Vanishing Polymorphism of (2E)-2-Cyano-3-[4 ... - ACS Publications

Vanishing Polymorphism of (2E)-2-Cyano-3-[4-(Diethylamino)phenyl]prop-2-enethioamide: X-ray Structural Study and Polymorph Prediction Tatiana V. Timofeeva,*,† Tiffany Kinnibrugh,† Oleg Ya. Borbulevych,‡ Boris B. Averkiev,† Vladimir N. Nesterov,† Andreanne Sloan,† and Mikhail Yu. Antipin†,#

CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 6 1265-1276

Department of Natural Sciences, New Mexico Highlands University, Las Vegas, New Mexico 87701, Department of Chemistry and Biochemistry, University of Notre Dame, Indiana 46556, and Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, 117813, Russia Received July 10, 2004;

Revised Manuscript Received September 20, 2004

ABSTRACT: Synthesis and crystallization of a polar organic compound (2E)-2-cyano-3-[4-(diethylamino)phenyl]prop-2-enethioamide (CDPE) gave two new crystalline polymorphs (1 and 2) and an acetonitrile solvate (pseudopolymorph, 3) of this compound. The third crystalline polymorph of CDPE (4) was described in the literature earlier. It was found that in crystalline polymorphs 1, 2, and 4 molecules adopt three different conformations. Experimental observations show that polymorph 1 is a predominant form of the CDPE compound, while all other crystalline forms we were unable to reproduce under different conditions. Quantum ab initio calculations of relative conformational energies of molecules found in these polymorphs revealed that the conformer in polymorph 1 has significantly lower energy than conformers in polymorphs 2 and 4. This fact explains the predominant formation of polymorph 1 under different experimental conditions. The polarity of CDPE molecules and distinctions in their molecular and crystal structures make CDPE polymorphs 1, 2, and 4 a perfect model for testing of the methodology of crystal structure prediction with the Polymorph Predictor module from the Cerius2 program package. It was shown that if the starting molecular model corresponds to X-ray data and considered to be rigid it is possible to predict all three polymorphs. In contrast, usage of a flexible molecular model does not give positive results. Reasons for such differences are discussed. Introduction Organic polymorphs are solid crystalline phases in which chemically identical molecules are packed in a different manner. In many cases, molecular packing in crystals defines such crystalline properties as density, melting point, solubility, conductivity, optical and nonlinear optical (NLO) characteristics, and hence defines their applications.1 Organic compounds possessing NLO properties have been intensively studied during the past decades because of their potential use in various fields of technology.2,3 However, practical application of such compounds is still quite limited due to rigorous requirements to their structure. In particular, to possess NLO properties an organic molecule should be polar, i.e., contain a π-electron conjugated system terminated by donor and acceptor groups (D-π-A).4 More crucial is that bulk NLO materials must form acentric media to manifest second harmonic generation (SHG) in the solid state.5 Therefore, X-ray structural studies of single crystals are necessary and an important step in the investigation of NLO organic compounds, including NLO polymorphs. An alternative approach to crystal structure determination is theoretical structure prediction based on usage of atom-atom potentials,6,7 which might be even more important since one can evaluate crystal structure * To whom correspondence should be addressed. Fax: 505 454 3103; e-mail: [email protected]. † New Mexico Highlands University. ‡ University of Notre Dame. # Russian Academy of Sciences.

before synthesis and crystallization of a compound. This could save a lot of efforts on many complicated experimental procedures. Because of that, an adequate prediction of crystal structure of an NLO compound, starting from the molecular structure, would have an enormous impact on development of this entire field. However, in general, correct crystal structure prediction is still a very complicated problem due to conceptual difficulties outlined in refs 8-10. To come closer to a solution of such a problem, more experimental results should be compared with results of crystal structure predictions in different approximations, under different conditions, and using different methodology. A search for adequate methodology of crystal structure prediction of polar molecules is an important goal of this project. In the present paper, we outline results obtained in the course of our systematic X-ray diffraction structural studies of polar organic compounds that crystallize in several polymorph modifications,11-15 and discuss an applicability of an atom-atom potential method for crystal structure prediction of this group of compounds. Deep understanding of crystal structure formation for such compounds is important for crystal engineering and design, including design of acentric crystals that possess NLO properties. For our consideration, we chose (2E)-2-cyano-3-[4-(diethylamino)phenyl]prop-2-enethioamide (CDPE), a compound that forms three crystalline polymorphs and one so-called “pseudopolymorph” or solvate crystal. One of these polymorphs was found earlier,16,17 and all other forms were found by us and presented in this paper. The molecular structure of

10.1021/cg0497647 CCC: $27.50 © 2004 American Chemical Society Published on Web 10/13/2004

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Table 1. Crystallographic Data, Details of Data Collection and Refinement formula Mr crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z Dc (g cm-3) µ (mm-1) F(000) T (K) crystal size (mm) 2θ range (°) diffractometer total reflections unique reflections Rint used reflections observed reflections with F > 4σ(F) no. of parameters wR2 R1 [F > 4σ(F)] S a

1 C14H17N3S 259.37 triclinic P1 h 8.753(4) 8.890(4) 10.830(5) 85.44(4) 69.76(3) 63.65(3) 705.8(6) 2 1.220 0.216 276 298(2) 0.4 × 0.3 × 0.2 2 ÷ 50 Siemens P3 2650 2476 0.0158 2476 1821 165 0.1001 0.0367 1.019

2 C14H17N3S 259.37 monoclinic P21/n 9.167(2) 13.023(3) 12.172(2) 90 93.97(3) 90 1449.6(5) 4 1.188 0.210 552 295(2) 0.5 × 0.3 × 0.2 2 ÷ 54 CAD-4 3310 3117 0.0272 3117 2319 165 0.1196 0.0389 1.028

3a 2C14H17N3S • 1/2CH3CN 539.26 monoclinic C2/c 39.370(8) 8.880(2) 17.056(3) 90 101.19(3) 90 5850(2) 16 1.225 0.212 2296 298(2) 0.6 × 0.4 × 0.3 2 ÷ 51 CAD-4 5510 5427 0.0501 5427 2758 344 0.1495 0.0505 0.991

4 C14H17N3S 259.37 monoclinic P21/n 10.755(1) 12.365(1) 10.860(1) 90 104.25(1) 90 1400.8(2) 4 1.24 0.183 552 291(2) 0.4 × 0.3 × 0.2 2 ÷ 70 CAD-4 2651 0.0272 1866 1866 171 0.083

Solvent is located on axis 2.

Scheme 1

CDPE does not correspond exactly to a classical D-π-A (where D, donor; π, conjugated bridge; A, acceptor) formula, but can be presented as D-π-A(D′), where D′ is an additional donor group that is in general weaker than main D group. We found recently18,19 that in many cases the introduction of an additional donor group, capable of binding of hydrogen bonds with an acceptor moiety of a polar molecule, brings the formation of a hydrogen bond system in the crystal. In all cases we have studied, hydrogen bonding caused significant elevation of the melting points of such compounds, and in many cases caused formation of acentric crystals, which predetermines their potential applications. Apparently, simplicity of the molecule CDPE does not suggest its conformational variations. Nevertheless, at least four conformations of the CDPE molecule (Scheme 1) can be indicated: cissoid (a) and transoid (b) arrangements considering the relative positions of double CdC and CdS bonds in the acceptor part of the molecule, and the same arrangements in a combination with different conformations of diethylamino groups (c) and (d). It should be mentioned that idealized conformations a and c and b and d can considered to be mirror images. However, corresponding conformers found in crystals are different. Molecules with three of these possible conformations were found in crystals. A cissoid arrangement (a) has

been found in polymorph 1 and solvate 3, a transoid conformation (b) was found in polymorph 2, and a transoid conformation with a different conformation of diethylamino group (d) was found in polymorph 4. So, for this compound “conformational” polymorphism was found and it makes it, along with the polar nature of the CDPE molecule, a very attractive model for testing of the methodology of crystal structure prediction, since in this case for prediction of all forms one can operate in a framework of a distinct force field without facing a problem of transferability of force field parameters. It is also worth mentioning that statistical analysis of Cambridge Structural Database entries revealed that some organic compounds are able to form both centrosymmetric and acentric polymorphs.20-22 The number of such examples is not large, but it indicates that if at present only a centrosymmetric form of the compound of interest is found it does not exclude the existence of a corresponding acentric phase. A computational search for such phases may give a valuable indication of the high probability of the existence of acentric phases and promote crystallization of such compounds under different experimental conditions. Methods Synthesis, Crystallization, X-ray Analysis, and Differential Scanning Calorimetry. The CDPE was synthesized by the Knoevenagel reaction. Red transparent plates (polymorph 1) were obtained at room temperature by recrystallization from ethanol solution. When we synthesized a thiazole derivative of CDPE by reaction of CDPE with 2-bromo1-(4-nitrophenyl)-ethanole in DMF, we found in a reaction mixture two types of crystals with different shapes. X-ray analysis revealed that one of them was a reaction product ((2E)-3-[4-(diethylamino)phenyl]-2-(4-phenyl-1,3-thiazol-2-yl)acrylonitrile) and the other was a monoclinic form of starting material (CDPE polymorph 2). Crystals 3 were obtained after recrystallization of CDPE from acetonirile, and it was shown that they contain solvent in a ratio of 4:1. The crystal growth

Vanishing Polymorphism of CDPE

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Figure 1. Molecular structures of CDPE conformers found in crystals 1-4. In parentheses a notation of conformers presented in Scheme 1 is given. Displacement ellipsoids are given for 1-3 at the 50% probability level. procedure for the polymorph 4 was not presented in original publications,16,17 so we were unable to reproduce the crystallization conditions and the crystalline form 4 of CDPE. Several other attempts to reproduce crystallization of polymorphs 2 and solvate 3 from the above-mentioned and several other solvents (methanol, acetonirile/methanol and acetonirile/ethanol mixtures) gave us only polymorph 1, which can be considered a predominate crystalline form of CDPE. Summary of the crystal data for the structures studied as well as results of the refinement are presented in Table 1. For comparison the available crystal data on polymorph 4 are also presented in Table 1. All diffraction data were collected at room temperature with four-cycle Siemens P3/PC and Enraf-Nonius CAD-4 diffractometers using MoKR-radiation, graphite monochromator, and θ/2θ-scan technique. The structures were solved by direct methods and refined by full matrix least-squares on F2 in the anisotropic approximation for non-hydrogen atoms. Positions of hydrogen atoms were found from the difference Fourier synthesis and included in refinement using a “riding” model with Uiso ) nUeq for the carbon atom connected to the relevant H-atom where n ) 1.5 for methyl groups and n ) 1.2 for other hydrogen atoms. General views of the molecular structures studied and atomic numbering schemes for polymorphs 1 and 2, solvate 3 (in a latter crystal two symmetrically independent molecules A and B were found), and polymorph 416,17 are

presented in Figure 1. Selected geometry parameters of molecules in crystals 1-4 are presented in Table 2. Detailed data on the crystal structures studied (1, 2, and 3) are presented in the supplemental CIF files (Supporting Information). We evaluated thermal properties of CDPE using thermal microscopy (hot stage HS1 with temperature controller STC200 from INSTEC, USA) and differential scanning calorimetery (DSC) (microcalorimeter DSM-3, USSR) with heating rate 16° min-1. Calculation of Molecular Structures and Molecular Hyperpolarizabilities. We used molecular mechanics and quantum chemical approaches for computation of molecular geometry of isolated CDPE molecule in conformations a-d. Molecular mechanics (MM) calculations were carried out with the Cerius2 program package23 using Dreiding force field.24 The obtained molecular geometry was used as a starting approximation for quantum chemical calculations that have been carried out with the Gaussian program25 on HF/6-31G** level of theory. Rotational barriers around C(1)-C(7) and C(8)C(10) in the CDPE molecule using quantum and MM methods have been calculated with interval 20°. In both cases (MM and ab inition calculations) complete relaxation of all molecular parameters were allowed except for the torsion angle in question. Absolute and relative energies of conformers a-d are listed in Table 3, and rotational barriers are depicted in

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Table 2. Selected Experimental (X-ray) and Calculated (Quantum) Bond Lengths, Bond Angles, and Torsion Angles in the Structures 1-4 1 X-ray

2 quantum

X-ray

3 quantum

X-ray (A)

X-ray (B)

quantum

1.407(4) 1.373(4) 1.394(4) 1.418(4) 1.366(4) 1.404(4) 1.433(4) 1.355(4) 1.422(4) 1.484(4) 1.148(4) 1.320(4) 1.368(4) 1.671(3)

1.401(4) 1.371(4) 1.410(4) 1.410(4) 1.357(4) 1.404(4) 1.425(4) 1.363(4) 1.421(4) 1.474(4) 1.144(4) 1.328(4) 1.351(4) 1.662(3)

1.400 1.372 1.409 1.413 1.370 1.403 1.445 1.352 1.439 1.483 1.139 1.326 1.364 1.676

1.418(8) 1.360(9) 1.409(8) 1.421(8) 1.374(8) 1.406(7) 1.427(8) 1.361(8) 1.445(7) 1.460(8) 1.139(8) 1.366(7) 1.365(8) 1.674(6)

1.398 1.374 1.401 1.408 1.411 1.401 1.454 1.347 1.440 1.489 1.137 1.338 1.367 1.652

116.2(3) 118.0(3) 125.8(3) 132.1(3) 123.1(3) 122.3(3) 114.6(3) 175.4(3) 114.9(3) 121.3(2) 123.8(2) 120.7(3) 122.9(3) 115.8(3)

115.9(3) 118.6(3) 125.4(3) 131.4(3) 121.2(3) 122.0(3) 116.6(3) 176.8(4) 116.6(3) 121.2(2) 122.2(2) 122.7(3) 121.9(3) 115.0(3)

116.3 117.0 126.7 132.9 122.8 120.9 116.2 176.7 115.6 120.3 124.1 122.0 122.1 115.9

116.2(5) 116.2(5) 127.5(5) 133.9(5) 121.2(5) 123.2(5) 115.6(5) 175.7(6) 115.8(5) 121.9(5) 122.4(4) 122.0(5) 122.0(5) 116.6(5)

116.3 117.3 126.4 133.1 122.8 120.7 116.4 177.4 115.0 122.2 122.8 122.0 122.1 116.0

Torsion Angles, deg. -11.1(3) -6.6 -3.4(6) 170.6(2) 173.9 176.7(3) -4.3(3) -1.4 1.3(5) -179.1(2) -177.4 -178.4(3) -20.1(2) -36.1 167.3(3) 164.8(2) 147.6 -12.4(4) 159.4(1) 142.1 -13.0(4) -15.7(2) -34.2 167.3(2) -11.8(3) -7.0 -1.8(5) -2.1(3) -6.1 -10.1(5) 94.2(2) 88.6 83.2(4) 85.6(2) 87.9 94.4(4)

-16.6(6) 165.7(3) -8.6(5) 177.2(3) -177.7(3) 7.9(4) 2.0(4) -172.5(2) -10.5(5) -1.7(5) 93.8(4) 83.8(4)

0.1 -179.9 0.0 180.0 179.9 -0.1 -0.1 179.9 -6.3 -6.3 88.2 88.2

10.2 -173.7 8.1 -175.4 21.2 -162.0 -158.5 18.2 5.5 0.0 -87.8 -90.5

6.6 -173.9 1.3 177.4 36.2 -147.5 -142.0 34.3 6.9 6.1 -88.6 -87.9

C(1)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(5)-C(6) C(1)-C(6) C(1)-C(7) C(7)-C(8) C(8)-C(9) C(8)-C(10) N(1)-C(9) N(2)-C(10) N(3)-C(4) S(1)-C(10)

1.399(3) 1.367(3) 1.412(3) 1.402(3) 1.362(3) 1.406(3) 1.435(2) 1.358(2) 1.429(3) 1.476(2) 1.144(2) 1.330(2) 1.362(2) 1.669(2)

1.400 1.372 1.409 1.413 1.370 1.403 1.445 1.352 1.439 1.483 1.139 1.326 1.364 1.676

Bond Lengths, Å 1.409(2) 1.398 1.361(2) 1.374 1.407(2) 1.401 1.415(2) 1.408 1.362(2) 1.411 1.410(2) 1.401 1.428(2) 1.454 1.367(2) 1.347 1.432(2) 1.440 1.468(2) 1.489 1.137(2) 1.137 1.327(2) 1.338 1.361(2) 1.367 1.672(1) 1.652

C(2)-C(1)-C(6) C(2)-C(1)-C(7) C(6)-C(1)-C(7) C(1)-C(7)-C(8) C(7)-C(8)-C(9) C(7)-C(8)-C(10) C(9)-C(8)-C(10) N(1)-C(9)-C(8) N(2)-C(10)-C(8) N(2)-C(10)-S(1) C(8)-C(10)-S(1) C(4)-N(3)-C(11) C(4)-N(3)-C(13) C(11)-N(3)-C(13)

115.5(2) 119.3(2) 125.2(2) 131.1(2) 121.4(2) 123.3(2) 115.2(2) 177.3(2) 115.6(2) 121.5(1) 122.9(1) 121.9(2) 121.7(2) 116.0(1)

116.3 117.0 126.7 132.9 122.8 120.9 116.2 176.7 115.6 120.3 124.1 122.0 122.1 115.9

Bond Angles, deg 115.9(2) 116.3 117.5(2) 117.3 126.7(2) 126.4 132.6(1) 133.1 121.8(1) 122.8 122.5(1) 120.7 115.4(1) 116.4 178.7(2) 177.3 117.5(1) 115.0 121.8(1) 122.2 120.6(1) 122.8 122.0(2) 120.0 121.4(1) 122.1 116.1(1) 116.0

-11.5(3) 168.0(2) -1.8(3) -177.8(2) 166.2(2) -10.0(2) -13.1(2) 170.7(1) 0.0(3) -6.0(3) 87.9(2) 86.9(2)

0.1 -179.9 0.0 180.0 179.9 -0.1 -0.1 179.9 -6.3 -6.3 88.2 88.2

C(6)-C(1)-C(7)-C(8) C(2)-C(1)-C(7)-C(8) C(1)-C(7)-C(8)-C(9) C(1)-C(7)-C(8)-C(10) C(7)-C(8)-C(10)-N(2) C(9)-C(8)-C(10)-N(2) C(7)-C(8)-C(10)-S(1) C(9)-C(8)-C(10)-S(1) C(11)-N(3)-C(4)-C(3) C(13)-N(3)-C(4)-C(5) C(4)-N(3)-C(11)-C(12) C(4)-N(3)-C(13)-C(14)

4

Figure 2. Selected geometry parameters of calculated molecular structures along with experimental values are presented in Table 2. For computation of molecular hyperpolarizabilities a modification of the static-field method26,27 developed in refs 28 and 29 was used. Multiple static-field calculations were performed using the MOPAC program30 and the AM1 Hamiltonian. Dipole moment (µ) and second-order polarizability tensor (β) were obtained using HYPER program.28 A more detailed description of the above-mentioned methods are given in refs 31, 32, and 33. We graphically depicted the dipole moment and vectorial part of second-order polarizability. The vectorial part of β is presented using the following relations:

βx ) βxxx + βxyy + βxzz βy ) βyyy + βyxx + βyzz βz ) βzzz + βzxx + βzyy For graphical presentation, we used the program described in ref 34. Table 4 presents calculated values of molecular dipole moments and hyperpolarizabilities. Crystal Structure Prediction. Predictions of probable crystal structures for conformers a, b, and d were performed with the Polymorph Predictor module incorporated into the Cerius2 program23 package. In all calculations described below, crystal packings with one molecule per asymmetrical unit were considered (Z′ ) 1). The crystal structure search was restricted

X-ray

quantum

Table 3. Calculated Absolute and Relative Energies of Conformers a-d conformer

energy, a.u.

relative energy, kcal mol-1

a b c d

-1100.9286621 -1100.9169870 -1100.9286621 -1100.9169869

0.0 7.34 0.0 7.34

Table 4. Calculated Dipole Moments and Second Order Polarizabilities of CDPE Conformers polymorph conformer dipole moment, D 1 2 3(A) 3(B) 4

a b a a d

6.08 10.91 5.93 5.97 11.17

hyperpolarizability, 10-51 C m3 V-2 142 155 140 147 170

to the eight most common for organic crystals space groups: P1 h , P21, P21/c, Cc, C2/c, Pbca, P212121, Pna21. Before crystal structure prediction, we tested several force fields incorporated in Cerius2 in the following manner. We used as a starting point an experimental crystal structure geometry, obtained from X-ray data and optimized crystal structures using the following force fields: Universal Force Field (UFF),33,36 CFF91,37,38 CVFF,39,40 Compass,41,42 Momany’s,43,44 Sheraga’s,45 and Dreiding.24 We performed that procedure twice, first using only van der Waals, and then using the sum of van der Waals



Figure 2. Dependence of energy of CDPE molecule vs torsion angles C(6)-C(1)-C(7)-C(8) and C(7)-C(8)-C(10)-N(2) obtained from ab initio (a, b) and MM (c, d) calculations. Diamonds present results of calculation, and dots are experimental (X-ray) data of corresponding torsion angles in crystals 1-4. Experimental values of torsion angles are conditionally placed on conformational curves. and electrostatic components of crystal energy. After optimization, we compared optimized and experimental unit cell parameters, and starting and final energies of crystal structures for three polymorphs, described above (1, 2, and 4). Comparison gave the best results for the Dreiding FF,24 which employs for calculations of intermolecular energy modified FF developed by Williams.46-49 The next three force fields with acceptable results were FF proposed by Momany et al.,43,44 Sheraga et al.,45 and Compass,42,43 developed by Accelrys (formerly MSI). Unfortunately, testing of the latter FF was excluded because the charge on the sulfur atom, which is one of the key atoms for the molecules under consideration, in our version of Cerius2 obtained from MSI was equal to zero, which is not realistic. So, we used the Dreiding 2.21 force field24 for all crystal structure computations presented in this paper. Atomic charges (where applicable) were estimated using the charge equilibration method50 and summation of electrostatic energy terms was carried out using Evald’s algorithm. Both Monte Carlo simulated annealing search of crystal structures and Cluster analysis of obtained structures were done in the Polymorph Predictor module using “Fine” option. The first two rounds of calculations (R and RC) consisted of polymorph predictions where the starting molecular models for conformers a, b, and d were taken from X-ray studies of CDPE polymorphs 1, 2, and 4. In round R only van der Waals (VDW) impacts into crystal structure energy have been

considered, while in round RC both van der Waals and electrostatic (Coulomb, C) impacts in monopole approximation have been taken into account. In both cases, the molecules were treated as rigid bodies. In Table 5 comparison of X-ray unit cell parameters and parameters obtained by minimization of energy starting from X-ray structure with Dreiding FF for polymorphs 1, 2, and 4 are presented. Crystal structure energies, where only VDW impacts (R) or VDW and electrostatic impacts (RC) have been considered, have also been compared with corresponding energies for X-ray nonoptimized structures. These comparison show, as it was mentioned above, that Dreiding FF24 gives quite acceptable results for reproduction of unit cell parameters, and that the energy of the experimental structure does not differ significantly from the energy of optimized structure. In the two second rounds of calculations, starting models for conformers a, b, and d were also taken from the X-ray results, but in this case rotation of rigid molecular fragments around C(1)-C(7) and C(8)-C(9) bonds was permitted, and the NEt2 substituent was considered to be flexible. These rounds might be considered semi-ab initio, since in this case the molecular conformation is flexible. Two types of calculations, where only VDW and (VDW + C) terms (F and FC respectively) have been taken into account, were performed

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Table 5. Comparison of X-ray and Calculated (minimized starting from X-ray Structure with Dreiding FF) Unit Cell Parameters and Crystal Energies for Polymorphs 1, 2, and 4, where Only VDW Impact (R) or VDW and Electrostatic Impacts (RC) Have Been Considered

1, X-ray 1, R 1, RC 2, X-ray 2, R 2, RC 4, X-ray 4, R 4, RC

a, Å

b, Å

c, Å

R, deg

β, deg

γ, deg

8.753 8.807 8.695 9.167 8.377 8.680 10.756 11.289 11.109

8.890 8.713 8.745 13.023 13.189 12.685 12.365 12.524 12.494

10.830 10.423 10.473 12.172 12.658 12.671 10.868 10.440 10.546

85.44 86.97 86.06 90.00 90.00 90.00 90.00 90.00 90.00

69.76 71.29 70.80 93.97 82.71 82.05 104.25 107.09 106.17

63.65 63.82 63.82 90.00 90.00 90.00 90.00 90.00 90.00

in this round. Totally we have carried out four types of predictions for every polymorph 1, 2, and 4: R, RC, F, and FC. Extended tables with predicted structures for each round of calculations are available as Supporting Information. Modeled crystal structures were sorted by energy criterion, starting with structure with the lowest energy (top position on predicted structure list). Since the Polymorph Predictor model and crystallography software (SHELXTL51) sometimes give different space group settings, we used an in-house computer program to convert the obtained results into the same settings.

Results and Discussion Molecular Structure of CDPE in Phases 1-4: X-ray Data and Quantum Calculations. The most remarkable finding of X-ray structural investigations of crystals 1-4 was that three conformations of CDPE molecule (from four possible conformations proposed in Scheme 1) have been found in these crystals. Figure 1 clearly shows a conformational difference between molecules in crystals 1-4, which consists of cissoid and transoid orientations of C(S)NH2 group around a single C(8)-C(10) bond and different orientations of ethyl branches in NEt2 substituent. In crystals 1 and 3 conformation a (Figure 1) was found, while in crystals 2 and 4 conformations b and d, respectively, were observed. An unexpected peculiarity of conformer b (polymorph 2) and conformer d (polymorph 4) is a very short intramolecular contact C(7)-H‚‚‚H-N(2) between the hydrogen atom attached to the double C(7)dC(8) bond and to the nitrogen atom of the amino group (1.95 and 2.04 Å, respectively). The presence of such very short intramolecular contacts indicates that conformers b and d might be less energetically preferable than the two other conformers a and c, where such short contact was not found. In structures 1-4, a “quinoid” character of bond lengths distribution in the benzene rings is observed (Table 2). Thus, all bonds C(2)-C(3) and C(5)-C(6) are significantly shortened, while the other phenyl ring bonds are elongated (see Table 2). This pattern of bond lengths distribution is rather typical for NLO compounds without ortho or meta substituents.4,5,32,33 Molecules 1-4 are not strictly planar in the crystals. Major deviations from planarity in π-conjugated fragment C(1)-C(7)dC(8)-C(10) are related to rotation around C(1)-C(7) and C(8)-C(10) single bonds (see Table 2). It is interesting that the torsion angles C(6)C(1)-C(7)-C(8) and C(7)-C(8)-C(10)-N(2) are noticeably different in the two independent molecules (A and B) in structure 3 (Table 2) that shows again that they are nonrigid.

-Ecr (R), kcal mol-1

-Ecr (RC), kcal mol-1

27.73 28.51

31.45

25.77 27.91 25.89 26.83

32.38 30.86 32.62 30.54 31.25

Molecular packing and hydrogen bonding characteristics in structures 1-4 will be discussed below together with the results of crystal structure modeling of polymorphs 1, 2, and 4. The goal of ab initio quantum chemical calculation was an evaluation of the relative energy of conformers a-d and heights of rotational barriers around single C(1)-C(7) and C(8)-C(10) bonds, which are mainly responsible for conformational diversity of CDPE molecules. Table 3 shows that conformers a and c have significantly lower energy than conformers b and d, and that energies of these two pairs of conformers are almost equal. The latter observation indicates that the relative orientation of Me groups in NEt2 substituents does not influence significantly the conformational energy. Figure 2 presents the dependence of energy of CDPE molecule vs torsion angles C(6)-C(1)-C(7)-C(8) and C(7)-C(8)-C(10)-N(2) (ab initio and MM calculations). From the conformational curve describing C(7)-C(8)C(10)-N(2) torsion angle it is clear that conformers b and d that was found in polymorphs 2 and 4 are significantly less preferable than conformers a and c (a found in structures 1 and 3; c has not been observed yet). According to ab initio calculations (Figure 2b) the barrier of rotational transition from conformers b,d to conformers a,c is very low, only about 2 kcal mol-1. These results give us a serious reason to consider conformers b and d less stable than conformers a and c. Results of DSC analysis for polycrystalline CDPE sample, obtained directly from the reaction mixture, are presented in Figure 3. It is obvious that there are at least two phases in this sample. We were able to measure melting point on a single crystalline sample under the microscope for only the predominant polymorph 1; it was equal to ∼148°C. So, it is possible to see that pick 1 on heating corresponds to melting of polymorph 1 (Figure 3a). Pick 2 corresponds to another polymorph, which we were unable to identify. After cooling and second heating of the same sample, only one pick was found (Figure 3b) that corresponds to melting point of polymorph 1. It is possible to conclude that from the reaction mixture at least two forms of CDPE were obtained. Most probably the melting process promoted conversion of less stable conformers into more stable (a) and its crystallization brought formation of the predominant polymorph 1. Characteristics of Polarizability of CDPE Conformers. To evaluate how conformational diversity of the CDPE molecule influences its electronic properties,


Figure 3. Data of DSC analysis of CDPE sample.

we calculated dipole moments (µ) and second-order polarizabilities (β) for conformers a, b, and d, which were found in crystalline polymorphs. Obtained results are presented in Table 4 and in Figure 4. It is obvious that the transoid conformers (b and d) have significantly larger dipole moments and that their relative orientation is different than in the cisoid conformer. On the contrary, orientation of the vectorial part of the beta tensor is very similar in both conformers and the increase of the average β value, presented as βav ) (βx2 + βy2 + βz2)1/2, in the transoid structure is less pronounced than for the dipole moment. As it was possible to expect, according to calculations, conformers with higher dipole moments are characterized with somewhat higher values of hyperpolarizability (Table 4). The significant values of dipole moments give us a reason to suggest that they should have some influence on molecular packing. Crystal structure modeling in part should prove or disprove this assumption. Experimental and Predicted Crystals Built of Conformer a: Polymorph 1 and Solvate 3. Since CDPE molecule contains at least three groups that


Figure 4. Graphical presentation of molecular dipole moment (µ) and vectorial part of a second-order polarizability (β) in arbitrary units. Centers of both vectors are arbitrary reconciled with the centers of mass of the conformers.

might form hydrogen bonds (NH2, -CN, and dS), Hbonding is definitely a very important factor in the crystal structures of this compound. It should be mentioned that the thioamide group C(dS)-NH2 as well as the C(CN)dCNH2 fragment due to H-bonds formation can participate in dimer or catemers (infinite associate) intermolecular patterns. Those patterns are often referred as supramolecular synthons.52 In crystal 1 molecular conformation (a) makes it possible for the reference molecule to participate in two centrosymmetric H-bonded dimers built with two C(CN)d CNH2 (eight-member cycle) or two C(dS)-NH2 (12member cycle) groups. The H-bond pattern in this structure can be clearly seen in Figure 5, presenting molecular packing in polymorph 1; corresponding Hbond parameters are listed in Table 6. It is interesting that one of these synthons (dimer formed with C(CN)dCNH2 groups) is also observed in crystal 3 (Figure 6). This observation confirms the importance of synthons in the formation of the threedimensional supramolecular unit (i.e., the crystal) with the participation of conformer a. However, in 3 these

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Table 6. Geometrical Parameters of Intermolecular H-Bonds in the Crystal Structures 1-3 and 4a Obtained from X-ray Structural Study and for Predicted Structures (calc) in RC Round H‚‚‚A, Å D-H‚‚‚A

X-ray

calc

D‚‚‚A, Å X-ray

D-H‚‚‚A, deg. calc

N(2)-H(2A)‚‚‚N(1)i N(2)-H(2B)‚‚‚S(1)ii

2.35 2.66

2.31 2.87

Polymorph 1 3.069(3) 3.068 3.481(3) 3.659

N(2)-H(2A)‚‚‚N(1)i N(2)-H(2B)‚‚‚S(1)ii

2.20 2.58

2.20 2.61

Polymorph 2 2.988(2) 3.008 3.421(2) 3.303

N(2A)-H(2AA)‚‚‚N(1B)i N(2A)-H(2AB)‚‚‚S(1B) N(2B)-H(2BA)‚‚‚N(1A)ii N(2B)-H(2BB)‚‚‚S(1A)

2.26 2.48 2.43 3.05

N(2)-H(2A)‚‚‚N(1)ii N(2)-H(2B)‚‚‚S(1)i

2.38 2.60

X-ray

calc

141 160

147 154

(i) -x, 1 - y, -z (ii) 1 - x, -y, -z

152 167

156 138

(i) 0.5 - x, 0.5 + y, 0.5 - z (ii) -x, 1 - y, 1 - z

Solvate 3

a

2.990(4) 3.294(3) 3.134(4) 3.887(3) 2.50 2.51

3.128 3.470

(i) x, 1 - y, z - 0.5

142 158 139 167

Polymorph 4 3.255 3.397

172 159

symmetry

(ii) x, -y + 1, z +0.5

174 163

(ii) 0.5 - x, -0.5 + y, -0.5 - z (i) -x, -y, -z

Refs 16 and 17.

dimers are not centosymmetric. It arises from the fact that they are formed between symmetrically independent molecules 3(A) and 3(B), having considerably different torsion angles C(6)-C(1)-C(7)-C(8) (-3.4(6) and -16.6(6)°, respectively). Results of crystal structure prediction for conformer a (polymorph 1) are presented in Table 7. For a rigid starting molecular model good correspondence of calculational and experimental data were found. When we

Experimental and Predicted Crystal Structures Built of Conformer b: Polymorph 2. In contrast to conformer a, conformer b has a cissoid orientation of -CN and CdS groups, and hence for this conformer the formation of dimer synthon for fragment C(CN)dCNH2 is impossible. According to X-ray data, molecules 2 in

Figure 5. Projection of crystal structure of polymorph 1 along axis a. Intermolecular H-bonds are shown with dashed lines.

Figure 6. Projection of crystal structure of CDPE/acetonotrile solvate 3 along axis b. Intermolecular H-bonds are shown with dashed lines.

took into account only VDW energy terms, the predicted structure that corresponds to the experimental one was with the lowest crystal energy (the first on the list of predicted structures). Superposition of experimental and predicted structures for polymorph 1 in this approximation is shown in Figure 7. When both VDW and C terms have been taken into account, the best correspondence to the experimental structure was found with the third predicted structure on the list. However, in this case the energy difference between the first and third structures is pretty low, only ∼0.2 kcal mol-1. On the contrary, polymorph prediction with a flexible starting model (rounds F and FC, Table 7) shows no match between predicted and experimental structures.

the crystal form essentially corrugated layers parallel to plane (101). Molecules in 2D H-bonded motif include one type of dimer with C-H‚‚‚S H-bonds inside the dimers and additional N-H‚‚‚N H-bonds between the dimers (Table 6, Figure 8). Crystal structure prediction for conformer b gave correct results in both R and RC rounds (Table 7, Figure 9). Rounds with flexible starting molecule gave qualitatively acceptable results in FC rounds, the third structure on the list (Table 7). However, this prediction cannot be considered completely successful, since in this case molecular conformation differs from the experimental one (see Figure 10).



Table 7. Comparison of X-ray and Calculateda Unit Cell Parameters and Crystal Energies for Polymorphs 1, 2, and 4, where Only VDW Impact (R, F) or VDW and Electrostatic Impacts (RC, FC) Have Been Consideredb

1, X-ray 1, R 1, RC 1, F 1, FC 2, X-ray 2, R 2, RC 2, F 2, FC 4, X-ray 4, R 4, RC 2, F 2, FC

structure position

a, Å

b, Å

1c 3d

8.753 8.81 8.64

8.890 8.71 8.79

1f

9.167 8.88 8.67

13.023 12.54 12.70

3

9.55

1e

10.756 1g

10.53

c, Å

R, deg

-Ecr (R,F), kcal mol-1

-Ecr (RC,FC), kcal mol-1

63.65 63.82 64.43

27.73 28.51

31.45

90.00 90.00 90.00

25.77 27.64

β, deg

γ, deg

Conformation a, Polymorph 1, P1 h 10.830 85.44 69.76 10.42 86.97 71.29 10.45 85.63 70.93 no match no match

Conformation b, Polymorph 2, P21/n 12.172 90.00 93.97 12.67 90.00 98.39 12.66 90.00 97.93 no match 12.58 11.92 90.0 98.92

Conformation d, Polymorph 4, P21/n 12.365 10.868 90.00 104.25 no match 12.50 11.12 90.00 106.26 no match no match

31.19

32.62 -9.79

90.00 90.00 90.00

30.86

25.89

30.54 31.25

a Polymorph predictor, starting from X-ray structure with Dreiding FF, in four rounds with rigid and flexible molecular models. Complete lists of predicted structures are presented as Supporting Information. c Next structure on the list of predicted structures has energy 27.31 kcal/mol. d Two structures has lower energies than structure #3 on the list (31.40 and 31.37 kcal/mol) and next structure has energy 31.03 kcal/mol. e Two next structures on the list of predicted structures have energies 27.62 and 27.31 kcal/mol. f Next structure on the list of predicted structures has energy 31.47 kcal/mol. g Next structure on the list of predicted structures has energy 30.43 kcal/ mol.

b

Figure 7. Comparison of experimental (solid line) and calculated (dashed line) molecular positions in polymorph 1. Calculated polymorph corresponds to the first predicted structure in round R. Graphical presentation of overlap of experimental and calculated structure obtained in round RC is almost identical to that depicted in this figure.

Despite differences in molecular structure of conformers b and d, which consists of different orientations of “branches” in NEt2 groups, their packing modes are very similar. Conformer d also forms dimers that are connected in the 2D system with H-bonds described in Table 6 and presented in Figure 11. In polymorph 4 the 2D H-bonded system is parallel to the (101) plane. In this case only round RC gave good correspondence of experimental and predicted structures (see Table 7 and Figure 12 with superposition of experimental and calculational molecular packings). Presented experimental results show that in all polymorphs studied, H-bonds play an important role in structure formation and that molecules with similar

conformations present similar packing modes (conformers b and d) or at least contain similar synthons (conformer a in polymorph 1 and solvate 3). It was also shown that despite short intramolecular contacts and high conformational energy, conformers b and d can occur under particular conditions. Testing of Dreiding FF for prediction of crystal structures of polymorphs 1, 2, and 4 gave positive results for a rigid (X-ray) molecular model with consideration of both VDW and C impacts in crystal energy (round RC). It was also possible to predict two (1 and 2) of three polymorph structures if one considers only the VDW impact in crystal energy. Some differences were found in hydrogen bonding in X-ray and calculated structures. Table 6 shows that H-bonds with amino groups are described by calculations better than with sulfur atoms. For models with flexible molecular structure, which is actually close to ab initio crystal structure prediction, all rounds failed. Our analysis of Dreiding FF indicated one important reason of such failure. In Figure 2 conformational curves from MM calculations for the same torsion angles that were used for quantum calculations are presented. A dramatic difference of curves describing the same conformational angles is obvious. This difference prevents flexible CDPE molecular models to adopt the same or similar conformation to what was found in crystals of polymorphs under consideration. In its turn conformational distinctions prevent in rounds F and FC from prediction of crystal structures that are similar to experiential ones. Estimation of torsion parameters that adequately described molecular conformation of CDPE and relative compounds in framework of molecular mechanics will help to circumvent the situation with ab initio crystal structure prediction of this series of compounds. It should be noted that almost no low-energy acentric structures have been found for all CDPE conformers under consideration. Moreover, in acentric structures

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Figure 8. Projection of crystal structure of polymorph 2 along axis a. Intermolecular H-bonds are shown with dashed lines.

Figure 11. Projection of crystal structure of polymorph 4 along axis b. Intermolecular H-bonds are shown with dashed lines. Figure 9. Comparison of experimental (solid line) and calculated (dashed line) molecular positions in polymorph 2. Calculated polymorph corresponds to the predicted structure with the lowest energy (first on the list) in round RC.

Figure 12. Comparison of experimental (solid line) and calculated (dashed line) molecular positions in polymorph 4. Calculated polymorph corresponds to the predicted structure with lowest energy (first on the list) in round RC.

Figure 10. Comparisons of molecular experimental structure of in polymorph 2 (solid line) with modeled molecular structure in round FC (dashed line).

that were found by the Polymorph Predictor module there were no reasonable systems of H-bonds, so we did not take them into further consideration. Most probably, formal analogy of the general structure of the CDPE molecule D-π-A(D′) with molecular structures described by us recently in refs 18 and 19 is not enough for formation of acentric crystals. Preliminary conclusion should necessarily include consideration of all types

of possible H-bonds. It is very likely that molecular dimers, which are predominant synthons in all CDPE structures, as we shown in ref 33, make a centrosymmetric type of packing more favorable, so prevent formation of acentric molecular structures. Energy difference between the predicted structure corresponding to the experimental one and next structure on the list (Table 7 and Supporting Information) shows that structures 1 and 4 are predicted with a high level of reliability. For structure 2 prediction is less reliable (see Figure 9 and Table 7). Polymorph predictor module gave us no acentric structures with low crystal energy.



Conclusion

(12) Borbulevych, O. Ya.; Golding I. R.; Shchegolikhin, A. N., Klemenkova, Z. S., Antipin, M. Yu. Acta Crystallogr. C 2001, 57, 996. (13) Timofeeva, T. V.; Nesterov, V. N.; Clark, R. D.; Penn, B.; Frazier, D.; Antipin, M. Yu. J. Mol. Struct. 2003, 647, 181. (14) Timofeeva, T. V.; Kuhn, G. H., Nesterov, V. V.; Nesterov, V. N.; Frazier, D. O.; Penn, B. G.; Antipin, M. Yu. Cryst. Growth Des. 2003, 3, 383. (15) Antipin, M. Yu.: Timofeeva, T. V.; Clark, R. D.; Nesterov, V. N.; Dolgushin, F. M.; Wu, J.; Leyderman, A. J. Mater. Chem. 2001, 11, 351. (16) Brunskill, J. S.; De, A.; Ewing, D. F.; Welch, A. J. Acta Crystallogr. C 1984, 40, 493. (17) Brunskill, J. S.; De, A.; Ewing, D. F. J. Chem. Soc., Perkin Trans. 1978, 629. (18) Nesterov, V. V.; Antipin, M. Yu.; Nesterov, V. N.; Moore, C. E.; Cardelino, B. H., Timofeeva, T. V. Cryst. Growth Des. 2004, 4, 521. (19) Nesterov, V. V.; Antipin, M. Yu.; Nesterov, V. N.; Penn, B. G.; Frazier D. O.; Timofeeva, T. V. J. Phys. Chem. 2004, 108, 8351. (20) Brock, C. P.; Schwezer, W. B.; Dunitz, J. D. J. Am. Chem. Soc. 1991, 113, 9811. (21) Kuleshova, L. N.; Antipin, M. Yu. Crystallogr. Rep. 2002, 47, 268-280. (22) Kuleshova, L. N.; Antipin, M. Yu. Crystallogr. Rep. 2003, 48, 293. (23) Cerius2 Program, Accelrys (former Molecular Simulations Inc., MSI), 1999, Molecular Simulations Inc., 9685 Scranton Road, San Diego, CA 92121, USA. (24) Mayo, S. L.; Olafson, B. D.; Goddard, W. A. III J. Phys. Chem. 1990, 94, 8897-8909. (25) Frisch, M. J., Trucks, G. W., Schlegel, H. B., Gill, P. M. W., Johnson, B. G., Robb, M. A., Cheeseman, J. R., Keith, T., Petersson, G. A., Montgomery, J. A., Raghavachari, K., AlLaham, M. A., Zakrzewski, V. G., Ortiz, J. V., Foresman, J. B., Cioslowski, J., Stefanov, B. B., Nanayakkara, A., Challacombe, M., Peng, C. Y., Ayala, P. Y., Chen, W., Wong, M. W., Andres, J. L., Replogle, E. S., Gomperts, R., Martin, R. L., Fox D. J., Binkley, J. S., Defrees, D. J., Baker, J., Stewart, J. P., Head-Gordon, M., Gonzales, C., Pople, J. A. Gaussian 94, Gaussian Inc., Pittsburgh, PA, 1994. (26) Dewar, M. J. S.; Stewart, J. J. P. Chem. Phys. Lett. 1984, 111, 416. (27) Kurtz, H. A.; Stewart, J. J. P.; Deiter, K. M. J. Comput. Chem. 1990, 11, 82. (28) Cardelino, B. H.; Moore, C. E.; Stikel R. E. J. Phys. Chem. 1991, 95, 8645. (29) Cardelino, B. H.; Moore C. E.; Frazier D. O. J. Phys. Chem. 1997, 101, 2207. (30) Stewart, J. J. P. MOPAC, Quantum Chemistry Program Exchange, University of Indiana, Bloomington, USA, Program 455. (31) Timofeeva, T. V.; Nesterov, V. N.; Antipin, M. Y.; Clark, R. D.; Sanghadasa, M.; Cardelino, B. H.; Moore, C. E.; Frazier, D. O. J. Mol. Struct. 2000, 519, 225. (32) Antipin, M. Y.; Barr, T. A.; Cardelino, B. H.; Clark, R. D.; Moore, C. E.; Myers, T.; Penn, B.; Romero, M.; Sanghadasa, M.; Timofeeva, T. V. J. Phys. Chem. B 1997; 101, 2770. (33) Antipin, M. Yu.; Timofeeva, T. V.; Clark, R. D.; Nesterov, V. N.; Sanghadasa, M.; Barr, T. A.; Penn, B.; Romero, L.; Romero, M. J. Phys. Chem. A 1998; 102, 7222. (34) Timofeeva, T. V.; Suponitsky, K. Y.; Cardelino, B. H.; Clark, R. D. SPIE 1999, 3796, 229. (35) Rappe, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard-III, W. A.; Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024. (36) Castonguay, L. A.; Rappe, A. K. J. Am. Chem. Soc. 1992, 114, 5832. (37) Dinur, U.; Hagler, A. T. New Approaches to Empirical Force Fields. In Reviews of Computational Chemistry; Kenny B. Lipkowitz, K. B., Boyd, D. B., Eds.; Wiley: New York, 1991; Vol. 2, Chapter 4. (38) Maple, J. R.; Dinur, U.; Hagler, A. T. Proc. Natl. Acad. Sci. U.S.A. 1988, 85, 5350. (39) Hagler, A. T.; Huler, E.; Lifson, S. J. Am. Chem. Soc., 1974, 96, 5319. (40) Lifson, S.; Hagler, A. T.; Dauber, P. J. Am. Chem. Soc., 1979, 101, 5111. (41) Sun, H.; Rigby, D. Spectrochim. Acta A 1997, 53, 1301,

Conformational polymorphs of CDPE have been discovered in the course of systematical studies of NLO materials. Structural and computational data along with thermal analysis of CDPE have shown that one of the conformations of CDPE (a) has significantly lower energy than the two other. We consider that high relative energy and steric hindrances in two conformations (b and d) make two polymorphs (2 and 4) “disappearing” or “vanishing” according to Bernstein’s1 classification, and their reappearance can be reproduced only under very explicit conditions, for instance, in the presence in solution or in a reaction mixture of other specific compounds under particular concentrations. It was possible to reproduce crystal structures of all three polymorphs with Polymorph Predictor if the initial molecular structure was taken from the X-ray data, the molecule during minimization was considered to be rigid, and both VDW and Coulomb interactions were taken into account. On the contrary, prediction of molecular packings of flexible CDPE molecules failed, most probably because of inadequate torsion potentials in Dreiding FF, and underestimation of H-bonds with a sulfur atom. We believe that reestablishment of torsion parameters for this group of compounds and improvement of H-bond parameters with sulfur can help to perform ab initio crystal structure prediction in this and similar materials. Acknowledgment. We gratefully acknowledge financial support of this research by AFOSR (Grant No F49620-01-1-0561) and NM EPSCoR program. We are grateful for Dr. Irina Dubovick for DSC measurement. Supporting Information Available: X-ray crystallographic information (CIF) files and tables with predicted structures for each round of calculations are available free of charge via the Internet http://pubs.acs.org.

References (1) Bernstein, J. Polymorphs in Molecular Crystals; Oxford Science Publications: New York, 2002. (2) Nalwa, H. S., Miyata S., Eds. Nonlinear Optics of Organic Molecules and Polymers; CRC Press: Boca Raton, FL, 1997. (3) Kuzyk, M. C., Dirk, C. W., Eds. Characterization Techniques and Tabulations for Organic Nonlinear Optical Materials; Marcel Dekker: New York, 1998. (4) Zyss, J.; Ledoux, I.; Nicoud, J.-F. In Molecular Nonlinear Optics; Academic Press: New York, 1994; pp 129-200. (5) Zyss, J.; Chemla, D. S. In Nonlinear Optical Properties of Organic Molecules and Crystals; Academic Press: New York, 1987; pp 32-198. (6) Pertsin, A. J.; Kitaigorodsky A. I. The Atom-Atom Potential Method. Applications to Organic Molecular Solids; SpringerVerlag: Berlin, 1987. (7) Timofeeva, T. V.; Chernikova, N. Yu.; Zorkii, P. M. Russ. Chem. Rev. 1980, 49, 509. (8) Gavezotti, A. Acc. Chem. Res. 1994, 27, 309. (9) Lommerse, J. P. M.; Motherwell, W. D. S.; Ammon, H. L.; Dunitz, J. D.; Gavezzotti, A.; Hofmann, D. W. M.; Leusen, F. J. J.; Mooij, W. T. M.; Price, S. L.; Schweizer, B.; Schmidt, M. U.; van Eijck, B. P.; Verwer, P.; Williams, D. E. Acta Crystallogr. B 2000, 56, 697. (10) Motherwell, W. D.; Ammon, H. L.; Dunitz, J. D.; Dzyabchenko, A.; Erk, P.; Gavezzotti, A.; Hofmann, D. W.; Leusen, F. J.; Lommerse, J. P.; Mooij, W. T.; Price, S. L.; Scheraga, H.; Schweizer, B.; Schmidt, M. U.; van Eijck B. P.; Verwer P.; Williams D. E. Acta Crystallogr. B 2002, 58, 647. (11) Timofeeva, T. V.; Nesterov, V. N.; Dolgushin, F. M.; Zubavichus, Y. V.; Goldshtein, J. T.; Sammeth, D. M.; Clark, R. D.; Penn, B.; Antipin, M. Yu. Cryst. Eng. 2001, Volume Date 2000, 3, 263.

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(42) Sun, H. J. Phys. Chem. 1998, 102, 7338, (43) Momamy, F. A.; Carruthers, L. M.; McGuire, R. F.; Scheraga, H. A. J. Phys. Chem. 1974, 78, 1595. (44) Momamy, F. A.; Carruthers, L. M.; Scheraga H. A. J. Phys. Chem. 1974, 78, 1621. (45) Nemethy, G.; Pottle, M. S.; Scheraga, H. A. J. Phys. Chem. 1983, 87, 1883. (46) Williams, D. E.; Cox, S. R. Acta Crystallogr. B 1984, 40, 404. (47) Williams, D. E.; Houpt, D. J. Acta Crystallogr. B 1986, 42, 286.

Timofeeva et al. (48) Williams, D. E.; Hsu, L. Y. Acta Crystallogr. A 1985, 41, 296. (49) Cox, S. R.; Hsu, L. Y.; Williams, D. E. Acta Crystallogr. A 1981, 37, 293. (50) Rappe´, A. K.; Goddard, W. A. J. Phys. Chem. 1991, 95, 3358. (51) Sheldrick G. M. 1998. SHELXTL Version 5.1, Structure Determination Software Suite, Bruker AXS, Madison, Wisconsin, USA. (52) Desiraju. G. R., Angew. Chem., Int. Ed. Engl. 1995, 34, 231.

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