Enclathration of Picoline Isomers by (rac)-TADDOLs: Structures

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Enclathration of picoline isomers by (rac)-TADDOLs: structures, selectivity and thermal analysis. Emma J. Tiffin, Nicole M. Sykes, Edwin Weber, Neil Ravenscroft, and Luigi R. Nassimbeni Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 23 Jan 2019 Downloaded from http://pubs.acs.org on January 23, 2019

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Crystal Growth & Design

Enclathration of picoline isomers by (rac)-TADDOLs: structures, selectivity and thermal analysis. Emma J. Tiffina, Nicole M. Sykesa, Edwin Weberb, Neil Ravenscrofta, and Luigi R. Nassimbenia*. aCentre

for Supramolecular Chemistry Research, Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa bInstitut für Organische Chemi, TU Bergakademie Freiberg, Leipziger Strasse 29, D-09596, Freiberg/Sachs, Germany

In this investigation, we studied the preferences of three TADDOL (α,α,α’,α’-tetraphenyl-l,3dioxolane-4,5-dimethanol) - derived host compounds towards the isomers of methyl-pyridines (picolines). Ten novel inclusion compounds were synthesised and their structural and thermal properties were further characterised. Binary competition experiments were performed and all three hosts discriminate between the picoline isomer guests. Interestingly, all three hosts display different preferences towards the isomers and these results were rationalised by their resulting crystal structures, packing analysis and correlated to their DSC results. DSC results showed a correlation between the thermal stability of an inclusion compound and the preference of the host towards a given isomer.

Luigi Nassimbeni Centre for Supramolecular Chemistry Research, Department of Chemistry, PD Hahn Building, University of Cape Town, Rondebosch 7701, South Africa [email protected] +27216505893 ACS Paragon Plus Environment

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Enclathration of picoline isomers by (rac)TADDOLs: structures, selectivity and thermal analysis. Emma J. Tiffina, Nicole M. Sykesa, Edwin Weberb, Neil Ravenscrofta, and Luigi R. Nassimbenia

aCentre

for Supramolecular Chemistry Research, Department of Chemistry, University of Cape

Town, Rondebosch 7701, South Africa bInstitut

für Organische Chemi, TU Bergakademie Freiberg, Leipziger Strasse 29, D-09596,

Freiberg/Sachs, Germany

Keywords: Selectivity, Picolines, TADDOLs, Structures, DSC

ACS Paragon Plus Environment

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Abstract: In this investigation, we studied the preferences of three TADDOL (α,α,α’,α’tetraphenyl-l,3-dioxolane-4,5-dimethanol) - derived host compounds towards the isomers of methyl-pyridines (picolines). Ten novel inclusion compounds were synthesised and their structural and thermal properties were further characterised. Binary competition experiments were performed and all three hosts discriminate between the picoline isomer guests. Interestingly, all three hosts display different preferences towards the isomers and these results were rationalised by their resulting crystal structures, packing analysis and correlated to their DSC results. DSC results showed a correlation between the thermal stability of an inclusion compound and the preference of the host towards a given isomer. 1. Introduction Tartaric acid and its derivatives are useful resolving agents for the resolution of racemic modifications. These include tartaric acid itself, TA, O,O’-dibenzoyl (DBTA), and its related O,O’-di-p-tolyl (DTTA) derivatives and TADDOLs, (α,α,α’,α’-tetraphenyl-l,3-dioxolane-4,5dimethanols), which can be obtained in their chiral or racemic forms. The chemistry of this TADDOL compound and its many derivatives and analogues has been reviewed.1 Their uses in asymmetric catalysis, synthesis, racemate resolution and separation of isomers in general make them versatile and important compounds.2 Host-guest chemistry is a useful technique for the separation of mixtures of compounds which possess similar physico-chemical properties such as boiling points, melting points, densities, and dipole moments, rendering standard techniques such as fractional distillation impractical. Mixtures of isomers often present a separation problem, and the example which is often cited is the case of the isomers of xylene, where normal boiling points vary from 138.4 to 144.4 °C and their separation by host-guest inclusion has attracted significant attention.3,4,5,6,7


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Other isomer mixtures where separation has been carried out in this manner include the isomers of lutidine8, phenylene diamine9, trimethoxybenzene10, and methyl and dimethyl piperidines11. The process of inclusion consists of exposing a host to a guest molecule in order to form a hostguest complex or clathrate. The latter are of three kinds: (a) The host molecule itself has a cavity which accommodates the guest. (b) The host molecules pack in such a manner that leaves cavities which may be occupied by the guests. (c) Organic framework structures formed by hydrogen-bonded molecules or metal-organic frameworks in which metals and ligands are covalently bound with guests often lying in channels/pores made by these frameworks.12,13,14 The formation of host-guest compounds (enclathration) is reversible, and this renders them industrially important. The application of clathrates includes the separation of mixtures (isomers, homologues and racemates). They can be used to stabilise sensitive compounds and form a matrix for polymerisation in the channels formed in the inclusion compound.15,16,17,18,19 Competition experiments between two guests (A and B) in the presence of a host is often carried out by dissolving the host in an equimolar mixture of the guests, allowing crystallisation to occur by slow evaporation or cooling, and analysing the composition of the crystalline product. The selectivity of the host, H, can be calculated from the selectivity coefficient KA:B = ZA/ZB * XB/XA which should be >10 for the separation to be regarded as useful (where X refers to the mol fraction of the guest in the starting solution and Z the mol fraction of guest in the ensuing crystal). However, a more comprehensive competition experiment can be carried out by exposing the host to a series of known guest compositions (XA = 0, 0.1, 0.2 ….. 1), harvesting the ensuing crystals and measuring their mole fractions ZA and ZB. A plot of ZA vs XA then describes the complete selectivity curve. The various types of selectivity curves that occur have been


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reviewed, and a three component competition of the three picolines by a cyclophane host has been mapped and the relevant host-guest structures elucidated. 20, 21 In this work, we present the crystal structures and the thermal analyses of three related TADDOL hosts with pyridine and the isomers of picoline. The line diagrams of the three hosts, H1, H2 and H3 are shown in scheme 1. The right hand panel shows the structures of the fours guests, 2picoline (2PIC), 3-picoline (3PIC), 4-picoline (4PIC) and pyridine (PYR).

Scheme 1: Structures of the TADDOL hosts, H1 (4RS,5RS)-2,2-dimethyl-α,α,α',α'tetrakis(p-tolyl)-1,3-dioxolane-4,5-dimethanol, H2 (4RS,5RS)-2,2-dimethyl-a,a,a',a'tetrakis(p-fluorophenyl)-1,3-dioxolane-4,5-dimethanol, and H3 (4RS, 5RS)-2,2-dimethylα,α,α′,α’-tetraphenyl -1,3-dioxolane-4,5-dimethanol along with the pyridine and methylpyridine (picoline) guests. The torsion angles in each structure are Ʈ1 = O1-C1-C2C3, Ʈ2 = C1-C2-C3-C4 and Ʈ3 = O4-C4-C3-C2. 2. Experimental 1.1 Materials: The host compounds, H1, H2 and H3 were synthesised by Weber and were used without further purification.22,23 The picoline and pyridine guests were obtained from SigmaAldrich and were used as received, except for when making H3•4PIC where the 4-picoline was distilled to obtain an anhydrous complex. Single crystals of the inclusion compounds were grown


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using slow evaporation, by dissolving the host compound in an excess of guest or binary guest moisture. The solutions were stirred for five minutes and left to evaporate at room temperature. 1.2 X-ray Crystallography: All crystal data was collected on a Bruker KAPPA APEX II DUO single crystal X-ray diffractometer with a graphite monochromated MoKα radiation (λ = 0.7107 Å) generated by a Bruker K780 generator (50 kV, 30 mA) at -100 °C using an Oxford cryostream 700. The data computation and cell refinement was performed using SAINT-Plus followed by XPREP which uses systematic absences in order to derive the space group. This data was verified by the refinement results after which XPREP was used to process and prepare the input data for the programs SHELXS-97 or SHELXT 2014/5 and SHELXL 2017/1.24 These programs were linked with the graphical interface X-Seed to solve and refine the crystal structures. The O-H bonds of the resulting structures were fixed using the method of Lusi and Barbour.25 Computing Packages: LAYER was used to determine the space group symmetry of the structures. PLATON was used to characterise the intermolecular interactions and geometrical relationships.26 Mercury was used to generate figures of the asymmetric unit, unit cell, packing and void spacing along with providing certain calculations such as void volumes. Hirshfeld surface plots were prepared using Crystal Explorer which allows quantification of various intermolecular interactions of the crystal structure.27,28,29 1.3 Thermal Analysis: Thermogravimetric (TG) samples were prepared by removing the crystals from their mother liquor, patting dry using filter paper and lightly ground into a powder. TGA was performed after obtaining PXRD traces of the samples in order to maximise the mass of sample for the experiment. Each sample was heated from room temperature (25 °C) to 250 °C at


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a heating rate of 10 °C∙min-1, which allowed for full guest release and host melt. The equipment used was a TA-Q500 thermogravimetric analyser and the resulting traces were analysed using TA Instruments software.30 For DSC analysis between 1 and 2 mg of powdered sample was weighed out into a standard aluminum pan which was sealed with a pierced aluminum lid. A reference pan containing no sample was prepared in the same way without the addition of sample. The sample and reference were heated from room temperature to 225 °C at a rate of 10 °C∙min-1. The equipment used was a TA DSC25 Discovery operating a nitrogen purge gas flow rate of 40 ml∙min-1 and Trios software was used to process the traces.31 1.4 NMR Analysis: Approximately 10 mg of representative samples were collected, blotted dry and crushed into powder. The sample was dissolved in 600 μl of D6-DMSO and placed into a 5 mm NMR tube for data collection. 1D 1H NMR spectra were recorded on a Bruker 400 MHz spectrometer at 30 °C and were processed using standard Bruker software (Topspin 3.5).31 The spectra were referenced relative to the residual solvent signal at 2.50 ppm and appropriate signals were integrated to determine the relative ratios of the guests. Crystals were harvested from the mother liquors of the equimolar picoline binary mixtures and analysed. The crystals were dried using blotting paper and no solvent was used to wash them to avoid possible guest exchange. Integration of the peaks of the methyl substituents of the picoline isomers was used to determine their relative proportions included in the various samples. Fig. 1 shows an overlay of the methyl region of the 1H NMR spectra of the guests (2PIC, 3PIC and 4PIC) and an example of a hostguest mixture (H1 and 2PIC/3PIC). Fig 1a has CH3-4 at 2.27 ppm for 4-picoline. Fig 1b has


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CH3-3 at 2.25 ppm for 3-picoline. Fig 1c has CH3-2 at 2.44 ppm for 2-picoline. These diagnostic peaks were used to determine the guest ratios in the resulting host-guest mixture. This is shown in Fig 1d where a relative ratio of 80/20 for 2-PIC and 3-PIC was observed. In the cases where 3-PIC and 4-PIC CH3 guest peaks overlapped with the H1 peaks, the host hydrogens were subtracted from the integral. Thus NMR analysis elucidated the relative ratio

Figure 1: 1H NMR spectra showing how the relative ratios of guest molecules were determined for the inclusion compounds.

of the guests present in host-guest mixtures.

3. Results and Discussion Structures H1 The structure of H1•PYR crystallises in P1

a)

b)

with Z=2. The crystallographic and refinement data for this and the other structures with H1 are given in Table 1. The asymmetric unit is shown

in

Fig

2a

which

displays

an

intramolecular hydrogen bond O-H···O(H) and

Figure 2: a) Asymmetric unit of H1•PYR showing the two hydrogen bonds. b) Packing of the PYR guests along channels.


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a host-guest hydrogen bond (host)O-H···N(guest). This feature is common to all the structures and locks the host molecule in a particular conformation which is described by the three torsion angles Ʈ1, Ʈ2 and Ʈ3 shown in Scheme 1. The packing, in which the PYR guests are located in channels running along [010] is shown in Fig. 2b. The metrics of the hydrogen bonds in this and the remaining structures are given in Table 4. The H1•2PIC structure crystallises in P1 with Z=2. The intramolecular and (host)O-H···N(2PIC) hydrogen bonds occur again, and the only significant difference is that the 2PIC guests are located in cavities while the 3PIC, 4PIC and PYR guests reside in channels. Table 1. Crystallographic data for the complexes formed by host 1 (H1) with pyridine and the isomeric methylpyridines. Compound code CCDC number structural formula molecular mass (g.mol-1) data collection temp (K) crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) volume (Å3) Z/Z’ D calc density (g.cm-3) Θ range ( °) Reflections collected No data I > 2σ (I) R Indices F > F0 Goodness-of-fit on F2

H1•PYR 1881570 C40H43NO4 601.75 173 Triclinic P1 10.240(2) 10.819(2) 17.846(4) 74.29(3) 88.68(3) 63.34(3) 1689.8(7) 2/1 1.183 2.240-34.584 29152 13239 0.0574 1.047

H1•2PIC 1881574 C41H45NO4 615.78 173 Triclinic P1 11.177(2) 11.199(2) 15.093(3) 75.81(3) 85.06(3) 68.82(3) 1707.9(7) 2/1 1.197 1.392-28.292 27619 8446 0.0488 1.050



The H1•3PIC and H1•4PIC structures are isomorphous with that of H1•PYR. The packing of these three structures was analysed using the program Crystal Explorer26,27,28 which produces


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fingerprint maps of the non-bonded contacts between a target molecule and the surrounding structures. The three maps are presented in Fig. 3. In these fingerprint plots, the target molecule is the guest in each case. The peaks at ① and ⑤ are associated with C···H interactions, the peaks at ③ are due to H···H contacts and peak ④ is from the intermolecular hydrogen bond (host)O-H···N (guest). An interesting feature is the small spike at ② in the H1•4PIC structure arising from the (guest methyl)C-H···O(host) interaction, which features less strongly in the other two structures.

a) H1•3PIC

b) H1•4PIC

c) H1•PYR

Figure 3: Hirshfeld Fingerprint plots of a) H1•3PIC, b) H1•4PIC and c) H1•PYR

H2 The crystal and refinement data for the structures with H2 are given in Table 2 and all guests are arranged along channels within the crystal. The H2•PYR structure crystallises in P1 with Z=2. The host H2 exhibits an intramolecular hydrogen bond O4-H4···O1 and a host···guest hydrogen bond O1-H1···N1(picoline). These hydrogen bonds occur in all the H1, H2 and H3 structures. The important difference is the F substitution at the para-positions of the host phenyl moieties. The interactions between the para-F substituents in all the structures with the H2 host were noted and recorded. These non-bonded interactions were regarded as significant when their interatomic


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distances were less than the sum of the van der Waals radii given by Bondi: H = 1.20 Å, C = 1.70 Å, O = 1.52 Å, N = 1.53 Å and F = 1.47 Å).28 H2•2PIC structure crystallises in P21/n with Z=8, Z’=2. There are thus two crystallographically independent host-guest pairs within the asymmetric unit, with O···N hydrogen bonds of 2.640 (0.002) and 2.664 (0.002) Å. The structure also displays a F-F contact of 2.91 Å, this time within the asymmetric unit between the two host molecules. There are a number of F-H and F-C contacts with have been included in the Supplementary Information (Table 1). Table 2. Crystallographic data for the complexes formed by host 2 (H2) with pyridine and the isomeric methylpyridines. Compound code CCDC number structural formula molecular mass (g.mol-1) data collection temp (K) crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) volume (Å3) Z/ Z’ D calc density (g.cm-3) Θ range (°) Reflections collected No data I > 2σ (I) R Indices F > F0 Goodness-of-fit on F2

H2•PYR 1881569 C36H31F4NO4 617.62 173 Triclinic P1 9.751(2) 9.754(2) 18.339(4) 88.32(3) 74.76(3) 63.78(3) 1502.1(7) 2/1 1.365 2.3235-31.995 32995 10448 0.0621 1.030

H2•2PIC 1881576 C37H33F4NO4 631.64 173 Monoclinic P21/n 19.316(4) 16.178(3) 22.229(4) 90 113.86(3) 90 6353.0(3) 8/2 1.321 2.365-22.820 52405 15797 0.0536 1.011

H2•3PIC 1881571 C37H33F4NO4 631.64 173 Triclinic P1 12.534(3) 17.007(3) 17.088(3) 118.73(3) 92.96(3) 98.58(3) 3126.2(14) 4/2 1.342 2.370-28.065 26927 15450 0.0550 0.997

H2•4PIC 1881575 C37H33F4NO4 631.64 173 Monoclinic P21/n 9.882(2) 11.690(2) 27.481(6) 90 96.28(3) 90 3155.4(11) 4/1 1.330 2.293-22.390 41183 7887 0.0466 1.010

The H2•3PIC structure again displays two host-guest pairs which are crystallographically independent, but the asymmetric unit consists of a host dimer which encloses one guest, and the second guest is loosely held in the crystal lattice. This is reflected in the TGA curve which yields


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a total guest loss of 14.8% (calc. 14.7), but is in two unequal steps of 12.2% and 2.6% respectively.

The H2•3PIC structure crystallises in P21/n with Z=4 and the packing is

characterised by guest channels running along [100]. H3 The crystal data for the structures with H3 are given in Table 3. Note that the structures of H3•PYR, H3•3PIC and H3•4PIC•H2O were previously elucidated by Benita Barton et al. and we report these crystal data for comparison in Table 3.34 Table 3. Crystallographic data for the complexes formed by host 3(H3) with pyridine and the isomeric methylpyridines. Compound code CCDC structural formula

H3•PYRa 1519654 C36H35NO4

H3•2PIC 1881577 C37H37NO4

H3•3PICa 1519652 C37H37NO4

H3•4PIC•H2Oa 1519653 3C31H30O4·4C6H7N ·0.877·H2O 1787.95

H3•1.5(4PIC) 1881568 C31H30O4· 1.5C6H7N 606.24

molecular mass 545.65 559.67 559.67 (g.mol-1) data collection temp 200 173 200 200 172 (K) crystal system Triclinic Monoclinic Triclinic Triclinic Triclinic space group P1 P1 P1 P1 P21/n a (Å) 11.447(1) 9.900(2) 9.363(1) 12.112(1) 9.473(1) b (Å) 13.790(1) 29.412(6) 9.782(1) 18.852(2) 9.882(1) c (Å) 20.155(1) 11.321(2) 17.011(1) 22.890(2) 18.363(2) 97.28(1) 90 92.27(1) 72.83(1) 92.21(1) α (°) 93.91(1) 112.45(3) 99.32(1) 77.44(1) 102.58(1) β (°) 111.47(1) 90 102.89(1) 82.96(1) 101.77 (1) γ (°) 3 volume (Å ) 2914.1(1) 3046.9(12) 1494.0(1) 4866.3(7) 1636.3(3) Z 4 4 2 2 2 D calc density 1.220 1.230 (g.cm-3) 2.331-28.830 2.281-28.270 Θ range (°) Reflections collected 70688 24298 No data I > 2σ (I) 7608 8162 R indices (all data) 0.0422 0.0488 Goodness-of-fit on F2 1.025 0.992 aNote that the structures of H3•PYR, H3•3PIC and H3•4PIC•H Oa were previously elucidated by Benita 2 Barton et al and are included for comparison.34


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The structure of H3 • 2PIC crystallises in P21/n with Z=4. The packing is characterised by restricted channels running along [101], with a minimum cross section of 3.6 Å x 4.2 Å. This is shown in Fig. 4. The H3•1.5(4PIC) structure crystallises in P1 with Z=2. One 4PIC guest lies in a general position and is H-bonded to the host. The second 4PIC is located on a centre of inversion at Wykoff position b. Table 4 reports the metrics of the H-bonds for all the structures. The torsion angles for all the structures have been recorded in Table 2 in the Supplementary Information. They show a remarkable consistency in that the three torsion angles; Ʈ1 (O4-C4C3-C2) averages -73.6° (range -61.9 to -80.4°). Ʈ2 (C4-C3-C2-C1) averages +89.6° (range +82 to +95.3°) and Ʈ2 (O1-C1-C2-C3) averages -64.2° (range -58.7 to -74.7°). This consistency is due to the intramolecular O4-H4···O1 hydrogen bond, a common feature in all structures.

Figure 4: Packing of H3•2PIC showing the restricted channels. The guests have been deleted and the void space calculated to show the channels (with the H atoms removed for clarity). A pore size of 1.2 Å was used to generate the channels.


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Table 4. Hydrogen bonding parameters associated with the host-guest complexes. Host H1

Guest PYR

Donor (D) Accepter (A) D···A (Å) D-H (Å)a H···A(Å) < D-H···A (°) O1 N1 2.771 (8) 0.967(5) 1.837 (8) 161 (2) O4 O1 2.710 (1) 0.979 (5) 1.742 (6) 170 (2) H1 2PIC O1 N1 2.735 (2) 0.988 (5) 1.760 (7) 169 (2) O4 O1 2.722 (2) 0.965 (5) 1.771 (7) 168 (2) H1 3PIC O1 N1 2.692 (2) 1.005 (5) 1.710 (8) 164 (2) O4 O1 2.697 (2) 0.979 (5) 1.720 (5) 176 (2) H1 4PIC O1 N1 2.717 (4) 0.981 (5) 1.748 (10) 168 (4) O4 O1 2.679 (3) 1.001 (5) 1.695(21) 166 (4) H2 PYR O1 N1 2.758 (7) 0.971 (5) 1.834 (9) 158 (2) O4 O1 2.710 (2) 0.970 (5) 1.757 (7) 167 (2) H2 2PIC O1 N1 2.664 (2) 1.028 (5) 1.651 (6) 167 (2) O4 O1 2.635 (2) 1.657 (6) 1.651 (8) 173 (2) O5 N2 2.640 (2) 1.050 (5) 1.664 (14) 153 (2) O8 O5 2.631 (2) 0.986 (5) 1.670 (9) 164 (2) H2 3PIC O1 N1 2.765 (3) 0.972 (5) 1.794 (6) 177 (3) O4 O1 2.705 (2) 0.974 (5) 1.758 (9) 163 (2) O5 N2 2.675 (3) 1.018 (5) 1.018 (5) 173 (3) O8 O5 2.666 (2) 0.977 (5) 1.714 (9) 164 (2) H2 4PIC O1 N1 2.658 (2) 1.035 (5) 1.636 (7) 168 (2) O4 O1 2.658 (2) 0.980 (5) 1.686 (6) 171 (2) H3 2PIC O1 N1 2.715 (1) 0.994 (5) 1.749 (8) 163 (2) O4 O1 2.707 (1) 0.972 (5) 1.743 (6) 170 (2) H3 4PIC O1 N1 2.759 (2) 0.976 (5) 1.798 (7) 168 (2) O4 O1 2.637 (1) 0.984 (5) 1.653 (5) 177 (2) a These donor-hydrogen distances were calculated using the method outlined by Lusi and Barbour.25

Thermal Analysis The inclusion compounds were analysed by TGA and DSC. These included the compounds reported by Barton et al which we resynthesised and subjected to thermal analysis.34 A typical profile is shown in Fig. 5 for the compound H1•2PIC in which the mass loss is in one single step (measured 15.1%, calculated 15.1%). The DSC profile displays a broad endotherm due to guest loss followed by a sharp endotherm associated with the host melt. The thermal results have been set out in Table 5 and compare the experimental versus


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calculated mass loss of guest desorption. The table also displays the Tpeak of the guest desorption endotherm as well as the Tpeak of the melting endotherm of the host compounds. It is noteworthy that the host melting points as measured by Tpeak for H1 and H2 are very close and that for H3 exhibits a definitive double melt after the H3•2PIC desorption, and a hint of a double melt for the H3•3PIC and H3•4PIC•H2O compounds. These double melts are associated with polymorphic changes of the host.

Figure 5: TGA (blue) and DSC (red) traces of H1•2PIC Table 5. Thermal data for the pyridyl complexes of H1, H2 and H3 Compound H1•2PIC H1•3PIC H1•4PIC H2•2PIC H2•3PIC H2•4PIC H3•2PIC

Mass Loss Expt % 15.1 15.2 15.1 13.5 14.9 14.9 16.5

TGA Mass Loss Calc % 15.1 15.1 15.1 14.7 14.7 14.7 16.6

Guest Endo Tpeak (°C) 155.0 142.8 138.4 117.2 140.8 148.3 108.3

Guest BP (°C) 128.5 144.0 145.0 128.5 144.0 145.0 128.5

DSC Guest Tpeak – Tbp (°C) +26.0 -1.2 -6.6 -11.3 -3.2 +3.3 -20.2

H3•3PIC H3•4PIC H1•2PIC H1•3PIC

16.4 21.4 15.1 15.2

16.6 22.7 15.1 15.1

140.9 133.2 155.0 142.8

144.0 145.0 128.5 144.0

-3.1 -11.8 +26.0 -1.2

Host Tmelt (°C) 211.8 211.9 211.7 198.5 201.0 200.5 214.8 / 217.5 217.3 217.5 211.8 211.9


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Competition Experiments These were carried out by dissolving the individual hosts in known mixtures of the picolines in pairs, such that the host:total guest ratio in the mother liquor was in great excess (≈ 2x103). The solutions were allowed to crystallise under slow evaporation and the resulting inclusion compounds analysed by 1H NMR. The mole fractions of the picoline guests in the crystals versus that in the mother liquor were plotted. The selectivity curves for each host: H1, H2 and H3, are shown for each pair of guests: 4PIC/2PIC, 4PIC/3PIC, 3PIC/2PIC. These nine plots have been deposited as Figs. 3.1-3.3 in the Supplementary Information. An example is given for H2 as Fig. 6a,b,c in which Z4PIC versus X4PIC is shown in Fig. 6a and similarly for the other guest pairs in Figs. 6b and 6c. We studied the competition plots and determined the overall preferences of each host for the three picoline guests. The overall results for the three hosts are: H1: 2PIC > 4PIC > 3PIC H2: 4PIC > 3PIC > 2PIC H3: 3PIC > 4PIC > 2PIC.

Paragon Plus Environment Figure 5: Selectivity for H2 and theACS picoline pairs.

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These competition results may be compared with those obtained from the DSC analysis shown in Table 5. The values of Tpeak – Tbp are a measure of the thermal stability of the host-guest compounds. Thus a large positive difference of Tpeak – Tbp for a given host-guest clathrate compound is a measure of its thermal stability. In a competition experiment of two guests A and B enclathrated by the host H, if A is preferred to B, then one may expect (Tpeak – Tbp)A to be greater than (Tpeak – Tbp)B.35 For H1, 2PIC > 3PIC > 4PIC, but it is noteworthy that the structure of H1•2PIC has the 2PIC guests firmly entrapped in cavities, while 3PIC and 4PIC are located in open channels. For H2, 4PIC > 3PIC > 2PIC and for H3, 3PIC > 4PIC > 2PIC. The latter two sequences are in agreement with the competition experiments. In addition we note that the solubility of H1 in 2PIC is significantly lower than in 3PIC or 4PIC (57g of 2PIC was required to dissolve 1g of H1 while 3PIC and 4PIC required only 15g and 17g respectively at room temperature while stirring). 4. Conclusion The structures of three similar TADDOL hosts: H1, H2 and H3, with pyridine and each isomer of picoline have been elucidated and further characterised by thermal analysis. Selectivity profiles for each host were obtained from competition experiments of pairs of picolines. The preferential enclathration for H1 was 2PIC > 4PIC > 3PIC while the thermal results yielded 2PIC > 3PIC > 4PIC. For H2: 4PIC > 3PIC > 2PIC and for H3: 3PIC > 4PIC >2PIC which match their thermal results.


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5. Conflict of Interest The authors declare no competing financial interest. 6. Supplementary Data CCDC reference numbers: 1881570 (H1•PYR), 1881574 (H1•2PIC), 1881573 (H1•3PIC), 1881572 (H1•4PIC), 1881569 (H2•PYR), 1881576 (H2•2PIC), 1881571(H2•3PIC), 1881575 (H2•4PIC), 1881577 (H3•2PIC) and 1881568 (H3•4PIC). These numbers contain the crystallographic data for this paper. These data can be obtained free of charge from the Cambridge

Crystallographic

Data

Centre

via

www.ccdc.cam.ac.uk/data_request/cif.

Supplementary information includes PXRD traces, full selectivity curves for all three hosts and certain structural information including torsion angles and hydrogen bonds. 7. References 1. Seebach, D.; Beck, A. K.; Heckel, A. TADDOLs, Their Derivatives, and TADDOL Analogues: Versatile Chiral Auxiliaries, Angew Chem Int Ed., 2001, 40, 92-138. DOI: https://doi.org/10.1002/1521-3773(20010105)40:13.0.CO;2-K. 2. Eißmann, D.; Katzsch, F.; Weber, E. Synthesis and solvent sorption characteristics of new types of tartaric acid, lactic acid and TADDOL derived receptor compounds, Tetrahedron., 2015, 71 (40),7695-7705, DOI: https://doi.org/10.1016/j.tet.2015.07.061 3. Campillo-Alvarado, G.; Vargas-Olvera, E. C.; Höpfl, H.; Herrera-España, A. D.; SánchezGuadarrama, O.; Morales-Rojas, H.; MacGillivray, L. R.; Rodríguez-Molina, B.; Farfán, N. SelfAssembly of Fluorinated Boronic Esters and 4,4′-Bipyridine into 2:1 N→B Adducts and Inclusion of Aromatic Guest Molecules in the Solid State: Application for the Separation of o,m,p ‑ Xylene, Cryst. Growth Des., 2018, 18 (5), 2726-2743, DOI: https://doi.org/10.1021/acs.cgd.7b01368 4. Barton, B.; Hosten, E. C.; Pohl, P. L. Discrimination between o-xylene, m-xylene, p-xylene and ethylbenzene by host compound (R,R)-(–)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4diol, Tetrahedron., 2016, 72, 8099-8105, DOI: https://doi.org/10.1016/j.tet.2016.10.062.


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5. Nath, K.; Biradha, K. Separation of Xylene Isomers through Selective Inclusion: 1D → 2D, 1D → 3D, and 2D → 3D Assembled Coordination Polymers via β-Sheets, Cryst. Growth Des., 2016, 16 (10), 5606-5611, DOI: https://doi.org/10.1021/acs.cgd.6b01311. 6. Kim, K.; Lee, S.; Yi, J.; Kim, W.; Ward, M. D. Mechanistic study on selective inclusion of xylenes into guanidinium p-toluenesulfonate host frame, Sep. Purif. Technol., 2008, 62, 517-522, DOI: https://doi.org/10.1016/j.seppur.2008.02.026 7. Davies, J. E. D.; Kemula, W.; Powell, H. M.; Smith, N. O. J. Inclusion Compounds Past, Present, and Future, Incl. Phenom. Macrocycl. Chem., 1983, 1, 3-44 DOI: https://doi.org/01677861/83/0011-0003506.30. 8. Bouanga Boudiombo, J.; Su, H.; Bourne, S. A.; Nassimbeni, L. R. Separation of Trimethoxybenzene Isomers by Bile Acids, Cryst. Growth Des., 2018, 18 (1), 424–430, DOI: https://doi.org/10.1021/acs.cgd.7b01423. 9. Caira, M. R.; Horne, A.; Nassimbeni, L R.; Okuda, K.; Toda, F. Selective inclusion of phenylenediamine isomers by 1, 1-bis(4-hydroxyphenyl)cyclohexane, J. Chem. Soc., Perkin Trans. 2, 1995, 1063-1067, DOI: https://doi.org/10.1039/P29950001063. 10. Bouanga Boudiombo, J.; Su, H.; Bourne, S. A.; Weber, E.; Nassimbeni, L. R. Separation of Lutidine Isomers by Selective Enclathration, Cryst. Growth Des., 2018, 18 (4), 2620-2627, DOI: https://doi.org/10.1021/acs.cgd.8b00251. 11. Sykes, N. M.; Su, H.; Weber, E.; Bourne, S. A.; Nassimbeni, L. R. Selective Enclathration of Methyl- and Dimethylpiperidines by Fluorenol Hosts, Cryst. Growth Des., 2017, 17 (2), 819– 826, DOI: https://doi.org/10.1021/acs.cgd.6b01661. 12. Vötle, F. In Supramolecular Chemistry, John Wiley, 1991, Chichester, Chapter 5 13. Pivovar, A. M.; Holman, K. T.; Ward, M. D. Shape-Selective Separation of Molecular Isomers with Tunable Hydrogen-Bonded Host Frameworks, Chem. Mater., 2001, 13 (9), 3018– 3031, DOI: https://doi.org/10.1021/cm0104452. 14. Maurin, G.; Serre, C.; Cooper, A.; Férey, G. The new age of MOFs and of their porousrelated solids, Chem. Soc. Rev., 2017, 46, 3104-3107, DOI: https://doi.org/10.1039/C7CS90049J. 15. Toda, F.;Tanaka, K.; Elguero, J.; Nassimbeni, L.; Niven, M. Freezing of Equilibrium of 1,2,4-Triazole by Complex Formation with 1,1-Di(2,4-dimethylphenyl)but-2-yn-1-ol, and X-Ray Crystal Structure of the Complex, Chem. Lett.,1987, 16 (12). 2317-2320, DOI: https://doi.org/10.1246/cl.1987.2317 16. Farina, M.; Di Silvestro, G.; Sozzani, P. Perhydrotriphenylene: A D3 Symmetric Host in Comprehensive Supramolecular Chemistry. Atwood, J.L.; Davies, J,E,D,; Macnicol, D.D.; Vögtle, F., Vol 6, Chapter 12, Macnicol, D.D.; Toda, F.; Bishop, R.; Pergamon, Oxford 1996 17. Sozzani, P.; Di Silvestro, G.; Gervasini, A. Inclusion polymerization in perhydrotriphenylene studied by ESR spectroscopy: Growing chain structure and conformation of methylsubstituted polybutadienes. J. Polym. Sci., Part A: Polym. Chem., 1986, 24, 815 DOI: https://doi.org/10.1002/pola.1986.080240501


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18. Ward, M.D., Photophysical Properties of Coordination Cages and their Host/Guest assemblies in Comprehensive Supramolecular Chemistry II, Atwood, J.L.; Gokel, G. W.; Barbour, L. J. Vol 6 Ch 6.14, Dalgarno, S. J., Elsevier, Amsterdam, 2017. 19. Stojakovic, J. and MacGillivray, L.R. Co-Crystals and Templates to Control Solid State [2+2] Photodimerisations in Comprehensive Supramolecular Chemistry II, Atwood, J.L.; Gokel, G. W.; Barbour, L. J. Vol 7, Ch 7.05, MacGillivray, L.R., Elsevier, Amsterdam, 2017. 20. Báthori, N. B.; Nassimbeni, L. R. In Supramolecular Chemistry: From Molecules to Nanomaterials, 2012, John Wiley, Chichester, pp 3009-3016 21. Apel, S.; Lennartz, M.; Nassimbeni, L. R.; Weber, E. Weak Hydrogen Bonding as a Basis for Concentration‐Dependent Guest Selectivity by a Cyclophane Host, Chem. Eur. J., 2002, 8, 3678 – 3686, DOI: https://doi.org/10.1002/1521-3765(20020816)8:163.0.CO;2-4. 22. Goldberg, I.; Stein, Z.; Weber, E.; Dörpinghaus, N.; Franken, S. Exploring the inclusion properties of new clathrate hosts derived from tartaric acid. X-Ray structural characterization of the free ligands and their selective interaction modes with alkylamine guests, J. Chem. Soc., Perkin Trans. 2, 1990, 953-963, DOI: https://doi.org/10.1039/P29900000953 23. Weber, E.; Dörpinghaus, N.; Wimmer, C.; Stein, Z.; Krupitaky, H.; Goldberg, I. New Crystalline Hosts Based on Tartaric Acid. Synthesis, Inclusion Properties, and X-ray Structural Characterization of Interaction Modes with Alcohol Guests, J. Org. Chem., 1992, 57, 6825-6833 24. Sheldrick G. M. SHELXL-97: Program for the refinement of crystal structure; University of Göttingen: Göttingen, Germany, 1997. 25. Lusi, M.; Barbour, L. J. Determining Hydrogen Atom Positions for Hydrogen Bonded Interactions: A Distance-Dependent Neutron-Normalized Method, Cryst. Growth Des., 2011, 11 (12), 5515–5521, DOI: https://doi.org/10.1021/cg201087s. 26. Speck, A L, PLATON, A multipurpose crystallographic tool, 1980-2000 27. McKinnon, J. J.; Spackman, M. A.; Mitchell, A. S. Novel tools for visualizing and exploring intermolecular interactions in molecular crystals, Acta Crystallogr., 2004, B60, 627-668 28. Spackman, M. A.; McKinnon, J. J. Fingerprinting intermolecular interactions in molecular crystals, Cryst. Eng. Comm., 2002, 4,378-392, DOI: http://dx.doi.org/10.1039/B203191B. 29. Spackman, M. A.; McKinnon, J. J.; Jayatilaka, D. Electrostatic potentials mapped on Hirshfeld surfaces provide direct insight into intermolecular interactions in crystals, Cryst. Eng. Comm., 2008, 10, 377-388, DOI: http://dx.doi.org/10.1039/B715227B. 30. TA Instruments, Universal Analysis version 4.5A, Waters LLC, 2000 31. TA Instruments, Trios v4.1.133073. 32. Bruker Biospin, pl 7, 2007. 33. Bondi, A. Van der Waals Volumes and Radii, J. Phys. Chem., 1964, 68(3)


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34. Barton, B.; Hosten, E. C.; Jooste, D. V. Comparative investigation of the inclusion preferences of optically pure versus racemic TADDOL hosts for pyridine and isomeric methylpyridine guests, Tetrahedron Lett., 2017, 73, 2662, DOI: https://doi.org/10.1016/j.tet.2017.03.049 35. Caira, M.R.; Nassimbeni, L.R.; Niven, M.L.; Schubert, W.D.; Weber, E.; Dörpinghaus, N. Complexation with hydroxy host compounds. Part 1. Structures and thermal analysis of a suberol-derived host and its host–guest complexes with dioxane and acetone, J. Chem. Soc., Perkin Trans. 2, 1990, 2129-2133, DOI: https://doi.org/10.1039/P29900002129


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For Table of Contents Use Only

Enclathration of picoline isomers by (rac)-TADDOLs: structures, selectivity and thermal analysis. Emma J. Tiffina, Nicole M. Sykesa, Edwin Weberb, Neil Ravenscrofta, and Luigi R. Nassimbenia

Inclusion complexes with 3 organic diol-based hosts and picoline isomers were synthesised. Binary competition experiments were conducted and selectivity curves generated. The three hosts exhibited different selectivity’s and these preferences were compared to the thermal stability of the synthesised inclusion compounds.


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Scheme 1: Structures of the TADDOL hosts, H1 (4RS,5RS)-2,2-dimethyl-α,α,α',α'-tetrakis(p-tolyl)-1,3dioxolane-4,5-dimethanol, H2 (4RS,5RS)-2,2-dimethyl-a,a,a',a'-tetrakis(p-fluorophenyl)-1,3-dioxolane-4,5dimethanol, and H3 (4RS, 5RS)-2,2-dimethyl-α,α,α′,α’-tetraphenyl -1,3-dioxolane-4,5-dimethanol along with the pyridine and methylpyridine (picoline) guests. The torsion angles in each structure are Ʈ1 = O1-C1C2-C3, Ʈ2 = C1-C2-C3-C4 and Ʈ3 = O4-C4-C3-C2. 338x114mm (300 x 300 DPI)



Figure 1: 1H NMR spectra showing how the relative ratios of guest molecules were determined for the inclusion compounds 158x127mm (96 x 96 DPI)


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Figure 2: a) Asymmetric unit of H1•PYR showing the two hydrogen bonds. b) Packing of the PYR guests along channels. 1312x559mm (96 x 96 DPI)



Figure 3: Hirshfeld Fingerprint plots of a) H1•3PIC, b) H1•4PIC and c) H1•PYR 436x144mm (96 x 96 DPI)


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Figure 4: Packing of H3•2PIC showing the restricted channels. The guests have been deleted and the void space calculated to show the channels (with the H atoms removed for clarity). A pore size of 1.2 Å was used to generate the channels. 928x556mm (96 x 96 DPI)



Figure 5: TGA (blue) and DSC (red) traces of H1•2PIC 386x224mm (72 x 72 DPI)


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Figure 6: Selectivity for H2 and the picoline pairs. 852x303mm (72 x 72 DPI)



Inclusion complexes with 3 organic diol-based hosts and picoline isomers were synthesised. Binary competition experiments were conducted and selectivity curves generated. The three hosts exhibited different selectivity’s and these preferences were compared to the thermal stability of the synthesised inclusion compounds. 352x141mm (72 x 72 DPI)


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Enclathration of Picoline Isomers by (rac)-TADDOLs: Structures

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