How Realistic Are Interactions Involving Organic Fluorine in Crystal

CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 1 47-52

Articles How Realistic Are Interactions Involving Organic Fluorine in Crystal Engineering? Insights from Packing Features in Substituted Isoquinolines† Angshuman Roy Choudhury and Tayur N. Guru Row* Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560012 India Received July 23, 2003;

Revised Manuscript Received August 23, 2003

ABSTRACT: Three new compounds have been synthesized based on the molecular motif, 6-methoxy-1,2-diphenyl1,2,3,4-tetrahydroisoquinoline, with fluorine substitution at para, meta, and ortho positions on the 1-phenyl ring and a fluorine in the ortho position on the 2-phenyl ring. The crystal structures of all three compounds have been determined by single-crystal X-ray diffraction at 100.0(2) K. The three structures, as compared to the corresponding structures with no fluorine atom on the 2-phenyl ring, generate motifs via C-H‚‚‚F and C-F‚‚‚π interactions. None of these structures have any significant interactions other than those involving fluorine. The changes in both conformational features and in the intra- and intermolecular interactions involving fluorine provide significant inputs for understanding packing features associated with organic fluorine. Introduction Intermolecular interactions such as hydrogen bonds provide precise topological control to design new novel materials. The packing of molecules in a crystalline organic solid generated by conventional hydrogen bonds such as O-H‚‚‚O, N-H‚‚‚O, O-H‚‚‚N, and N-H‚‚‚N has been well studied.1-6 Interactions of the type C-H‚‚‚π and π‚‚‚π provide weak but highly directional packing motifs, which aid in the evaluation of molecular assemblies.7-9 Packing modes generated through interactions involving halogens, especially chlorine and bromine, add to the list of crystal engineering tools.10,11 It has been argued that “organic fluorine” does not readily accept interactions involving hydrogen.12-16 However, recent literature has provided evidence for the propensity for the formation of interactions such as C-F‚‚‚F′-C′, C-H‚‚‚F′-C′, and C-F‚‚‚π.17-22 X-ray crystallographic analysis of 1,2-diphenyl-6-methoxy1,2,3,4-tetrahydroisoquinoline with fluorine substitution at para, meta, and ortho positions, respectively, on the † Crystallographic details (excluding structure factors) on the structure analyses of compounds 1-3 have been deposited with the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ (UK); fax: (+44) 1223-336-033; e-mail: [email protected]. These may be obtained on quoting the depository numbers CCDC 200875-200877, respectively. * Corresponding author: Professor T. N. Guru Row, Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 India. Phone: +91-80-2932796; FAX: +91-80-3601310; e-mail: [email protected].

1-phenyl ring20 indicate that fluorine dictates packing motifs via interactions of the types C-F‚‚‚F′-C′, C-H‚‚‚F′-C′, and C-F‚‚‚π. The occurrence of such interactions, especially in the absence of any other significant intermolecular interactions, suggests a clear influencing factor on the packing modes. We have recently reported the conformational and packing features of the corresponding derivatives with chlorine and bromine substitutions at para, meta, and ortho positions, respectively, on the 1-phenyl ring.23 The comparison of these structures with different halogen atoms bring out the features that demonstrate on one hand that the isostructurality index is not an indicator for evaluating the similarity in packing in crystal lattice and on the other hand show that interactions involving fluorine do contribute to stabilizing crystal structures. It has been shown that, in the same chemical environment, fluorine behaves differently than chlorine and bromine and provides well-defined fluorine based interactions, which are not observed in case of chloro- or bromo- derivatives. The effective nonbonding (van der Waals) shapes in C-X (X ) Cl, Br, and I) are short along the atom to carbon bond vector and are retained from crystal to crystal in similar chemical environments.24 The anisotropy of repulsion plays a greater role for short interatomic contacts in lighter halogen (fluorine and to a certain extent chlorine) than weak polarization induced attractive forces, which dominate the contacts involving intermolecular bromo‚‚‚bromo and iodo‚‚‚iodo

10.1021/cg034137n CCC: $27.50 © 2004 American Chemical Society Published on Web 09/30/2003

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Crystal Growth & Design, Vol. 4, No. 1, 2004

Choudhury and Guru Row Table 1. Crystal Data of Compounds 1, 2, and 3

Figure 1. Compound 1: R2 ) R3 ) H, R1 ) R4 ) F; compound 1′: R2 ) R3 ) R4 ) H, R1 ) F; compound 2: R1 ) R3 ) H, R2 ) R4 ) F; compound 2′: R1 ) R3 ) R4 ) H, R2 ) F; compound 3: R1 ) R2 ) H, R3 ) R4 ) F; compound 3′: R1 ) R2 ) R4 ) H, R3 ) F.

contacts.25 It has been observed that the occurrence of C-H‚‚‚F, C-F‚‚‚π, and C-F‚‚‚F in fluorine-rich structures depends on the H/F ratio in crystalline aromatic azines.26 These specific examples demonstrate that the formation of interactions involving fluorine is yet to be harnessed. In fact, the relative weakness of interactions involving fluorine and the frequent occurrence of C-F groups in many drug and drug intermediates indicate the possible use of C-H‚‚‚F, C-F‚‚‚π, and C-F‚‚‚F as routine elements in crystal engineering in drugs and pharmaceuticals. Interestingly, all significant short F‚‚‚F interactions hitherto observed are across a crystallographic center of symmetry.19,20,27 In this article, we present the crystal and molecular structures of 1-(4-fluorophenyl)-2-(2-fluorophenyl)-6methoxy-1,2,3,4-tetrahydroisoquinoline (compound 1, Figure 1), 1-(3-fluorophenyl)-2-(2-fluorophenyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (compound 2, Figure 1) and 1,2-bis-(2-fluorophenyl)-6-methoxy-2-phenyl1,2,3,4-tetrahydroisoquinoline (compound 3, Figure 1). These structures are compared with the corresponding mono fluoro-derivatives reported earlier by us.20 The absence of any other hydrogen bonding potential (conventional like O-H‚‚‚O, N-H‚‚‚O, etc. and weak but highly directional like C-H‚‚‚π and π‚‚‚π, etc.) in these compounds provide a unique opportunity to examine the features associated with interactions involving “organic fluorine”. Experimental Section The compounds 1-3 (Figure 1) were synthesized by the procedure given in the literature.28 Single crystals of all the three compounds were grown from a solution in acetone by slow evaporation process at 5 °C. The single-crystal X-ray diffraction data were collected on a Bruker AXS SMART APEX CCD diffractometer at 100.0(2) K using the OXFORD Cryosystem with N2 flow. The data were collected using graphite monochromated Mo KR radiation, and the intensities were measured using ω scan with a scan width of 0.3°. A total of 606 frames per set were collected in three different settings of φ (0°, 90°, and 180°) keeping the sample to detector distance of 6.03 cm and 2θ value fixed at -25°. The data were reduced by SAINTPLUS29 and an empirical absorption correction was applied using SADABS29 available in the Bruker software package. All the structures were solved using SIR9230 and refined using SHELXL31 present in the WINGX32 (version 1.64.03b) program suite. ORTEP diagrams of all the compounds were generated by ORTEP3233 and packing diagrams were generated using CAMERON34 available in the WINGX program suite. The geometric calculations were done by PARST9535 and PLATON.36

formula formula weight color cryst morph cryst syst a/Å b/Å c/Å R/° β/° γ/° volume/Å3 space group Z density/g cm-3 radiation wavelength/Å temp/K µ/mm-1 F000 diffractometer detector θmin, max/° unique reflns R, Rw Fmin, Fmax/e Å-3 GOF

compound 1

compound 2

compound 3

C22H19NOF2 351.4 colorless prismatic orthorhombic 13.232(2) 11.158(2) 23.235(2) 90.0 90.0 90.0 3430.1(1) Pbca 8 1.36 MoKR 0.7107 100.0(2) 0.098 1471.8 Bruker AXS SMART APEX CCD 1.8, 26.4 3505 0.037, 0.097 -0.23, 0.31 1.056

C22H19NOF2 351.4 colorless prismatic monoclinic 38.592(8) 6.124(1) 15.885(3) 90.0 104.937(4) 90.0 3439.1(4) C2/c 8 1.36 MoKR 0.7107 100.0(2) 0.098 1471.8 Bruker AXS SMART APEX CCD 2.3, 26.4 3507 0.038, 0.098 -0.23, 0.54 1.053

C22H19NOF2 351.4 colorless prismatic monoclinic 15.991(4) 6.149(1) 17.628(4) 90.0 103.034(4) 90.0 1688.4(2) P21/a 4 1.36 MoKR 0.7107 100.0(2) 0.099 735.9 Bruker AXS SMART APEX CCD 2.4, 26.4 3428 0.036, 0.093 -0.30, 0.31 1.083

Table 2. Relevant Torsion Angles in (a) Compounds 1 and 1′, (b) Compounds 2 and 2′, and (c) Compounds 3 and 3′ (a) Compounds 1 and 1′ torsion angle

compound 1 expt/theo

compound 1′ expt/theo

C8-C1-C10-C11 C10-C1-N1-C16 C1-N1-C16-C17 C9-C8-C1-C10 C1-N1-C2-C3 C4-C5-O1-C22

-139.8(1)/-143.67 -60.7(1)/-59.71 -66.8(1)/-68.62 -103.1(1)/-108.41 64.8(1)/67.19 -171.8(1)/179.51

91.0(2)/-145.03 -79.8(2)/-60.22 -166.1(2)/-70.35 -103.5(2)/-107.78 -32.5(3)/67.76 174.7(2)/179.68

(b) Compounds 2 and 2′ torsion angle




143.0(1)/-143.20 52.1(2)/-59.60 71.1(2)/+68.46 114.1(1)/-108.6 -66.2(1)/+66.69 -1.24(2)/+179.72

146.5(2)/-144.66 -103.2(2)/-60.20 -158.9(2)/-70.22 -84.8(2)/-107.94 -7.8(2)/+67.56 -1.0(3)/+179.96

(c) Compounds 3 and 3′ torsion angle




144.6(1)/-142.05 56.7(1)/-59.77 74.0(1)/-83.40 107.9(1)/-109.82 -66.5(1)/+68.21 -2.1(2)/+179.97

142.0(3)/-109.63 -57.5(4)/+61.07 -75.2(4)/-24.39 -108.0(4)/-135.43 66.5(4)/-69.22 2.2(5)/-179.88

Results and Discussion The data on all the three compounds (1-3) have been collected at 100.0(2) K to ensure accuracy in the estimate of intermolecular interactions and also to determine the hydrogen positions accurately from the difference Fourier map rather than fix the positions and use the riding hydrogen option. The details of the data collection and refinement are shown in Table 1. Results based on our earlier study20 on compounds 1′-3′ are

Interactions Involving Organic Fluorine

Crystal Growth & Design, Vol. 4, No. 1, 2004 49

Table 3. (a) Distances of C1, C2, and C3 from Least Square Plane (P1) Passing through C8, C9, and N1 and (b) Angular Disposition of the Least-Squares Planes Passing 1-Phenyl (P2) 2-Phenyl (P3) Rings in Compounds 1, 1′; 2, 2′; and 3, 3 1

1′

2

2′

3

3′

0.510(2) -0.118(2) 0.510(2)

-0.202(1) -0.720(1) -0.116(1)

0.221(4) 0.727(4) 0.145(4)

79.91(7)

44.90(4)

46.21(13)

dC1‚‚‚P1/Å dC2‚‚‚P1/Å dC3‚‚‚P1/Å

0.292(1) 0.712(1) 0.210(1)

0.266(2) -0.363(3) 0.264(3)

(a) -0.144(1) -0.728(1) -0.098(1)

∠P2‚‚‚P3

54.34(3)

82.6(8)

(b) 48.88(4)

Table 4. (a) F‚‚‚F and C-H‚‚‚F Interactions and (b) Intramolecular C-F‚‚‚π Interactions (a) F‚‚‚F and C-H‚‚‚F Interactions D-B‚‚‚A compound 1

D‚‚‚A

C20-H20‚‚‚F1′ C1-H1‚‚‚F2 compound 1′ C13-F1‚‚‚F1′ compound 2 C2-H2B‚‚‚F2′ C18-H18‚‚‚F1′ C1-H1‚‚‚F2 compound 2′ C7-H7‚‚‚F1′ compound 3 C2-H2A‚‚‚F2′ C21-H21‚‚‚F1′ C19-H19‚‚‚F1′ C1-H1‚‚‚F2 compound 3′ C21-H21‚‚‚F1′ C19-H19‚‚‚F1′

B‚‚‚A

∠D-B‚‚‚A

3.273(2) 2.63(2) 2.983(2) 2.31(1) 2.777(2) 3.502(2) 2.59(1) 3.148(2) 2.52(2) 3.042(1) 2.43(1) 3.455(2) 2.55(2) 3.194(1) 2.36(2) 3.556(1) 2.59(1) 3.258(1) 2.58(1) 3.065(2) 2.46(2) 3.622(5) 2.67(4) 3.362(5) 2.71(3)

125(1) 125(1)a 171.0(1) 155(1) 123(1) 120(1)a 145(2) 144(1) 169(2) 127(1) 120(1)a 166(2) 124(2)

(b) Intramolecular C-F‚‚‚π Interactions D-F‚‚‚A compound 3 C11-F1‚‚‚C16 C11-F1‚‚‚C17 compound 3′ C11-F1‚‚‚C16 C11-F1‚‚‚C17 a

F‚‚‚A/ Å 3.141(2) 3.020(2) 3.200(4) 3.127(5)

F‚‚‚Cg/ ∠D-F‚‚‚ ∠D-F‚‚‚ Å A/° Cg/° 3.383(1) 3.383(1) 3.448(4) 3.448(4)

79.2 105.0 80.0 105.4

91.0 91.0 91.7 91.7

Intramolecular.

given whenever required to allow for comparisons. Table 2a-c contain relevant torsion angles in 1-3 and 1′-3′. The molecular conformation based on RHF theoretical calculations at STO-3G level using Gaussian9837 is also included in these tables. Table 3a-b contains information on the details of the analysis of least-squares planes and Table 4a-b lists all short interactions involving fluorine. Figure 2a-c contains the ORTEP diagrams for the compounds 1-3, while Figure 3a-c depicts the corresponding packing diagrams. Figure 4a-c show the interaction regions in compounds 1-3. Structure of 1. The compound 1 (Figure 2a) crystallizes in the space group Pbca with Z ) 8. The volume of the unit cell [3430.1(1) Å3] is close (data on 1 is at 100 K) to that of structure 1′ [3477.0(1) Å3] though the space group and the cell dimensions differ. However, the longest axis [c] is conserved.20 Theoretically calculated molecular conformations37 of 1 and 1′ are different from those in the crystal lattice (Table 2a) indicating that packing interactions influence the molecular conformation. However, it is of interest to note that for structure 1, the torsion angle values are fairly close to those suggested by theory (within tolerance of ( 10°). The most significant observation is the absence of F‚‚‚F short intermolecular interaction in the structure of 1 as compared to the structure of 1′ and the appearance of two short C-H‚‚‚F interactions (Table 4a), one intramolecular and the other intermolecular in nature. In structure 1, the angle between the least squares planes passing through 1-phenyl and 2-phenyl rings is 54.34(3)°, while in 1′ it is 82.60(8)° (Table 3b). It is

Figure 2. ORTEP diagrams of the compounds 1-3 drawn to a 50% probability level; hydrogen atoms are excluded for clarity.

noteworthy that these fluorine based interactions (CH‚‚‚F in 1 and C-F‚‚‚F in 1′) in the absence of any other significant intermolecular interactions such as hydrogen bonds or C-H‚‚‚π serve as crystal engineering tools in generating different molecular assemblies. Conse-

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Figure 3. (a) Packing diagram of 1 viewed down the b axis; hydrogen atoms are excluded for clarity. (b) Packing diagram of 2 viewed down the b axis; hydrogen atoms are excluded for clarity. (c) Packing diagram of 3 viewed down the b axis; hydrogen atoms are excluded for clarity.

Choudhury and Guru Row

Figure 4. (a) Region of weak interactions in compounds 1 and 1′; other hydrogen atoms are excluded for clarity. (b) Region of weak interactions in compounds 2 and 2′; hydrogen atoms are excluded for clarity. (c) Regions of weak interactions in compounds 3 and 3′; hydrogen atoms are excluded for clarity.

Interactions Involving Organic Fluorine

quently, this observation provides an indirect proof for the occurrence of short F‚‚‚F interaction in compound 1′. Structure of 2. Compound 2 (Figure 2b) crystallizes in the space group C2/c with Z ) 8. The volume of the unit cell differs (data on 2 is at 100 K) from that of structure 2′ as also the space group and the cell dimensions. However, here again the longest axis is conserved. The most significant observation is the occurrence of new, additional C-H‚‚‚F short intermolecular interactions (one intramolecular and two intermolecular) in 2 in lieu of the short C-H‚‚‚F interaction observed in 2′ (Table 4a) resulting in an entirely different packing arrangement in the unit cell. Theoretically calculated molecular conformations37 of 2 and 2′ are different from that in the crystal lattice (Table 2b) indicating that packing interactions influence the molecular conformation. However, it is of interest to note that for structure 2, the torsion angle values are fairly close to those suggested by theory (within tolerance of ( 10°). In structure 2, the angle between the least squares planes passing through 1-phenyl and 2-phenyl rings is 48.88(4)°, while in 2′ it is 79.91(7)° (Table 3b). It is significant to note that the C-H‚‚‚F interactions in compound 2 involve the carbon atoms C1 and C2 which are a part of the flexible saturated ring along with C18 which is a part of 2-phenyl ring, whereas, in compound 2′, the C-H‚‚‚F interaction involved C7 which is a part of aromatic moiety of the isoquinoline motif (Table 4a). These results reinforce the view that C-H‚‚‚F interactions have a significant influence on the supramolecular structure of organic solids. Structure of 3. Compound 3 (Figure 2c) crystallizes in the space group P21/a with Z ) 4. It is remarkable to note that the crystal structure of 3 is isomorphous with 3′. The most significant observation is the retention of intramolecular C-F‚‚‚π interaction in 3 (Table 4b). It is interesting to note that the packing in the crystal lattice is conserved. The molecular conformation also does not show significant deviations (Tables 2c and 3a) with the introduction of fluorine in the ortho position of the 2-phenyl ring. Theoretically calculated molecular conformations37 of 3 and 3′ are different from those found in the crystal lattice (Table 2c) indicating that packing interactions influence the molecular conformation. However, it is of interest to note that for structure 3, the torsion angle values are fairly close to that suggested by theory (within tolerance of ( 10°). It is noteworthy that, although the crystal structures of 3 and 3′ are isostructural, the deviations in the torsion angles from theoretical values for 3′ are significantly different. In structure 3, the angle between the least squares planes passing through 1-phenyl and 2-phenyl rings is 44.90(4)°, while in 3′ it is 46.21(13)° (Table 3b). The vicinity of the two fluorine atoms along with minor alterations in the conformations introduces additional C-H‚‚‚F interactions in 3 (Table 4a). It is noteworthy that the C-F‚‚‚π interaction in compounds 3 and 3′ provide the stability in the packing motif conserving the conformational and crystallographic symmetry, characteristic of a crystal engineering tool (Table 4b). Conclusion In this work, we have shown that with the addition of one fluorine atom in the ortho position on the

Crystal Growth & Design, Vol. 4, No. 1, 2004 51

2-phenyl ring generates altered packing modes depending on the nature of interactions involving “organic fluorine”. It is obvious from these structural studies that interactions such as F‚‚‚F, C-H‚‚‚F, and C-F‚‚‚π provide stability to form molecular assemblies, especially in absence of any other strong intermolecular forces as hydrogen bonding, C-H‚‚‚π or π‚‚‚π interactions. Theoretical calculations using atom-atom potential and/or accurate charge density analysis using high-resolution X-ray diffraction data would lead to the understanding of the nature of these interactions. Indeed, charge density analysis of 1 and 1′ are currently under progress. Our current results suggest that while interactions involving “organic fluorine” have a significant influence in generating supramolecular assemblies in organic solids, their general use to a priori predict packing motifs is yet to be harnessed. Acknowledgment. We thank Dr. K. Nagarajan for useful discussions, Mr. Kabirul Islam for assistance during the synthesis, and Prof. G. Mehta for kindly allowing use of laboratory facilities. A.R.C. thanks IISc for providing senior research fellowship and we acknowledge financial support from the Department of Science and Technology and the Council of Scientific and Industrial Research, India. We also thank IRHPA-DST for providing the CCD facility at IISc, Bangalore. References (1) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University Press, Inc: New York, 1997. (2) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and Biology; Oxford University Press: Oxford, 1999. (3) Guru Row, T. N. Coord. Chem. Rev. 1999, 183, 81. (4) Desiraju, G. R. Curr. Opin. Solid State Mater. Sci. 1997, 2, 451. (5) Aakeroy, C. B. Acta Crystallogr., Sect B 1997, 53, 569. (6) Subramanian, S.; Zaworotko, M. J. Coord. Chem. Rev. 1994, 137, 357. (7) Umezawa, Y.; Tsuboyama, S.; Honda, K.; Uzawa, J.; Nishio, M. Bull. Chem. Soc. Jpn. 1998, 71, 207. (8) Nishio, M.; Umezawa, Y.; Hirota, M.; Takeuchi, Y. Tetrahedron 1995, 51, 8665. (9) Desiraju, G. R.; Gavezzotti, A. J. Chem. Soc. Chem. Commun. 1989, 621. (10) Ramasubbu, N.; Parthasarathy, R.; Murray-Rust, P. J. Am. Chem. Soc. 1986, 108, 4308. (11) Sakurai, T.; Sundaralingam, M.; Jeffrey, G. A. Acta Crystallogr. 1963, 16, 354. (12) Taylor, R.; Kennard, O. J. Am. Chem. Soc. 1982, 104, 5063. (13) Dunitz, J. D.; Taylor, R. Chem. Eur. J. 1997, 3, 89. (14) Desiraju, G. R.; Partasarathy, R. J. Am. Chem. Soc. 1989, 111, 8725. (15) Howard, J. A. K.; Hoy, V. J.; O’Hagan, D.; Smith, G. T. Tetrahedron 1996, 52, 12613. (16) Shimoni, L.; Glusker, J. P. Struct. Chem. 1994, 5, 383. (17) Prasanna, M. D.; Guru Row, T. N. CrystEngComm 2000, 25. (18) Prasanna, M. D.; Guru Row, T. N. Cryst. Eng. 2000, 3, 135. (19) Prasanna, M. D.; Guru Row, T. N. J. Mol. Struct. 2001, 55, 562. (20) Choudhury, A. R.; Urs, U. K.; Guru Row: T. N.; Nagarajan, K. J. Mol. Struct. 2002, 605, 71. (21) Choudhury, A. R.; Urs, U. K.; Smith, P. S.; Goddard, R.; Howard, J. A. K.; Guru Row, T. N. J. Mol. Struct. 2002, 641, 225. (22) Thalladi, V. R.; Weise, H.-C.; Boese, R.; Nangia, A.; Desiraju, G. R. Acta Crystallogr., Sect. B 1999, 55, 1005. (23) Choudhury, A. R.; Guru Row, T. N. Cryst. Eng. 2003, 6, 43. (24) Nyburg, S. C.; Faerman, C. H. Acta Crystallogr., Sect B 1985, 41, 274. (25) Cso¨regh, I.; Brehmer, T.; Bomicz, P.; Weber, E. Cryst. Eng. 2001, 4, 343.

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CG034137N

How Realistic Are Interactions Involving Organic Fluorine in Crystal

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