- Email: [email protected]
Conformational aspects of dibenzo-tetroxecin: A structural, Raman spectroscopic and computational study
Journal of Molecular Structure 1145 (2017) 321e328
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Conformational aspects of dibenzo-tetroxecin: A structural, Raman spectroscopic and computational study Keith C. Gordon, C. John McAdam, Stephen C. Moratti, Georgina E. Shillito, Jim Simpson* Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 October 2016 Received in revised form 18 May 2017 Accepted 22 May 2017 Available online 23 May 2017
Crystalline dibenzo-tetroxecin (I) has been prepared from a reaction between catechol and dichloromethane and its molecular and crystal structure, together with the Raman spectrum of the material in the solid state and in solution, is reported. The molecular structure shows the molecule adopts an anti or stepped conformation. Density functional theory (DFT) optimisation and frequency calculations using the B3LYP functional with the 6-31G(d) basis set showed the presence of syn- and anti-conformers of (I), with the anti-conformer predicted to be the lower in energy by 13.6 kJ mol1. The vibrational frequencies and relative Raman intensities of the anti-conformer are well modelled by the DFT calculations. The bond lengths and angles obtained for the anti-conformer are also in good agreement with the crystal structure. The crystal structure of (I) is stabilised by intermolecular CeH/O hydrogen bonds that generate a three dimensional network. © 2017 Elsevier B.V. All rights reserved.
Keywords: Dibenzo-tetroxecin Conformation Crystal structure FT-Raman DFT
1. Introduction Dibenzo-tetroxecins are an under-reported class of compounds, generally formed by the reaction of pyrocatechol with dihalomethanes in the presence of base [1e4]. Our interest in these compounds relates to their potential for coordination, particularly the possibility of affinity for lithium cations. Graphical representation of dibenzo-tetroxecin (I) shows it to be the smallest conceivable member of the dibenzo-crown ether family [5] (Scheme 1). The larger dibenzo-18-crown-6 (II) [6], has received much theoretical interest, and has proven itself in practical applications [7,8]. The dibenzo- ‘wings’ provide scope for tailoring [5] and tethering [9,10] of the coordination pocket. In comparison, the smaller dibenzo-12-crown-4 (III) has a poor affinity for cations attributed to the large deviation from planarity of the four oxygen atoms [11]. The crystal structure shows this deviation is related to the geometry of the two ethylene arms [12]. We have recently been able to prepare crystalline samples of (I) from the reaction of catechol and dichloromethane and we report here a structural investigation of the compound, DFT calculations on minimised potential structures and Raman spectra of the anti- (or stepped)
* Corresponding author. E-mail address: [email protected] (J. Simpson). http://dx.doi.org/10.1016/j.molstruc.2017.05.103 0022-2860/© 2017 Elsevier B.V. All rights reserved.
and syn- (or boat) conformations of the compound. We also note the spatial consequences of the small methylene linkers in the 10crown-4 ring, the solid state packing arrangement, and the implications for coordination. 2. Experimental and theoretical methods 2.1. Synthesis Compound (I) was prepared adapting the methodology of Cabiddu et al. [1]. A mixture of NaOH (15 g) and catechol (20 g) in DMF (100 mL) was heated to 110 C under nitrogen. Dichloromethane (total 19 g) was added in three batches over 30 min, and stirred at 120 C for 5 h. The mixture was poured into water, extracted with a mixture of 1:1 ethyl acetate/hexane, and the organic fraction reduced under vacuum to give ca. 20 g of a dark crude gum. This was steam distilled from aqueous NaOH (100 mL, 0.1 M), topped up with water as required) and the non-volatile residue was extracted from the remaining water to give ca. 10 g of a gum. This was columned (neutral alumina, CH2Cl2:diethyl ether 9:1 to give the desired product (0.62 g). Crystals were grown from slow infusion of cyclohexane into a solution in CHCl3. 1 H NMR (CDCl3, d ppm): 7.10 (s, 4H), 5.68 (s, 2H). 13C NMR (CDCl3, d ppm): 150.1, 125.7, 121.4, 98.6. m.p. 260e262 C (lit [1] 262 C).
322
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
2.3. X-ray crystallography
Scheme 1. .
Table 1 Crystal data and structure refinement for (I). Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta ¼ 25.242 Absorption correction Max. and min. transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)] R indices (all data) Largest diff. peak and hole
C14H12O4 244.24 93(2) K 0.71073 Å Monoclinic P 21/c a ¼ 10.0788(14) Å a ¼ 90 . b ¼ 6.6704(9) Å b ¼ 101.214(6) . c ¼ 8.7588(10) Å g ¼ 90 . 577.61(13) Å3 2 1.404 Mg/m3 0.103 mm1 256 0.24 0.20 0.06 mm3 3.685e28.137 . 13 h 13, 8 k<¼8, 11 l 11 7658 1405 [R(int) ¼ 0.0388] 99.9% Multi-scan 0.7457 and 0.6858 Full-matrix least-squares on F2 1405/0/100 1.064 R1 ¼ 0.0382, wR2 ¼ 0.0873 R1 ¼ 0.0518, wR2 ¼ 0.0960 0.267 and 0.213 e.Å3
A square plate of (I) with dimensions 0.24 0.20 0.06 mm3 was used for the data collection. X-ray diffraction data were collected at 93(2) K on a Bruker ApexII CCD diffractometer using graphite moderated Mo Ka (l ¼ 0.7107 Å) radiation. Intensities were measured with the 4 and u-scans using APEX2 [13]. Data were processed with SAINT [13] and multi-scan absorption corrections, were applied using SADABS [13]. The structure was solved using SHELXT [14] and refined by full matrix least squares with SHELXL2014/7 [15] and TITAN [16]. With a good quality crystal and excellent diffraction data it was possible to refine the coordinates of all of the hydrogen atoms in the structure isotropically, with Uiso ¼ 1.2Ueq(C). All molecular plots and packing diagrams were drawn using Mercury [17]. Additional metrical data were calculated using PLATON [18] and tabular material was produced using WINGX [19]. Details of the X-ray measurements and crystal data for all of the complexes are given in Table 1. 2.4. Computational methods DFT calculations using the B3LYP functional and the 6-31G(d) basis set were performed to locate a lowest energy optimised geometry of each conformer. Vibrational frequencies from their optimised geometries were calculated utilising the same parameters. The lack of negative frequencies indicated that a minimum and not a transition state had been located for each conformer. Calculations were performed both in vacuo and in solution. A dichloromethane solvent field was generated using the integral equation formalism (IEFPCM) variant of the Polarizable Continuum Model (PCM). The predicted Raman spectra were scaled by a factor of 0.975 and were generated using GaussSum 2.2.5 [20]. Calculations were performed using Gaussian09 [21] and vibrational modes were illustrated using Molden [22]. 3. Results and discussion
2.2. Instrumentation FT-Raman spectra were measured on a powder sample and in a dichloromethane solution, averaging 500 and 5000 scans respectively, with a spectral resolution of 4 cm1. The spectra were recorded using a MultiRAM spectrometer bench (Bruker Optics, Ettlingen, Germany) equipped with a liquid nitrogen cooled D418T Germanium detector and 1064 nm Nd:YAG laser excitation source (75 mW). The system was controlled by Bruker Opus v7.5 software. A solvent subtraction was performed for the solution phase spectrum.
3.1. The molecular structure of (I) The molecular structure of (I) is shown in Fig. 1. The molecule lies about a centre of symmetry located at the centre of the tetroxecin ring and has a ‘stepped’ or antiperiplanar conformation similar to that displayed by dibenzo-12-crown ether [12]. The geometrical parameters for the structure are detailed in Table 2 together with the equivalent values computed using B3LYP/631G(d)]. Fig. 2(a) shows the lowest energy minimised structure of the molecule which compares extremely well with both the conformation and the metrical data derived from the X-ray
Fig. 1. The molecular structure of (I) with ellipsoids drawn at the 50% probability level. Labelled atoms are related to unlabelled atoms by the symmetry operation -xþ1, -yþ1, -zþ1.
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328 Table 2 Bond lengths [Å] and angles [ ] for (I) and their computed values at the [B3LYP/631G(d)] level of approximation.
O(1)eC(7) O(1)eC(1)a O(2)eC(2) O(2)eC(1) C(2)eC(3) C(2)eC(7) C(3)eC(4) C(4)eC(5) C(5)eC(6) C(6)eC(7) C(7)eO(1)eC(1)a C(2)eO(2)eC(1) O(2)eC(1)eO(1)a O(2)eC(2)eC(3) O(2)eC(2)eC(7) C(3)eC(2)eC(7) C(4)eC(3)eC(2) C(5)eC(4)eC(3) C(4)eC(5)eC(6) C(7)eC(6)eC(5) C(6)eC(7)eO(1) C(6)eC(7)eC(2) O(1)eC(7)eC(2)
(1)
(1)calc
1.3891(15) 1.4224(16) 1.3858(15) 1.4138(16) 1.3910(18) 1.3920(18) 1.390(2) 1.385(2) 1.387(2) 1.3848(19) 113.43(10) 116.61(10) 110.74(10) 122.11(12) 117.97(11) 119.77(12) 119.83(13) 120.18(13) 120.01(13) 120.08(13) 120.52(12) 120.12(12) 119.34(11)
1.382 1.410 1.382 1.410 1.396 1.402 1.395 1.395 1.395 1.396 116.8 116.8 113.4 121.2 119.0 119.7 120.4 119.9 119.9 120.4 121.1 119.7 119.0
Symmetry transformation used to generate equivalent atoms: a -xþ1,-yþ1,-zþ1.
323
structure determination. The two benzene rings are strictly parallel to one another, with their respective meanplanes separated by approximately 2.14 Å. The O1 and O2 atoms lie close to these planes with O2eC2eC3eC4 and O1eC7eC6eC5 dihedral angles 175.68(12) and 179.90(11) respectively, while the O1eC1eO2 planes subtend angles of 74.56(8) to the benzene ring planes. Ten membered ring structures comparable to that of (I) are not common with only three discrete examples in the Cambridge Database [23,24]. Both centrosymmetric and non-centrosymmetric forms of the archetypical 1,3,6,8-tetraoxacyclodecane are found, both of which adopt anti conformations in the solid state [25]. More closely related to (I) however, are the two isomeric forms of 4,5:9,10-bis(cyclohexano)1,3,6,8-tetraoxecane that crystallise in both the trans-syn-trans[26] and trans-anti-trans- forms [27]. Interestingly structures have also been reported for a series of related orthocyclophanes (IV) [28e30] (Scheme 2). These can adopt chair or boat conformations similar to those proposed for (I) but solid state structures reveal the predominance of the stepped chair conformation, an observation supported by MM2 and MM3 calculations. The extension of preference for this conformation to the solution phase was also confirmed by variable temperature NMR measurements for all but the dioxa [3,3]cyclophane derivative, (IV, Y ¼ O) where NMR evidence confirmed the boat conformation [30]. Interestingly, dibenzo-tetroxecin showed no inclination to coordinate to simple alkali metal cations. No significant shifts in the
Fig. 2. The structures of two conformers of (I) minimised using the B3LYP functional and the 6-31G(d) basis set. (a) The lower energy anti- (or stepped) conformer; (b) the higher energy syn- (or boat) conformer.
324
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
Scheme 2. . (IV) Y ¼ CH2, CD2, O, S, Se.
Table 3 Hydrogen bonds for (I) [Å and ].
1
D-H/A
d(D-H)
d(H/A)
d(D/A)
<(DHA)
C(1)eH(11)/O(1)a C(6)eH(6)/O(2)b C(1)eH(12)/O(2)c
0.980(16) 0.975(16) 1.002(16)
2.486(17) 2.478(16) 2.655(16)
3.2962(17) 3.3920(17) 3.4699(16)
139.8(12) 156.1(12) 138.6(12)
Symmetry transformations used to generate equivalent atoms a x,yþ1,z. b x,-yþ1/2,z-1/2. c -xþ1,yþ1/2,-zþ3/2.
H NMR spectra of (I) were seen with either sodium or lithium salts in either D6-DMSO or D4-DMF, nor could any co-complexes be induced to crystallise between (I) and a range of alkali metals from a variety of solvents. This is almost certainly due to the inability of all four of the oxygen atoms to coordinate in a tetradentate fashion to a single metal centre due to the stepped conformation of the 10membered ring.
Fig. 3. Hydrogen bond contacts for (I), shown as dashed lines, generating (a) R22(7) and (b) R22(6) ring motifs.
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
325
Fig. 4. Overall packing for (I). Viewed along (a) the b and (b) the c axis directions.
3.2. Geometry optimisation calculations
3.3. Crystal packing of (I)
DFT calculations provided lowest energy optimised geometries for the anti, Fig. 2(a) and syn Fig. 2(b) conformers of (I). The calculations predict that the anti-conformer is the lower in energy by 13.6 kJ mol1 in vacuo. The bond lengths and angles obtained from crystallographic data, provided in Table 2, are also consistent with those calculated for the anti-conformer. There is an average deviation of 0.041 Å between the measured and calculated bond lengths and an average deviation of 0.8 for the bond angles. As might be expected the level of agreement for the bond lengths is greater than that for the angles. This is related to the forces requisite in each dimension and has been noted in previous studies [31e33].
In the crystal structure of (I) atom O2 acts as a bifurcated acceptor forming C1eH12/O2 and C6eH6/O2 hydrogen bonds, Table 3, and enclosing an R22(7) ring [34], Fig. 3(a). Inversion dimers form from C1eH11/O1 hydrogen bonds forming R22(6) ring motifs, Fig. 3(b). These contacts combine with the inversion symmetry of the molecule itself to form a three dimensional network with molecules stacked along both the b and c crystallographic axes, Fig. 4(a) and (b). PLATON [18] reveals that the shortest centroid to centroid contact between adjacent benzene rings in this molecule is 5.3993(11) for rings related by the symmetry operation x, yþ1/ 2, zþ1/2. This separation is significantly greater than the 4.0 Å widely recognised to be a maximum distance between centroids in
326
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
Fig. 5. DFT predicted Raman spectrum of the a) the syn-conformer; b) the anti-conformer; compared with c) the experimental FT-Raman spectrum of the solid sample of (I), taken at 1064 cm1. Yellow highlighted areas correspond to key differences in frequency and band splitting between the syn- and anti-conformers while blue highlights indicate the presence or absence of certain modes found experimentally. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 6. Key vibrational modes of the anti- and syn-conformers of (I).
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
327
Fig. 7. FT-Raman spectra of (I); recorded in dichloromethane (upper) and as a solid (lower).
such systems for the contact to be significant [35,36]. Hence any contribution from offset p … p stacking interactions to the packing can be discounted for this structure. 3.4. Raman spectroscopy The DFT predicted Raman vibrational modes for the syn- and anti-conformers were compared with the experimentally measured FT-Raman spectrum and are presented in Fig. 5. Unsurprisingly, the spectra of the conformers are similar, with many concurrent vibrational modes such as the out of plane symmetric distortion of the two phenyl rings, illustrated in Fig. 6, predicted to occur at 736 cm1 in both conformers. However, the highlighted regions in Fig. 5 show the most notable spectral differences between the syn- and anti-conformers, with the spectrum of anticonformer possessing greater similarity to the experimental data. The 526 cm1 band in the experimental spectrum can be assigned to the 520 cm1 mode in the anti- spectrum and corresponds to a symmetric rotation of both phenyl rings about the CeO bonds, as illustrated in Fig. 6. However, in the syn-conformer spectrum this instead appears as a series of bands centred around 508 cm1 where the vibrations correspond to greater stretching of the phenyl rings. Similarly, the 580 cm1 experimental band is well predicted in the anti-conformer calculation, appearing as a single medium intensity band at 577 cm1, whereas in the syn-conformer calculation the band is split into two distinct signals at 577 and 586 cm1. This extra splitting is also observed at higher energy, where the single peak measured at 1593 cm1 is split into two signals at 1603 and 1612 cm1. The spectrum of the anti-conformer predicts two vibrations but they are sufficiently close in energy to appear as a single vibration at 1609 cm1. Some features present in the experimental spectrum, such as those at 634 and 1456 cm1, are predicted in the calculations for the anti-conformer at 607 cm1 and 1463 cm1 but are missing in the syn-conformer calculations. Likewise, modes predicted to occur at 1230 cm1 and 1111 cm1 in
the syn-conformer do not appear experimentally. These results show that DFT can be successfully used to model the geometries of the anti- and syn- conformers such that their predicted Raman vibrational spectra can be distinguished, with the spectrum of the anti-conformer showing greater resemblance to the experimental spectrum. Raman spectra were also taken in a dichloromethane solution, as shown in Fig. 7. The distinct similarity between the solid phase and solution spectra, indicates that (I) also likely adopts the anticonformation in solution. This is in agreement with the DFT calculations which predict that in a dichloromethane solvent field, the anti-conformer is 12.0 kJ mol1 lower in energy than its syncounterpart. 4. Conclusions The X-ray structure of dibenzo-tetroxecin (I) reveals that it adopts a deeply stepped or anti- conformation in the solid state. This conformation agrees well with the lowest energy optimised geometry predicted by DFT calculations. These calculations in turn predict Raman frequencies that are in good agreement with the observed Raman spectrum of a powdered sample of the material. It is found that (I) does not readily coordinate to alkali metal cations, a predictable observation if the anti-conformation persists in the solution phase. In this conformation the potential donor oxygen atoms will not be available to bind to the metal cation in a tetradentate fashion, as the pairs of oxygen atoms point in opposite directions with respect to the ten-membered ring. Inversion of the conformation to the syn-form could more readily promote the complexation process as was found for dicyclohexano-12-crown-4 [11] but clearly in this instance the energetics are unfavourable. Acknowledgements We thank the NZ Ministry of Business Innovation and
328
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
Employment Science Investment Fund (Grant No UOO-X1206) for support of this work and the University of Otago for the purchase of the diffractometer. Appendix A. Supplementary material CCDC 1510336 contains the supplementary crystallographic data for (I). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. References [1] M.G. Cabiddu, E. Cadoni, S. De Montis, C. Fattuoni, S. Melis, M. Usai, A re-examination of the methylenation reaction, Tetrahedron 59 (24) (2003) 4383e4387. [2] F. Dallacker, R. Semmler, 4-Alkyl-6-tert-butyl-5-hydroxy-1,3-benzodioxoles, Chem.-Ztg 109 (1) (1985) 13e15. [3] W.J. Gensler, C.M. Samour, A dimer of methylenedioxybenzene, J. Org. Chem. 18 (1953) 9e15. [4] E.D. Laskina, T.A. Devitskaya, Some reactions of methylene chloride at atmospheric pressures in high boiling solvents, II, Zh. Prikl. Khim. Peterbg. Russ. Fed. 34 (1961) 2338e2341. [5] C.J. Pedersen, Cyclic polyethers and their complexes with metal salts, J. Am. Chem. Soc. 89 (26) (1967) 7017e7036. [6] C.J. Pedersen, Macrocyclic polyethers: dibenzo-18-crown-6 polyether and dicyclohexyl-18-crown-6 polyether, Org. Synth. 52 (1972) 66e74. [7] J.D. Anderson, E.S. Paulsen, D.V. Dearden, Alkali metal binding energies of dibenzo-18-crown-6: experimental and computational results, Int. J. Mass Spectrom. 227 (1) (2003) 63e76. [8] P.D.J. Grootenhuis, P.A. Kollman, Molecular mechanics and dynamics studies of crown ether - cation interactions: free energy calculations on the cation selectivity of dibenzo-18-crown-6 and dibenzo-30-crown-10, J. Am. Chem. Soc. 111 (6) (1989) 2152e2158. [9] J.-P. Bourgeois, P. Seiler, M. Fibbioli, E. Pretsch, F. Diederich, L. Echegoyen, Cyclophane-type fullerene-dibenzo[18]crown-6 conjugates with trans-1, trans-2, and trans-3 addition patterns: regioselective templated synthesis, x-ray crystal structure, ionophoric properties, and cation-complexationdependent redox behavior, Helvetica Chim. Acta 82 (10) (1999) 1572e1595. [10] I. Suzuki, K. Obata, J.-i. Anzai, H. Ikeda, A. Ueno, Crown ether-tethered cyclodextrins: superiority of the secondary-hydroxy side modification in binding tryptophan, J. Chem. Soc. Perkin Trans. 2 (8) (2000) 1705e1710. [11] G.W. Buchanan, R.A. Kirby, J.P. Charland, C.I. Ratcliffe, 12-Crown-4 ethers: solid-state stereochemical features of dibenzo-12-crown-4, derived dicyclohexano-12-crown-4 isomers, and a lithium thiocyanate complex as determined via carbon-13 CPMAS nuclear magnetic resonance and x-ray crystallographic methods, J. Org. Chem. 56 (1) (1991) 203e212. [12] J.-P. Charland, G.W. Buchanan, R.A. Kirby, Reinvestigation of the structure of dibenzo-12-crown-4 ether, Acta Cryst. C 45 (1) (1989) 165e167. [13] APEXII, SAINT and SADABS, Bruker AXS Inc, Madison, Wisconsin, USA, 2004. [14] G. Sheldrick, SHELXT - integrated space-group and crystal-structure determination, Acta Cryst. A 71 (1) (2015) 3e8. [15] G. Sheldrick, Crystal structure refinement with SHELXL, Acta Cryst. C 71 (1) (2015) 3e8. [16] K.A. Hunter, J. Simpson, TITAN2000, University of Otago, New Zealand, 1999. [17] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood, Mercury CSD 2.0new features for the visualization and investigation of crystal structures, J. Appl. Cryst. 41 (2) (2008) 466e470. [18] A. Spek, Structure validation in chemical crystallography, Acta Cryst. D. 65 (2)
(2009) 148e155. [19] L. Farrugia, WinGX and ORTEP for windows: an update, J. Appl. Cryst. 45 (4) (2012) 849e854. [20] N.M. O'Boyle, A.L. Tenderholt, K.M. Langner, cclib: a library for packageindependent computational chemistry algorithms, J. Comput. Chem. 29 (5) (2008) 839e845. [21] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M.J. Bearpark, J. Heyd, E.N. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.P. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N.J. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, € Farkas, J.B. Foresman, J.V. Ortiz, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. J. Cioslowski, D.J. Fox, Gaussian 09, Gaussian, Inc., Wallingford, CT, USA, 2009. [22] G. Schaftenaar, J.H. Noordik, Molden: a pre- and post-processing program for molecular and electronic structures*, J. Computer-Aided Mol. Des. 14 (2) (2000) 123e134. [23] C.R. Groom, F.H. Allen, The Cambridge Structural database in retrospect and prospect, Angew. Chem. Int. Ed. 53 (3) (2014) 662e671. [24] C.R. Groom, I.J. Bruno, M.P. Lightfoot, S.C. Ward, The Cambridge structural database, Acta Cryst. B 72 (2) (2016) 171e179. [25] I.W. Bassi, R. Scordamaglia, L. Fiore, X-Ray crystal structure of 1,3,6,8tetraoxacyclodecane, J. Chem. Soc. Perkin Trans. 2 (11) (1975) 1129e1132. [26] A. Terzis, T.B. Grindley, J.B. Faught, The conformation of a ten-membered ring: the crystal and molecular structure of trans-syn-trans-4,5:9,10biscyclohexano-1,3,6,8-tetraoxecane, Can. J. Chem. 55 (14) (1977) 2692e2699. [27] A. Terzis, T.B. Grindley, Crystal structures of medium ring compounds. Part III. The crystal and molecular structure of trans-anti-trans-4,5:9,10biscyclohexano-1,3,6,8-tetraoxecane, Can. J. Chem. 57 (16) (1979) 2154e2158. [28] T. Okajima, Z.-H. Wang, Y. Fukazawa, Structures of 2,11-dithia[3.3]orthocyclophane and its diselena analogue, Tetrahedron Lett. 30 (12) (1989) 1551e1554. [29] Z.-H. Wang, S. Usui, Y. Fukazawa, Synthesis and structure of [3.3]Orthocyclophane, Bull. Chem. Soc. Jpn. 66 (4) (1993) 1239e1243. [30] T. Okajima, Z.-H. Wang, Y. Fukazawa, Structure of 2,11-Dioxa[3.3]orthocyclophane, Chem. Lett. 20 (1) (1991) 37e40. [31] T.M. Clarke, K.C. Gordon, D.L. Officer, S.B. Hall, G.E. Collis, A.K. Burrell, Theoretical and spectroscopic study of a series of styryl-substituted terthiophenes, J. Phys. Chem. A 107 (51) (2003) 11505e11516. [32] Keith C. Gordon, Anthony K. Burrell, Timothy J. Simpson, Simon E. Page, G. Kelso, Matthew I.J. Polson, A. Flood, Probing the nature of the redox products and lowest excited state of [(bpy)2Ru(m-bptz)Ru(bpy)2]4þ: a resonance Raman study, Eur. J. Inorg. Chem. 2002 (3) (2002) 554e563. [33] K.E. Riley, B.T. Op't Holt, K.M. Merz, Critical assessment of the performance of density functional methods for several atomic and molecular properties, J. Chem. Theory Comput. 3 (2) (2007) 407e433. [34] J. Bernstein, R.E. Davis, L. Shimoni, N.-L. Chang, Patterns in hydrogen bonding: functionality and graph set analysis in crystals, Angew. Chem. Int. Ed. Engl. 34 (15) (1995) 1555e1573. [35] C. Janiak, A critical account on p-p stacking in metal complexes with aromatic nitrogen-containing ligands, J. Chem. Soc. Dalton Trans. (21) (2000) 3885e3896. [36] T. Dorn, C. Janiak, K. Abu-Shandi, Hydrogen-bonding, p-stacking and Cleanion-p interactions of linear bipyridinium cations with phosphate, chloride and [CoCl4]2 anions, CrystEngComm 7 (106) (2005) 633e641.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Conformational aspects of dibenzo-tetroxecin: A structural, Raman spectroscopic and computational study Keith C. Gordon, C. John McAdam, Stephen C. Moratti, Georgina E. Shillito, Jim Simpson* Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 October 2016 Received in revised form 18 May 2017 Accepted 22 May 2017 Available online 23 May 2017
Crystalline dibenzo-tetroxecin (I) has been prepared from a reaction between catechol and dichloromethane and its molecular and crystal structure, together with the Raman spectrum of the material in the solid state and in solution, is reported. The molecular structure shows the molecule adopts an anti or stepped conformation. Density functional theory (DFT) optimisation and frequency calculations using the B3LYP functional with the 6-31G(d) basis set showed the presence of syn- and anti-conformers of (I), with the anti-conformer predicted to be the lower in energy by 13.6 kJ mol1. The vibrational frequencies and relative Raman intensities of the anti-conformer are well modelled by the DFT calculations. The bond lengths and angles obtained for the anti-conformer are also in good agreement with the crystal structure. The crystal structure of (I) is stabilised by intermolecular CeH/O hydrogen bonds that generate a three dimensional network. © 2017 Elsevier B.V. All rights reserved.
Keywords: Dibenzo-tetroxecin Conformation Crystal structure FT-Raman DFT
1. Introduction Dibenzo-tetroxecins are an under-reported class of compounds, generally formed by the reaction of pyrocatechol with dihalomethanes in the presence of base [1e4]. Our interest in these compounds relates to their potential for coordination, particularly the possibility of affinity for lithium cations. Graphical representation of dibenzo-tetroxecin (I) shows it to be the smallest conceivable member of the dibenzo-crown ether family [5] (Scheme 1). The larger dibenzo-18-crown-6 (II) [6], has received much theoretical interest, and has proven itself in practical applications [7,8]. The dibenzo- ‘wings’ provide scope for tailoring [5] and tethering [9,10] of the coordination pocket. In comparison, the smaller dibenzo-12-crown-4 (III) has a poor affinity for cations attributed to the large deviation from planarity of the four oxygen atoms [11]. The crystal structure shows this deviation is related to the geometry of the two ethylene arms [12]. We have recently been able to prepare crystalline samples of (I) from the reaction of catechol and dichloromethane and we report here a structural investigation of the compound, DFT calculations on minimised potential structures and Raman spectra of the anti- (or stepped)
* Corresponding author. E-mail address: [email protected] (J. Simpson). http://dx.doi.org/10.1016/j.molstruc.2017.05.103 0022-2860/© 2017 Elsevier B.V. All rights reserved.
and syn- (or boat) conformations of the compound. We also note the spatial consequences of the small methylene linkers in the 10crown-4 ring, the solid state packing arrangement, and the implications for coordination. 2. Experimental and theoretical methods 2.1. Synthesis Compound (I) was prepared adapting the methodology of Cabiddu et al. [1]. A mixture of NaOH (15 g) and catechol (20 g) in DMF (100 mL) was heated to 110 C under nitrogen. Dichloromethane (total 19 g) was added in three batches over 30 min, and stirred at 120 C for 5 h. The mixture was poured into water, extracted with a mixture of 1:1 ethyl acetate/hexane, and the organic fraction reduced under vacuum to give ca. 20 g of a dark crude gum. This was steam distilled from aqueous NaOH (100 mL, 0.1 M), topped up with water as required) and the non-volatile residue was extracted from the remaining water to give ca. 10 g of a gum. This was columned (neutral alumina, CH2Cl2:diethyl ether 9:1 to give the desired product (0.62 g). Crystals were grown from slow infusion of cyclohexane into a solution in CHCl3. 1 H NMR (CDCl3, d ppm): 7.10 (s, 4H), 5.68 (s, 2H). 13C NMR (CDCl3, d ppm): 150.1, 125.7, 121.4, 98.6. m.p. 260e262 C (lit [1] 262 C).
322
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
2.3. X-ray crystallography
Scheme 1. .
Table 1 Crystal data and structure refinement for (I). Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta ¼ 25.242 Absorption correction Max. and min. transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)] R indices (all data) Largest diff. peak and hole
C14H12O4 244.24 93(2) K 0.71073 Å Monoclinic P 21/c a ¼ 10.0788(14) Å a ¼ 90 . b ¼ 6.6704(9) Å b ¼ 101.214(6) . c ¼ 8.7588(10) Å g ¼ 90 . 577.61(13) Å3 2 1.404 Mg/m3 0.103 mm1 256 0.24 0.20 0.06 mm3 3.685e28.137 . 13 h 13, 8 k<¼8, 11 l 11 7658 1405 [R(int) ¼ 0.0388] 99.9% Multi-scan 0.7457 and 0.6858 Full-matrix least-squares on F2 1405/0/100 1.064 R1 ¼ 0.0382, wR2 ¼ 0.0873 R1 ¼ 0.0518, wR2 ¼ 0.0960 0.267 and 0.213 e.Å3
A square plate of (I) with dimensions 0.24 0.20 0.06 mm3 was used for the data collection. X-ray diffraction data were collected at 93(2) K on a Bruker ApexII CCD diffractometer using graphite moderated Mo Ka (l ¼ 0.7107 Å) radiation. Intensities were measured with the 4 and u-scans using APEX2 [13]. Data were processed with SAINT [13] and multi-scan absorption corrections, were applied using SADABS [13]. The structure was solved using SHELXT [14] and refined by full matrix least squares with SHELXL2014/7 [15] and TITAN [16]. With a good quality crystal and excellent diffraction data it was possible to refine the coordinates of all of the hydrogen atoms in the structure isotropically, with Uiso ¼ 1.2Ueq(C). All molecular plots and packing diagrams were drawn using Mercury [17]. Additional metrical data were calculated using PLATON [18] and tabular material was produced using WINGX [19]. Details of the X-ray measurements and crystal data for all of the complexes are given in Table 1. 2.4. Computational methods DFT calculations using the B3LYP functional and the 6-31G(d) basis set were performed to locate a lowest energy optimised geometry of each conformer. Vibrational frequencies from their optimised geometries were calculated utilising the same parameters. The lack of negative frequencies indicated that a minimum and not a transition state had been located for each conformer. Calculations were performed both in vacuo and in solution. A dichloromethane solvent field was generated using the integral equation formalism (IEFPCM) variant of the Polarizable Continuum Model (PCM). The predicted Raman spectra were scaled by a factor of 0.975 and were generated using GaussSum 2.2.5 [20]. Calculations were performed using Gaussian09 [21] and vibrational modes were illustrated using Molden [22]. 3. Results and discussion
2.2. Instrumentation FT-Raman spectra were measured on a powder sample and in a dichloromethane solution, averaging 500 and 5000 scans respectively, with a spectral resolution of 4 cm1. The spectra were recorded using a MultiRAM spectrometer bench (Bruker Optics, Ettlingen, Germany) equipped with a liquid nitrogen cooled D418T Germanium detector and 1064 nm Nd:YAG laser excitation source (75 mW). The system was controlled by Bruker Opus v7.5 software. A solvent subtraction was performed for the solution phase spectrum.
3.1. The molecular structure of (I) The molecular structure of (I) is shown in Fig. 1. The molecule lies about a centre of symmetry located at the centre of the tetroxecin ring and has a ‘stepped’ or antiperiplanar conformation similar to that displayed by dibenzo-12-crown ether [12]. The geometrical parameters for the structure are detailed in Table 2 together with the equivalent values computed using B3LYP/631G(d)]. Fig. 2(a) shows the lowest energy minimised structure of the molecule which compares extremely well with both the conformation and the metrical data derived from the X-ray
Fig. 1. The molecular structure of (I) with ellipsoids drawn at the 50% probability level. Labelled atoms are related to unlabelled atoms by the symmetry operation -xþ1, -yþ1, -zþ1.
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328 Table 2 Bond lengths [Å] and angles [ ] for (I) and their computed values at the [B3LYP/631G(d)] level of approximation.
O(1)eC(7) O(1)eC(1)a O(2)eC(2) O(2)eC(1) C(2)eC(3) C(2)eC(7) C(3)eC(4) C(4)eC(5) C(5)eC(6) C(6)eC(7) C(7)eO(1)eC(1)a C(2)eO(2)eC(1) O(2)eC(1)eO(1)a O(2)eC(2)eC(3) O(2)eC(2)eC(7) C(3)eC(2)eC(7) C(4)eC(3)eC(2) C(5)eC(4)eC(3) C(4)eC(5)eC(6) C(7)eC(6)eC(5) C(6)eC(7)eO(1) C(6)eC(7)eC(2) O(1)eC(7)eC(2)
(1)
(1)calc
1.3891(15) 1.4224(16) 1.3858(15) 1.4138(16) 1.3910(18) 1.3920(18) 1.390(2) 1.385(2) 1.387(2) 1.3848(19) 113.43(10) 116.61(10) 110.74(10) 122.11(12) 117.97(11) 119.77(12) 119.83(13) 120.18(13) 120.01(13) 120.08(13) 120.52(12) 120.12(12) 119.34(11)
1.382 1.410 1.382 1.410 1.396 1.402 1.395 1.395 1.395 1.396 116.8 116.8 113.4 121.2 119.0 119.7 120.4 119.9 119.9 120.4 121.1 119.7 119.0
Symmetry transformation used to generate equivalent atoms: a -xþ1,-yþ1,-zþ1.
323
structure determination. The two benzene rings are strictly parallel to one another, with their respective meanplanes separated by approximately 2.14 Å. The O1 and O2 atoms lie close to these planes with O2eC2eC3eC4 and O1eC7eC6eC5 dihedral angles 175.68(12) and 179.90(11) respectively, while the O1eC1eO2 planes subtend angles of 74.56(8) to the benzene ring planes. Ten membered ring structures comparable to that of (I) are not common with only three discrete examples in the Cambridge Database [23,24]. Both centrosymmetric and non-centrosymmetric forms of the archetypical 1,3,6,8-tetraoxacyclodecane are found, both of which adopt anti conformations in the solid state [25]. More closely related to (I) however, are the two isomeric forms of 4,5:9,10-bis(cyclohexano)1,3,6,8-tetraoxecane that crystallise in both the trans-syn-trans[26] and trans-anti-trans- forms [27]. Interestingly structures have also been reported for a series of related orthocyclophanes (IV) [28e30] (Scheme 2). These can adopt chair or boat conformations similar to those proposed for (I) but solid state structures reveal the predominance of the stepped chair conformation, an observation supported by MM2 and MM3 calculations. The extension of preference for this conformation to the solution phase was also confirmed by variable temperature NMR measurements for all but the dioxa [3,3]cyclophane derivative, (IV, Y ¼ O) where NMR evidence confirmed the boat conformation [30]. Interestingly, dibenzo-tetroxecin showed no inclination to coordinate to simple alkali metal cations. No significant shifts in the
Fig. 2. The structures of two conformers of (I) minimised using the B3LYP functional and the 6-31G(d) basis set. (a) The lower energy anti- (or stepped) conformer; (b) the higher energy syn- (or boat) conformer.
324
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
Scheme 2. . (IV) Y ¼ CH2, CD2, O, S, Se.
Table 3 Hydrogen bonds for (I) [Å and ].
1
D-H/A
d(D-H)
d(H/A)
d(D/A)
<(DHA)
C(1)eH(11)/O(1)a C(6)eH(6)/O(2)b C(1)eH(12)/O(2)c
0.980(16) 0.975(16) 1.002(16)
2.486(17) 2.478(16) 2.655(16)
3.2962(17) 3.3920(17) 3.4699(16)
139.8(12) 156.1(12) 138.6(12)
Symmetry transformations used to generate equivalent atoms a x,yþ1,z. b x,-yþ1/2,z-1/2. c -xþ1,yþ1/2,-zþ3/2.
H NMR spectra of (I) were seen with either sodium or lithium salts in either D6-DMSO or D4-DMF, nor could any co-complexes be induced to crystallise between (I) and a range of alkali metals from a variety of solvents. This is almost certainly due to the inability of all four of the oxygen atoms to coordinate in a tetradentate fashion to a single metal centre due to the stepped conformation of the 10membered ring.
Fig. 3. Hydrogen bond contacts for (I), shown as dashed lines, generating (a) R22(7) and (b) R22(6) ring motifs.
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
325
Fig. 4. Overall packing for (I). Viewed along (a) the b and (b) the c axis directions.
3.2. Geometry optimisation calculations
3.3. Crystal packing of (I)
DFT calculations provided lowest energy optimised geometries for the anti, Fig. 2(a) and syn Fig. 2(b) conformers of (I). The calculations predict that the anti-conformer is the lower in energy by 13.6 kJ mol1 in vacuo. The bond lengths and angles obtained from crystallographic data, provided in Table 2, are also consistent with those calculated for the anti-conformer. There is an average deviation of 0.041 Å between the measured and calculated bond lengths and an average deviation of 0.8 for the bond angles. As might be expected the level of agreement for the bond lengths is greater than that for the angles. This is related to the forces requisite in each dimension and has been noted in previous studies [31e33].
In the crystal structure of (I) atom O2 acts as a bifurcated acceptor forming C1eH12/O2 and C6eH6/O2 hydrogen bonds, Table 3, and enclosing an R22(7) ring [34], Fig. 3(a). Inversion dimers form from C1eH11/O1 hydrogen bonds forming R22(6) ring motifs, Fig. 3(b). These contacts combine with the inversion symmetry of the molecule itself to form a three dimensional network with molecules stacked along both the b and c crystallographic axes, Fig. 4(a) and (b). PLATON [18] reveals that the shortest centroid to centroid contact between adjacent benzene rings in this molecule is 5.3993(11) for rings related by the symmetry operation x, yþ1/ 2, zþ1/2. This separation is significantly greater than the 4.0 Å widely recognised to be a maximum distance between centroids in
326
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
Fig. 5. DFT predicted Raman spectrum of the a) the syn-conformer; b) the anti-conformer; compared with c) the experimental FT-Raman spectrum of the solid sample of (I), taken at 1064 cm1. Yellow highlighted areas correspond to key differences in frequency and band splitting between the syn- and anti-conformers while blue highlights indicate the presence or absence of certain modes found experimentally. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 6. Key vibrational modes of the anti- and syn-conformers of (I).
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
327
Fig. 7. FT-Raman spectra of (I); recorded in dichloromethane (upper) and as a solid (lower).
such systems for the contact to be significant [35,36]. Hence any contribution from offset p … p stacking interactions to the packing can be discounted for this structure. 3.4. Raman spectroscopy The DFT predicted Raman vibrational modes for the syn- and anti-conformers were compared with the experimentally measured FT-Raman spectrum and are presented in Fig. 5. Unsurprisingly, the spectra of the conformers are similar, with many concurrent vibrational modes such as the out of plane symmetric distortion of the two phenyl rings, illustrated in Fig. 6, predicted to occur at 736 cm1 in both conformers. However, the highlighted regions in Fig. 5 show the most notable spectral differences between the syn- and anti-conformers, with the spectrum of anticonformer possessing greater similarity to the experimental data. The 526 cm1 band in the experimental spectrum can be assigned to the 520 cm1 mode in the anti- spectrum and corresponds to a symmetric rotation of both phenyl rings about the CeO bonds, as illustrated in Fig. 6. However, in the syn-conformer spectrum this instead appears as a series of bands centred around 508 cm1 where the vibrations correspond to greater stretching of the phenyl rings. Similarly, the 580 cm1 experimental band is well predicted in the anti-conformer calculation, appearing as a single medium intensity band at 577 cm1, whereas in the syn-conformer calculation the band is split into two distinct signals at 577 and 586 cm1. This extra splitting is also observed at higher energy, where the single peak measured at 1593 cm1 is split into two signals at 1603 and 1612 cm1. The spectrum of the anti-conformer predicts two vibrations but they are sufficiently close in energy to appear as a single vibration at 1609 cm1. Some features present in the experimental spectrum, such as those at 634 and 1456 cm1, are predicted in the calculations for the anti-conformer at 607 cm1 and 1463 cm1 but are missing in the syn-conformer calculations. Likewise, modes predicted to occur at 1230 cm1 and 1111 cm1 in
the syn-conformer do not appear experimentally. These results show that DFT can be successfully used to model the geometries of the anti- and syn- conformers such that their predicted Raman vibrational spectra can be distinguished, with the spectrum of the anti-conformer showing greater resemblance to the experimental spectrum. Raman spectra were also taken in a dichloromethane solution, as shown in Fig. 7. The distinct similarity between the solid phase and solution spectra, indicates that (I) also likely adopts the anticonformation in solution. This is in agreement with the DFT calculations which predict that in a dichloromethane solvent field, the anti-conformer is 12.0 kJ mol1 lower in energy than its syncounterpart. 4. Conclusions The X-ray structure of dibenzo-tetroxecin (I) reveals that it adopts a deeply stepped or anti- conformation in the solid state. This conformation agrees well with the lowest energy optimised geometry predicted by DFT calculations. These calculations in turn predict Raman frequencies that are in good agreement with the observed Raman spectrum of a powdered sample of the material. It is found that (I) does not readily coordinate to alkali metal cations, a predictable observation if the anti-conformation persists in the solution phase. In this conformation the potential donor oxygen atoms will not be available to bind to the metal cation in a tetradentate fashion, as the pairs of oxygen atoms point in opposite directions with respect to the ten-membered ring. Inversion of the conformation to the syn-form could more readily promote the complexation process as was found for dicyclohexano-12-crown-4 [11] but clearly in this instance the energetics are unfavourable. Acknowledgements We thank the NZ Ministry of Business Innovation and
328
K.C. Gordon et al. / Journal of Molecular Structure 1145 (2017) 321e328
Employment Science Investment Fund (Grant No UOO-X1206) for support of this work and the University of Otago for the purchase of the diffractometer. Appendix A. Supplementary material CCDC 1510336 contains the supplementary crystallographic data for (I). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. References [1] M.G. Cabiddu, E. Cadoni, S. De Montis, C. Fattuoni, S. Melis, M. Usai, A re-examination of the methylenation reaction, Tetrahedron 59 (24) (2003) 4383e4387. [2] F. Dallacker, R. Semmler, 4-Alkyl-6-tert-butyl-5-hydroxy-1,3-benzodioxoles, Chem.-Ztg 109 (1) (1985) 13e15. [3] W.J. Gensler, C.M. Samour, A dimer of methylenedioxybenzene, J. Org. Chem. 18 (1953) 9e15. [4] E.D. Laskina, T.A. Devitskaya, Some reactions of methylene chloride at atmospheric pressures in high boiling solvents, II, Zh. Prikl. Khim. Peterbg. Russ. Fed. 34 (1961) 2338e2341. [5] C.J. Pedersen, Cyclic polyethers and their complexes with metal salts, J. Am. Chem. Soc. 89 (26) (1967) 7017e7036. [6] C.J. Pedersen, Macrocyclic polyethers: dibenzo-18-crown-6 polyether and dicyclohexyl-18-crown-6 polyether, Org. Synth. 52 (1972) 66e74. [7] J.D. Anderson, E.S. Paulsen, D.V. Dearden, Alkali metal binding energies of dibenzo-18-crown-6: experimental and computational results, Int. J. Mass Spectrom. 227 (1) (2003) 63e76. [8] P.D.J. Grootenhuis, P.A. Kollman, Molecular mechanics and dynamics studies of crown ether - cation interactions: free energy calculations on the cation selectivity of dibenzo-18-crown-6 and dibenzo-30-crown-10, J. Am. Chem. Soc. 111 (6) (1989) 2152e2158. [9] J.-P. Bourgeois, P. Seiler, M. Fibbioli, E. Pretsch, F. Diederich, L. Echegoyen, Cyclophane-type fullerene-dibenzo[18]crown-6 conjugates with trans-1, trans-2, and trans-3 addition patterns: regioselective templated synthesis, x-ray crystal structure, ionophoric properties, and cation-complexationdependent redox behavior, Helvetica Chim. Acta 82 (10) (1999) 1572e1595. [10] I. Suzuki, K. Obata, J.-i. Anzai, H. Ikeda, A. Ueno, Crown ether-tethered cyclodextrins: superiority of the secondary-hydroxy side modification in binding tryptophan, J. Chem. Soc. Perkin Trans. 2 (8) (2000) 1705e1710. [11] G.W. Buchanan, R.A. Kirby, J.P. Charland, C.I. Ratcliffe, 12-Crown-4 ethers: solid-state stereochemical features of dibenzo-12-crown-4, derived dicyclohexano-12-crown-4 isomers, and a lithium thiocyanate complex as determined via carbon-13 CPMAS nuclear magnetic resonance and x-ray crystallographic methods, J. Org. Chem. 56 (1) (1991) 203e212. [12] J.-P. Charland, G.W. Buchanan, R.A. Kirby, Reinvestigation of the structure of dibenzo-12-crown-4 ether, Acta Cryst. C 45 (1) (1989) 165e167. [13] APEXII, SAINT and SADABS, Bruker AXS Inc, Madison, Wisconsin, USA, 2004. [14] G. Sheldrick, SHELXT - integrated space-group and crystal-structure determination, Acta Cryst. A 71 (1) (2015) 3e8. [15] G. Sheldrick, Crystal structure refinement with SHELXL, Acta Cryst. C 71 (1) (2015) 3e8. [16] K.A. Hunter, J. Simpson, TITAN2000, University of Otago, New Zealand, 1999. [17] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood, Mercury CSD 2.0new features for the visualization and investigation of crystal structures, J. Appl. Cryst. 41 (2) (2008) 466e470. [18] A. Spek, Structure validation in chemical crystallography, Acta Cryst. D. 65 (2)
(2009) 148e155. [19] L. Farrugia, WinGX and ORTEP for windows: an update, J. Appl. Cryst. 45 (4) (2012) 849e854. [20] N.M. O'Boyle, A.L. Tenderholt, K.M. Langner, cclib: a library for packageindependent computational chemistry algorithms, J. Comput. Chem. 29 (5) (2008) 839e845. [21] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M.J. Bearpark, J. Heyd, E.N. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.P. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N.J. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, € Farkas, J.B. Foresman, J.V. Ortiz, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. J. Cioslowski, D.J. Fox, Gaussian 09, Gaussian, Inc., Wallingford, CT, USA, 2009. [22] G. Schaftenaar, J.H. Noordik, Molden: a pre- and post-processing program for molecular and electronic structures*, J. Computer-Aided Mol. Des. 14 (2) (2000) 123e134. [23] C.R. Groom, F.H. Allen, The Cambridge Structural database in retrospect and prospect, Angew. Chem. Int. Ed. 53 (3) (2014) 662e671. [24] C.R. Groom, I.J. Bruno, M.P. Lightfoot, S.C. Ward, The Cambridge structural database, Acta Cryst. B 72 (2) (2016) 171e179. [25] I.W. Bassi, R. Scordamaglia, L. Fiore, X-Ray crystal structure of 1,3,6,8tetraoxacyclodecane, J. Chem. Soc. Perkin Trans. 2 (11) (1975) 1129e1132. [26] A. Terzis, T.B. Grindley, J.B. Faught, The conformation of a ten-membered ring: the crystal and molecular structure of trans-syn-trans-4,5:9,10biscyclohexano-1,3,6,8-tetraoxecane, Can. J. Chem. 55 (14) (1977) 2692e2699. [27] A. Terzis, T.B. Grindley, Crystal structures of medium ring compounds. Part III. The crystal and molecular structure of trans-anti-trans-4,5:9,10biscyclohexano-1,3,6,8-tetraoxecane, Can. J. Chem. 57 (16) (1979) 2154e2158. [28] T. Okajima, Z.-H. Wang, Y. Fukazawa, Structures of 2,11-dithia[3.3]orthocyclophane and its diselena analogue, Tetrahedron Lett. 30 (12) (1989) 1551e1554. [29] Z.-H. Wang, S. Usui, Y. Fukazawa, Synthesis and structure of [3.3]Orthocyclophane, Bull. Chem. Soc. Jpn. 66 (4) (1993) 1239e1243. [30] T. Okajima, Z.-H. Wang, Y. Fukazawa, Structure of 2,11-Dioxa[3.3]orthocyclophane, Chem. Lett. 20 (1) (1991) 37e40. [31] T.M. Clarke, K.C. Gordon, D.L. Officer, S.B. Hall, G.E. Collis, A.K. Burrell, Theoretical and spectroscopic study of a series of styryl-substituted terthiophenes, J. Phys. Chem. A 107 (51) (2003) 11505e11516. [32] Keith C. Gordon, Anthony K. Burrell, Timothy J. Simpson, Simon E. Page, G. Kelso, Matthew I.J. Polson, A. Flood, Probing the nature of the redox products and lowest excited state of [(bpy)2Ru(m-bptz)Ru(bpy)2]4þ: a resonance Raman study, Eur. J. Inorg. Chem. 2002 (3) (2002) 554e563. [33] K.E. Riley, B.T. Op't Holt, K.M. Merz, Critical assessment of the performance of density functional methods for several atomic and molecular properties, J. Chem. Theory Comput. 3 (2) (2007) 407e433. [34] J. Bernstein, R.E. Davis, L. Shimoni, N.-L. Chang, Patterns in hydrogen bonding: functionality and graph set analysis in crystals, Angew. Chem. Int. Ed. Engl. 34 (15) (1995) 1555e1573. [35] C. Janiak, A critical account on p-p stacking in metal complexes with aromatic nitrogen-containing ligands, J. Chem. Soc. Dalton Trans. (21) (2000) 3885e3896. [36] T. Dorn, C. Janiak, K. Abu-Shandi, Hydrogen-bonding, p-stacking and Cleanion-p interactions of linear bipyridinium cations with phosphate, chloride and [CoCl4]2 anions, CrystEngComm 7 (106) (2005) 633e641.