Influence of Fluorine Substitution on the Crystal Packing of N

CRYSTAL GROWTH & DESIGN

Influence of Fluorine Substitution on the Crystal Packing of N-Phenylmaleimides and Corresponding Phthalimides Anke Schwarzer and Edwin Weber* Institute of Organic Chemistry, Technische UniVersita¨t Bergakademie Freiberg, Leipziger Strasse 29, D-09596 Freiberg/Sachsen, Germany

2008 VOL. 8, NO. 8 2862–2874

ReceiVed NoVember 26, 2007; ReVised Manuscript ReceiVed February 7, 2008

ABSTRACT: The X-ray crystallographic structures of 18 fluorinated N-phenylmaleimides and corresponding phthalimides of different degree and positions of fluorine substituents, including two compounds each in two polymorphic forms, have been determined in order to study the effect of fluorine substitution on the solid state organization in competition with stronger oxygen and nitrogen H-acceptor sites. The data suggest that C-H · · · O contacts formed in the crystalline packings play the dominant role but C-H · · · F contacts are also of relevance with the fluorine atoms being more specific in making a selection from potential hydrogen contacts. The F · · · F and F · · · πF contacts observed are rather secondary in these structures and mostly determined by the packing. Unexpectedly, a π · · · πF interaction is found only in two exceptional cases for dimer formation contradicting the common opinion of π · · · πF stacking as being a robust supramolecular synthon. Introduction Fluoroorganic compounds are characterized by a unique set of unusual and sometimes extreme physical and chemical behavior.1 A large number of polymers,2 liquid crystals3 and other advanced materials owe their pairticular property profile to this specific influence coming from a fluorine substitution.1 While fluoroorganic compounds are almost completely foreign to the biosphere, many modern pharmaceuticals and agrochemicals,4 on the other hand, also contain fluorine atoms, which usually have a very special function in this area.5 According to the World Drug Index (WDI) in 2002, e.g., there were not fewer than 128 fluorinated compounds with U.S. trademarks in clinical use.6 Depending on the number and position, a fluorine substitution not only affects the electronic and structural properties of the molecule itself but also gives rise to uncommon intermolecular behavior.1 This is observed to have marked consequences on the solubility and surface activity properties of a compound,7 e.g. a solid drug preparation, or will perhaps influence the formation of new polymorphs.8 Indeed, replacement of hydrogen by fluorine has been shown to lead to distinct changes in between crystal structure,9 turned to good account in solid state reactions10 and crystalline inclusion chemistry.11 Hence, to study the crystal engineering of fluoroorganic compounds has become a very actual topic.12 This, however, requires a proven knowledge of the various modes of supramolecular interactions involving fluorine atoms in organic crystals.13 While, in the meantime, the Ar-ArF stacking motif formed between nonfluorinated and perfluorinated aromatic rings is rated an important supramolecular synthon,14 the contacts of C-F · · · H,15 C-F · · · F16 and C-F · · · πF 17 type are not yet sufficiently clear18 but still controversial.13,19 In particular, the problem arises if other competing interactions are present. However, it will hardly be necessary to do some thinking about cases where strong hydrogen bonds (O-H · · · O, N-H · · · O, N-H · · · N)20 are in favor, since they will certainly predominate the structure. On the other hand, weaker hydrogen bonds (O-H · · · π, C-H · · · π)21,22 or X · · · X contacts between representatives of the higher halogens23 are the cases that are * Corresponding author. E-mail: [email protected].

worthwhile for undergoing a test. This has stimulated the present comparative study of crystal structures, including a systematic series (18 species) of fluorinated N-phenylmaleimides and corresponding phthalimides of different degree and positions of fluorine substitution, with the object of improving the general knowledge on organofluorine interactions being of use to future crystal engineering of fluoroorganic compounds. Results and Discussion Molecular Design, Synthesis of Compounds and Crystal Preparation. A model compound suitable for the planned study should meet the following requirements: (a) a clear symmetric overall constitution being conformationally defined as far as possible; (b) a possibility for systematic replacement of hydrogen for fluorine atoms; (c) the presence of heteroatomic sites (O, N) being able to fairly compete with the fluorine derived contacts; (d) aromatic units to make possible π-stacking and other π-donor interactions; (e) absence of O-H and N-H groups which would dominate the packing; (f) preparation of the compounds from easily available building blocks by using a standardized procedure. All these requirements apply to the compounds 1-18 specified in Scheme 1. These compounds feature N-phenylmaleimides (1-6) and corresponding phthalimides (7-18) of different degree and with different positions of fluorine substitution, both at the phenyl and imide moieties of these molecular constructions. Hence, we will make a further distinction between the phthalimides that have a nonfluorinated (7-12) or perfluorinated imide moiety (13-18) leading to the three classes of compounds in Scheme 1, which will be discussed in this order. Even though importance is attached to an interchangeability fluorine for hydrogen, as complete as possible, we like to retain C2 symmetry of the molecules. This is reflected in a mirror plane, including the 1,4positions of the phenyl unit, and will have a positive consequence on the structural discussion of the fluorine contacts. All compounds (1-18) were prepared by a standarized synthesis following a known procedure.24 This involves reaction of the respective anhydride (maleic anhydride, phthalic anhydride) with the corresponding anilines to yield the intermediate acyclic amide acids, which were subsequently condensed to give the target compounds. The crystals, suitable for the X-ray

10.1021/cg7011638 CCC: $40.75  2008 American Chemical Society Published on Web 06/24/2008

Fluorine Involved Contacts in N-Arylimides

Crystal Growth & Design, Vol. 8, No. 8, 2008 2863 Scheme 1. Compounds Studied in This Paper

diffraction studies, were obtained by slow evaporation from solution of the compounds using different solvents for the three classes of substances, which are cyclohexane, ethanol, and an equimolar mixture of cyclohexane and acetone in the cases of the maleimides, phthalimides, and tetrafluorophthalimides, respectively. The time of crystal growing took between one day and one week. In the case of 12 and 13, two polymorphic crystalline forms could be isolated of which 12A and 13A were obtained from the given solvents, whereas a special treatment led to 12B and 13B. Formation and structural details of these latter polymorphs are being described in a separate chapter. X-ray Single-Crystal Structures. Except for the parent maleimide 125 and the fluorine free phthalimide 7,26 all the other compounds gave no reference of a reported crystal structure. However, since the data of 7 proved incomplete in the hydrogen atoms, a structure solution was redone. On the other hand, we failed growing crystals of high quality for the pentafluoromaleimide 6, which is the only blank in this study. Hence, in this paper, we describe and comparatively discuss a total of 19 different crystal structures including compound 1 and polymorphs of compounds 12 (12A, 12B) and 13 (13A, 13B), the crystallographic data and structure refinement parameters of which are summarized in Table 1. For the description of the crystal structures, intermolecular contacts within the sum of the van der Waals radii suggested by Bondi27 for the pair of interacting atoms O · · · H, F · · · H and F · · · F and an angular cutoff of >110° have been used. Contacts between the aryl units and the hydrogen or fluorine atoms are based upon the center of the ring. Selected geometric features of the structures, involving interplanar relationships and intermolecular hydrogen bond type C-H · · · O and C-H · · · F contacts, are represented in Tables 2–4, respectively. Molecular Structure Description. Although the molecular structure of the fluorine free compound 1 is known from a previous report,25 it is important to include its relevant features into the discussion because 1 is the basic nonfluorinated parent compound of this study. The molecular structure of 1 is best described by the N-C(dO) and Caryl-N bond lengths and the interplanar angle between the five-membered imide ring and the aromatic unit. The torsion between these planes is about 49° due to intramolecular attractive and repulsive forces between the carbonyl oxygen atoms and the ortho phenyl hydrogens. The question arises how the molecular geometry will change with fluorine substitution at the aromatic ring as a consequence of the strong electron withdrawing effect of the fluorine atoms. Actually, on going in the series of maleimides from compound 1 to 5 no such trend reflecting a respective fluorine involvement becomes obvious in the structures with reference to the N-C(dO) bond length (mean 1.404 Å). However, relating to the Caryl-N bonds, their lengths are little shorter in the case of the maleimides 3

and 5 with fluorine substitution in the ortho positions as compared with 2 and 4 having hydrogens in the ortho positions. On the other hand, the torsion along the Caryl-N bond, i.e. the interplanar angle between the imide plane and the phenyl unit, does not show a corresponding clear correlation. Considering the phthalimides 7-12, lacking fluorine substituents at the phthalimide unit, a small increase of the N-C(dO) bond length is observed (mean 1.411 Å) in comparison with the maleimides, while the respective bond lengths in the fluorine substituted analogous compounds 13-18 (mean 1.407 Å) are similar to the maleimides due to electronic effects. Access to a more detailed structural comparison of all compounds is provided by the data summarized in Table 2. ORTEP plots of molecules being representative examples of the different compound classes that feature identical fluorine substitution of the phenyl rings are illustrated in Figure 1 (a-c), respectively. As a general result of these data, it is obvious that the molecular geometry of these compounds is not significantly influenced by the different fluorine substitution. However, one may expect a more pronounced bearing on the crystalline packing of the molecules. Crystal Packing of Compounds 1-5. All crystalline packings of the maleimides 1-5 are mainly dominated by C-H · · · O contacts ranging from 2.38 to 2.65 Å and angles ranging between 136.5° and 164.5° (Table 3). Nevertheless, increasing of the fluorine ratio in the molecule leads to more relevant C-H · · · F contacts (2.39-2.62 Å, 115.9-166.0°) being shorter than the sum of the van der Waals radii (Table 4). In the nonfluorinated N-phenylmaleimide (1), two C-H · · · O contacts form chains along both the crystallographic a and b axes connected by the strongest interaction of this type (C-H · · · O: 2.54 Å, 148°). Although the introduction of the aromatic fluorine such as in 2-5 does not entail drastic changes of the intermolecular packing behavior, a consequence is that chains instead of dimers and zigzag chains are preferably formed according to the C-H · · · O contacts (Figure 2). Most of these C-H · · · O interactions include olefinic protons causing the formation of dimers, whereas the olefinic C-H · · · F contacts lead to the formation of zigzag chains along the particular crystallographic axis. While the meta positioned hydrogen atoms, involved in C-H · · · O interactions, are mainly responsible for the formation of zigzag chains, the ortho hydrogen atoms do not form C-F · · · H contacts in any crystal structures of the maleimides. Compound 4 takes up a special position, being the only maleimide that contains no meta hydrogen atoms. Moreover, it is the only compound of this type that shows a C-H · · · π interaction (C-Hortho · · · π: 2.91 Å, 158°) leading to zigzag chains along the crystallographic c axis. Furthermore, the shortest C-Hortho · · · O contact (2.49 Å, 164.5°) among all the maleimides is represented in compound 4. Also, in the case of

2864 Crystal Growth & Design, Vol. 8, No. 8, 2008

Schwarzer and Weber

Table 1. Crystallographic Data of Compounds 2-5 and 7-18

empirical formula formula weight T (K) crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z, Z′ Dcalcd (g m-3) µ (mm-1) F(000) θmax (°) limiting indices h, k, l Ntotal Nind Nobs restraints/parameters goodness-of-fit on F2 R1 [I > 2σ(I)] wR2 [all data] max/min (e Å-3)


empirical formula formula weight T (K) crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z, Z′ Dcalcd (g m-3) µ (mm-1) F(000) θmax (°) limiting indices h, k, l

1a

2

3

4

C10H7NO2

C10H6FNO2 191.16 93(2) monoclinic P21/c 10.6834(10) 3.7658(3) 20.6001(16) 90 93.708(3) 90 827.04(12) 4, 1 1.535 0.123 392 2.66-25.99 -12, 13; (4; -25, 24 6888 1623 1359 0/127 1.108 0.0392 0.0975 0.204 and -0.183

C10H5F2NO2 209.15 93(2) orthorhombic Pbcn 5.0513(3) 18.4919(12) 9.3014(6) 90 90 90 868.83(9) 4, 0 1.599 0.141 424 2.20-25.49 (6; (22; (11 9545 811 645 0/70 1.040 0.0284 0.0774 0.184 and -0.212

C10H5F2NO2 209.15 93(2) monoclinic P21/c 9.3188(3) 11.7229(4) 7.9564(3) 90 96.446(2) 90 863.69(5) 4, 1 1.608 0.142 424 2.80-25.50 (11; (14; (9 8583 1602 1417 0/136 1.060 0.0291 0.0779 0.219 and -0.184

monoclinic P21/n 3.9051(8) 10.762(2) 19.362(4) 90.00 93.93(3) 90.00 811.8(3)

5

7

8

9

C10H4F3NO2 227.14 93(2) orthorhombic Pbcn 7.8592(2) 10.7066(3) 10.8179(3) 90 90 90 910.28(4) 4, 0 1.657 0.157 456 3.22-25.00 (9; (12; ( 12 11789 801 759 0/75 1.066 0.0263 0.0737 0.208 and -0.203

C14H9NO2 223.22 93(2) orthorhombic Pbca 11.5777(7) 7.4958(4) 23.6936(13) 90 90 90 2056.2(2) 8, 1 1.442 0.098 928 2.46-25.50 -13, 14; (9; -28, 25 17723 1908 1406 0/154 1.053 0.0365 0.0886 0.185 and -0.259

C14H8FNO2 241.21 93(2) orthorhombic Pbca 15.1513(19) 5.6544(6) 25.276(3) 90 90 90 2165.4(4) 8, 1 1.480 0.112 992 3.14-25.05 (18; (6; (30 19014 1923 1272 0/163 1.031 0.0446 0.1214 0.234 and - 0.297

C14H7F2NO2 259.21 93(2) orthorhombic Pbca 11.4528(3) 7.9586(3) 23.7353(8) 90 90 90 2163.43(12) 8, 1 1.592 0.131 1056 2.47-25.49 (13; (9; (28 21378 2013 1709 0/172 1.053 0.0313 0.0880 0.248 and - 0.212

10

11

12A

12B

C14H7F2NO2 259.21 93(2) triclinic P1j 7.1381(5) 11.9045(9) 13.3533(10) 89.699(4) 77.931(3) 76.802(3) 1079.24(14) 4, 2 1.595 0.131 528 1.56-26.00 (8; (14; (16

C14H6F3NO2 277.20 93(2) triclinic P1j 7.3804(5) 8.1615(5) 10.5780(7) 90.195(4) 108.809(4) 109.163(4) 565.45(6) 2, 1 1.628 0.143 280 2.66-25.49 (8; ( 9; (12

C14H4F5NO2 313.18 93(2) monoclinic C2/c 21.880(2) 7.9432(9) 13.7584(15) 90 98.710(6) 90 2363.6(4) 8, 1 1.760 0.171 1248 1.88-25.25 (26; ( 9; (16

C14H4F5NO2 313.18 298(2) orthorhombic Pca21 13.8799(6) 12.8307(5) 13.4761(5) 90.00 90.00 90.00 2399.94(17) 8, 2 1.734 0.169 1248 2.64-31.66 (20; 18, 17; (19


Crystal Growth & Design, Vol. 8, No. 8, 2008 2865 Table 1. Continued

Ntotal Nind Nobs restraints/parameters goodness-of-fit on F2 R1 [I > 2σ(I)] wR2 [all data] max/min (e Å-3)


empirical formula formula weight T (K) crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z, Z′ Dcalcd (g m-3) µ (mm-1) F(000) θmax (°) limiting indices h, k, l Ntotal Nind Nobs restraints/parameters goodness-of-fit on F2 R1 [I > 2σ(I)] wR2 [all data] max/min (e Å-3) a

10

11

12A

12B

17741 17741 12045 0/344 0.897 0.0400 0.1116 0.228 and - 0.225

8633 2092 1691 0/181 1.025 0.0346 0.0891 0.265 and - 0.262

11936 2120 1623 0/199 1.076 0.0528 0.1333 0.477 and - 0.364

57434 4197 2823 1/397 1.080 0.0478 0.1368 0.242 and -0.288

13A

13B

14

15

C14H5F4NO2 295.19 93(2) orthorhombic P212121 7.056(2) 8.179(3) 19.928(6) 90.00 90.00 90.00 1150.0(6) 4, 1 1.705 0.158 592 2.69-28.00 (9; (10; -25, 26 12786 1625 1396 0/190 1.101 0.0696 0.1826 0.497 and -0.486

C14H5F4NO2 295.19 93(2) orthorhombic C2221 5.6255(8) 25.622(3) 7.7159(12) 90.00 90.00 90.00 1112.1(3) 4, 0 1.763 0.164 592 3.08-26.79 -6, 7; -32, 31; (9 4839 1191 924 0/97 1.065 0.0647 0.1722 0.255 and -0.350

C14H4F5NO2 313.18 93(3) orthorhombic C2221 5.5055(3) 26.8347(12) 7.6690(4) 90.00 90.00 90.00 1133.01(10) 4, 0 1.836 0.178 624 3.04-27.49 -7, 6; (34; (9 5859 1303 1086 0/102 1.061 0.0356 0.0896 0.213 and -0.202

C14H3F6NO2 331.17 93(2) monoclinic P21/c 10.1505(8) 25.0550(18) 10.5400(9) 90.00 114.897(4) 90.00 2431.4(3) 8, 2 1.809 0.183 1312 3.24-32.00 -14, 15; -37, 34; -15, 8 30607 8043 6379 0/415 1.076 0.0358 0.1014 0.468 and -0.242

16

17

18

C14H3F6NO2 331.17 293(2) monoclinic P21/n 14.1065(18) 5.1836(5) 16.834(2) 90.00 96.238(6) 90.00 1223.6(2) 4, 1 1.798 0.182 656 2.91-25.50 -17, 12; (6; -20, 16 7063 2272 1451 0/208 0.921 0.0402 0.1156 0.154 and -0.185

C14H2F7NO2 349.17 93(2) triclinic P-1 9.9578(5) 10.2991(5) 13.6127(6) 98.314(3) 99.646(3) 112.165(3) 1241.16(10) 4, 2 1.869 0.196 688 2.19-26.00 (12; (12; (16 24599 4756 3369 0/433 1.015 0.0493 0.1328 0.312 and - 0.332

C14F9NO2 385.15 298(2) orthorhombic Pbca 19.157(2) 6.3289(6) 21.617(2) 90.00 90.00 90.00 2620.9(5) 8, 1 1.952 0.216 1504 2.16-25.50 (23; -5, 7; (26 43249 2435 1448 0/235 1.005 0.0383 0.1157 0.222 and -0.228

See ref 25.

4, the para positioned H-atom is involved in an intermolecular C-H · · · O contact (2.52 Å, 158.9°) leading to zigzag chains, unlike compounds 1 and 3 where these hydrogens play only an inferior role. Considering the structures of all maleimides, the centroid-centroid distances of the aromatic units range between 3.98 and 5.24 Å (plane-plane distances: 3.34-4.97 Å), not

suggesting intermolecular stacking interaction, and relevant F · · · F contacts are not observed as well. Crystal Packing of Compounds 7-12A. In the crystal packings of the N-arylmaleimides, the olefinic hydrogen atoms were shown to be distinctly involved in intermolecular C-H · · · O and C-H · · · F interactions. Thus, the question arises on what


Schwarzer and Weber

Table 2. Selected Geometric Features in Compounds 1-5 and 7-18

2′- and 6′-substitution imid/phenyl interplanar angle (°) N-C(dO) (Å) Caryl-N (Å)

2′- and 6′-substitution imid/phenyl interplanar angle (°) N-C(dO) (Å) Caryl-N (Å)

1a

2

3

4

5

H 48.60 1.400 1.402 1.434

H 48.95(4) 1.405(2) 1.408(2) 1.432(2)

F 58.96(7) 1.4080(18)

H 52.33(4) 1.4028(17) 1.4059(17) 1.4268(16)

F 66.45(4) 1.4044(14)

1.416(3)

1.414(2)

7

8

9

10-1

10-2

11

12A

12B-1

12B-2

H 56.73(4) 1.400(2) 1.410(2) 1.432(2)

H 58.79(6) 1.412(3) 1.416(3) 1.434(3)

F 58.90(4) 1.4121(18) 1.4151(18) 1.4161(18)

H 60.68(5) 1.4035(18) 1.4202(18) 1.4366(18)

H 60.37(6) 1.4123(17) 1.4148(18) 1.4276(18)

F 59.13(6) 1.414(2) 1.416(2) 1.418(2)

F 64.05(8) 1.415(3) 1.420(3) 1.418(3)

F 66.59(14) 1.405(5) 1.406(5) 1.426(4)

F 65.90(15) 1.409(4) 1.410(4) 1.420(4))

13A

13B

14

15-1

15-2

16

17-1

17-2

18

2′- and 6′-substitution imid/phenyl interplanar angle (°) N-C(dO) (Å)

H 48.72(15) 1.405(4)

H 59.18(8) 1.408(2)

Caryl-N (Å)

1.438(6)

H 56.46(17) 1.402(5) 1.410(6) 1.429(5)

F 59.07(7) 1.4071(13) 1.4076(14) 1.4186(14)

F 61.23(4) 1.4068(14) 1.4105(14) 1.4150(14)

H 74.23(6) 1.397(3 1.403(3) 1.434(3)

F 57.33(12) 1.404(4) 1.420(4) 1.412(5)

F 62.27(12) 1.406(4) 1.412(4) 1.414(4)

F 62.38(9) 1.406(3) 1.411(3) 1.416(3)

a

1.428(3)

See ref 25. Table 3. Intermolecular Hydrogen Bond (C-H · · · O) Lengths (Å) and Angles (deg) for Compounds 1, 2, 4, 5, 7, 8 and 10-17

compound

C-H · · · O

H· · ·O

C· · ·O

C-H · · · O

symmetry operator

contact

a

C2-H2 · · · O1 C6-H6 · · · O2 C7-H7 · · · O1 C5-H5 · · · O1 C10-H10 · · · O2 C8-H8 · · · O2 C4-H4 · · · O1 C6-H6 · · · O2 C5-H5 · · · O1 C6-H6 · · · O1 C14-H14 · · · O2 C11-H11 · · · O2 C11-H11 · · · O4 C8-H8 · · · O3 C25-H25 · · · O2 C22-H22 · · · O2 C14-H14 · · · O3 C28-H28 · · · O1 C6-H6 · · · O1 C13-H13 · · · O2 C7-H7 · · · O1 C14-H14 · · · O2 C13-H13 · · · O2 C14-H14 · · · O2 C11-H11 · · · O1 C12-H12 · · · O4 C6-H6 · · · O1 C7-H7 · · · O1 C8-H8 · · · O1 C4-H4 · · · O1 C4-H4 · · · O1 C4-H4 · · · O1 C21-H21 · · · O3 C4-H4 · · · O2 C5-H5 · · · O3 C19-H19 · · · O4

2.54 2.64 2.64 2.57 2.63 2.65 2.49 2.52 2.38 2.64 2.64 2.59 2.45 2.47 2.48 2.53 2.53 2.53 2.66 2.43 2.56 2.56 2.56 2.50 2.56 2.62 2.56 2.66 2.65 2.71 2.64 2.67 2.57 2.51 2.48 2.59

3.37 3.37 3.41 3.440(2) 3.470(2) 3.382(2) 3.4121(16) 3.4203(17) 3.2121(14) 3.314(2) 3.375(2) 3.340(3) 3.2903(18) 3.3963(19) 3.3600(18) 3.2704(18) 3.4062(18) 3.4121(18) 3.4313(19) 3.187(2) 3.2484(19) 3.160(3) 3.171(3) 3.362(4) 3.438(5) 3.489(5) 3.426(6) 3.247(6) 3.231(6) 3.372(5) 3.270(3) 3.577(2) 3.3462(15) 3.345(2) 3.304(4) 3.305(4)

148.5 136.1 140.4 156.9 151.2 136.5 164.5 158.9 145.5 128.3 134.2 136.3 148.1 163.5 153.3 134.6 153.4 154.5 138.8 136.5 129.6 121.1 122.5 155.0 157.7 156.0 152.1 120.4 120.3 127.1 124.6 159.1 138.6 149.6 145.5 132.0

-x, 1-y, -z -1 + x, y, z -1/2 - x, -1/2 + y, 1/2 - z 1 - x, -1/2 + y, 1/2 - z -x, -y, -z x, 1 + y, z -x, -y, 1 - z 1 - x, -1/2 + y, 3/2 - z 1/2 + x, 1/2 - y, 1 - z 2 - x, 1/2 + y, 1.5 - z 1/2 + x, 1.5 - y, 1 - z 1 - x, 2 - y, 1 - z 1 - x, 1 - y, 2 - z

dimer chain zigzag chain zigzag chain dimer chain dimer zigzag chain chain assembly zigzag chain zigzag chain dimer chain dimer chain chain chain dimer dimer chain dimer chain chain chain chain dimer zigzag chain chain chain zigzag chain chain chain dimer chain dimer dimer

1

2

4 5 7 8 10

11 12A 12B

13A

13B 14 15 16 17 a

1 - x, 1 - y, 2 - z -1 + x, y, z 2 - x, 1 - y, 1 - z 2 - x, 1 - y, 1 - z 2 - x, 2 - y, 1 - z x, 1 + y, z 1 - x, -y, -z x, 1 + y, z x, 1 + y, z -1/2 + x, 1 - y, z 1/2 + x, 1 - y, z x, y, z 2 - x, 1/2 + y, 1.5 - z 1 + x, y, z 1 + x, y, z -1 + x, 2 - y, 1 - z 1 + x, 2 - y, -z 1 + x, y, z -x, 1 - y, 1 - z x, 1 + y, z 2 - x, 1 - y, 1 - z 1 - x, 1 - y, 1 - z

See ref 25.

will be the consequence if an aromatic unit is condensed to this site as presented in the phthalimides. Actually, as a result of this modification, the intermolecular contacts are now primarily coming from the phthalimide unit resulting in zigzag chains along the crystallographic a and c axes but also in straight chains and dimers. The few interactions involving the fluorinated phenyl rings are only weak and connect the chains generated by the phthalimidic hydrogen atoms. Similar to 4 in the maleimides series, also among the phthalimides, the 3,5disubstituted imide 10 takes a particular position, in that here

the only contacts formed by an ortho substituted hydrogen atom of the phenyl ring are found (C-Hortho · · · O: 2.47 Å, 163.5° and 2.53 Å, 134.6°, respectively). Each on its own results in a dimer, but in combination with the other contacts, chains along the crystallographic a axis are developed [Figure 3(a)]. Moreover, the shortest F · · · F contact (F · · · F: 2.6921(12) Å, 119.22(9)° and 177.27(8)°, respectively) of all N-phenylphthalimides is found in 10 leading to intermolecular cross-linkage of chains. Though there are other F · · · F contacts featuring distances and angles typical of this kind of interaction in the lattices of 11


Crystal Growth & Design, Vol. 8, No. 8, 2008 2867

Table 4. Intermolecular Hydrogen Bond (C-H · · · F) Lengths (Å) and Angles (deg) for Compounds 3-5, 8, 9 and 11-17 compound 3 4 5 8 9 11

12A 12B 13A 13B 14 15 16 17

C-H · · · F

H· · · F

C· · · F

C-H · · · F

symmetry operator

C1-H1 · · · F4 C5-H5 · · · F4 C1-H1 · · · F7 C1-H1 · · · F6 C1-H1 · · · F4 C12-H12 · · · F6 C13-H13 · · · F6 C13-H13 · · · F8 C5-H5 · · · F8 C12-H12 · · · F6 C5-H5 · · · F6 C12-H12 · · · F8 C12-H12 · · · F5 C13-H13 · · · F8 C12-H12 · · · F6 C4-H4 · · · F11 C7-H7 · · · F12 C6-H6 · · · F12 C6-H6 · · · F12 C5-H5 · · · F11 C7-H7 · · · F22 C6-H6 · · · F5 C7-H7 · · · F18

2.55 2.62 2.39 2.52 2.55 2.49 2.63 2.47 2.61 2.51 2.62 2.64 2.47 2.58 2.48 2.51 2.63 2.64 2.64 2.61 2.36 2.64 2.38

3.4664(17) 3.5473(18) 3.1526(16) 3.0559(16) 3.2458(14) 3.326(2) 3.455(2) 3.0503(17) 3.1008(17) 3.212(2) 3.150(2) 3.2309(19) 3.292(3) 3.394(3) 3.116(4) 3.392(5) 3.417(6) 3.401(5) 3.401(5) 3.528(2) 3.2253(14) 3.508(3) 3.294(4)

161.3 166.0 136.7 115.9 130.2 147.2 145.2 119.2 112.8 130.7 115.7 120.8 145.0 143.7 125.6 153.8 140.9 137.5 137.5 162.3 150.7 155.1 160.8

1/2 - x, 1/2 - y, 1/2 + z -x, 1 - y, 1 - z -1 + x, 1/2 - y, -1/2 + z x, -1 + y, z 1 - x, -y, 1 - z x, 1.5 - y, -1/2 + z x, 1/2 - y, -1/2 + z 1 - x, 1 - y, 1 - z 1/2 + x, y, 1.5 - z 1 + x, 1 + y, 1 + z -x, -1 - y, -z 2 - x, 1 - y, 1 - z -1/2 + x, 1/2 + y, z -x, 1 + y, 1/2 - z x, 1 + y, z -1/2 + x, 1.5 - y, 2 - z 2.5 - x, 1 - y, -1/2 + z 1.5 - x, 1/2 + y, 1/2 - z -1/2 + x, 1/2 + y, z 1 + x, 2 - y, -z 1 + x, 1/2 - y, 1/2 + z 1.5 - x, -1/2 + y, 1.5 - z x, -1 + y, z

and 12A, they show only a secondary effect on the crystal structure, considering the more efficient C-H · · · O and C-H · · · F contacts.

Figure 1. ORTEP plots of compounds (a) 5, (b) 11, and (c) 17 including atom numbering scheme. Thermal ellipsoids are at the 50% probability level, respectively.

contact zigzag dimer chain chain zigzag zigzag zigzag dimer zigzag dimer dimer dimer dimer zigzag chain zigzag zigzag chain chain chain dimer dimer dimer

chain

chain chain chain chain

chain chain chain

Remarkably, face-to-face contacts of the aromatic units do not occur in the crystal packings in the sense of extended stacking interactions,28 except of a dimer forming motif in 12A with the shortest distance of 3.64 Å between the ring centers (plane--plane distance: 3.7 Å). In addition, C-H · · · π interactions are only determined in the basic nonfluorinated compound 7 (distance to the center of the aryl ring 2.94 Å, 150°) resulting in zigzag chains along the b axis. Furthermore, in 7 intermolecular contacts between the carbonyl oxygens and imide units can be observed. These contacts (C-O · · · π: 2.91 Å, 136.6°, related to the center of the imide ring) create additional chains along the crystallographic b axis. Here, the oxygen is orientated to the carbonyl carbon atoms C2, C9 and the nitrogen atom N1 [3.009(2) Å, 3.189(2) Å and 3.007(3) Å, respectively] indicating a lack of electron density. A similar situation is found in compound 9, also giving rise to chain formation along the b axis. In the structure of the pentafluorinated compound 12A, another type of intermolecular interaction involving the aromatic unit and a fluorine atom (C7-F4 · · · πF: 3.16 Å, 132° and C6-F3 · · · πF: 3.47 Å, 119°) supports the chains along the crystallographic b axis. The fluorine atoms are orientated to C8 and C5, demonstrating the decreased electron density of carbons in perfluorinated aryl rings. Finally, it is worthwhile to note that the structures of 7 and 9 are isostructural. Crystal Packing of Compounds 13A-18. In compounds 13A-18, all the hydrogens of the phthalimide unit are substituted by fluorine atoms, leading to the expectation of a higher ratio of phenyl hydrogens in intermolecular interactions and F · · · F contacts in the crystal packing. This proves true in either sort of interaction. While the C-H · · · O contacts involving ortho hydrogen atoms in 13, 14 and 16 [Figure 3(b)] lead to chain formation, the meta hydrogen atoms in 14 give rise to the creation of dimers. They both seem to be of less strength than the similar C-H · · · F contacts resulting in zigzag chains, dimers and straight chains. Another interesting point is that, for both the C-H · · · O and C-H · · · F contacts, the para positioned hydrogen atoms play only an inferior role. Moreover, in all analyzed crystal structures of the arylimides no C-H · · · F contact of an ortho positioned hydrogen atom was observed except for 13A. Here, this rather strong interaction (C-Hortho · · · F: 2.51 Å, 153.8°) results in the formation of zigzag


Schwarzer and Weber

Figure 2. Packing diagrams of (a) 2 along the a axis, (b) 3 along the c axis, (c) 4 along the b axis, and (d) 5 along the c axis. The C-H · · · F and C-H · · · O contacts are shown as broken lines. Nonrelevant hydrogen atoms are omitted for clarity.

Figure 3. Packing diagrams of (a) 10 along the b axis and (b) 16 in the specified view. The C-H · · · O and F · · · F contacts are shown as broken lines. Nonrelevant hydrogen atoms are omitted for clarity.

chains along the a axis. The F · · · F contacts found in 14-18 are also involved in the creation of zigzag chains. However, all these contacts are close to the sum of the van- der Waals radii

(2.83-2.84 Å) and therefore rated rather weak, with compounds 17 and 18 showing the shortest distances (2.74-2.80 Å) in this compound series. As contrasted with the C-H · · · O, C-H · · · F and F · · · F contacts, the interactions involving the aromatic units are less important in engineering the organization of the crystal packings. Indeed, the distances between the centers of the aryl rings (3.68-5.10 Å, plane-plane distances: 3.41-4.91 Å) are too long for being ascribed a propagating stacking interaction. Only in 13A, the distance of 3.68 Å (plane-plane distances: 3.41 Å) may give an account for a molecular dimer stack.28 Furthermore, no C-H · · · π-interactions are found but only C-X · · · πF/π contacts with X ) F, O that are present in all crystal structures. Once again, in the case of oxygen being involved in the interaction, the O is orientated to a carbonyl carbon atom of a neighboring molecule in accordance with the decreased electron density at this atomic site. Polymorphs 12B and 13B. Most of the existing crystalline polymorphs have been obtained as a result of random accidental discovery.29 This is also true for 12B and 13B being polymorphs of 12A and 13A with reference to compounds 12 and 13, respectively. We happened to meet with the two polymorphs as follows. It is known from the literature that by using aryl-perfluoroaryl stacking interactions,14 mixtures of aryl and corresponding perfluoroaryl compounds are systems favorable to form cocrystals.30 Hence, we crystallized a 1:1 stoichiometric mixture of compounds 12 and 13 from acetone, hoping to yield a cocrystal. This, however has not been confirmed, but two different types of crystals were obtained having plate and bulky needle shapes, respectively [Figure 4(a)]. Measuring their cell



Figure 4. Photographs of the hot stage microscopy determination: (a) mixture of 12B (plate) and 13B (bulky needles); (b) sample of 13B (fine needles) and 13A (bulky needles) at 20 °C, (c) at 120 °C, and (d) at 160 °C.

constants provided evidence of being different from those of 12A and 13A. On the other hand, heating crystal samples of 12A and 13A to 150 and 120 °C, respectively, yielded the crystals being identical with the species obtained from the cocrystallization experiment, i.e. 12B and 13B, respectively. A corresponding crystalline transformation of 13A to 13B, supported by a temperature increase, is illustrated with Figures 4(b-d), showing a change from fine to bulky needles. Therefore, 12A/12B and 13A/13B refer to polymorphism which has been approved by X-ray structural determination of 12B and 13B, in comparison with 12A and 13A. However, it was not possible to follow the phase transitions by DSC. While 12B crystallizes in the noncentrosymmetric space group Pca21, the polymorph 12A was found to crystallize in the monoclinic space group C2/c. Regarding the molecular structure, there are no significant differences in bond lengths and angles observable in the polymorphic forms of 12. By way of contrast, the interplanar angle between the imide plane and the phenyl unit shows a significant difference due to the crystal packing, being reflected in the intermolecular interaction (Figure 5). In fact, in 12A the C-H · · · F contacts are much more prominent than in 12B. This is exhibited in the structure of 12A by two short C-H · · · F contacts, one of which forming a chain and the other a zigzag chain, giving rise to a plane parallel to the crystallographic ab plane. These planes are connected through a C-H · · · O contact while other weak F · · · F and C-F · · · πF contacts complete the crystal packing. However, the polymorph 12B is mostly stabilized by short C-H · · · O contacts forming chains along the crystallographic a and c axes. Only one C-H · · · F contact leads to dimers being connected by an additional C-H · · · O contact to yield chains along the b axis. On the other hand, the large number of F · · · F contacts, being visible in the structure, seem to be a result of the crystal packing, considering the influence of the C-H · · · O and C-H · · · F interactions.22 Hence, the main difference between the two polymorphic structures is demonstrated with the prominence in number of weak F · · · F and comparatively stronger C-H · · · O interactions in the case of 12B, and weak C-H · · · F contacts in the case of 12A.

Figure 5. Stereo packing of (a) 12A and (b) 12B (top view to an imide plane). The C-H · · · F and C-H · · · O contacts are shown as broken lines.

With reference to 13A and 13B, the crystal systems reveal the relation a13A ) c13B, 3b13A ) b13B, c13A ) 4a13B. A closer inspection of the crystal structures (Figure 6) indicates that the molecular structures of 13A and 13B show up no significant differences in the Caryl-N bond lengths but in the interplanar angles and the N-C(dO) bond lengths due to crystal packing effects and intermolecular interactions such as C-H · · · O contacts in 13A. In the polymorph 13B, a weak bifurcated C-H · · · O contact gives rise to a zigzag chain resulting in a network due to the symmetry given by the space group. A short C-H · · · F contact, being also involved in a weak F · · · F contact, takes part in the three-dimensional network. By way of contrast, the polymorph 13A displays a lower symmetry leading to a higher number of hydrogen involved intermolecular contacts. Indeed, C-H · · · F interactions form zigzag chains along the crystallographic a and c axes supported by a bifurcated weak C-H · · · O contact. In addition, an aryl-perfluoraryl contact creates dimers, not being related to the infinite stacking structure expected from the aryl-perfluoroaryl motif.14a As a final remark, it is worthwhile to mention that the structures of 13B and 14 are isostructural. Comparative Reflection and Conclusions Rating the fluorine involved supramolecular contacts in competition with stronger hydrogen acceptor atoms such as oxygen and nitrogen, provided by a series of compounds that will allow a reasonable comparison, has been the object of the present study. For this purpose, the crystal structures of 18 species of fluorinated N-phenylmaleimides and corresponding phthalimides, featuring different degree and positions of fluorine


Schwarzer and Weber Scheme 3. Diagram Showing the Relevant Intermolecular C-H · · · F (Green) and C-H · · · O (Red) Contacts of the Different Compounds Dependent on the Hydrogen Atom Position

Figure 6. Stereo packing of (a) 13A and (b) 13B (top view to an imide plane). The F · · · F contacts are shown as broken lines.

Scheme 2. Ratio of Intermolecular Contacts (X ) F, O) Based on the Crystal Structures (Allocated to the Compound Classes)

substitution, and including also the parent nonfluorinated compounds (1-18), have been determined. Several general conclusions can be obtained from the analysis of the X-ray data. Perhaps the most significant finding is that the aryl-perfluoroaryl intermolecular stacking arrangement, commonly attributed a rather robust supramolecular synthon,14a has not been determined a dominant motif in the present structures. However, there is a balance of hydrogen interactions to oxygen and fluorine atoms, fluorine-fluorine contacts and special contacts between an oxygen atom and the electron deficient ring. As follows from the diagram, given in Scheme 2, the amount of CH/X · · · π/πF interactions (X ) F, O) increases in the order maleimides < phthalimides < tetrafluorophthalimides. Moreover, it is an obvious consequence that, with increasing the number of fluorine

atoms in the molecule, the F · · · F contacts increase while the C-H · · · O and C-H · · · F contacts decrease, corresponding to the lower number of hydrogen atoms. It is also shown that the C-H · · · π contacts are rather secondary here, though this type of interaction is otherwise important.22 A more specialized comparison between the different compounds refers to the contacts involving hydrogen and oxygen or hydrogen and fluorine atoms, which were found to depend significantly on the position of the hydrogen atom in the respective molecule. In the series of the maleimides (1-5), the olefinic hydrogens are mainly concerned in the formation of C-H · · · O and C-H · · · F contacts, possibly because they are the most acidic ones. Changing over to the phthalimides (7-12), this position is taken up by the phthalimidic hydrogens. And, logically, substitution of these hydrogens for fluorine atoms, such as in the tetrafluorophthalimides (13-17), gives rise to a shifting from the phthalimidic to the phenyl hydrogens, now interacting with the hydrogen acceptors. Moreover, it is given evidence that the fluorine atoms, unlike the oxygen atoms, are partial to contact to hydrogens of the maleimide and phthalimide rings, even in the presence of phenyl hydrogens, thus indicating that fluorine is more specific in making a selection from potential H-contacts. This particular behavior can be extracted from the data plotted in Scheme 3, while in Scheme 4 the corresponding motifs for each compound class, involving the C-H · · · O and C-H · · · F contacts, are specified in more detail dependent on the respective hydrogen position. With reference to the phenyl unit, it is shown that the meta hydrogen atoms are much more numerous involved in C-H · · · F contacts than the ortho and para hydrogens, whereas the ortho hydrogens predominate the C-H · · · O contacts and with some weaker tendency also the hydrogen in the meta position. The motifs being formed by the meta C-H · · · F contacts of the phthalimides are mainly dimers and zigzag chains. On the other hand, the C-H · · · O contacts of the phthalimides are less committed to a particular selection of motifs. Regarding the tetrafluorophthalimides, the only one case of a C-H · · · F contact involving an ortho hydrogen of the phenyl ring is observed, considering the entire series of compounds under discussion. Otherwise, all types of interaction motifs and hydrogen positions are met with the tetrafluorophthalimides both referring to the C-H · · · F and C-H · · · O contacts. A more detailed analysis of the contact modes considering the positions of fluorine substituents is given in Scheme 5. The

Fluorine Involved Contacts in N-Arylimides Scheme 4. Diagram Showing the Motifs of Intermolecular C-H · · · F (Green) and C-H · · · O (Red) Contacts Dependent on the Hydrogen Atom Position, Demonstrated with the Parent Model Molecules (a)-(c) for Each of the Compound Classes Irrespective of the Fluorine Substitutiona


understanding of the influence of the organic fluorine interactions, particulary in the presence of moderate oxygen and nitrogen hydrogen acceptor sites. On the whole, it looks as if these fluorine contacts do not substantially control the packing under the given competitive conditions but are there mostly in addition. A remarkable notice in this connection is that the potential π · · · πF stacking interaction, commonly attributed an important synthon in the crystal engineering,13,14,30 is of no consequence here. Hence, the study of organic fluorine interactions continues to be a promising field of research. Experimental Section

a Motifs are chains, zigzag chains and dimers. The digits depict the number of motifs found in compounds 1-5 and 7-18.

Scheme 5. Diagram Showing the Motifs of Intermolecular C-H · · · F (Green) Contacts Dependent on the Position of the Fluorine Substitution, Demonstrated with the Perfluoro Model Moleculea

a Motifs are chains, zigzag chains and dimers. The digits depict the number of motifs found in compounds 2-5 and 8-18.

diagram shows that the fluorine atoms in ortho position of the phenyl ring are the most active in the contact formation. This stands in a sharp contrast to the corresponding H-donorship referring to this position, which is avoided in the latter case. It is also obvious from this analysis that the ortho positioned fluorine atoms give the supramolecular zigzag chain and dimer formation priority. In conclusion, the above results suggest that although the study is broad and systematic, and based on a selected series of compounds, the finding of a predetermined pattern of organic fluorine involved supramolecular interactions is a difficult problem that cannot be solved at present. Nevertheless, the crystalline packing structures of the organic fluorine compounds discussed here indicate some trends in the observed C-H · · · F, F · · · F, F · · · πF and π · · · πF contacts, giving rise to some specific

General. Melting points were determined using a microscope heating stage PHMK Rapido (VEB Wa¨getechnik). IR spectra were measured on FT-IR 510 Nicolet as KBr pellets. 1H, 13C and 19F NMR spectra were measured in chloroform solution at room temperature on a Bruker Avance DPX 400 at 400, 100 and 376 MHz, respectively. Mass spectra were obtained using a Hewlett-Packard GC-MS 5890. Elemental analyses were performed on a Heraeus CHN rapid analyzer. Materials. Tetrafluorophthalic anhydride was prepared from tetrafluorophthalic acid with acetyl chloride and purified by sublimation in vacuo at 110 °C according to the literature procedure.31 All other starting compounds and solvents were obtained commercially and used without further purification, except aniline, which was distilled before use. Synthesis of N-Phenylmaleimide (1). Exemplary Procedure24 for All Other Maleimides (2-6) and Phthalimides (7-18). To a stirred solution of maleic anhydride (1.96 g, 20 mmol) in diethyl ether (45 mL), a solution of aniline (1.86 g, 20 mmol) in diethyl ether (10 mL) was added. Stirring of the mixture was continued for 1 h. The formed solid was collected and dried in vacuum to yield the intermediate compound N-phenylmaleamic acid. Without further purification, the N-phenylmaleamic acid (2.87 g, 15 mmol) and sodium acetate (0.60 g, 7.3 mmol) were added to acetic anhydride (5 mL). The mixture was heated on a water bath for 0.5 h, and then cooled down to room temperature with water (10 mL). The solid was collected, washed three times with water and dried. Recrystallization of the crude product from cyclohexane yielded 2.66 g (77%) of maleimide 1 as yellow crystals: mp 90 °C (lit.32 mp 90-91 °C). N-(4-Fluorophenyl)maleimide (2). 4-Fluoroaniline (2.22 g, 20 mmol) and maleic anhydride (1.96 g, 20 mmol) were used. Recrystallization from cyclohexane yielded 2.46 g (64%) as pale yellow crystals: mp 154-155 °C (lit.33 mp 155 °C). N-(2,6-Difluorophenyl)maleimide (3). 2,6-Difluoroaniline (2.58 g, 20 mmol) and maleic anhydride (1.96 g, 20 mmol) were used. Recrystallization from cyclohexane yielded 3.20 g (77%) of colorless crystals: mp 91-93 °C; νmax (KBr)/cm-1 3089 (CdCH), 1791, 1725 (CdO), 1646 (CdC), 1596 (CdCAr), 1378, 1161 (C-N-C); 1H NMR (CDCl3) δH 7.43 (m, 2H, H-5, H-7), 7.05 (m, 1H, H-6), 6.96 (s, 2H, HCdCH); 13C NMR (CDCl3) δC 167.77 (CdO), 160.24/157.71 (d, C-4, 1JC-F ) -254.5 Hz), 135.02 (HCdCH), 130.97 (C-6), 112.17 (d, C-5, C-7, 2JC-F ) 21.3 Hz), 108.43 (C-3); 19F NMR (CDCl3) δF -117.55 (m, F-4, F-8). Anal. Calcd for C10H5F2NO2: C, 57.43; H, 2.41; N, 6.70. Found: C, 57.18; H, 2.36; N, 6.52%. MS: m/e 209 [M]+, 139, 127, 100, 54. N-(3,5-Difluorophenyl)maleimide (4). 3,5-Difluoroaniline (2.58 g, 20 mmol) and maleic anhydride (1.96 g, 20 mmol) were used. Recrystallization from cyclohexane yield 2.53 g (61%) of pale yellow crystals: mp 86-89 °C; νmax (KBr)/cm-1 3091 (CdCH), 1773, 1732 (CdO), 1632 (CdC), 1606 (CdCAr),


1299, 1124 (C-N-C); 1H NMR (CDCl3) δH 7.05 (m, 2H, H-4, H-8), 6.89 (s, 2H, HCdCH), 6.83 (m, 1H, H-6); 13C NMR (CDCl3) δC 168.50 (CdO), 164.12/161.65 (d, C-5, C-7, 1JC-F ) -248.5 Hz), 134.39 (HCdCH), 133.42 (C-3), 108.70 (t, C-4, C-8, 2JC-F ) 28.8 Hz), 103.08 (d, C-6, 2JC-F ) 25.2 Hz); 19F NMR (CDCl3) δF -108.89 (m, F-5, F-7). Anal. Calcd for C10H5F2NO2: C, 57.43; H, 2.41; N, 6.70. Found: C, 56.38; H, 2.29; N, 6.43%. MS: m/e 209 [M]+, 139, 100, 54. N-(2,4,6-Trifluorophenyl)maleimide (5). 2,4,6-Trifluoroaniline (2.94 g, 20 mmol) and maleic anhydride (1.96 g, 20 mmol) were used. Recrystallization from cyclohexane yielded 2.44 g (54%) of colorless crystals: mp 102-103 °C; νmax (KBr)/ cm-1 3083 (CdCH), 1783, 1726 (CdO), 1645 (CdC), 1524 (CdCAr), 1356, 1150 (C-N-C); 1H NMR (CDCl3) δH 6.94 (s, 2H, HCdCH), 6.84 (s, 2H, Ar-H); 13C NMR (CDCl3) δC 167.63 (CdO), 164.20/161.69 (d, C-6, 1JC-F ) -253.0 Hz), 160.61/158.06 (d, C-4, C-8, 1JC-F ) -256.5 Hz), 135.05 (HCdCH), 105.08 (t, C-3, 2JC-F ) 17.1 Hz), 101.20 (t, C-5, C-7, 2JC-F ) 25.5 Hz); 19F NMR (CDCl3) δF -104.82 (m, F-6), -114.12 (m, F-4, F-8). Anal. Calcd for C10H4F3NO2: C, 52.88; H, 1.78; N, 6.17. Found: C, 52.69; H, 1.86; N, 6.02%. MS: m/e 227 [M]+, 183, 157, 145, 54. N-(2,3,4,5,6-Pentafluorophenyl)maleimide (6). 2,3,4,5,6Pentafluoroaniline (3.66 g, 20 mmol) and maleic anhydride (1.96 g, 20 mmol) were used. Recrystallization from cyclohexane yielded 2.79 g (53%) of colorless crystals: mp 105-106 °C (lit.33 mp 105.5 °C). N-Phenylphthalimide (7). Aniline (1.86 g, 20 mmol) and phthalic anhydride (2.96 g, 20 mmol) were used. Recrystallization from ethanol yielded 1.65 g (37%) of colorless crystals: mp 210 °C (lit.34 mp 211 °C). N-(4-Fluorophenyl)phthalimide (8). 4-Fluoroaniline (2.22 g, 20 mmol) and phthalic anhydride (2.96 g, 20 mmol) were used. Recrystallization from ethanol yielded 2.37 g (49%) of colorless crystals: mp 181 °C (lit.35 mp 180-181.5 °C, lit.36 mp 150-152 °C). N-(2,6-Difluorophenyl)phthalimide (9). 2,6-Difluoroaniline (2.58 g, 20 mmol) and phthalic anhydride (2.96 g, 20 mmol) were used. Recrystallization from ethanol yielded 3.80 g (73%) of colorless crystals: mp 163-164 °C; νmax (KBr)/cm-1 3079 (CHAr), 1790, 1748 (CdO), 1600, 1513 (CdCAr), 1378, 1104 (C-N-C); 1H NMR (CDCl3) δH 7.99-7.82 (m, 4H, H-11, H-12, H-13, H-14), 7.45 (m, 2H, H-5, H-7), 7.11 (m, 1H, H-6); 13 C NMR (CDCl3) δC 165.72 (CdO), 160.29/157.76 (d, C-4, C-8, 1JC-F ) -254.5 Hz), 134.54 (C-12, C-13), 133.06 (C-1, C-10), 130.94 (C-6), 124.09 (C-11, C-14), 112.18 (d, C-5, C-7, 2 JC-F ) 22.9 Hz), 108.87 (t, C-3, 2JC-F ) 17.0 Hz); 19F NMR (CDCl3) δF -117.05 (m, F-4, F-8). Anal. Calcd for C14H7F2NO2: C, 64.87; H, 2.72; N, 5.40. Found: C, 64.87; H, 2.71; N, 5.39%. MS: m/e 259 [M]+, 215, 104, 76. N-(3,5-Difluorophenyl)phthalimide (10). 3,5-Difluoroaniline (2.58 g, 20 mmol) and phthalic anhydride (2.96 g, 20 mmol) were used. Recrystallization from ethanol yielded 2.86 g (55%) of colorless crystals: mp 208-209 °C; νmax (KBr)/cm-1 3089 (CHAr), 1788, 1716 (CdO), 1605 (s, ν CdCAr), 1399, 1128 (C-N-C); 1H NMR (CDCl3) δH 8.03-7.80 (m, 4H, H-11, H-12, H-13, H-14), 7.14 (m, 2H, H-4, H-8), 6.86 (m, 1H, H-6); 13 C NMR (CDCl3) δC 166.41 (CdO), 164.09/161.62 (d, C-5, C-7, 1JC-F ) - 248.5 Hz), 134.80 (C-12, C-13), 133.86 (C-3), 131.36 (C-1, C-10), 124.04 (C-11, C-14), 109.5 (d, C-4, C-8, 2 JC-F ) 20.1 Hz), 103.41 (d, C-6, 2JC-F ) 25.3 Hz); 19F-NMR (CDCl3) δF -109.05 (m, F-5, F-7). Anal. Calcd for C14H7F2NO2: C, 64.87; H, 2.72; N, 5.40. Found: C, 64.73; H, 2.78; N, 5.32%. MS: m/e 259 [M]+, 215, 104, 76.

Schwarzer and Weber

N-(2,4,6-Trifluorophenyl)phthalimide (11). 2,4,6-Trifluoroaniline (2.94 g, 20 mmol) and phthalic anhydride (2.96 g, 20 mmol) were used. Recrystallization from ethanol yielded 2.08 g (38%) of colorless crystals: mp 196-199 °C; νmax (KBr)/cm-1 3084 (CHAr), 1787, 1744 (CdO), 1607, 1520 (CdCAr), 1391, 1112 (C-N-C); 1H NMR (CDCl3) δH 7.99-7.81 (m, 4H, H-11, H-12, H-13, H-14), 6.87 (s, 2H, H-5, H-7); 13C NMR (CDCl3) δC 165.51 (CdO), 164.12/161.61 (d, C-6, 1JC-F ) -252.5 Hz), 160.54/158.00 (d, C-4, C-8, 1JC-F ) -255.5 Hz), 134.53 (C12, C-13), 131.85 (C-1, C-10), 124.04 (C-11, C-14), 105.71 (t, C-3, 2JC-F ) 17.2 Hz), 101.11 (d, C-5, C-7, 2JC-F ) 24.2 Hz); 19 F NMR (CDCl3) δF - 105.08 (m, F-6), -113.62 (m, F-4, F-8). Anal. Calcd for C14H6F3NO2: C, 60.66; H, 2.18; N, 5.05. Found: C, 60.37; H, 1.94; N, 4.83%. MS: m/e 277 [M]+, 232, 104, 76. N-(2,3,4,5,6-Pentafluorophenyl)phthalimide (12). 2,3,4,5,6Pentafluoroaniline (3.66 g, 20 mmol) and phthalic anhydride (2.96 g, 20 mmol) were used. Recrystallization from ethanol yielded 3.73 g (56%) of colorless crystals: mp 164-166 °C (lit.36 mp 128-130 °C); νmax (KBr)/cm-1 3100 (CHAr), 1790, 1738 (CdO), 1631, 1521 (CdCAr), 1369, 1109 (C-N-C); 1H NMR (CDCl3) δH 8.09 -7.79 (m, 4H, Ar-H); 13C NMR (CDCl3) δC 164.86 (CdO), 145.43/142.93 (d, C-4, C-8, 1JC-F ) -251.0 Hz), 143.45/140.89 (d, C-6, 1JC-F ) -258.4 Hz), 139.32, 136.81 (d, C-5, C-7, 1JC-F ) -252.9 Hz), 134.99 (C12, C-13), 131.74 (C-1, C-10), 124.44 (C-11, C-14), 107.03 (t, C-3, 2JC-F ) 15.4 Hz); 19F NMR (CDCl3) δF -143.10 (m, F-4, F-8), -151.92 (m, F-6), -161.54 (m, F-5, F-7). Anal. Calcd for C14H4F5NO2: C, 53.69; H, 1.29; N, 4.47. Found: C, 53.59; H, 1.28; N, 4.47%. MS: m/e 313 [M]+, 269, 104, 76. N-Phenyltetrafluorophthalimide (13). Aniline (0.47 g, 5 mmol) and tetrafluorophthalic anhydride (1.10 g, 5 mmol) were used. Recrystallization from cyclohexane/acetone (1:1) yielded 0.73 g (49%) of colorless crystals: mp 208 °C (lit.37 mp 210 °C). N-(4-Fluorophenyl)tetrafluorophthalimide (14). 4-Fluoroaniline (0.56 g, 5 mmol) and tetrafluorophthalic anhydride (1.10 g, 5 mmol) were used. Recrystallization from cyclohexane/ acetone (1:1) yielded 0.93 g (59%) of colorless crystals: mp 236 °C; νmax (KBr)/cm-1 3079 (CHAr), 1784, 1725 (CdO), 1604, 1509 (CdCAr), 1413, 1087 (C-N-C); 1H NMR (DMSOd6) δH 7.45-7.23 (m, 4H, Ar-H); 13C NMR (DMSO-d6) δC 162.99/161.78 (t, C-6, 1JC-F ) -246.5 Hz), 161.78 (CdO), 145.52/142.98 (d, C-11, C-14, 1JC-F ) -264.6 Hz), 143.92/ 141.37 (d, C-12, C-13, 1JC-F ) -256.5 Hz), 129.69 (C-4, C-8), 127.16 (d, C-3, 2JC-F ) 3.0 Hz), 116.10 (d, C-5, C-7, 2JC-F ) 23.1 Hz), 114.10 (C-1, C-10); 19F NMR (CDCl3) δF -113.76 (m, F-6), -140.46 (m, F-12, F-13), -145.30 (m, F-11, F-14). Anal. Calcd for C14H4F5NO2: C, 53.69; H, 1.29; N, 4.47. cm-1. Found: C, 53.66; H, 1.33; N, 4.45%. MS: m/e 313 [M]+, 269, 176, 148. N-(2,6-Difluorophenyl)tetrafluorophthalimide (15). 2,6Difluoroaniline (0.65 g, 5 mmol) and tetrafluorophthalic anhydride (1.10 g, 5 mmol) were used. Recrystallization from cyclohexane/acetone (1:1) yielded 1.11 g (67%) of colorless crystals: mp 223 °C; νmax (KBr)/cm-1 3068 (CHAr), 1795, 1740 (CdO), 1599, 1500 (CdCAr), 1413, 1099 (C-NC); 1H NMR (CDCl3) δH 7.52-7.48 (m, 1H, H-6), 7.13-7.09 (m, 2H, H-5, H-7); 13C NMR (CDCl3) δC 160.06/157.52 (d, C-4, C-8, 1JC-F ) -255.5 Hz), 159.69 (CdO), 146.79/144.10 (d, C-11, C-14, 1 JC-F ) -270.6 Hz), 145.16/142.55 (d, C-12, C-13, 1JC-F ) -262.6 Hz), 131.80 (C-6), 113.86 (d, C-1, C-10, 2JC-F ) 7.1 Hz), 112.33 (d, C-5, C-7, 2JC-F ) 23.1 Hz), 107.78 (t, C-3, 2 JC-F ) 17.0 Hz); 19F NMR (CDCl3) δF - 117.04 (m, F-4,


F-8), -134.55 (m, F-11, F-14), - 141.73 (m, F-12, F-13). Anal. Calcd for C14H3F6NO2: C, 50.77; H, 0.91; N, 4.23. Found: C, 50.54; H, 0.99; N, 4.36%. MS: m/e 331 [M]+, 287, 176, 148. N-(3,5-Difluorophenyl)tetrafluorophthalimide (16). 3,5Difluoroaniline (0.65 g, 5 mmol) and tetrafluorophthalic anhydride (1.10 g, 5 mmol) were used. Recrystallization from cyclohexane/acetone (1:1) yielded 0.72 g (55%) of colorless crystals: mp 201 °C; νmax (KBr)/cm-1 3074 (CHAr), 1790, 1726 (CdO), 1608, 1501 (CdCAr), 1411, 1097 (C-N-C); 1H NMR (CDCl3) δH 7.07-6.89 (m, 3H, H-6, H-4, H-8); 13C NMR (CDCl3) δC 164.21/161.73 (d, C-5, C-7, 1JC-F ) -249.5 Hz), 160.61 (CdO), 146.91/144.21 (d, C-11, C-14, 1JC-F ) -271.6 Hz), 145.28/142.67 (d, C-12, C-13, 1JC-F ) -262.6 Hz), 132.52 (C-3), 113.19 (d, C-1, C-10, 2JC-F ) 6.7 Hz), 109.69 (d, C-4, C-8, 2JC-F ) 20.3 Hz), 104.42 (t, C-6, 2JC-F ) 25.2 Hz); 19F NMR (CDCl3) δF -108.09 (m, F-5, F-7), -134.89 (m, F-11, F-14), - 141.13 (m, F-12, F-13). Anal. Calcd for C14H3F6NO2: C, 50.77; H, 0.91; N, 4.23. Found: C, 50.66; H, 1.03; N, 4.00%. MS: m/e 331 [M]+, 287, 176, 148. N-(2,4,6-Trifluorophenyl)tetrafluorophthalimide (17). 2,4,6′Trifluoroaniline (0.74 g, 5 mmol) and tetrafluorophthalic anhydride (1.10 g, 5 mmol) were used. Recrystallization from cyclohexane/acetone (1:1) yielded 0.46 g (26%) of colorless crystals: mp 179 °C; νmax (KBr)/cm-1 3089 (CHAr), 1798, 1746 (CdO), 1608, 1503 (CdCAr), 1416, 1102 (C-N-C); 1H NMR (CDCl3) δH 6.89 (m, 2H, H-5, H-7); 13C NMR (CDCl3) δC 164.72/162.19 (d, C-6, 1JC-F ) -254.5 Hz), 160.48/157.93 (d, C-4, C-8, 1JC-F ) -256.5 Hz), 159.62 (CdO), 146.82/144.19 (d, C-11, C14, 1JC-F ) -264.6 Hz), 145.20/142.54 (d, C-12, C-13, 1JC-F ) -267.6 Hz), 113.69 (d, C-1, C-10, 2JC-F ) 7.1 Hz), 104.43 (t, C-3, 2JC-F ) 17.2 Hz), 101.45 (d, C-5, C-7, 2 JC-F ) 23.4 Hz); 19F NMR (CDCl3) δF -103.29 (m, F-6), -113.64 (m, F-4, F-8), -134.35 (m, F-11, F-14), -141.47 (m, F-12, F-13). Anal. Calcd for C14H2F7NO2: C, 48.16; H, 0.58; N, 4.01. Found: C, 47.94; H, 0.79; N, 4.25%. MS: m/e 349 [M]+, 305, 176, 148. N-(2,3,4,5,6-Pentafluorophenyl)tetrafluorophthalimide (18). 2,3,4,5,6-Pentafluoroaniline (0.92 g, 5 mmol) and tetrafluorophthalic anhydride (1.10 g, 5 mmol) were used. Recrystallization from cyclohexane/acetone (1:1) yielded 0.71 g (37%) of colorless crystals: mp 199 °C; νmax (KBr)/cm-1 3101 (CHAr), 1786, 1738 (CdO), 1536, 1514 (CdCAr), 1410, 1100 (C-N-C). 13C NMR (CDCl3) δC 158.93 (CdO), 147.07/144.37 (d, C-11, C-14, 1JC-F ) -271.6 Hz), 145.38, 142.71 (C-4, C-8, C12, C-13), 143.97/141.39 (d, C-6, 1JC-F ) -259.5 Hz), 139.34/ 136.77 (d, C-5, C-7, 1JC-F ) -258.5 Hz), 113.47 (d, C-1, C-10, 2 JC-F ) 7.2 Hz), 105.62 (t, C-3, 2JC-F ) 12.3 Hz); 19F NMR (CDCl3) δF -133.32 (m, F-11, F-14), -140.42 (m, F-12, F-13), -142.92 (m, F-4, F-8), -149.96 (m, F-6, -160.56 (m, F-5, F-7). Anal. Calcd for C14F9NO2: C, 43.66; N, 3.64. Found: C, 43.55; N, 3.79%. MS: m/e 385 [M]+, 341, 176, 148. X-Ray Crystallography. Crystals suitable for X-Ray crystallography studies were grown by slow evaportation of the solvent used for recrystallization. All crystals were measured on a Bruker Kappa Apex II using graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). Data collection: SMART.38 Cell refinement: SMART.38 Data reduction: SAINT.38 Preliminary structure models were derived by Direct Methods39 and were refined by full-matrix least-squares calculation based on F2 for all reflections.40 All non-hydrogen atoms were refined anisotropically. Compound 10 was measured as a twin with two domains in the ratio of 62:38. The two domains were detected with CELL_NOW,41 integrated with SAINTPLUS38 and scaled with TWINABS41 as a nonabsorber. The hydrogen atoms were


included in the models in calculated positions. All crystal data and experimental parameters are summarized in Table 1. In some cases (12B, 16, 18), moderate crystal quality gave rise to significant decrease in scattering power, which explains relatively low data/parameter ratio. Supporting Information Available: ORTEP plots for compounds 2-4, 7-10, 12-16, 18 and packing diagrams for compounds 7-9, 11-15, 17 and 18. This material is available free of charge via the Internet at http://pubs.acs.org.

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CG7011638

Influence of Fluorine Substitution on the Crystal Packing of N

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