Interplay between Hydrogen and Halogen bonding in Co-Crystals of

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Interplay between Hydrogen and Halogen bonding in Co-Crystals of Dipyridinylmethyl oxalamides and Tetrafluorodiiodobenzenes Baillie A. DeHaven, Anna L. Chen, Emily A Shimizu, Sahan R. Salpage, Mark D. Smith, and Linda S. Shimizu Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b00796 • Publication Date (Web): 22 Aug 2019 Downloaded from pubs.acs.org on August 26, 2019

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Crystal Growth & Design

Interplay between Hydrogen and Halogen bonding in Co-Crystals of Dipyridinylmethyl oxalamides and Tetrafluorodiiodobenzenes Baillie A. DeHaven, Anna L. Chen, Emily A. Shimizu, Sahan R. Salpage, Mark D. Smith, and Linda S. Shimizu* Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina USA KEYWORDS: Co-crystal, halogen bond, hydrogen bond, tetrafluorodiiodobenzene, oxalamide ABSTRACT: Herein, we examine how the combination of multiple intermolecular interactions influences the supramolecular assembly of dipyridinylmethyl oxalamides and tetrafluorodiiodobenzenes into distinct well-defined nanostructures. A series of six regioisomers were selected and crystallized resulting in eleven co-crystals and one co-crystal solvate. Three halogen and hydrogen bonded supramolecular macrocycles were observed, two of which form large enough channels to accommodate disordered guest molecules. In another case, packing of infinite chains formed columnar channels, which were occupied with stacks of the halogenated co-formers. Molecular electrostatic potential surfaces were calculated to qualitatively rank each binding site in order make inferences about the expected assembly patterns. Although the oxalamide oxygen was not always predicted to be the best acceptor, self-association of this building block satisfies two donors and two acceptors and was primarily observed. Further N···I halogen bonding interactions formed from pyridyl acceptors and halobenzene donors. Simple electrostatic potential calculations prove to be practical guidelines for predicting the outcome of multiple component crystallizations. But when cooperative directing units, such as oxalamides are employed, additional factors including the number and proximity of functional groups as well as geometric constraints appear to be necessary.

INTRODUCTION Understanding how supramolecular interactions drive solidstate assembly, including the rules that govern their hierarchy, is essential for predictable design of functional materials. Gaining control over the assembly of multiple components within complex co-crystals is of particular interest to the electronics industry where assembly of aryl systems could enhance the efficiency of properties such as emission, lightharvesting, and conductivity.1-6 Herein, we examine the interplay of hydrogen bonding (HB), halogen bonding (XB), and aryl interactions in a systematic series of cocrystallizations. We investigate three dipyridyloxalamide (DPOA) ligands as co-formers in crystallizations with three regioisomers of activated halogen bond formers, tetrafluorodiiodobenzenes (TFDIBs), Figure 1. We further examine electrostatic potential as a tool to predict the outcome of co-crystal assemblies to assess the scope of this simple calculation and to determine the situations when it is unable to predict the outcome of co-crystals. Oxalyl amides have great utility in directing assembly through hydrogen bonding and constructing supramolecular systems.7,8 Pyridyloxalamides have been used to form cocrystals with carboxylic acids or iodoalkynes.9,10 The alignment of the diiodobutadiynes within these co-crystals can be optimal for subsequent polymerization.11-13 These multitopic organic building blocks have also been employed as ligands for coordination polymers forming infinite chains and even double helical structures.14-18 In comparison to the urea assembly unit, the oxalamide set a longer repeat distance of ~ 5.0 Å vs ~4.6 Å.16,17 We have recently examined dipyridylmethylureas with the regio-isomers of TFDIBs and

found modified structures were more likely when there was a structural mismatch between the co-formers and were observed with the geometrically challenging odipyridylmethylurea.19 Competition between the o-DPOA and anthranilic acid has been reported and showed disruption of the oxalamide assembly motif.10 Herein, we seek to develop more precise rules for predicting the outcomes when multiple potential hydrogen and halogen donors and acceptors are combined. RESULTS AND DISCUSSION

Figure 1. Potential hydrogen and halogen bond co-formers selected for this study consisting of a series of dipyridyloxalamide (DPOA) and tetrafluorodiiodobenzene (TFDIB) constitutional isomers accompanied by their calculated electrostatic potential maps.

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Table 1. Calculated Electrostatic Potential Values (kJ/mol)

Figure 2. The predicted outcome of the crystallizations based on calculated electrostatic potential. Best donor/acceptor pair for (I) m-DPOA and p-DPOA (II) o-DPOA. Second best donor/acceptor pair for (III) m-DPOA and p-DPOA (IV) oDPOA.

Fifteen X-ray quality crystals (11 co-crystals, 1 co-crystal solvate and three DPOA ligands) were obtained through either slow evaporation or vapour diffusion methods. For the cocrystals, a two-step procedure was used in which 1:1 stoichiometric ratios of DPOAs to TFDIBs were first ground with a couple drops of chloroform. Then the ground solids were crystallized by slow evaporation or vapour diffusion methods (Table S1). The following crystal structures were obtained: o-DPOA, (o-DPOA)2o-TFDIB, o-DPOAmTFDIB(solv)x, (o-DPOA)2p-TFDIB, o-DPOA(p-TFDIB)2, m-DPOAH2O, m-DPOAo-TFDIB(solv)x, m-DPOAmTFDIB, m-DPOA(m-TFDIB)2DMSO, m-DPOAp-TFDIB, p-DPOA, p-DPOAo-TFDIB, p-DPOAm-TFDIB, pDPOA(m-TFDIB)2, p-DPOAp-TFDIB. All new structures

were deposited into the Cambridge Crystallographic Data Centre (CCDC), 1921257-1921270. A search of the Cambridge Structural Database (CSD) was performed on June 5, 2019. Only one structure obtained had already been deposited in the database (neat p-DPOA, CCDC No. 649075, code CICYOD) therefore it was not deposited. 20,21 Electrostatic Potential Discussion Per Etter’s Rules of hydrogen bonding for organic compounds, all good proton donors and acceptors will try to be satisfied by hydrogen bonding.22 In the case of intermolecular hydrogen bonding interactions, the best proton donor and acceptor will form hydrogen bonds with one another.22,23 Therefore, molecular electrostatic potential surfaces (MEPS) were used to predict the most likely assembly motif of any obtained co-crystals.24,25 Using MEPS, the best donor and acceptors in a crystallization were ranked with the most negative electrostatic potential indicating the best acceptor while the most positive designates the best donor.26 The halogen bond donors of the TFDIBs were first calculated and range from 161.9-165.4 kJ/mol. While the DPOA molecules have multiple donating and accepting sites: two amide N-H donors, two carbonyl oxygen acceptors, and two pyridyl nitrogen acceptors. In comparison to the TFDIB iodo-donor, the DPOA oxalamide N-H is the clear winner, with electrostatic potentials ranging from 200.5 to 241.9 kJ/mol. For the o-DPOA compound the carbonyl oxygen acceptor is the winner in comparison to the pyridyl nitrogen with an electrostatic potential of -184.9 vs. -181.3 kJ/mol. Of course, we expected to observe competition considering that the potentials are so close, within 3.6 kJ/mol. Interestingly, for the m-DPOA and p-DPOA co-formers the pyridyl nitrogen is ranked as the best acceptor with an average potential of -193.1 kJ/mol vs -176.5 kJ/mol for the carbonyl oxygen, a difference of >16 kJ/mol, which would heavily favour the NH···N interaction if all donors and acceptors were satisfied. However, electrostatic differences of less than 30 kJ/mol are expected to be too small to direct assembly in high fidelity.24 Mismatch of geometry could afford unsatisfied sites and further alter these preferences. For example, formation of NH to pyridyl N in (I), Figure 2, would likely generate unsatisfied acceptors. Ideally, thermodynamics favour stronger

Figure 3. SC-XRD structures of the parent DPOA ligands (A) o-DPOA, views down the a-axis (B) m-DPOA, views down the b-axis and (C) p-DPOA, views down the a-axis.


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Crystal Growth & Design interactions while minimizing sites with unsatisfied interaction.27 Parent crystal structure analysis Solvent-free crystals of parent o-DPOA were obtained as transparent needle-like crystals through slow evaporation of the neat ligand in acetonitrile, Figure 3A. The sample crystallized in the triclinic system in the non-centrosymmetric P1 (No. 1) space group with strong pseudosymmetry. The oDPOA ligands conform to a c-shape organizing as dimers across the bc plane with a pyridyl group from one monomer inserted in between both pyridyls of the other monomer. The ligands are stacked along the crystallographic a-axis through oxalamide N-H···O hydrogen bonding interactions ranging in

distance from 2.837(3) Å to 2.849(3) Å and hydrogen bond angles ranging from 150(3)° to 156(3)°. Transparent crystalline needles of hydrated m-DPOA were obtained via slow evaporation of the parent DPOA in acetonitrile, Figure 3B. The ligand crystallized in the monoclinic system in the P21/n space group. Like the parent oDPOA ligand, m-DPOA conforms to a c-shape and also organizes as dimers with one pyridyl unit of one monomer inserted into the c-shape of a neighboring molecule across the ac plane. Two water molecules connect two DPOA monomers of neighboring dimers through O-H···O water-to-water and OH···N hydrogen bonding interactions of the pyridyl nitrogen. Zig-zagged chains of water hydrogen bonds accompanied by

Figure 4. SC-XRD structures of the co-crystals formed in the o-DPOA series (A) (o-DPOA)2o-TFDIB, (B) o-DPOAm-TFDIB (solv)x, (C) (o-DPOA)2p-TFDIB, and (D) o-DPOA(p-TFDIB)2.



infinite chains of oxalamide N-H···O interactions organize the DPOA molecules along the crystallographic b-axis stacking neighboring molecules on top of one another. Oxalamide NH···O hydrogen bonding interactions range in distance of 2.801(13) Å to 2.822(13) Å with dihedral angles ranging between 151(1)° and 156(2)°. Slow evaporation of THF from a solution of the p-DPOA ligand afforded flat colourless needle-like crystals in the monoclinic system with the P21/n space group, Figure 3C. The pyridyl arms are outstretched on either side of the oxalamide linker. Two independent p-DPOA molecules form a dimer through oxalamide hydrogen bonding interactions with NH···O distances ranging from 2.886(2) Å to 2.913(2) Å and angles from 154(2)° to 156(2)°. These dimers are assembled into herringbone-patterned sheets along the bc plane via NH···N hydrogen bonding interactions between the oxalamide N-H groups and the pyridyl nitrogen with distances from 2.905(2) Å to 2.924(2) Å and angles 159(2)° to 162(2)°. This was the only structure to exhibit some competition for the NH donor between pyridine and the oxalamide acceptors. Crystal structure analysis of the ortho DPOA series Colourless flat needle-like crystals of o-DPOA and oTFDIB were obtained via vapour diffusion of water into a DMSO solution of both co-formers resulting in a 2:1 cocrystal, Figure 4A. The sample crystallized in the monoclinic system in space group P21/n. The o-DPOA ligands conform to a c-shape and pack similarly to the parent crystals, forming dimers with one pyridyl arm inserted between both arms of the complementary monomer. Both iodines of the o-TFDIB are fully satisfied with N···I halogen bonding interactions (2.733(12)-3.012(7) Å, 172(2)-174(3)°) connecting

neighboring o-DPOA ligands through the pyridyl arms, leaving one pyridyl one arm of each o-DPOA “unsatisfied”. Infinite tapes of oxalamide hydrogen bonding interactions zip the o-DPOA ligands on top of each other down the a-axis through N-H···O hydrogen bonding interactions with bond distances as close as 2.851(3) Å and angles as wide as 159(3)°. Slow evaporation of a o-DPOA and m-TFDIB chloroform solution resulted in the formation of a colourless 1:1 needlelike co-crystal in the monoclinic system with a P21/n space group, Figure 4B. Hydrogen bonding interactions between the oxalamide units drive assembly down the b-axis with N-H···O distances of 2.836(4) Å and 2.846(4) Å and angles of 152(4)° and 152(4)°. Halogen bonding interactions between the pyridyl nitrogen and the TFDIB co-former results in the formation of macrocycles, which are hexagonally packed across the ac plane, with N···I halogen bonding interactions of 2.882(3) Å and 174.4(1)°. The channels are filled with disordered solvent that could not be resolved, but is presumably the solvent of crystallization, chloroform. A 2:1 co-crystal of o-DPOA and p-TFDIB was obtained as colourless needles through slow evaporation of acetonitrile, Figure 4C. The sample crystallized in the triclinic system in space group P-1. The DPOA ligands conform to a c-shape forming dimers with one pyridyl ring on one monomer inserted between both pyridyl rings of the other monomer. Halogen bonding interactions between the pyridyl nitrogen of the DPOA ligand the iodine of the TFIDB connect monomers of neighboring dimers leaving one pyridyl nitrogen acceptor without a donor. Typical N-H···O hydrogen bonds stack the DPOA molecules on top of one another with N-H···O

Figure 5. SC-XRD structures of the co-crystals obtained with the m-DPOA ligands. (A) Schematic representation of the coils formed by the m-DPOAo-TFDIB co-crystals. Crystal packing of (B) m-DPOAo-TFDIB(solv)x, (C) m-DPOAm-TFDIB, and (D) mDPOAp-TFDIB.


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Crystal Growth & Design distances of 2.846(3) and 2.861(3) Å and angles from 157(3) to 159(3)°. Colourless needles of o-DPOA and p-TFDIB were also obtained as a 1:2 co-crystal through vapour diffusion of water into a DMSO solution, Figure 4D. Like the first co-crystal for this pairing, the sample crystallized in the triclinic system in space group P-1. However, infinite chains of hydrogen and halogen bonded sheets drive assembly in two directions. Down the a-axis DPOA molecules are zipped together through N-H···O hydrogen bonding tapes (2.842(5) Å, 162(6)°). N···I halogen bonding interactions pack the DPOA and TFDIB through infinite chains (2.790(4) Å, 176(2)°) resulting in a zigzag motif along the c-axis. These sheets pack such that there are columnar cavities between the two sheets, which are occupied with stacks of encapsulated TFDIB molecules. Crystal structure analysis of the meta DPOA series Crystallization of m-DPOA and o-TFDIB resulted in the formation of a 1:1 transparent needle-like co-crystal via slow evaporation from THF, Figures 5A and 5B. The co-formers crystallized in the monoclinic system with a P21/n space group and are linked together through N···I halogen bonding interactions (2.733(12) Å, 174(3)°) between the pyridyl of the DPOA ligand and the iodine of the TFDIB forming an infinite oblong spiral down the b-axis, Figure 5B. Oxalamide N-H···O hydrogen bonding interactions stack the DPOA ligands on top of one another (2.866(2), 2.868(2) Å and 155(2)°). Disordered solvent molecules fill the void channel within the spiral, which occupies 22.4% of the total unit cell volume. A 1:1 solvent free co-crystal of m-DPOA and m-TFDIB was obtained through slow evaporation of the co-formers in tbutanol (triclinic, space group P-1 (No. 2) Figure 5C). The DPOA molecules are assembled through the usual 1D hydrogen bonded strands of N-H···O interactions (2.862(1), 2.864(1)Å; 157(2)°, 156(2)°). In the stack of DPOA ligands down the b-axis both (symmetry-equivalent) pyridyl nitrogens of every other DPOA molecule are fully satisfied with N···I

halogen bonding interactions (2.832(1) Å, 173.4(1)°). The unsatisfied pyridyl nitrogen faces in the opposite direction to the satisfied pyridyl, Figure S14B. A second crystal structure of m-DPOA and m-TFDIB was obtained via vapour diffusion of water into a solution of the co-formers in DMSO resulting in a 1:2:1 solvated co-crystal consisting of one DPOA ligand, two TFDIB co-formers, and one molecule of DMSO. The crystals were not stable upon removal of solvent, Figure S15. Vapour diffusion of water into a DMSO solution of the coformers afforded a 1:1 co-crystal of m-DPOA and p-TFDIB (triclinic, space group P-1, Figure 5D). The colourless needles are assembled through infinite strands of halogen bonding interactions (N···I, 2.854(1) Å, 172(1)°). The DPOA ligands conform to a z-shape and the halogen-bonded strands are linked into infinite 2D sheets through the typical 1D hydrogen bonded tapes of N-H···O interactions down the a-axis (2.831(2) Å, 151(2)°). Crystal structure analysis of the para DPOA series Slow evaporation of a p-DPOA and o-TFDIB methanol solution resulted in a 1:1 co-crystal, Figure 6A. The transparent needle-like sample crystallized in the triclinic system with space group P-1. As usual, oxalamide hydrogen bonds form tapes of DPOA molecules along the a-axis, with N-H···O hydrogen bond distances ranging from 2.755(7)2.896(8) Å and angles from 137(6)-160(8)°. The DPOA molecules conform to a z-shape and are linked through halogen bonding interactions with TFDIB into a supramolecular macrocycle with N···I halogen bonding interactions as close as 2.938(6) Å and angles as wide as 171(3)°. The supramolecular cycle is shaped like a cyclohexane chair conformation and pack in columns parallel to the [100]. Slow evaporation of an acetonitrile solution of p-DPOA and m-TFDIB resulted in the formation of a 1:1 co-crystal (Figure S19). The colourless needles in the triclinic system in space group P-1 (No. 2). The co-formers organize through HB and

Figure 6. SC-XRD structures of the co-crystals obtained with the p-DPOA ligands. Crystal packing of (A) p-DPOAo-TFDIB, (B) pDPOA(m-TFDIB)2, and (C) p-DPOAp-TFDIB.



XB interactions in a herringbone pattern, with DPOA molecules stacked into chains of N-H···O hydrogen bonds of the oxalamide unit down the crystallographic a-axis with NH···O distances of 2.819(3) – 2.879(3) Å and angles of 154(3)-161(3)°. Complementary N···I XB interactions drive assembly along the bc plane resulting fully satisfied donor and acceptor sites with N···I distances as close as 2.806(3) Å. A second co-crystal of p-DPOA and m-TFDIB was obtained through vapour diffusion of water into a DMSO solution of the co-formers, resulting in a 1:2 co-crystal, Figure 6B. The colourless needles also crystalized in the triclinic system in space group P-1 (No. 2), though exhibiting a more complex assembly motif. Tapes of N-H···O HB interactions guide assembly down the crystallographic a-axis with distances of 2.787(3) to 2.836(3) Å. Further, N···I and O···I interactions result in the formation of 2D sinusoidal slabs along the bc plane. The N···I interactions are short, ranging in distance between 2.736(2) to 2.777(2) Å while the O···I interaction is longer (3.005(2) Å). Interestingly, F···I interactions are also present between the slabs with distances of 3.22 Å which is >0.2 Å shorter than the sum of the van der Waals radii of the two atoms. Finally, vapour diffusion of water into a DMSO solution of p-DPOA and p-TFDIB afforded a 1:1 co-crystal, Figure 6C. The colourless needles crystallized in the triclinic system in space group P-1 (No. 2). Oxalamide molecules are linked to neighbouring TFDIB molecules through short N···I interactions ranging from 2.789(18) to 2.833(18) Å forming strands of XB interactions along the crystallographic bc-plane. These strands are linked into 2D sheets by N-H···O oxalamide HB interactions with distances of 2.895(2) and 2.909(2) Å along the a-axis. Analysis of Electrostatic Potential Predictions All crystal structures obtained were compared to the predicted outcome as determined by MEPS calculations. In the o-DPOA series the best donor was determined by the calculations to be the oxalamide N-H units, while the best acceptor was predicted to be the oxalamide carbonyl groups. Thus, leaving the pyridyl nitrogen acceptor to be free to form halogen bonds with the TFDIB iodo-donor. The competition between the acceptors (oxalamide carbonyl vs. pyridyl nitrogen) could be strong, as the difference in electrostatic potential is small, only 3.5 kJ/mol. However, no competition was observed between these acceptors and all crystal structures obtained for the o-DPOA series displayed the oxalamide assembly motif. The calculations proved to be an effective prediction tool, as they accurately predicted the outcome of the crystallizations. For both the m- and p-DPOA series the best acceptor was predicted to be the pyridyl nitrogen, while the best donor was remained the oxalamide N-H. The carbonyl oxygen of the oxalamide groups would then be available to form halogen bonds with the TFDIB iodine. As the MEPS predictions separate the acceptors by ~ 16 KJ/mol competition between the acceptors, purely based on electrostatics, is expected to favour the pyridyl···HN. However, the compact structure of the oxalyl amide positions the two NH donors and two carbonyl acceptors in close proximity, effectively and efficiently affording a stronger assembly unit than simple MEPS predicts. Additionally, this proximity likely precludes competition from a different acceptor, as spacial constraints would make it difficult to position a second donor leading to unsatisfied groups. In solution such proximity might also

induce stronger interactions or cooperative processes, although the solid-state equivalent is difficult to define. In these cocrystal studies, no structures were observed that primarily displayed the NH···N interaction and most structures fully satisfy all donor and acceptor interaction sites. Thus, future data science methods should likely include number and proximity of functional groups and geometric constraints in addition to MEPS calculations for more accurate predictions of co-crystal outcomes. CONCLUSIONS We have examined a series of 11 co-crystals and 1 co-crystal solvate from three dipyridyloxalamide ligands with the three tetrafluorodiiodobenzenes regioisomers, which contain activated halogen bond formers. Overall, the four-point (2 donors, 2 acceptors) oxalamide self-assembly motif proved to be a strong and consistent assembly directing unit, appearing in all twelve co-crystals with additional halogen bonding interactions affording well defined structures. This is reflected in the recurrence of the shortest crystallographic axis repeat distance of approximately 5.0 Å, a direct result of the dominant N-H···O oxalamide hydrogen-bonding motif. The short axis is always aligned with the H-O vector within the hydrogen-bonded columns. The two exceptions are mDPOAm-TFDIB, with two crystallographically unique molecules (repeat distance 10 Å) and the parent ligand pDPOA, an anomalous structure in which N-H···pyridyl interactions between dimer units disrupts the infinite hydrogen-bonded chains. Predictions of best donors and acceptors from MEPS underestimated the directing ability of the oxalamides acceptors in the m- and p-DPOA ligands. Cocrystals exhibited the typical hydrogen bonded oxalamide assembly even when MEPS calculations favored the pyridyl nitrogen acceptor by ~16 kJ/mol, suggesting that the number, proximity and geometry of donor/acceptor pairs should be considered for similar highly functional assembly motifs. Indeed, the oxalamide unit proved to be even more reliable and consistent as compared with similar dipyridylurea ligands.19 Short pyridyl to TFDIB halogen bonds gave cocrystals which displayed average N···I interactions of 81.2% of the van der Waals radii for the o-DPOA series, 80.7% for the m-DPOA series, and 81.4% for the p-DPOA series. Future work will examine the stability of the supramolecular macrocycles obtained, their propensity to uptake guest molecules, and ability to undergo SC-SC transformations. EXPERIMENTAL SECTION Materials. The oxalamide-based co-formers were previously synthesized and characterized using NMR and IR. The TFDIB compounds as well as the organic solvents were ordered from VWR and were used without further purification. Crystal Growth. Co-crystals were synthesized using a 1:1 stoichiometric ratio of TFDIB to DPOA ligands, which were ground for approximately 2 min with 3-5 drops of CHCl3. Half of this mixture was then dissolved in a solvent, and water was allowed to vapour diffuse into the solution for approximately 5 days. The other half of the mixture was heated and completely dissolved into a minimal amount of solvent and allowed to slowly evaporate for 4-6 days. Both of these methods were repeated with multiple solvents until co-crystals were obtained. Co-crystals were then submitted for single crystal xray diffraction (SC-XRD). The DPOA ligands (20 mg) were dissolved in a minimal volume of solvent, filtered, and left to


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Crystal Growth & Design slowly evaporate for 3-5 days to obtain crystals of the parent ligands. Crystals formed were submitted for SC-XRD. Electrostatic potential calculations. Electrostatic potentials were calculated using Spartan 10’ software package. The electrostatics for the TFDIB compounds were obtained from reference 19. The crystal structure files (CIFs) of the oxalamide compounds were imported and energetically optimized. The energies were then calculated using DFT B3YLP level of theory, using a 6-311++G** basis set under vacuum. Electrostatic potentials for best donor and acceptor were determined using the electrostatic potential map (0.002 e a.u. isovalue) as automatically calculated by the Spartan 10’ software. Electrostatic potentials of other donors and acceptors were obtained by manually searching the atom of interest until the value with the largest absolute value was found. SC-XRD analysis. X-ray intensity data was collected at 100(2) K using a Bruker D8 QUEST diffractometer equipped with a PHOTON-100 CMOS area detector and an Incoatec microfocus source (MoKα radiation, λ = 0.71073 Å). The raw area detector data frames were reduced and corrected for absorption effects using the Bruker APEX3, SAINT+ and SADABS programs.28,29 Final unit cell parameters were determined by least-squares refinement of reflections taken from the data set. The structure was solved with SHELXT.30 Subsequent difference Fourier calculations and full-matrix least-squares refinement against F2 were performed with SHELXL-201631 using OLEX2.32 IR analysis. FT-IR spectra was obtained using a Perkin Elmer Spectrum 100 FT-IR Spectrometer. Background spectra were recorded from 650 to 4000 cm-1 and taken in 4 scans. The crystalline sample was then added to the sample stage until transmittance was less than 85%. Each spectrum was recorded as an average of 32 scans from 650 to 4000 cm-1 to obtain spectra.

Hydrogen bond, HB; halogen bond, XB; single-crystal x-ray diffraction, SC-XRD; N,N-bis(pyridin-2-ylmethyl) oxalamide, oDPOA; N,N-bis (pyridin-3-ylmethyl)oxalamide, m-DPOA; N,Nbis(pyridin-4-ylmethyl)oxalamide, p-DPOA; 1,2,3,4-tetrafluoro5,6-diiodobenzene, o-TFDIB; 1,2,3,5-tetrafluoro-4,6diiodobenzene, m-TFDIB; 1,2,4,5-tetra fluoro-3,6-diiodobenzene, p-TFDIB; dipyridyloxalamide, DPOA; tetrafluorodiiodobenzene, TFDIB; tetrahydrofuran, THF; dimethylsulfoxide, DMSO; chloroform, CHCl3; molecular electrostatic potential surfaces, MEPS.

REFERENCES 1. 2. 3. 4. 5.

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9. 10.

ASSOCIATED CONTENT 11.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website.

12.

Supporting Information including NMR, mass spec, and crystal structure data (PDF)

13.

CIF Files of the crystal structures (CIF)

14. 15.

AUTHOR INFORMATION Corresponding Author

16.

*[email protected] 17.

Author Contributions All authors have given approval to the final version of the manuscript.

18.

Funding Sources

19.

This work was funded in part by the National Science Foundation, CHE-1608874. 20.

ACKNOWLEDGMENT We thank Professor Daniel Reger for the DPOA co-formers.

ABBREVIATIONS

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Crystal Growth & Design FOR TABLE OF CONTENTS USE ONLY Interplay between Hydrogen and Halogen bonding in Co-Crystals of Dipyridinylmethyl oxalamides and Tetrafluorodiiodobenzenes Baillie A. DeHaven, Anna L. Chen, Emily A. Shimizu, Sahan R. Salpage, Mark D. Smith, and Linda S. Shimizu* TOC Graphic:

Synopsis: A systematic series of dipyridinylmethyl oxalamide and tetrafluorodiiodobenzene regioisomers was examined through cocrystallization and calculations. Molecular electrostatics potential surfaces were used to qualitatively rank the donors and acceptors. Despite not always predicted as the best donor:acceptor pair, self-association of the oxalamide satisfies two donors and two acceptors and was consistently observed. Pyridyl N···I halogen bonding interactions further organized the co-crystals.


Interplay between Hydrogen and Halogen bonding in Co-Crystals of

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