of (1). However, contrary to (1), these chains in (2) form separate and not strongly interacting planes. The pattern of the interactions for (2) is presented in Fig. 6. In the case of (3) the dimers of carboxylic acids did not form chains but separate planes11 as in (2). The geometry of the interactions in the crystals of (1) and (2) is gathered in Table 3 and for (3) in ref. 4. Reactivity


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We analysed the values of the geometrical parameters describing the susceptibility of molecules of (1), (2) and (3) to the [2+2] photodimerization (Table 4). They are close to the ideal ones for all compounds and indicate the possibility of the [2+2] photodimerization. Moreover, the comparison of the values of these parameters can lead to the conclusion that (2) should be more reactive, or at least in the same degree as (1) and (3). Nevertheless, our research revealed the opposite observation: the best reacting compound was (3) and the worst reacting was (2). Likewise, it seems that the volume of free space is not responsible for the differences in the reactivity between (1), (2) and (3). The voids for all three compounds are positioned similarly, namely between the stacks of molecules, but not between the molecules in one stack. According to our previous research,11 this should help to maintain the geometry suitable for the reaction. Moreover, the volume of the free space is the biggest for (3) and the smallest for (1), but both compounds react better than (2). The above considerations mean that although the geometrical reactivity parameters can correctly predict the occurrence of the reaction, they failed to predict its efficiency and that also other factors have an impact on the reactivity, namely, the electronic effects of the substituents. The electronic effects occurring in the studied molecules depend on the positions of fluorine at the benzene ring. In our case, only the ortho substituents contribute to the resonance effect (for fluorine σR = -0.3343,44). There are two ortho-F atoms in the molecule of (3) and one ortho-F and one meta-F in the molecule of (1). Owing to this, the reacting double bond in both these compounds features higher π electron density and should be more reactive than (2). This explanation is consistent with our experimental data. Such rationalization can also be done for bromocinnamic acids.45


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There is an important conclusion in remembering while designing crystals for the [2+2] photodimerization: the halogen atoms can be used as not only the steering groups for the desired intermolecular interactions, but also as influencing the intramolecular electron features. The next effect related to the reactivity is the influence of pressure. In the case of compound (3)11 it was observed that pressure increased the reaction rate in the following manner: 0.1 MPa < 0.5 GPa < 1.1 GPa ≤ 2.1 GPa. A similar relationship is observed for (1): the reaction rate at 0.3 GPa and 0.9 GPa is higher than at 0.1 MPa, but there is not a significant difference between 0.3 and 0.9 GPa. Similarly to (3), above a certain level of pressure it is not possible to increase the reaction rate. The relationship between the monomer content in the crystals along with the time of UV irradiation for (1) at 0.3 GPa and 0.9 GPa is shown in Fig. 7.

Conclusions In this paper, we have analysed the changes induced by the [2+2] photodimerization in the crystal structures, the influence of high pressure on these changes and on the photochemical reactivity. The reaction of (1) was conducted at ambient (0.1 MPa) and high pressures of 0.3 GPa and 0.9 GPa. Along with the progress of the reaction, the unit cell parameters and the content of the dimer were monitored. The reaction was faster at high pressure, but there was no significant difference between 0.3 GPa and 0.9 GPa. The influence of pressure is similar to the one observed for (3).11 The monitoring of the unit cell parameters of (2) at 0.1 MPa and 0.4 GPa showed the lower photochemical reactivity of (2) than (1) and (3) and that (2) is more reactive at 0.4 GPa than at 0.1 MPa. The intermolecular geometrical parameters and the volume of free space did not


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explain the observed order in the reactivity of all three compounds: (2) ˂ (1) ˂ (3). This sequence is consistent with the electron effects of the fluorine substituents at the benzene ring.

Acknowledgements This work was financed by the statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of the Wroclaw University of Science and Technology.

ASSOCIATED CONTENT Accession Codes CCDC 1559114-1559125, 1585793 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

AUTHOR INFORMATION Corresponding Author *Email: [email protected]


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Funding Sources The Polish Ministry of Science and Higher Education Notes The authors declare no competing financial interest.

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Scheme 1. The geometrical parameters for the [2+2] photodimerization in crystals.

Scheme 2. The equation for the [2+2] photodimerization of the derivatives of cinnamic acid.


21


Page 22 of 41

Table 1. The experimental and crystal data for (1).

Pressure

0.1 MPa

0.3 GPa

Irradiation time/sec 0

3600

Reaction progress

100% M

70.0% M

Chemical formula

C9H6F2O2

Formula weight Crystal dimensions/mm

0.9 GPa

0

60

120

0

120

240

480

100% D

100% M

91.4% M

87.5% M

100% M

89.0% M

74.0% M

54.8% M

C9H6F2O2

C18H12F4O4 x C7H8

C9H6F2O2

C9H6F2O2

C9H6F2O2

C9H6F2O2

C9H6F2O2

C9H6F2O2

C9H6F2O2

184.14

184.14

414.34

184.14

184.14

184.14

184.14

184.14

184.14

184.14

0.30 x 0.10 x 0.10

0.30 x 0.10 x 0.10

0.30 x 0.20 x 0.20

0.17 x 0.10 x 0.17 x 0.10 x 0.17 x 0.10 x 0.21 x 0.16 0.07 0.07 0.07 x 0.12

0.21 x 0.16 x 0.12

0.21 x 0.16 x 0.12

0.21 x 0.16 x 0.12

Crystal system

Monoclinic

Monoclinic

Triclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Space group

P21/c

P21/c

P1ത

P21/c

P21/c

P21/c

P21/c

P21/c

P21/c

P21/c

a/Å

3.7824(2)

3.7754(6)

8.1633(9)

3.668(3)

3.674(2)

3.663(3)

3.6348(3)

3.6115(17)

3.588(2)

3.5131(16)

b/Å

10.7191(5)

11.034(3)

8.9315(9)

10.43(5)

10.470(3)

10.491(13)

10.2669(19)

10.380(11)

10.419(16)

10.588(11)

c/Å

19.8394(10)

19.912(3)

14.9936(16)

19.659(18)

19.729(12)

19.775(16)

19.654(2)

19.695(19)

19.72(2)

19.763(14)

90.93(6)

90.07(6)

90.10(6)

91.453(7)

90.11(6)

90.77(7)

93.33(5)

α/°

95.261(8)

β/°

91.034(4)

93.60(2)

γ/°

103.245(9) 110.428(10)

V/Å3

804.24(7)

827.9(3)

979.37(19)

752(4)

758.9(7)

759.9(13)

733.21(17)

738.3(11)

737.1(14)

733.9(10)

4

4

2

4

4

4

4

4

4

4

1.521

1.477

1.405

1.626

1.612

1.609

1.668

1.657

1.659

1.667

µ/mm

0.14

0.13

0.12

0.15

0.14

0.14

0.15

0.15

0.15

0.15

T/K

299

299

299

299

299

299

299

299

299

299

2602

2577

6505

3528

3548

3278

3571

3544

3511

3451

1575

1461

3834

609

617

551

711

726

728

712

1246

489

2060

273

235

176

421

266

241

196

0.008

0.042

0.023

0.185

0.182

0.287

0.066

0.132

0.137

0.182

Z -3

Dx/Mg m -1

Reflections collected Reflections independent Reflections observed Rint 2

2

R, wR (F >2σ(F )), 0.038, 0.086, 0.116, 0.260, 0.071, 0.178, 0.090, 0.214, 0.101, 0.265, 0.136, 0.335, 0.066, 0.164, 0.124, 0.305, 0.131, 0.311, 0.148, 0.382, S 1.08 1.06 1.01 0.94 0.93 1.00 1.06 1.03 1.04 1.20 ∆ρmax, ∆ρmin/eÅ-3

0.12, -0.16

0.25, -0.20

0.22, -0.31

0.28, -0.22

0.25, -0.28

0.30, -0.36

0.25, -0.20

0.35, -0.27

0.37, -0.27

0.38, -0.31

* M - monomer, D - dimer


22

Page 23 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2. The experimental and crystal data for (2).

Pressure

0.1 MPa

Reaction progress

100% M

100% D

100% M

Chemical formula

C9H6F2O2

C18H12F4O4 x C7H8

C9H6F2O2

Formula weight

184.14

414.34

184.14

Crystal dimensions/mm

0.20 x 0.20 x 0.10

0.60 x 0.12 x 0.10

0.10 x 0.08 x 0.06

Crystal system

Triclinic

Triclinic

Triclinic

Space group

P1ത

P1ത

P1ത

a/Å

3.7782(5)

8.6068(6)

3.639(2)

b/Å

7.2804(6)

8.9712(9)

7.139(3)

c/Å

15.1930(10)

14.2119(12)

14.954(12)

α/°

97.571(7)

97.467(8)

97.55(5)

β/°

96.051(9)

102.239(6)

94.98(7)

99.890(8)

112.946(8)

98.52(4)

404.59(7)

959.60(15)

378.6(4)

2

2

2

Dx/Mg m

1.512

1.434

1.615

µ/mm-1

0.14

0.12

0.14

T/K

299

299

299

Reflections collected

4099

6353

1839

Reflections independent

2961

3758

417

Reflections observed

2095

2307

181

Rint

0.027

0.026

0.090

R, wR (F2>2σ(F2)), S

0.047, 0.132, 1.04

0.066, 0.135, 1.07

0.143, 0.339, 1.21

0.24, -0.22

0.32, -0.34

γ/° 3

V/Å Z

-3

∆ρmax, ∆ρmin/eÅ-3 0.15, -0.18 * M - monomer, D - dimer

0.4 GPa


23


Page 24 of 41

Table 3. The geometry of the interactions in the crystals of (1) and (2). Bond

(1)

(2)

O–H /Å

0.89(3)

1.19(4)

H···O /Å

1.76(3)

1.43(4)

O···O /Å

2.6499(17)

2.6176(19)

177(2)

177(3)

C–H /Å

0.939(17)

0.919(17)

H···F /Å

2.743(16)

2.502(19)

C···F /Å

3.147(15)

3.306(15)

∠(C–H···F) /°

106.9(13)

146.2(14)

C–H /Å

0.975(19)

0.926(18)

H···F /Å

2.652(21)

2.632(19)

C···F /Å

3.487(16)

3.516(14)

∠(C-H···F) /°

143.8(16)

159.6(15)

O–H···Oa

∠(O–H···O) /° C–H…Fb

C–H…Fc

a

O1–HO1···O2i for (1) and (2), i = -x,-y, 1-z

b

C5–H5···F1ii for (1) and C7–H7···F2iii for (2), ii= 1-x, -0.5+y, 0.5-z, and iii= x, -1+y, z

c

C3–H3···F2iv for (1) and C3–H3···F1v for (2), iv= 1-x, -y, -z , and v= 3-x, 2-y, 2-z


24

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Table 4. The reactivity parameters for the studied compounds. The best value in each category is marked with a star. Compound

(1)

(2)

(3)

D /Å

3.782

3.778 *

3.8856

α /°

102.09 *

113.63

102.2

κ /°

63.24

89.35 *

64.1

τ /°

0

0

0

φ /°

0

0

0

SUM /Å

3.8414

3.039 *

3.6885

Voids /%

5.9

6.6

8.4


25


Page 26 of 41

Figure 1. The changes in the unit cell parameters of (1) induced by pressure and by radiation.


26

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Figure 2. The structure of the partly reacted crystal containing 70.0 % of the monomer of (1) at ambient pressure. The atomic displacement ellipsoids were drawn at the 10% probability level and the spheres for the hydrogen atoms were artificially diminished for the reasons of clarity. The asymmetric unit contains one monomer molecule (empty bonds) and one dimer molecule (full bonds).35 Standard uncertainties for the bond lengths are in the ranges 0.011−0.012 and 0.016−0.018 Å for the reactant and the product, respectively.


27


Page 28 of 41

Figure 3. The free spaces seen along (a) the a axis and (b) the b axis at 0.1 MPa and 0.9 GPa in (1).36

Figure 4. The O–H···O and C–H···F intermolecular interactions in the crystal of (1).


28

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Figure 5. The interactions of the dimers of (1), (2) and (3).


29


Page 30 of 41

Figure 6. The plane of the O–H···O and C–H···F intermolecular interactions in the crystal of (2).

Figure 7. The content of the monomer versus the time of the UV irradiation for (1) at 0.1 MPa, 0.3 GPa and 0.9 GPa.


30

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For Table of Contents Use Only

Structural transformations in crystals induced by radiation and pressure. Part 6. The reactivity of difluorocinnamic acids under ambient and high pressures - comparative studies

Tomasz Galica, Julia Bąkowicz, Krzysztof Konieczny, Ilona Turowska-Tyrk*

Pressure influences the photo-induced structural changes and the reactivity of molecules in crystals.


31


Scheme 1. The geometrical parameters for the [2+2] photodimerization in crystals. 62x47mm (300 x 300 DPI)


Page 32 of 41

Page 33 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 2. The equation for the [2+2] photodimerization of the derivatives of cinnamic acid. 29x10mm (300 x 300 DPI)



Figure 1. The changes in the unit cell parameters of (1) induced by pressure and by radiation. 131x100mm (300 x 300 DPI)


Page 34 of 41

Page 35 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. The structure of the partly reacted crystal containing 70.0 % of the monomer of (1) at ambient pressure. The atomic displacement ellipsoids were drawn at the 10% probability level and the spheres for the hydrogen atoms were artificially diminished for the reasons of clarity. The asymmetric unit contains one monomer molecule (empty bonds) and one dimer molecule (full bonds).35 Standard uncertainties for the bond lengths are in the ranges 0.011−0.012 and 0.016−0.018 Å for the reactant and the product, respectively. 113x157mm (300 x 300 DPI)



Figure 3. The free spaces seen along (a) the a axis and (b) the b axis at 0.1 MPa and 0.9 GPa in (1).36 134x105mm (300 x 300 DPI)


Page 36 of 41

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Figure 4. The O–H···O and C–H···F intermolecular interactions in the crystal of (1). 63x48mm (300 x 300 DPI)



Figure 5. The interactions of the dimers of (1), (2) and (3). 216x564mm (300 x 300 DPI)


Page 38 of 41

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Figure 6. The plane of the O–H···O and C–H···F intermolecular interactions in the crystal of (2). 45x24mm (300 x 300 DPI)



Figure 7. The content of the monomer versus the time of the UV irradiation for (1) at 0.1 MPa, 0.3 GPa and 0.9 GPa. 62x46mm (300 x 300 DPI)


Page 40 of 41

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45x26mm (300 x 300 DPI)


Structural Transformations in Crystals Induced by Radiation and

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