Article pubs.acs.org/crystal
Parallel and Perpendicular Packing in Mixed-Stack Cocrystals of Trimeric Perfluoro-ortho-phenylene Mercury and Benzo[1,2‑b:6,5‑b′]dithiophene-4,5-dione Derivatives Raúl Castañeda,† Marina S. Fonari,†,‡ Chad Risko,§ Yulia A. Getmanenko,†,∥ and Tatiana V. Timofeeva*,† †
Department of Biology and Chemistry, New Mexico Highlands University, Las Vegas, New Mexico 87701, United States Institute of Applied Physics, Academy of Sciences of Moldova, Academy Str., 5 MD2028 Chisinau, Moldova § Department of Chemistry and Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506-0055, United States ∥ School of Chemistry & Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States ‡
S Supporting Information *
ABSTRACT: Seven cocrystals derived from 2,7-substituted benzo[1,2-b:6,5-b′]dithiophene-4,5-diones (BDDO) and trimeric perfluoro-o-phenylene mercury (TPPM) exhibit two prominent packing motifs: parallel mixed stacks and T-shaped columnar structures. The varied packing patterns reveal an interplay of noncovalent intermolecular interactions that depend on the nature of the BDDO 2,7-substituents and on the crystallization conditions. Quantum-chemical analyses show little charge-transfer character in the mixed-stack structures, suggesting limited electronic interaction among the mixed TPPM and BDDO constituents. The variations in molecular packing with rather minimal change in chemical structure expose the ability to fine-tune the structure of these molecular cocrystals.
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INTRODUCTION Cocrystals with mixed-stack donor−acceptor architectures1 provide a versatile approach to modify the electronic properties of crystalline systems. Recent theoretical2,3 and experimental4−8 studies demonstrating the semiconducting and room-temperature ferroelectric properties of the mixed-stack donor− acceptor materials have brought to light this intriguing class of organic materials for electronics applications. However, many questions remain as how to fully develop the characteristics of these materials, in particular with the vast array of donor and acceptor moieties available. In addition to mixed-stack donor−acceptor cocrystals formed from purely organic materials, the possibility also exists to develop mixed cocrystals from a combination of organic and organometallic species. For instance, trimeric perfluoro-ophenylene mercury (TPPM) (Figure 1) is a cyclic organometallic macrocycle with strong π-electron accepting properties (the reduction potential is −1.70 V vs Cp2Fe0/+ in 0.1 M © XXXX American Chemical Society
Figure 1. Structure of trimeric perfluoro-o-phenylene mercury (TPPM) acceptor and benzo[1,2-b:6,5-b′]dithiophene-4,5-dione (BDDO) derivatives used in this study.
tetrabutylammonium hexafluorophosphate in dichloromethane9) and oxo- and thiophilicity,9,10 that has been shown to Received: January 1, 2016 Revised: March 2, 2016
A
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
CCDC number empirical formula formula weight T, K crystal system space group a, Å b, Å c, Å α, ° β, ° γ, ° V, Å3 Z D (calcd) kg/m3 μ, mm−1 F(000) reflections collected independent reflections data/restraints/ parameters GOF on F2 final R indices [I > 2σ(I)] R1, wR2 R indices (all data) R1, wR2
compound
1444406 C66H6Cl6F24Hg6O6S6
2959.31 100(2) rhombohedral R3̅ 15.6197(13) 15.6197(13) 15.6197(13) 104.62 104.62 104.62 3358.2(5) 2 2.927
14.213 2688 15154
3698 [R(int) = 0.0627]
3698/0/212
0.984 0.0548, 0.1302
0.0737, 0.1363
2860.61 100(2) rhombohedral R3̅ 15.371(5) 15.371(5) 15.371(5) 104.438(5) 104.438(5) 104.438(5) 3213(2) 2 2.957
14.622 2592 16364
2996 [R(int) = 0.0769]
2996/0/325
0.987 0.0375, 0.0770
0.0773, 0.0920
2(TPPM)·3(Cl−BDDO)
1444401 C66H6F30Hg6O6S6
2(TPPM)·3(F−BDDO)
B
0.0246, 0.0481
1.045 0.0210, 0.0472
5999/0/451
5999 [R(int) = 0.0308]
17.918 1292 17793
1442.02 100(2) triclinic P1̅ 9.834(2) 11.555(3) 15.003(4) 103.238(4) 91.161(4) 112.187(3) 1525.9(6) 2 3.139
1444160 C28H4Br2F12Hg3O3S2
0.0332, 0.0568
0.977 0.0261, 0.0548
6536/0/496
6536 [R(int) = 0.0334]
16.499 1352 14101
1504.53 100(2) triclinic P1̅ 10.6085(18) 10.9943(19) 15.240(3) 106.775(2) 93.011(2) 99.072(2) 1671.5(5) 2 2.989
1444116 C29H3Br2ClF12Hg3O2S3
(TPPM)·(Br−BDDO)· (H2O) (TPPM)·(Br−BDDO)·(0.5(CS2)·0.5(DCM)
0.0424, 0.0883
0.991 0.0343, 0.0833
10488/0/469
10488 [R(int) = 0.0364]
15.554 1428 20539
1602.91 100(2) triclinic P1̅ 10.8919(13) 11.0066(13) 15.1911(18) 106.060(2) 93.178(2) 99.448(2) 1716.5(4) 2 3.101
1444265 C29H4Cl2F12Hg3I2O2S2
((TPPM)·I−BDDO)· (DCM)
0.0529, 0.0789
1.007 0.0363, 0.0746
14649/23/749
14649 [R(int) = 0.0327]
9.121 1746 29629
1864.39 100(2) triclinic P1̅ 13.839(3) 14.551(3) 15.555(3) 80.040(3) 67.913(3) 66.040(3) 2651.7(10) 2 2.335
1444206 C55H18ClF12Hg3O4S8
(TPPM)·2(Th−BDDO)· 0.5(DCE)
0.0623, 0.0594
0.978 0.0354, 0.0546
16994 [R(int) = 0.0805] 16994/0/1003
12.259 5184 96859
1410.57 100(2) monoclinic P21/n 13.299(3) 27.413(6) 21.234(5) 90 98.347(4) 90 7659(3) 8 2.447
1444207 C34H20F12Hg3O2S2Si2
(TPPM)·(TMS− BDDO)
Table 1. Crystal Data and Structure Refinement Parameters for 2(TPPM)·3(F−BDDO), 2(TPPM)·3(Cl−BDDO), (TPPM)·(Br−BDDO)·(H2O), (TPPM)·(Br−BDDO)· 0.5(CS2)·0.5(DCM), (TPPM)·(I−BDDO)·(DCM), and (TPPM)·2(Th−BDDO)·0.5(DCE)
Crystal Growth & Design Article
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 2. Fragment of the D−A stack in the complex 2(TPPM)·3(F−BDDO) with partial numbering scheme and thermal ellipsoids (a); and in space filling mode (b), color scheme: F - green, S - yellow, O - red, C - dark gray, Hg and H - light gray.
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RESULTS AND DISCUSSION General. In the cocrystallization experiments with TPPM as a π-acceptor (A), the following BDDO π-donors (D) were used: 2,7-difluoro-BDDO (F−BDDO), 2,7-dichloro-BDDO (Cl−BDDO), 2,7-dibromo-BDDO (Br−BDDO), 2,7-diiodoBDDO (I−BDDO), 2,7-bis(thiophen-2-yl)-BDDO (Th− BDDO), 2,7-bis(trimethylsilyl)-BDDO (TMS−BDDO), and unsubstituted BDDO (Figure 1). The single crystal structures of these BDDO derivatives, with the exception of BDDO and Th-BDDO, were recently reported.23 As observed in our previous experiments with TPPM,13 finding the best conditions for the growth of the crystals suitable for single-crystal X-ray studies required tuning the solvent and molecular ratio. No cocrystals suitable for single crystal X-ray diffraction analysis were obtained with unsubstituted BDDO from dichloromethane (DCM), ethyl acetate, a 1:1 mixture of DCM and 1,2-dichloroethane (DCE), a 1:1 mixture of DCM and carbon disulfide. Single crystals of pure BDDO were isolated and characterized (Figure S4). Two new solvatomorphs of I−BDDO with DCE (Figure S5) and 2methoxyethanol (MOE) (Figure S6) were obtained, and their structures are discussed in the Supporting Information. The details of the cocrystal growth are provided in the Experimental Details. Out of the seven cocrystals described here, two are binary solids with an unusual 3:2 D:A ratio (2(TPPM)·3(F−BDDO) and 2(TPPM)·3(Cl−BDDO)); three are solvates with 1:1 D:A ratio ((TPPM)·(Br−BDDO)·(H2O) and two isomorphic structures, (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM) and (TPPM)·(I−BDDO)·(DCM)); one is a DCE solvate with a 2:1 D:A ratio ((TPPM)·2(Th−BDDO)·0.5(DCE)), and only one has the more commonly reported 1:1 D:A ratio ((TPPM)· (TMS−BDDO)). Unless otherwise specified, only the Hg···C, O, S, Hal (Hal = F, Cl, Br, I), Hal···Hal, and CH···Hal interatomic contacts, and other interactions shorter than the sum of van der Waals radii for the corresponding atoms (RHg = 1.73−2 Å, RO = 1.52 Å, RS = 1.8−2.03 Å, RC = 1.7 Å, RF = 1.47 Å, RCl = 1.75 Å, RBr = 1.85 Å, and RI = 1.98 Å31) are discussed. Mixed-Stack Layered Structures. In the cocrystals 2(TPPM)·3(F−BDDO), 2(TPPM)·3(Cl−BDDO), and (TPPM)·(Br−BDDO)·(H2O), the BDDO and TPPM molecules are arranged in parallel with varying interstacking motifs. Cocrystals 2(TPPM)·3(F−BDDO), 2(TPPM)·3(Cl−BDDO) are isomorphous compounds with an unusual 3:2 D−A molar
form mixed-stack complexes with a variety of planar aromatic moleculese.g., dithieno[3,2-b:2′,3′-d]thiophene,9 azulene,11 tetrathiafulvalene (TTF),12 carbazole,13 N-methylindole,14 Nmethylcarbazole,15 fluorene,16 and nonplanar aromaticse.g., corannulene,17 and bicorannulenyl.18 In these cocrystals, the TPPM forms mixed stacks with the organic moieties in a 1:1 ratio, with solvent molecules remaining in some instances. Interestingly, perpendicular T-shaped packing arrangements have been observed for mixtures comprising TPPM with nitrobenzene,19 carbonyl-containing benzophenone,20 and Michler’s ketone,21 indicating that Hg(TPPM)···O interactions can be structure-determining. Extention of the aromatic core in 5-nitroacenaphthene and 1-nitropyrene19 results in parallel mixed-stack structures with both π−π and Hg(TPPM)··· O(NO2) interactions present. Recently we developed an efficient synthetic approach toward 2,7-bis(trimethylsilyl)benzo[1,2-b:6,5-b′]dithiophene4,5-dione 22 (TMS−BDDO) and its derivatives, 2,7dihalobenzo[1,2-b:6,5-b′]dithiophene-4,5-diones and 2,7-bis(thiophene-2-yl)benzo[1,2-b:6,5-b′]dithiophene-4,5-dione (Th−BDDO).23 These planar tricyclic molecules have large electron affinities and have been studied as molecular-based thin-film electron-transport semiconductors.23−25 Here we take advantage of the versatility of TPPM interactionsincluding (i) its oxo- and thiophilic properties resulting in short Hg···O(S) contacts, (ii) the propensity to form mixed-stack cocrystals with various π-donors, and (iii) the presence of fluorine atoms available to form meaningful F···halogen interactions26−28to develop cocrystals with a series of BDDO derivatives (from the electronic point of view the BDDO derivatives are stronger acceptors in comparison with TPPM; reduction potentials for BDDO compounds are in the range from −0.89 to −1.01 V vs ferrocene/ferrocenium,22,23 but they can act as π-donors (D) in cocrystals with TPPM (A)) (Figure 1). The interplay of O(S)···Hg, πdonation, and halogen−halogen interactions, which have been extensively used in crystal engineering29 to modify the electronic properties of organic semiconductors,30 open a wide space for exploration and can provide insight into the structure-determining interactions that drive cocrystal formation. C
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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ratio being crystallized in a rhombohedral R3̅ space group; 2(TPPM)·3(Cl−BDDO) has a slightly larger unit cell due to larger size of BDDO chlorine substituents in comparison with fluorine-substituted BDDO (Table 1). The supramolecular motifs are similar, two crystallographically different TPPM molecules (A1 and A2) reside on the 3-fold axis, while one BDDO molecule (F−BDDO or Cl−BDDO) occupies a general position. The stacks obey 3-fold symmetry: each TPPM, possessing D3h symmetry, alternates with three BDDO molecules related by the 3-fold axis and situated in one plane. The molecular stacks are organized in an A1A1(D3)A2A2(D3)A1A1 (A = TPPM, D = BDDO) sequence, where the planes of A and D molecules are almost parallel (the interplanar D/A angle is 1.68° in 2(TPPM)·3(F−BDDO) and 0.42° in 2(TPPM)·3(Cl−BDDO)) with the interplanar distances A1− A1, A1−D, D−A2, and A2−A2 of 2.971, 3.144, 3.208, and 3.177 Å in 2(TPPM)·3(F−BDDO), and 3.100, 3.208, 3.205, and 3.112 Å in 2(TPPM)·3(Cl−BDDO). The TPPM molecules A1 and A2 lie exactly above each other (Figure 2), while the BDDO molecules are shifted from the centers of the trimercury cycles, revealing rather long Hg···O “side” contacts, with participation of two Hg atoms and one O atom (Hg(1)···O(2) = 3.462(8) and Hg(2)···O(2) = 3.482(8) Å in 2(TPPM)·3(F− BDDO), Hg(1)···O(2) = 3.657(3) and Hg(2)···O(2) = 3.760(3) Å in 2(TPPM)·3(Cl−BDDO)). Because of the different side interactions, the TPPM molecules deviate from planarity; i.e., the mercury atoms do not form planar structures with planes of perfluorinated phenyl rings (0.183 at 0.099 Å for 2(TPPM)·3(F−BDDO); 0.142 and 0.149 Å in 2(TPPM)· 3(Cl−BDDO)). Similar to the previously reported complex 2(TPPM)· TTF,8,32 the lateral interstack interactions involving halogen atoms have significant impact on crystal packing. These lateral interactions combine the components from adjacent stacks in the layers running parallel to the (111) plane (Figure 3). Within a layer of the 2(TPPM)·3(F−BDDO) cocrystal, each triad of F−BDDO molecules are held together via short contact, C(19)−H(19)···O(1) = 2.54(1) Å, and are surrounded by six molecules of TPPM, which are self-associated via meaningful F···F contacts with the CFF angles close to 180°. (These F···F contacts might be referred to the Type II in classification suggested in ref.33 and considered significant for the stabilization of the crystal lattice. The calculated F···F distances and C−F···F angles for the fluorine atoms (Figure 3) are as follows: F(3)···F(11) = 2.71(1) Å, ∠C(3)F(3)F(11) = 163.8(8)°; F(4)···F(10) = 2.83(1) Å, ∠C(10)F(10)F(4) = 159.1°.) Other intermolecular interactions within the layer occur through two S···F contacts (3.13(1) Å and 3.25(1) Å). The less dense layer in 2(TPPM)·3(Cl−BDDO) is due to the difference in the atomic radii of chlorine and fluorine, which contributes to the observation of different interactions within the layer, such as formation of the short contact O(2)···Cl(1) = 3.225(9) Å, an increase in F···F distances beyond the meaningful limit, and involvement of chlorine in the heterogeneous D···A contact (Cl(1)···F(10) = 2.922(8) Å) in addition to homogeneous D···D contact. The parallel stacks formed by 2(TPPM)·3(F−BDDO) and 2(TPPM)·3(Cl−BDDO) are interesting structural motifs in light of recent reports on the ambipolar charge-carrier transport of mixed-stack donor−acceptor cocrystals.2,6,8,34−37 The structures here are particularly intriguing given their ···A-AD3-A-A-D3··· stacking arrangement. The arrangement is akin to one recently reported by Vermeulen and co-workers36 for a
Figure 3. Fragments of crystal packings in 2(TPPM)·3(F−BDDO) and 2(TPPM)·3(Cl−BDDO): (a) fragment of layer in 2(TPPM)· 3(F−BDDO) supported by F···F, CH···O, S···F, and CH···F interactions; (b) fragment of layer in 2(TPPM)·3(Cl−BDDO) supported by Cl···F, O···Cl, S···F, and CH···O interactions with indication of unit cell (the same unit cell arrangement is in 2(TPPM)· 3(F−BDDO)).
pyrene−TCNQ cocrystal, though here the π-donor layer is made up of three noncovalently bound BDDO moieties. Note that the results for the F−BDDO and Cl−BDDO mixed stacks are quite similar, and so only the 2(TPPM)·3(F−BDDO) will be discussed. Unfortunately, there is very limited, if any, charge transfer evidence among the TPPM- and BDDO-based molecules in the cocrystals. This is due in part to the nature and poor energetic alignment of the frontier orbitals. Starting with the isolated molecules, the frontier orbitals of TPPM are combinations of Hg d-orbitals and the carbon σ- and π-frameworks, consistent with previous reports.9 For the HOMO, there are four nearly isoenergetic molecular orbitals, lying within 0.1 eV, while the LUMO is fairly well spaced (0.65 eV) from the next unoccupied orbitals. On the other hand, the frontier orbitals of the BDDO species are the π-orbitals that makeup the conjugated framework, as previously reported;23 see Figure 4 for representative examples. Importantly, the BDDO HOMO and LUMO both fall in the gap of the TPPM HOMO−LUMO gap. Hence, there is limited opportunity, treating the systems as isolated molecules, for the TPPM to interact strongly with the BDDO; the charge-transfer character is an important parameter observed in previous donor−acceptor mixed-stack crystals. D
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 4. Selected F−BDDO and TPPM frontier molecular orbital energies and representations of the wave functions as determined at the B3LYP/ 6-311G(d,p)/LANL2DZ level of theory. Note that the HOMO for TPPM is nearly isoenergetic with three additional molecular orbitals (within 0.1 eV).
Figure 5. Selected (left) (F−BDDO)3, denoted D3, (TPPM)2, denoted A-A, [center] D3-A-A-D3, and (right) A-D3-A frontier molecular orbital energies and representations of the wave functions as determined at the B3LYP/6-311G(d,p)/LANL2DZ level of theory. Note that in each case there are nearly isoenergetic orbitals near the HOMO, LUMO, or both.
complex; the lone exception is for the D3-A-A-D3 construct where one of the near isoenergetic HOMOs shows some weight on both the D3 and A-A moieties, with the A-A component of the wave function being solely a σ-orbital within the carbon framework. These results are consistent with the lack of charge-transfer character observed experimentally and suggest the presence of flat electronic bands in the mixed-stack crystal.9 A third cocrystal with layered packing, (TPPM)·(Br− BDDO)·(H2O), crystallizes in triclinic P1̅ space group. The water oxygen atom is situated above the TPPM mean plane at the distance of 2.362(4) Å and coordinates strongly to the Hg(3) atom (Hg(3)···O(1) = 2.894(4) Å) and to two other Hg
The limited electronic interactions are further shown by examining the molecular orbitals for complexes extracted from the crystal structures (Figure 5). As with the isolated molecules, the HOMO and LUMO energies of the D3 unit, comprised of three F−BDDO molecules, fall within the HOMO−LUMO gap of the TPPM dimer, denoted AA. Hence, exploring different donor−acceptor clustersfor instance D3-A-A-D3 and A-D3-Areveals that the HOMO and LUMO reside on the D3 unit. As one would expect, there are a number of nearly isoenergetic orbitals with the HOMO and LUMO in these clusters. However, taking these orbitals into account, as well as those outside of the range, there is little evidence of charge transfer among the donor and acceptor molecules in the E
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 6. Fragments of crystal packing in (TPPM)·(Br−BDDO)·(H2O): (a) mode of aggregation of formula units into centrosymmetric hexamer with short contacts shown as dashed and dotted lines; (b) fragment of cocrystal in space-filling mode; color scheme: F - green, Br - brown, S - yellow, O - red, C - dark gray, Hg and H - light gray.
Figure 7. Fragments of crystal packing in (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM) and (TPPM)·(I−BDDO)·(DCM). (a) Overlay diagram of two adducts (solvent molecules are not shown). (b) View of the D−A unit in (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM) with partial numbering scheme and indication of short Hg···O contacts. (c) Mode of aggregation of centrosymmetric tetramers into ribbons supported by O···Br, F···F short contacts and π−π-stacking interactions, short contacts are shown by dashed lines. (d) The ribbon shown in space filling mode; color scheme: F green, I - purple, S - yellow, O - red, C - dark gray, Hg and H - light gray. (e) Fragment of crystal packing with solvent inclusion.
F
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 8. Fragments of crystal packing in (TPPM)·(TMS−BDDO): (a, b) view of two crystallographically different binary D−A units with partial numbering scheme and indication of short Hg···O contacts; (c) pseudocentrosymmetric heterotetramers formed by TPPM and TMS-BDDO.
the crystal, is further discussed in detail (only the corresponding numerical values in (TPPM)·(I−BDDO)· (DCM) are added for comparison). In the D−A formula units, the tricyclic donor molecules Br− BDDO and I−BDDO are practically perpendicular to the mean plane of TPPM with the dihedral angles between the planes of 84.85(3)° and 84.10(3)°, respectively (Figure 7b). Such arrangement provides the best fit of the molecules for the μ3tripod coordination (Hg···O distances range from 2.890(3) to 2.984(3) Å in (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM), and from 2.902(5) to 2.938(3) Å in (TPPM)·(I-BDDO)·(DCM)) of one carbonyl oxygen to all three mercury atoms,38 while the second carbonyl oxygen atom has a monodentate coordination to Hg atom (Hg···O distance is 2.977(4) Å in (TPPM)·(Br− BDDO)·0.5(CS2)·0.5(DCM), and 2.981(4) Å in (TPPM)·(I− BDDO)·(DCM).) The binary adducts pack into tight centrosymmetric heterotetramers with perfectly overlapping tricyclic BDDO molecules separated by 3.351 Å in (TPPM)· (Br−BDDO)·0.5(CS2)·0.5(DCM) and 3.375 Å in (TPPM)· (I−BDDO)·(DCM), which indicates slightly closer packing in comparison with pure Br−BDDO with 3.398 Å separation.23 These tetramers are further combined into ribbons (Figure 7c) supported by the Hal(Br/I)···O short contacts, O(1)···Br(2) = 2.875(3) Å and O(1)···I(2) = 2.952(4) Å; these contacts have been also observed by us in the pure BDDO molecules.23 The crystal packing is reinforced by F···F contacts between the partially overlapping perfluorinated rings of TPPM acceptor (for (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM): F(10)··· F(17) = 2.877(5) Å, F(9)···F(9) = 2.725(7) Å; for (TPPM)· (I−BDDO)·(DCM): F(10)···F(17) = 2.803(6) Å, F(9)···F(9)
atoms with longer distances (Hg(1)···O(1) = 3.080(3) Å, and Hg(2)···O(1) = 3.111(5) Å). The shielding of the TPPM cavity by a water molecule results in a monodentate “side” coordination of Br−BDDO donor with TPPM via one short contact, Hg(3)···O(2) = 3.025(4) Å. The Br−BDDO molecule is almost parallel to TPPM with the dihedral angle between the mean planes of 4.43(4)°. Two formula units are combined into centrosymmetric hexamers via OH···O hydrogen bond with participation of the water molecule (W) and one of the carbonyl oxygen atoms, O(1)···O(3) = 2.845(5) Å (Figure 6a). These hexamers comprise stacks with the sequence of molecules AA(D2W2)AA(D2W2)AA, that run along the crystallographic a axis (Figure 4b). Additional contacts, e.g. F(2)···F(16) = 2.825(4) Å, Br(1)···F(5) = 2.940(2) Å, C(20)− H(20)···F(8) = 2.38 Å lateral contacts, and π−π stacking interactions between the partly overlapping perfluorinated phenyl rings that combine the components in double layers running parallel to the (2 1̅ 1) crystallographic plane (Figure S1) result in dense crystal packing. Cocrystals with T-Shaped Packing. Cocrystals (TPPM)· (Br−BDDO)·0.5(CS 2 )·0.5(DCM), (TPPM)·(I−BDDO)· (DCM), and (TPPM)·2(Th−BDDO)·0.5(DCE) crystallize as solvates with DCM and CS2, DCM and DCE inclusion, respectively. The cocrystals (TPPM)·(Br−BDDO)·0.5(CS2)· 0.5(DCM) and (TPPM)·(I−BDDO)·(DCM) with the 1:1:1 molar ratio are isomorphic (Figure 7a) and crystallize in the triclinic P1̅ space group with the unit cell volume increased by 45 Å3 in the latter one. Only the packing in the complex (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM), in which the DCM and CS2 molecules alternate with equal probabilities in G
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 9. Fragments of crystal packing in (TPPM)·2(Th−BDDO)·0.5(DCE): (a) view of the D−A unit with partial numbering scheme and indication of short Hg···O contacts; (b) mode of aggregation of formula units in columns with indication of short contacts and cell axes; (c) the column shown in space filling mode; color scheme: F - green, S - yellow, O - red, C - dark gray, Hg and H - light gray.
Hg(3)···Hg(4) = 3.4050(7) Å, between TPPM molecules. Between the columns the most meaningful contacts are the CH···F ones with involvement of terminal methyl groups that form the 3D network (Figure S3). It is noteworthy that the cocrystallization of Th−BDDO with TPPM allowed for the description of the solid-state molecular structure of Th−BDDO, which has not been previously reported. Similar to the alkyl-substituted analogue,23 two crystallographically different Th−BDDO molecules have almost planar skeletons with the dihedral angles between the tricyclic core and terminal thiophene rings equal to 4.83(6)° and 10.5(1)° in one molecule, and 6.39(9)° and 19.2(1)° in the other. Cocrystal (TPPM)·2(Th−BDDO)·0.5(DCE) crystallizes in the centrosymmetric triclinic P1̅ space group with DCE solvent molecule residing on inversion center, and three other molecules occupying general positions. In the T-shaped D−A arrangement one of the Th−BDDO molecules locates exactly above the center of the TPPM cavity and has two coordination modes, μ3-bridging coordination of one of the carbonyl oxygens to all three mercury atoms (Hg···O distances are ranging from 2.799(4) to 2.866(4) Å), and the monodentate coordination of the second carbonyl oxygen to the single Hg atom with Hg···O distance of 2.992(4) Å. Two Th−BDDO molecules locate in the parallel planes with the dihedral angle between their skeletons of 2.15(3)°, and the second one participates in the only one monodentate “side” coordination via single Hg(3)··· O(4) = 2.866(3) Å short contact (Figure 9a). The trimeric formula units pack in columns with stacks of Th−BDDO molecules surrounded by the TPPM molecules from both sides (Figure 9b). The π−π distance between the Th−BDDO molecules in stacks varies from 3.625 to 3.753 Å. The neighboring stacks meet the TTPM acceptor molecules with short mercurophilic contacts, Hg(3)···Hg(2) = 3.8175(6) Å (Figure S2).39
= 2.774(1) Å and F(5)···F(5) = 2.555(2)). The solvent molecules occupy the space between the donor and acceptor columns (Figure 7e). The increase of the size of the substituents at positions 2 and 7 of BDDO results in some specific features in the packing of cocrystals TPPM·2(Th−BDDO)·0.5(DCE) and (TPPM)· (TMS−BDDO). Cocrystal (TPPM)·(TMS−BDDO) crystallizes in the monoclinic centrosymmetric P21/n space group. The formula unit comprises two asymmetric 1:1 D−A complexes being in the T-shaped arrangement with dihedral angles between the molecular mean planes of 57.42(4)° and 60.40(4)°, respectively. These complexes vary by the donor− acceptor coordination modes that also differ from those described above. Although in both cases there is the μ2bidentate bridging coordination of one of carbonyl oxygen atoms and monodentate coordination of the second carbonyl oxygen, in the first binary unit they include only two mercury atoms (Hg(1)···O(2) = 2.907(4), Hg(2)···O(2) = 3.018(4), Hg(1)···O(1) = 2.740(4) Å), while in the second one all three Hg atoms participate in short contacts (Hg(4)···O(4) = 2.819(4), Hg(5)···O(4) = 2.990(4), and Hg(6)···O(3) = 2.868(4) Å) (Figure 8a,b). Two binary complexes pack in tight pseudocentrosymmetric heterotetramers similar to those found in (TPPM)·(Br−BDDO)·0.5(CS2)·0.5(DCM) and (TPPM)·(I−BDDO)·(DCM), with the interplanar angle between two BDDO molecules of 2.5(1)° and short intermolecular contacts of 3.27−3.30 Å between them (Figure 8c). These contacts are somewhat shorter in comparison with the ones observed in pure TMS−BDDO, for which the distances are in the range of 3.30−3.41 Å (C···S contacts);22 the planes of BDDO π-donors in cocrystals are closer to parallel arrangement in comparison with pure TMS−BDDO, in which the interplanar angle is 11.7°.22 Tetramers in (TPPM)·(TMS−BDDO) stack in columns along the [1 0 1] direction with short mercurophilic contacts, H
DOI: 10.1021/acs.cgd.6b00001 Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
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heteromeric O···Hg D−A interactions and are involved in the homomeric D−D CH···O and O···Cl interactions. These interactions provide the alignment of π-donor F/Cl-BDDO molecules in the homomeric triads alternated in stacks with acceptor TPPM molecules. The interstack interactions include halogen and sulfur atoms combining components of adjacent stacks into layers. In (TPPM)·(Br−BDDO)·(H2O), the only hydrate in the series, water molecule shields TPPM cavity and provides “side” coordination of one carbonyl oxygen of the BDDO molecule, thus assisting in the D−A parallel alignment. With increase of the size of the substituents at positions 2 and 7 of BDDO in diiodo-, bis(TMS)- and bis(thiophen-2-yl)-BDDO derivatives Hg(TPPM)···O(dione moiety of BDDO) interactions become significant and structure-determining resulting in T-shaped complexes. The packing in these cocrystals, assisted by specific interactions with participation of halogen substituents, demonstrates different stacking patterns of π-donor BDDO molecules, including antiparallel dimers and columns contrary to the cofacial stacks in the BDDO pure forms. Quantum-chemical analysis indicates lack of charge transfer character in the studied mixed-stack cocrystals due to poor alignment of the molecular orbitals. Charge-transfer integrals for holes calculated for the stacks of dimers of Th−BDDO in cocrystal (TPPM)·2(Th−BDDO)·0.5(DCE) varied from 43 to 139 meV, which are larger than that estimated for electrons indicating that the hole charge transport through the Th− BDDO stacks is expected to be more efficient than the electron charge transport.
Transfer integrals for a series of four Th−BDDO nearestneighbor molecular pairs (three of which are unique), predominantly arranged along the a-axis of the (TPPM)· 2(Th−BDDO)·0.5(DCE) cocrystal, were computed as an initial evaluation of the charge-carrier transport characteristics, Figure 10.
Figure 10. Effective transfer integrals for holes (th) and electrons (te) for nearest-neighbor molecular pairs within the Th−BDDO stack of the (TPPM)·2(Th−BDDO)·0.5(DCE) cocrystal, computed at the B3LYP/6-311G(d,p)/LANL2DZ level of theory.
The effective transfer integrals were calculated through the fragment orbital approach40 in combination with a basis set orthogonalization procedure41 at the B3LYP/6-31G(d,p) level of theory. For holes, the (HOMO:HOMO) transfer integrals range from 43 to 139 meV, though the dimers with the strong electronic communication are shielded from each other by dimers with weaker electronic coupling (i.e., stacks of dimers). For electrons, the (LUMO:LUMO) transfer integrals are in general substantially smaller (
