Competitive Interactions in the Crystal Structures of Benzils Effected by

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Competitive Interactions in the Crystal Structures of Benzils Effected by Different Halogen Substitution Marika Felsmann, Frank Eissmann, Anke Schwarzer, and Edwin Weber* Institut f€ur Organische Chemie, Technische Universit€at Bergakademie Freiberg, Leipziger Strasse 29, D-09596 Freiberg/Sachsen, Germany

bS Supporting Information ABSTRACT: To understand the consequences of halogen substitutions on the crystalline packing behavior of benzils, benzil itself and its derivatives with fluorine, chlorine, bromine, and iodine substituents in the p-position of the phenyl rings were studied and compared with respect to their crystal structures, which are new for the chloro, bromo, and iodo derivatives. While the molecular structures in the crystal are relatively unaffected by the substitution, this is not the case for their packing. In particular, in the chloro, and seemingly in some weaker tendency also in the bromo and iodo derivatives, a leading influence of the halogen atoms to cause specific halogen 3 3 3 halogen contact modes is shown, whereas the influence of the fluorine atom is minor.

’ INTRODUCTION Crystal engineering, as a rapidly expanding discipline of supramolecular chemistry,1-4 is defined as the design and synthesis of solid state structures with desired properties based on understanding and exploitation of intermolecular interactions.5 Much of the previous work on purely organic systems that has been done in this respect focused on the use of strong hydrogen bonds as a powerful tool.6-8 However, recently, those studies involving the interplay of weaker supramolecular synthons9 such as aryl 3 3 3 aryl,10 C-H 3 3 3 X,11 and halogen 3 3 3 halogen interactions12,13 are becoming increasingly important. Improvement of our knowledge on the principles underlying this kind of interactions is thus a vital point with reference to crystal engineering. In particular, model compounds that show a clear control of weak interactions on the crystalline packing mode are expected to make a helpful contribution to the understanding of the problem.14,15 It should be appreciated that compounds of this type should have not only an uncomplicated constitutional structure but also a rather invariable conformation.16,17 Here, we report such a promising system of model compounds 1-5 (Scheme 1) being derived from benzil (1) as the parent molecule and including their p-substituted halogen derivatives (2-5) with fluorine, chlorine, bromine, and iodine atoms as the varying substituents. Therefore, the crystal structures of this particular series of compounds will give information about the influencing control on the crystal packing being due to the r 2011 American Chemical Society

respective halogen substituent. Owing to the overall constitutions of the molecules, it will also be possible to study a potential competition between oxygen and halogen involved or aryl 3 3 3 aryl derived interactions concerning the supramolecular synthon formation. Along these lines, in the present paper the crystal structures of compounds 3-5 have been determined and are comparatively discussed, including the known polymorphic structures of 118-20 and that of 2,21 in order to gain some useful information contributing to the promising field of crystal engineering.

’ EXPERIMENTAL SECTION Materials. The benzils 322 and 523 were prepared by oxidation of the corresponding benzoins following described procedures. The benzil 4 was synthesized via a bromination-hydrolysis sequence from 4,5diphenylimidazolin-2-one.24 The starting benzoins were prepared from the corresponding benzaldehydes via cyanide catalyzed benzoin condensations.23,25,26 Crystals suitable for X-ray investigations were obtained by slow evaporation of solutions of the compounds in chloroform (3), ethyl acetate-DMSO-DMF (1:1:1, v/v/v) (4), and p-xylene (5). Received: March 31, 2010 Revised: January 27, 2011 Published: February 25, 2011 982

dx.doi.org/10.1021/cg101495f | Cryst. Growth Des. 2011, 11, 982–989

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were subjected to a DSC analysis in order to examine the existence of an analogous polymorphic behavior. However, no corresponding property was found for the halogen substituted benzils 2-5 in the temperature range (173-373 K) accessible to our study. Also, measurement of the cell parameters at different temperatures (between 153 and 295 K) gave no indication of a phase transition. Molecular illustrations of 1-5 including atom numbering are presented in Figure 1, while the packing diagrams of 1-5 are shown in Figures 2-5, respectively. Relevant crystallographic data are summarized in Table 1. A selection of bond distances and angles is presented in Table 2, while the parameters for noncovalent contacts of compounds 3-5, including also the data for the low-temperature (LT) and high-temperature (HT) phases of 118,20 and for 221 from literature, are given in Table 3. As already mentioned at the beginning, in order to answer the raised question, the model compound should have an uncomplicated constitutional structure and whenever possible also a rather invariable conformation, regardless of an added substituent such as a halogen atom.15-17 This is largely met with the series of benzils 1-5, where 1 is the parent and 2-5 (Figure 1) are the derivative molecules. Apart from the halogen substituents, the compounds show almost coinciding molecular structures in the crystalline state (Figure ESI-1 of the Supporting Information), including the polymorphs of 1 of which the LTphase contains three crystallographically independent molecules.20 In a more detailed inspection, the lengths of the C(CdO)C(aryl) bonds in the molecules of 1-5 range between 1.467(6) for HT-1 and 1.4816(19) Å for 3, i.e. between a single and double bond. The CdO bond lengths range between 1.205(12) and

X-ray Crystallography. The intensity data were collected on a Bruker APEX II diffractometer with Mo KR radiation (λ = 0.71073 Å) using ω- and j-scans. Reflections were corrected for background, Lorentz, and polarization effects. Preliminary structure models were derived by application of direct methods27 and were refined by fullmatrix least-squares calculation based on F2 for all reflections.27 All hydrogen atoms were included in the models in calculated positions and were refined as constrained to bonding atoms. The crystal data and experimental parameters are summarized in Table 1.

’ RESULTS AND DISCUSSION The crystal structures of compounds 3-5 were studied using an X-ray diffraction technique. Measurements were undertaken at temperatures of 153, 93, and 153 K for 3, 4, and 5, respectively. Since for the parent benzil 1 a rhombohedral high-temperature phase (T = 100 K or room temperature) and a hexagonal lowtemperature phase (T = 70 K) with a crystalline phase transition at 83.5 K have been found18-20 that were thoroughly studied during a long space of time,28-30 the crystals of compounds 2-5 Scheme 1. Chemical Structures of Compounds Involved in This Study

Table 1. Crystallographic and Structure Refinement Data of Compounds 3-5 compd

3

4

5

chemical formula

C14H8Cl2O2

C14H8Br2O2

M(g mol-1)

279.10

368.02

462.00

crystal system a (Å)

monoclinic 6.0292(2)

orthorhombic 6.0063(12)

orthorhombic 5.8782(8)

b (Å)

3.86880(10)

26.006(5)

27.120(4)

c (Å)

25.3201(8)

4.0378(8)

4.1474(4)

a (deg)

90

90

90

β (deg)

92.004(2)

90

90

C14H8I2O2

γ (deg)

90

90

90

V (Å3)

590.25(3)

630.7(2)

661.17(14)

temperature (K) space group

153(2) P2/n

93(2) P21212

153(2) P21212

Z

2

2

2

Dcalc (g cm-3)

1.570

1.938

2.321

crystal size (mm3)

0.50 0.38 0.11

0.25 0.20 0.09

0.55 0.39 0.10

radiation type

Mo KR

Mo KR

Mo KR

μ (mm-1)

0.538

6.415

4.746

θ (deg)

3.22-28.50

3.13-27.49

3.55-28.98

no. of reflections measured no. of independent reflections

11092 1492

12690 1443

15687 1742

data/restraints/parameters

1492/0/82

1443/0/82

1742/0/82

R values [I > 2σ(I)]

R1 = 0.0339, wR2 = 0.0799

R1 = 0.0243, wR2 = 0.0485

R1 = 0.0230, wR2 = 0.0576

R values (all data)

R1 = 0.0389, wR2 = 0.0820

R1 = 0.0297, wR2 = 0.0496

R1 = 0.0232, wR2 = 0.0577

goodness of fit on F2

1.163

1.105

1.368

983

dx.doi.org/10.1021/cg101495f |Cryst. Growth Des. 2011, 11, 982–989


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Figure 1. Perspective views of compounds 1 (a), 2 (b), 3 (c), 4 (d), and 5 (e) including atom numbering scheme. Thermal ellipsoids are at the 50% probability level.

1.239(12) Å, involving two different molecules 1 of the LTphase. The benzoyl fragments of the molecules deviate only little from planarity, with a maximum deviation from the mean plane of this molecular segment of 0.060(7) Å for one of the carbonyl oxygens of LT-1 and a minimum deviation of 0.023(31) Å for C(5) of the aryl ring in compound 5. A more detailed inspection in this respect, according to tendency, shows a decreasing deviation from planarity for the carbonyl oxygen in the range from 1 to 5. Regardless of this variation, conjugation of the πelectron system is suggested in the benzoyl section of the molecules. However, the conjugation does not cover the whole molecule, as indicated by the bond distances between the carbonyl groups [1.526(13) to 1.551(8) Å] and the twisted conformation around the central diketo unit (torsion angles range between 103.2(10) and 118.5(2)°; Table 2), giving rise to an overall helical structure of the molecules. Moreover, the structural parameters of 1-5 point to intramolecular hydrogen bond contacts involving each of the carbonyl oxygens and an ortho hydrogen of the neighboring aryl ring (Table 3). While the basic molecular conformations of compounds 1-5 are not very different, which has been an essential prerequisite for the intended comparative study, the packing structures are showing the specific influence exerted by the particular substitution. Making a comparison between 1 and 2, it is shown that the intermolecular contact modes in both the low- and high-temperature phases of 118,20 are in essential agreement and basically similar to those found in the crystal of 2, i.e. dominated by faceto-face π-stacking31,32 and C-H 3 3 3 O type11 interactions, leading to the formation of intermolecular chains (Figures 2a and 3a). In 1, these chains are linked to each other by weak C-H 3 3 3 O contacts (Figure 2b) while 2, aside from C-H 3 3 3 O interaction, also makes use of weak C-H 3 3 3 F33 contacts (Figure 3b). It is worth mentioning at this point that organic fluorine involved interactions,34 including C-H 3 3 3 F contacts, have

been discussed rather controversially during the last few years.35,36 However, a number of more recent studies, which have been carried out, show that organic fluorine may generate different types of packing motifs via C-H 3 3 3 F, C-F 3 3 3 F, and C-F 3 3 3 π contacts, especially in the absence of strong hydrogen bond donors and/or acceptors, such as N-H, O-H, or CdO groups.37-42 It has also been demonstrated that C-F 3 3 3 F contacts increase with increasing number of fluorine atoms in the molecule while, as an obvious consequence, the C-H 3 3 3 F contacts decrease.17 However, being below a bottom limit of fluorine atoms, as in the case of compound 2, it seems that fluorine would rather form C-H 3 3 3 F interactions than CF 3 3 3 F contacts.42 With reference to the four possible patterns of C-H 3 3 3 F synthons of crystalline fluoro aromatic compounds, defined by Boese et al.,43 the present mode of C-H 3 3 3 F interaction corresponds to the catemeric chain type. By way of contrast, the crystal structure of the 4,40 -dichlorobenzil (3) contains layer-like domains of CdO 3 3 3 H connected molecules running parallel to the crystallographic ab-plane (Figure 4a). Moreover, π-stacking interactions31,32 contribute to stabilize the crystal in the b-direction. However, the special feature of the crystal structure refers to the presence of Cl 3 3 3 Cl contacts connecting the layers. Similar to the above C-H 3 3 3 F contacts, interactions between organic chlorine atoms in crystals have also been a subject of debate for many decades12,44,45 and continue to be of topical interest due to the potential use as design elements in crystal engineering.46 Interactions of this type are usually taken for granted if the interhalogen distance is significantly less than the sum of the accepted van der Waals radii of contacting halogen atoms.47 In the crystal of 3, this shortest contact criteria is represented with a distance of 3.3657(8) Å, falling 0.13 Å below the sum of the van der Waals radii of two chlorine atoms (3.50 Å),48 thus giving evidence of a Cl 3 3 3 Cl interaction.49 984



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Figure 3. Crystal packing of 2 showing the face-to-face π-stacking contacts in the supramolecular chain motif (a) as well as an illustration of the aggregated chains (b). Noncovalent interactions are represented as broken lines.

Figure 2. Crystal packing of 1 showing the supramolecular chain formation (a) as well as a view down the crystallographic c-axis (b). Noncovalent interactions are represented as broken lines.

Previous studies have also shown that there are two preferred geometries for halogen 3 3 3 halogen contacts, based on the values of the two C-Hal 3 3 3 Hal angles, θ1 and θ2.45,47 One is termed a type I or “head-on” interaction with θ1 = θ2 and the other a type II or “side-on” interaction with θ1 ∼ 180 and θ2 ∼ 90°. According to this classification, the Cl 3 3 3 Cl contact in 3 is of the “head-on” synthon mode [θ = 163.83(2)°], giving rise to supramolecular chain formation, as depicted in Figure 4b. Compared with the data discussed in a recent very detailed combined crystallographic and theoretical study taking into consideration hybridization of the ipso carbon atom, the Cl 3 3 3 Cl contact in 3 ranges on the one hand at the short interaction distance side and on the other hand at the large interaction angle side of the respective histograms.12 This behavior can be attributed to the additional electron withdrawing effect coming from the carbonyl groups of the benzil. Also the structure of 4,40 -dibromobenzil (4) is layer-like, with the layers held together by C-H 3 3 3 O interactions11 (Figure 5a). The layers come into contact via the bromine atoms, pointing to the presence of a particular Br 3 3 3 Br interaction. Although the interaction strength of Br 3 3 3 Br is usually considered to be superior to that of Cl 3 3 3 Cl,45 the Br 3 3 3 Br contact distance in 4 is larger (0.145 Å) than the sum of the van der Waals radii (3.70 Å)48 Nevertheless, it seems that Br 3 3 3 Br contacts are relevant for stabilization of the crystal structure of 4. This follows

Figure 4. (a) Crystal packing of 3 viewed down the crystallographic baxis. Noncovalent bonds are represented as broken lines. (b) Synthon mode of Cl 3 3 3 Cl interaction (“head-on” contact) found in the crystal structure of 3, giving rise to supramolecular chain formation (θ1 and θ2 represent interaction angles). 985



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Figure 5. Crystal packings of 4 (a) and 5 (b) viewed down the crystallographic c-axis, respectively. Noncovalent interactions are represented as broken lines.

Table 2. Selected Geometric Parameters of Compounds 1-5 1 (T = 70 K)20 compd

10 a

100 a

1000 a

1 (T = 100 K)20

221

3

4

5

Bond Lengths/Å C(1)-C(1A)

1.549(16)b 1.526(13)b 1.532(14)b

1.529(6)

1.5358(15)b

1.543(3)

1.541(5)

1.551(8)

C(1)-C(2)

1.478(13) 1.479(13) 1.474(13)

1.467(6)

1.4764(15)

1.4816(19)

1.476(4)

1.475(5)

C(8)-C(9)

1.475(14) 1.469(14) 1.484(13)

1.2194(18)

1.213(3)

1.210(5)

C(1)-O(1)

1.227(12) 1.222(12) 1.209(11)

C(8)-O(2)

1.205(12) 1.224(12) 1.239(12)

1.4751(15) 1.217(5)

1.2193(13) 1.2209(14)

C(5)-X(1) C(12)-X(2)

1.3536(14) (X = F) 1.7385(15) (X = Cl) 1.903(3) (X = Br) 2.098(4) (X = I) 1.3551(13) (X = F)

Torsion Angles/deg C(1A)-C(1)-C(2)-C(7)

-6.5(11)c -10.5(13) -9.7(13)

C(1)-C(8)-C(9)-C(14)

-13.1(13) -9.5(13) -7.2(13)

O(1)-C(1)-C(1A)-O(1A) 107.8(10)d 113.8(10)d 103.2(10)d a 0

-9.7(7)

1.26(15)c

-6.52(18)

-6.1(3)

-7.8(5)

118.5(2)

116.1(4)

114.5(6)

-11.03(15) 110.65(12)d

107.3(6)

, 100 , and 1000 c

1 refer to the three independent molecules in the asymmetric unit of the crystal structure of 1 in its low temperature (LT) phase. b C(1)C(8). C(8)-C(1)-C(2)-C(7). d O(1)-C(1)-C(8)-O(2).

from the finding that each of the bromine atoms shows an orientation with reference to bromine atoms of two neighboring molecules, giving rise to contact angles of 161.71(2) and 95.20(3)°, typical of a “side-on” contact for organic bound bromine atoms.45 The change of the contact mode of the halogen atoms from “head-on” in 3 to “side-on” in 4 leads to a different orientation of the molecules with reference to neighboring layers, being almost colinear in 3 and herringbone type in 4. A packing mode of the molecules corresponding with 4 is shown for the crystal structure of 4,40 -diiodobenzil (5) (Figure 5b). Hence, the crystal structures of the dibromo and diiodobenzils 4 and 5, respectively, can be described as

isostructural. Remarkably, in 5 the contact distance of the “side-on” I 3 3 3 I interaction [3.9602(5) Å] is exactly identical with the sum of the van der Waals radii for two iodine atoms. Finally, it seemed to us that the crystal packings, aside from 4 and 5 involving also the dichlorobenzil 3, will make an interesting point of comparison. Under the circumstance that for compound 3 the cell axes b and c are interchanged, a comparison of the axes a, b, and c of compounds 3, 4, and 5 shows that they do not differ significantly and thus are expected to behave isostructurally all among each other. A closer examination of the packing arrangements viewed along the a axis (Figure ESI-2 of the Supporting Information) reveals an identical molecule alignment for 4 and 5 986



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Table 3. Geometric Parameters for Noncovalent Interactions within the Crystal Structures of Compounds 1-5 distance/Å interaction

symmetry

H3 3 3A

angle/deg

D3 3 3A

D-H 3 3 3 A

C-X 3 3 3 Y

20

1 (T = 100 K) C(3)-H(3) 3 3 3 O(1) C(5)-H(5) 3 3 3 O(1) C(7)-H(7) 3 3 3 O(1) Cg(1) 3 3 3 Cg(1) 221

a

C(3)-H(3) 3 3 3 O(1) C(6)-H(6) 3 3 3 O(1) C(7)-H(7) 3 3 3 F(2) C(10)-H(10) 3 3 3 O(2) C(11)-H(11) 3 3 3 F(1) C(13)-H(13) 3 3 3 O(2) Cg(1) 3 3 3 Cg(1)a

x, y, z

2.47(4)

2.852(6)

105(3)

x, y - 1, z

2.48(4)

3.365(7)

155(3)

-x þ y, -x, z - 1/3

2.41(4)

3.253(5)

142(3)

-y, x - y, z þ 1/3

3.805(4)

x, y, z

2.53

2.8240(14)

98

x, -y þ 5/2, z þ 1/2 -x þ 1, y þ 1/2, -z þ 1/2

2.51 2.62

3.3098(16) 3.4101(15)

145 143

x, y, z

2.57

2.8510(15)

98

x - 1, -y þ 5/2, z - 1/2

2.60

3.3653(15)

139

x, y - 1, z

2.40

3.2648(15)

155

-x þ 2, -y þ 2, -z þ 1

3.7150(7)

Cg(2) 3 3 3 Cg(2)a 3

-x þ 1, -y þ 2, -z

3.6416(6)

C(1)-Cl(1) 3 3 3 Cl(1) C(3)-H(3) 3 3 3 O(1)

-x þ 2, -y þ 1, -z þ 1 x, y, z

2.53

3.3657(8) 2.8208(18)

98.0

C(6)-H(6) 3 3 3 O(1) C(7)-H(7) 3 3 3 O(1) C(7)-H(7) 3 3 3 O(1)

x þ 1, y - 1, z

2.47

3.2819(19)

143.3

-x þ 1/2, y, -z þ 1/2

2.55

3.0581(18)

113.8

-x þ 1/2, y - 1, -z þ 1/2

2.70

3.3320(18)

124.6

Cg(1) 3 3 3 Cg(1)a 4

x, y - 1, z

C(1)-Br(1) 3 3 3 Br(1) C(1)-Br(1) 3 3 3 Br(1) C(3)-H(3) 3 3 3 O(1)

x - 1/2, -y þ 1/2, -z

3.8445(6)

x þ 1/2, -y þ 1/2, -z x, y, z

3.8445(6) 2.819(3)

C(6)-H(6) 3 3 3 O(1) C(7)-H(7) 3 3 3 O(1) Cg(1) 3 3 3 Cg(1)a

163.83(2) (X, Y = Cl)

3.8688

2.53

161.71(2) (X, Y = Br) 95.20(3) (X, Y = Br) 97.8

x - 1, y, z - 1

2.49

3.319(3)

146.5

-x þ 1, -y, z

2.59

3.092(3)

113.7

x, y, z - 1

4.0378(8)

x þ 1/2, -y - 1/2, -z

3.9602(5)

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

3.9602(5)

5 C(1)-I(1) 3 3 3 I(1) C(1)-I(1) 3 3 3 I(1) C(3)-H(3) 3 3 3 O(1) C(6)-H(6) 3 3 3 O(1)

a

C(7)-H(7) 3 3 3 O(1) Cg(1) 3 3 3 Cg(1)a

163.86(4) (X, Y = I) 100.10(4) (X, Y = I)

x, y, z x þ 1, y, z - 1

2.54 2.47

2.833(5) 3.298(5)

97.7 145.2

-x þ 1, -y, z

2.53

3.119(5)

112.3

x, y, z þ 1

4.1474(4)

Cg(1) and Cg(2) are the centroids of the C(2)-C(7) and C(9)-C(14) benzene rings, respectively.

with an ABAB layer structure parallel to the ac plane. At first glance, an ABAB layer structure similar to that of 4 and 5 is also found for 3, but a detailed view shows that the molecular arrangement within the B layers is different from that of 4 and 5 in the orientation of the OdC—CdO moiety. An even better impression of the structural relationship between compounds 3, 4, and 5 can be obtained from the packing motifs viewed along the b axis for 3 and accordingly the c axis for 4 and 5 (Figure ESI-3 of the Supporting Information). Again, an identical packing arrangement is observed for compounds 4 and 5 (ABAB layer structure parallel to the ac plane). However, regarding 3, an obviously different ABAB alignment (layers parallel to the ab plane) with a different orientation of the molecules in the B layers compared to the case of 4 and 5 is found. In summary, the examination of the three crystal structures shows that the bromo and iodo substituted benzils 4 and 5, respectively, are totally

isostructural, whereas the same does not apply to the chloro derivative 3, which is isostructural to neither 4 nor 5.

’ CONCLUSIONS In order to define the consequences of halogen substitutions, involving fluorine, chlorine, bromine, and iodine atoms, on the crystalline packing mode of benzils, the crystal structures of 1 as the basic compound and 2-5 as the testing substances have been studied and comparatively discussed, presenting the following conclusions. Being compatible with the desired condition for soundness of this study, the molecular structures of 1-5, including polymorphs of 1, were found rather unaffected both by the halogen substitution and the effects of packing, showing nearly planar benzoyl fragments and a twisted conformation around the central 987



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diketo unit. This conformational correspondence is attributable to a strongly developed balance between π-conjugation, dipoledipole interaction, and intramolecular hydrogen bonding, being a common feature of the molecules and similarly reflected in the crystal structures of other p-substituted derivatives of benzils.50 By way of contrast, substitution of the p-position of the parent molecule 1 by the halogen atoms changes the intermolecular contacts and crystalline packing modes to a different degree, dependent on the kind of the halogen substituent. Actually, we see only a moderate change for the transformation of the unsubstituted parent compound 1, in both phases, to the fluorine substituted derivative 2, which is in agreement with the weak property of interaction known for organic fluorine substituents.34 In the case of these two compounds, π-stacking and C-H 3 3 3 O interactions, forming molecular chains, determine the structure while C-H 3 3 3 F contacts, although present in 2, are secondary and F 3 3 3 F contacts are not observed. There is a marked alteration when changing from 1 to the chlorine derivative 3. Now the chlorine involved contacts show distinct influence on the packing structure, being expressed by the directive “head-on” Cl 3 3 3 Cl interactions in the crystal lattice. Owing to this change, a layer mode of packing is formed, while retaining C-H 3 3 3 O and π-stacking contacts. Similarly, the bromo and iodo substituents of 4 and 5 considerably contribute to the packing structure, however, using the “side-on” mode of interactions, which is preferred of the heavier halogens.12,45 Hence, the results of this study fit in well with and thus corroborate previous work involving investigation of halogen interactions based on other isostructural molecular motifs13-18,40,42,51 regarding directionality of contacts and competitive behavior with other weakly interacting groups, being carbonyl functions and aromatic units in the present case. It is to be supposed that these findings should not only be of use for benzils, which are known for various practical applications, such as piezoelectricity52 and other materials properties,53,54 including packing dependent solid-state color50b and pharmacological aspects,55 but also for the crystal engineering1-4 of structurally related compounds.

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’ ASSOCIATED CONTENT

bS

Supporting Information. Molecular overlay plot of HT1 and 2-5 and packing diagrams for compounds 3-5 viewed from different lines of sight; and cif data. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: þ49 373139-3170.

’ REFERENCES (1) Tiekink, E. R. T., Vittal, K., Eds. Organic Crystal Engineering; Wiley: Chichester, 2010. (2) Braga, D., Greponi, F., Eds. Making Crystals by Design: Methods, Techniques and Applications; Wiley-VCH: Weinheim, 2007. (3) Desiraju, G. R., Ed. Crystal Design—Structure and Function, Perspectives in Supramolecular Chemistry; Wiley: Chichester, 2003. (4) Weber, E., Ed. Design of Organic Solids, Topics in Current Chemistry; Springer: Berlin-Heidelberg, 1998; Vol. 198. 988



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Competitive Interactions in the Crystal Structures of Benzils Effected by

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