Structural and thermal study of solvent-free tetrabutylammonium chloride and its novel solvates

Journal Pre-proof Structural and thermal study of solvent-free tetrabutylammonium chloride and its novel solvates Wiktoria Dołębska, Tomasz Jaroń PII:

S0022-2860(20)30072-7

DOI:

https://doi.org/10.1016/j.molstruc.2020.127748

Reference:

MOLSTR 127748

To appear in:

Journal of Molecular Structure

Received Date: 13 September 2019 Revised Date:

24 December 2019

Accepted Date: 17 January 2020

Please cite this article as: W. Dołębska, T. Jaroń, Structural and thermal study of solvent-free tetrabutylammonium chloride and its novel solvates, Journal of Molecular Structure (2020), doi: https:// doi.org/10.1016/j.molstruc.2020.127748. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Wiktoria Dołębska: data curation, formal analysis, investigation, visualization, writing Tomasz Jaroń: conceptualization, supervision, software, writing – review and editing, validation

Structural and thermal study of solvent-free tetrabutylammonium chloride and its novel solvates Wiktoria Dołębska1 and Tomasz Jaroń2* 1

Faculty of Physics, University of Warsaw, Poland

2

Centre of New Technologies, University of Warsaw, Poland; *e-mail: [email protected]

Abstract Here we discuss the crystal structure of solvent-free TBACl and its solvates – TBACl∙0.5C7H8, and TBACl∙xH2O, x≈0.1, obtained from single-crystal X-ray diffraction experiments and DFT calculations. Solvent-free TBACl and the hydrate crystallize in P21/n space group, with the ions adopting deformed trigonal coordination and forming layers in the (1 0 1) plane. Similar coordination is observed in TBACl∙0.5C7H8, I2/a. The hydrate is stabilized by rather strong O–H…Cl hydrogen bond, as it is indicated by DFT optimization required for obtaining more realistic position of water molecule. According to TGA/DSC results, dry TBACl melts at 76.3 oC (onset), with a DSC peak at 79.4 oC, and vaporizes during further heating above 170 oC, decomposing into smaller fragments, as observed in the MS spectra. Keywords tetraalkylammonium salts; halides; crystal structure; Hirshfeld analysis; DFT; thermal stability Introduction Tetrabutylammonium chloride, [(n-C4H9)4N]Cl, shortly TBACl, and related compounds, have been a subject of wide-spread research as they are involved in a variety of applications. Due to relatively weak cation-anion interactions such salts constitute a useful basis for ionic liquids [1] and deep eutectic solvents [2]. Both these forms are being investigated for utilization in electrochemistry and extraction of diverse species due to their nonflammability, wide liquid range, high thermal stability, negligible vapor pressure, and high solvation capacity [3,4]. The low lattice energies renders the salts of large cations useful in ion metathesis performed in non-aqueous solutions [5–9]. Another interesting feature of TBACl is the ability to form ionic (semi)clathrate hydrates with a very high content of water, e.g. (C4H9)4NCl∙32.2H2O [10]. In such structures, related to gas hydrates, the molecules of water and the chloride anions are arranged in a framework bound via the network of hydrogen bonds, whereas the quaternary ammonium cations place themselves in the cavities of this water-anion host lattice. However, not all of the cavities in such systems are occupied. In the TBACl clathrate hydrates there exist dodecahedron cages, which do not have enough space to accept tetrabutylammonium cations inside. In these vacant places smaller molecules can be absorbed. Therefore such clathrates have been explored as hydrogen-storage materials [11], gas separation systems [12] and medium for CO2 absorption [13,14], remaining stable up to room temperature under ca. 4.5 MPa. As the range of melting temperatures of such semiclathrate hydrates ranks within the desirable range for air cooling and such systems show significant enthalpy of fusion, they have also been tested for potential use as thermal energy storage in air-conditioning systems [15]. Despite such widespread interest in physico-chemistry of TBACl, its crystal structure has not been reported, contrary to the (C4H9)4NCl∙xH2O clathrates mentioned above, or other tetrabutylammonium salts like bromide and iodide [16–18]. To the best of our knowledge, there is also no information reported on thermal decomposition of this salt. In this work, we present and 1

discuss the crystal structure of TBACl and its novel toluene and water solvates, TBACl∙0.5C7H8, and TBACl∙xH2O, x≈0.1, respectively. We make a comparison with the structures of related salts: tetrabutylammonium bromide (TBABr), tetrabutylammonium iodide (TBAI), tetrabutylammonium borohydride (TBABH4) and tetrabutylammonium tetrafluoroborate (TBABF4). We also examine the thermal decomposition of TBACl. As theoretical calculations are often used to supply additional data related to the crystal structures [19], we have compared the obtained crystal structures with those optimized computationally using density functional theory (DFT) utilizing ultrasoft, Vanderbilt-type pseudopotentials for approximation of the core electrons [20] and generalized gradient approximation (GGA) of Perdew Burke and Ernzerhof functional for solids (PBEsol) [21]. Methods If not stated otherwise, all the manipulations were performed under inert conditions (Schlenk-type vacuum lines and MBraun Labmaster DP glovebox with <0.5 ppm O2 and <0.5 ppm H2O). The solvents were dried according to standard procedures to avoid formation of hydrates. Tetrabutylammonium chloride (>97%, Sigma-Aldrich) has been dried under vacuum (<10-3 mbar) at room temperature. Crystallization from a few solvents and their mixtures (CH2Cl2, C6H14, C6H5CH3) resulted either in crystals of insufficient quality or in a solvate, however, a crystal suitable for diffraction measurements has been finally selected directly from the dried sample. The obtained crystals were measured n Agilent Supernova X-ray diffractometer with CuKα microsource. Data collection and reduction were performed with CrysAlisPro software [22], while SHELXT [23] and Olex2 [24,25] programs were applied for structure solution and refinement, respectively. Powder diffraction pattern of the sample placed inside a sealed quartz capillary of 1 mm diameter has been measured using Bruker D8 Discover diffractometer (parallel beam; the CuKα1 and CuKα2 radiation intensity ratio of ca. 2:1). CCDC 1923277–1923280 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre. The Hirshfeld plots were calculated and analyzed using CrystalExplorer software [26]. Thermal characterization included thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC) and mass spectrometry (MS) of the gaseous products. We used Netzsch STA409 PG Lux apparatus. Ca. 5 mg of TBACl has been placed in the previously annealed Al2O3 crucible with a lid and measured under argon flow of 80 ml∙min−1 at 5 oC min-1 heating rate. The DFT calculations have been performed in the CASTEP code included in Biovia Materials Studio package [27]. We have used ultrasoft pseudopotentials for approximation of the core electrons and generalized gradient approximation (GGA) of Perdew Burke and Ernzerhof functional for solids (PBEsol) [21]. A plane-wave basis set with 800 eV cutoff energy was applied, while the Brillouin zone has been sampled with the k-point separation of 0.07 Å-1. The SCF convergence criterion has been set to 5∙10-7 eV/atom. The structures were optimized using BFGS algorithm with a fixed basis quality for the calculations with variable unit cells. During the structure optimization, the following convergence criteria have been used: the maximum ionic displacement tolerance of 0.0005 Å, the maximum ionic force of 0.005 eV Å-1, the maximum energy change of 5∙10-6 eV/atom, the maximum stress component of 0.01 GPa. The lattice-energy minimizations lead to static structures and as such refer to T = 0 K.

Results and discussion

2

The structural results concerning the crystals of TBACl, and its solvates, [(n-C4H9)4N]Cl∙0.1H2O and [(nC4H9)4N]Cl∙0.5(C7H8), are summarized in Table 1. These ionic compounds crystallize in the centrosymmetric space groups of monoclinic system – TBACl and the hydrate in a primitive P21/n group, while the toluene solvate in a centered I2/a group (Fig. 1).

Fig. 1. The unit cells of TBACl (left) and TBACl∙0.5C7H8 (right). The disorder of alkyl groups as well as hydrogen atoms have been removed for image clarity. C—black, N—blue, Cl —green.

Table 1. The selected parameters of the crystal structures presented in this work. Compound T [K] Space group a [Å] b [Å] c [Å] o β[ ] 3 V [Å ] Z 3 Vm [Å ] -3 dcalc [g cm ] Final R Final wR2 d(N–C)min [Å] d(N–C)max [Å] a(C–N–C)min [o] a(C–N–C)max [o] d(C–C)min [Å] d(C–C)max [Å] a(N–C–C)min [o] a(N–C–C)max [o] a(C–C–C)min [o] a(C–C–C)max [o] d(N…Cl)min [Å] d(N…N)min [Å] d(Cl…Cl)min [Å]

TBACl 298 P21/n 9.0336(2) 14.2595(2) 15.0550(3) 103.237(2) 1887.78(6) 4 471.95 0.978 0.0417 0.1360 1.5156(17) 1.5248(16) 106.57(10) 111.15(11) 1.486(3) 1.524(2) 114.97(11) 115.91(11) 110.10(16) 114.0(2) 4.2653(11) 6.338(2) 6.5759(8)

100 P21/n 8.8122(1) 14.0295(2) 14.8170(2) 102.025(1) 1791.64(4) 4 447.91 1.030 0.0298 0.0799 1.5170(12) 1.5258(11) 106.57(7) 111.25(7) 1.5171(18) 1.5335(13) 114.92(8) 115.41(8) 109.48(8) 113.48(9) 4.2436(9) 6.1651(16) 6.5941(5)

3

TBACl∙xH2O, x≈0.1 100 P21/n 8.8512(1) 14.0409(2) 14.8099(3) 102.072(2) 1799.85(5) 4 449.96 1.031 0.0367 0.1028 1.5176(13) 1.5252(13) 106.60(8) 111.23(8) 1.5189(16) 1.5322(16) 114.95(9) 115.46(9) 109.98(10) 113.68(10) 4.2523(11) 6.1717(18) 6.6041(5)

TBACl∙0.5C7H8 100 I2/a

14.66160(10) 14.61540(10) 19.6885(2) 101.3090(10) 4137.04(6) 8 517.13 1.040 0.0871 0.2071 1.515(5) 1.526(5) 105.7(3) 111.6(3) 1.395(5) 1.542(5) 115.2(3) 116.5(3) 109.7(3) 123.5(14) 4.172(4) 6.396(7) 6.1089(18)

Due to a branched nature of the lightweight tetrabutylammonium cation, the moiety packing in these compounds remains rather sparse. Their densities are therefore close to 1 g cm-3, comparable to similar tetrabutylammonium salts, Tab. 2. The centers of the cation-anion sublattices of these ionic species form loosely connected, slightly folded surfaces, Fig. 2. In the unsolvated salt these layers propagate in the (1 0 1) plane and have zigzag-like shape (with ion centers alternatingly above and below the plane), while in the toluene solvate, they are parallel to the (0 0 1) plane and adopt a wave-like shape (Fig. 2).

Fig. 2. The cation-anion packing in TBACl (left) and TBACl∙0.5C7H8 (right). In both compounds the ionic layers are visible which are rather loosely bound to each other. To preserve image clarity, only the ion centers were shown, as represented by N (blue) and Cl (green) atoms. In the TBACl crystal each TBA+ cation is surrounded by three Cl- anions remaining within the layer, which are separated by similar distances (4.2436(9) – 4.7667(8) Å at 100 K) (Fig. 3a and S1 in the Supplementary Information). The fourth closest anion is contained in the adjacent layer in the cationanion sublattice, and therefore the corresponding N…Cl distance is significantly larger (7.5377(9) Å). This is also manifested in the Hirshfeld surface of the cation where the three areas indicating distances shorter than the sum of van der Waals radii are observed in the directions pointing towards the Cl- anions [28,29], cf. Fig. S3. As the layers of cations and anions are better separated in the structure of TBACl∙0.5C7H8, every cation is surrounded here by the three anions, forming a deformed trigonal planar geometry Fig. 3b, and S2. The coordination remains rather close to planar, and the sum of the Cl…N…Cl angles is ca. 338ᴼ. The fourth closest Cl- anion is firmly separated, with the N…Cl distance of 8.307(4) Å, ca. 0.8 Å further than in the case of solvent-free TBACl. The toluene molecules are rather weakly bound in the structure, which manifests in easy desolvation, even under moderate vacuum, which hampers further investigation of this solvate. However, its FTIR spectrum clearly reveals the bands characteristic for toluene in addition to those related to TBA+ moiety, Fig. S13. The bands originating from the latter remain virtually unaffected by the solvent.

4

Fig. 3. The neighborhood of cations in (a) TBACl salt and (b) TBACl∙0.5C7H8 solvate, with the bond distances shown. To preserve image clarity, hydrogen atoms are omitted. C – black, N – blue, Cl – green. The comparison of structural parameters of unsolvated TBACl with the reported crystal structures of related salts is presented in Table 2. TBACl crystallizes in significantly smaller unit cell (Z = 4, vs. Z = 8– 24) with lower molar volume than the other TBA salts, as it could be expected on a basis of ionic radii of the anions. As the Cl- ions are smaller than Br-, I-, BH4- and BF4- discussed here, the cation-anion, anion-anion and cation-cation distances in TBACl are also shorter, e.g. d(N…An)min=4.2436(9) Å for An = Cl- while for the larger anions it remains within the range of 4.404(18)–5.0477(14) Å. Interestingly, TBAF – containing a smaller anion than the Cl- investigated here, due to a high charge density on F- is extremely hygroscopic. Therefore, preparation of this salt in a solvent-free form requires special methodology, and, according to our knowledge, its crystal structure remains unknown [30]. The coordination of cations in the related compounds has been shown in Fig. 4. TBABr and TBAI are isostructural, with the four anions forming twisted squares around the nitrogen atom. The neighborhoods of the cation in TBABH4 and TBABF4 are also similar to each other – in both these compounds there are two types of coordination, one remaining not far from tetrahedral, while the other – from trigonal. The latter one resembles that observed in TBACl and its toluene solvate reported here. The lower number of Cl- anions surrounding TBA+ cation in TBACl as compared to its analogues containing the heavier halides (Br, I) is in accordance with their relative cationic radii. Interestingly, in the structures of TBABr and TBAI also the cation-anion layers parallel to the (0 0 1) plane can be distinguished, while in TBABH4 and in TBABF4 the cations and the anions form threedimensional networks. The N–C–C and C–C–C angles, as well as the C–C distances adopt very similar values in TBACl, TBABr, TBAI and TBABF4 which indicates that the anion choice has little impact in these cases on the butyl chains, remaining rather relaxed. Contrastingly, in the structure of TBABH4 the discrepancy from the idealized quasi-tetrahedral geometry is evident. However, in this case the atomic positions might be biased by significant disorder present in the crystal structure.

5

Fig. 4. Cation environments of the related TBA salts: a) TBAI, b) TBABr, c) TBABH4, d) TBABF4. Only the ion centers atoms are shown to preserve image clarity; N – blue, I – purple, Br – brown, B – orange.

Table 2. Comparison of structure parameters of selected TBA-salts. Compound Reference T [K] Space group a [Å] b [Å] c [Å] o β[ ] 3 V [Å ] Z 3 Vm [Å ] d(N–C)min [Å] d(N–C)max [Å] o a(C–N–C)min [ ] o a(C–N–C)max [ ] d(C–C)min [Å] d(C–C)max [Å] o a(N–C–C)min [ ] o a(N–C–C)max [ ] o a(C–C–C)min [ ] o a(C–C–C)max [ ] d(N…An)min [Å] d(N…N)min [Å] d(An…An)min [Å]

TBACl This work 100 P21/n 8.8122(1) 14.0295(2) 14.8170(2) 102.025(1) 1791.64(4) 4 447.91 1.5170(12) 1.5258(11) 106.57(7) 111.25(7) 1.5171(18) 1.5335(13) 114.92(8) 115.41(8) 109.48(8) 113.48(9) 4.2436(9) 6.1651(16) 6.5941(5)

TBABr [17] 150 C2/c 13.9773(9) 13.8623(9) 20.0450(14) 110.383 (10) 3640.7(4) 8 455.09 1.519(3) 1.526(3) 108.39(18) 111.35(18) 1.513(3) 1.526(3) 114.89(16) 115.45(17) 109.86(18) 111.6(2) 4.913(3) 6.887(3) 6.9720(8)

TBAI [18] 100 C2/c 14.2806(6) 14.1864(6) 19.5951(7) 111.149(3) 3702.4(3) 8 463.05 1.517(2) 1.522(2) 108.64(12) 111.05(12) 1.517(2) 1.523(2) 114.87(13) 115.41 (13) 109.82(14) 111.34(15) 5.0477(14) 7.123(3) 7.2140(4)

6

TBABH4 [31] 100 P2/c 26.003(3) 13.0324(9) 25.392(3) 118.583(13) 7556.16 16 472.26 1.483(14) 1.546(12) 91.8(9) 119.2(13) 1.46(3) 1.551(13) 111.7(7) 117.2(10) 102.1(11) 121.4(12) 4.404(18) 6.548(13) 6.55(3)

TBABF4 [32] 100 P2/c 33.6961(14) 13.1536(5) 26.8730(10) 100.437(2) 11713.7(8) 24 488.07 1.519(2) 1.526(3) 108.4(2) 111.3(2) 1.513(4) 1.527(3) 114.9(2) 115.5(2) 109.9(2) 111.6(2) 4.717(7) 6.439(7) 7.588(6)

Fig. 5. The Hirshfeld fingerprint plots for the tetrabutylammonium cation in the TBACl structure. (a) T = 100 K, (b) T = 298 K, (c) DFT optimization. * - the spike belonging to the branch of H…Cl contacts. Cf. refs. [28,29] for the corresponding definitions. The powder X-ray diffraction pattern measured at room temperature agrees very well with that generated from the structure of TBACl from the single crystal diffraction data obtained at 298 K, Fig. S4. The crystal structure obtained at 100 K and 298 K are virtually identical, therefore the roomtemperature structure differs mostly by ca. 5.4% volume expansion and larger temperature factors. The atomic positions remain nearly unchanged, Fig. S5. Such minor differences manifest in very similar Hirshfeld surface fingerprint plots, Fig. 5 (a) and (b), and Fig. S6. The theoretically-optimized TBACl structure is expanded by ca. 7.5%, which is within the values expected for the GGA formalism used for calculations with no dispersion corrections [19,33], Tab. S1. The corresponding atoms are shifted only slightly, Fig. S7, and the fingerprint plots show very similar features, Fig. 5. However, the latter reveals a few percent longer minimal H…H contacts and larger possible voids (by ca. 0.2 Å as measured by the shift in the longest di and de distances). TBACl is highly hygroscopic, therefore its crystals easily become partially hydrated during contact with air. We have measured the crystal of such hydrate, TBACl∙xH2O, with x refined to approach 0.1. This hydrate has significantly lower water content than those reported previously, e.g. (C4H9)4NCl∙32.2H2O [10], Fig. S8. The observed Cl…O distance of 3.159(18) Å implies that a hydrogen bond should form between the corresponding moieties, as this is shorter than the mean H–O–H…Cl distance of 3.190(3) Å typical to hydrogen bonds with chloride [34]. However, due to low occupancy of H2O molecule, the positions of its hydrogen atoms are significantly biased. Therefore the d(O– H…Cl)min distance of 2.3(3) Å is only obtained with low accuracy, Tab. S2. This problem with determination of the positions of hydrogen atoms in H2O moiety is demonstrated in the Hirshfeld fingerprint plot of tetrabutylammonium cation as very short external distances (de), marked with an asterisk in Fig. 6(a), and a clear red spot on the Hirshfeld surface, indicating the contact closer than the sum of the van der Waals radii, Fig. S11 (left). Therefore we have optimized this structure computationally, using a stoichiometric structure, i.e. TBACl∙H2O. In this case the expansion of the unit cell (6.8%) is less pronounced than for the solvent-free compound, Tab. S2, while the most significant changes of the atomic positions are related to those of H2O molecule, Fig. S9. Consequently, the short O–H…H–C distances are not present in the TBACl∙H2O structure optimized by DFT, as it is demonstrated by the corresponding Hirshfeld surfaces and fingerprint plots, Fig. 6, Fig. S10–S11. The calculated d(O–H…Cl)min of 2.040 Å although shorter than the mean distance reported 7

for hydrated chloride anions (2.237(3) Å), however similar or even distances were also observed, especially for the O–H…Cl angles close to 180o, which is the case here [34,35].

Fig. 6. The Hirshfeld fingerprint plots for the tetrabutylammonium cation in the TBACl∙0.1H2O structure. (a) T = 100 K, (b) DFT optimization (full occupancy of H2O). * – the branch related to the short O–H…H–C distances.

We have examined thermal properties of TBACl using a combined TGA/DSC/MS apparatus, Fig. 7. The sample melts at 76.3 oC (onset), with a DSC peak at 79.4 oC. Melting at this temperature range has been confirmed by visual analysis of the sample heated in a glass vial. Interestingly, the DSC peak attributed to melting is preceded by a smaller endothermic shoulder at 75.5 oC, which could originate from an overlapping polymorphic transition. A few values of melting temperature of TBACl have been reported according to the U.S. NIST Ionic Liquids Database, ILThermo (v2.0) [36,37], ranging from 41 oC [38] to 92 oC [39]. Our present results are closest to the values reported by Kabachnik et al. (76 oC) [40] or by Gu et al. (75 oC) [41], while the range reported by Shim et al. falls at 8

higher temperatures (83–86 oC) [42]. This could be caused by variable sample purity or different experimental methods and conditions used to determine the temperature of fusion. The integrated heat of fusion of ca. 14.5 kJ mol-1 is about 25% lower than 20.5 kJ mol-1 reported by Coker, et al. [38]; the dynamic conditions in our measurements can be one of the sources of such discrepancy. The TBACl sample vaporizes above ca. 170 oC, with the corresponding DSC peak at 200.5 oC. The MS spectra of the gases evolved, Fig. S12, reveals only the smaller fragments like those of M/Z = 27, 29, 43, 56, while the larger ones, i.e. M/Z > 70 are not visible, despite they appear as strong signals in the previously published MS spectrum [43]. Such difference may indicate that vaporization of TBACl occurs parallel with its thermal decomposition in the conditions applied in our experiments. The overal mass loss of >98% well corresponds to the sample nominal purity.

Fig. 7. TGA/DSC measurements of TBACl. The artifact at the DSC curve has been marked with an asterisk (*).

Conclusion At 100 K and at 298 K solvent-free TBACl crystallizes in P21/n space group, with the ions adopting deformed trigonal coordination and forming layers in the (1 0 1) plane. This structure differs from the crystal structures of other tetrabutylammonium halides in terms of Z and coordination of ions. The structure of TBACl∙0.1H2O is closely related to the anhydrous form, and is stabilized by hydrogen bond of rather significant strength. This finding is supported by the periodic DFT geometry optimization. Similar deformed trigonal coordination is observed in TBACl∙0.5C7H8, I2/a, which also forms layers of ions propagating in (0 0 1) plane. According to TGA/DSC results, dry TBACl melts at 76.3 oC (onset), with a DSC peak at 79.4 oC, and vaporizes during further heating above 170 oC, decomposing into smaller fragments, as observed in the MS spectra.

Acknowledgements The financial support has been provided by Foundation for Polish Science – HOMING Programme, agreement no. POIR.04.04.00-00-221F/16-00. The authors thank the Biopolymers Laboratory, Faculty of Physics, University of Warsaw, for the access to Agilent Supernova X-ray single-crystal diffractometer, co-financed by the European Union within the ERDF Project POIG.02.01.00-14122/09. Competing Interests

9

The authors have no conflict of interests to declare.

References [1]

E. Duan, Y. Guan, B. Guo, M. Zhang, D. Yang, K. Yang, Effects of water and ethanol on the electrical conductivity of caprolactam tetrabutyl ammonium halide ionic liquids, J. Mol. Liq. 178 (2013) 1–4. doi:10.1016/j.molliq.2012.10.026.

[2]

D.J.G.P. Van Osch, L.F. Zubeir, A. Van Den Bruinhorst, M.A.A. Rocha, M.C. Kroon, Hydrophobic deep eutectic solvents as water-immiscible extractants, Green Chem. 17 (2015) 4518–4521. doi:10.1039/c5gc01451d.

[3]

H. Jadhav, E. Taarning, C.M. Pedersen, M. Bols, Conversion of d-glucose into 5hydroxymethylfurfural (HMF) using zeolite in [Bmim]Cl or tetrabutylammonium chloride (TBAC)/CrCl 2, Tetrahedron Lett. 53 (2012) 983–985. doi:10.1016/j.tetlet.2011.12.059.

[4]

E. Duan, H. Sun, Y. Wang, L. Shi, Absorption of No and No2 in caprolactam tetrabutyl ammonium halide ionic liquids, J. Air Waste Manag. Assoc. 61 (2011) 1393–1397. doi:10.1080/10473289.2011.623635.

[5]

T. Jaroń, P.A. Orłowski, W. Wegner, K.J. Fijałkowski, P.J. Leszczyński, W. Grochala, Hydrogen Storage Materials: Room-Temperature Wet-Chemistry Approach toward Mixed-Metal Borohydrides, Angew. Chemie Int. Ed. 54 (2015) 1236–1239. doi:10.1002/anie.201408456.

[6]

T. Jaroń, W. Wegner, K.J. Fijałkowski, P.J. Leszczyński, W. Grochala, Facile formation of thermodynamically unstable novel borohydride materials by a wet chemistry route, Chem. - A Eur. J. 21 (2015) 5689–5692. doi:10.1002/chem.201404968.

[7]

A. Starobrat, M.J. Tyszkiewicz, W. Wegner, D. Pancerz, P.A. Orłowski, P.J. Leszczyński, K.J. Fijalkowski, T. Jaroń, W. Grochala, Salts of highly fluorinated weakly coordinating anions as versatile precursors towards hydrogen storage materials, Dalt. Trans. 44 (2015) 19469–19477. doi:10.1039/c5dt02005k.

[8]

T.E. Gilewski, P.J. Leszczyński, A. Budzianowski, Z. Mazej, A. Grzelak, T. Jaroń, W. Grochala, Ag2S2O8 meets AgSO4: the second example of metal-ligand redox isomerism among inorganic systems, Dalt. Trans. 45 (2016) 18202–18207. doi:10.1039/c6dt03283d.

[9]

R. Owarzany, K.J. Fijalkowski, T. Jaroń, P.J. Leszczyński, Ł. Dobrzycki, M.K. Cyrański, W. Grochala, Complete Series of Alkali-Metal M(BH3NH2BH2NH2BH3) Hydrogen-Storage Salts Accessed via Metathesis in Organic Solvents, Inorg. Chem. 55 (2016) 37–45. doi:10.1021/acs.inorgchem.5b01688.

[10]

T. Karpova, A.Y. Manakov, V.Y. Komarov, G. Villevald, L. Aladko, T. Rodionova, V.Y. Komarov, G. Villevald, L. Aladko, T. Karpova, A.Y. Manakov, Calorimetric and Structural Studies of Tetrabutylammonium Chloride Ionic Clathrate Hydrates, J. Phys. Chem. B. 114 (2010) 11838– 11846. doi:10.1021/jp103939q.

[11]

J. Deschamps, D. Dalmazzone, Hydrogen storage in semiclathrate hydrates of tetrabutyl ammonium chloride and tetrabutyl phosphonium bromide, J. Chem. Eng. Data. 55 (2010) 3395–3399. doi:10.1021/je100146b.

[12]

T. Makino, T. Yamamoto, K. Nagata, H. Sakamoto, S. Hashimoto, T. Sugahara, K. Ohgaki, Thermodynamic stabilities of tetra-n-butyl ammonium chloride + H 2 , N 2 , CH 4 , CO 2 , or C 2 H 6 semiclathrate hydrate systems, J. Chem. Eng. Data. 55 (2010) 839–841. doi:10.1021/je9004883. 10

[13]

S. Li, S. Fan, J. Wang, X. Lang, Y. Wang, Semiclathrate hydrate phase equilibria for CO2 in the presence of tetra-n-butyl ammonium halide (bromide, chloride, or fluoride), J. Chem. Eng. Data. 55 (2010) 3212–3215. doi:10.1021/je100059h.

[14]

N. Mayoufi, D. Dalmazzone, W. Fürst, A. Delahaye, L. Fournaison, CO2 enclathration in hydrates of peralkyl-(Ammonium/Phosphonium) salts: Stability conditions and dissociation enthalpies, J. Chem. Eng. Data. 55 (2010) 1271–1275. doi:10.1021/je9006212.

[15]

K. Sato, H. Tokutomi, R. Ohmura, Phase equilibrium of ionic semiclathrate hydrates formed with tetrabutylammonium bromide and tetrabutylammonium chloride, Fluid Phase Equilib. 337 (2013) 115–118. doi:10.1016/j.fluid.2012.09.016.

[16]

Q. Wang, A. Habenschuss, A. Xenopoulos, B. Wunderlich, Mesophases of Alkylammonium Salts. VI. The Crystal Structures of Tetra-n-butylammonium Bromide and Iodide, Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A. Mol. Cryst. Liq. Cryst. 264 (1995) 115–129. doi:10.1080/10587259508037306.

[17]

M.R.J. Elsegood, Tetran-butylammonium bromide: A redetermination at 150 K addressing the merohedral twinning, Acta Crystallogr. Sect. E Struct. Reports Online. 67 (2011). doi:10.1107/S1600536811032612.

[18]

W. Prukała, B. Marciniec, M. Kubicki, Tetra-n-butyl-ammonium iodide: A space-group revision, Acta Crystallogr. Sect. E Struct. Reports Online. 63 (2007). doi:10.1107/S1600536807008446.

[19]

J. van de Streek, M.A. Neumann, Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations, Acta Crystallogr. Sect. B Struct. Sci. 66 (2010) 544–558. doi:10.1107/S0108768110031873.

[20]

D. Vanderbilt, Soft self-consistent pseudopotentials in a generalized eigenvalue formalism, Phys. Rev. B. 41 (1990) 7892–7895. doi:10.1103/PhysRevB.41.7892.

[21]

J.P. Perdew, A. Ruzsinszky, G.I. Csonka, O.A. Vydrov, G.E. Scuseria, L.A. Constantin, X. Zhou, K. Burke, Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces, Phys. Rev. Lett. 100 (2008) 136406. doi:10.1103/PhysRevLett.100.136406.

[22]

Agilent (2014). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England, (2014).

[23]

G.M. Sheldrick, SHELXT - Integrated space-group and crystal-structure determination, Acta Crystallogr. Sect. A. 71 (2015) 3–8. doi:10.1107/S2053273314026370.

[24]

O. V Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, OLEX2: a complete structure solution, refinement and analysis program, J. Appl. Crystallogr. 42 (2009) 339–341. doi:10.1107/S0021889808042726.

[25]

L.J. Bourhis, O. V Dolomanov, R.J. Gildea, J.A.K. Howard, H. Puschmann, The anatomy of a comprehensive constrained, restrained refinement program for the modern computing environment - Olex2 dissected, Acta Crystallogr. Sect. A. 71 (2015) 59–75. doi:10.1107/S2053273314022207.

[26]

M.A.S. M. J. Turner, J. J. McKinnon, S. K. Wolff, D. J. Grimwood, P. R. Spackman, D. Jayatilaka, CrystalExplorer17, (2017). http://hirshfeldsurface.net/.

[27]

S.J. Clark, M.D. Segall, C.J. Pickard, P.J. Hasnip, M.I.J.J. Probert, K. Refson, M.C. Payne, First principles methods using CASTEP, Zeitschrift Fur Krist. 220 (2005) 567–570. doi:10.1524/zkri.220.5.567.65075.

[28]

M.A. Spackman, D. Jayatilaka, Hirshfeld surface analysis, CrystEngComm. 11 (2009) 19–32. doi:10.1039/B818330A. 11

[29]

J.J. McKinnon, M.A. Spackman, A.S. Mitchell, Novel tools for visualizing and exploring intermolecular interactions in molecular crystals, Acta Crystallogr. Sect. B Struct. Sci. 60 (2004) 627–668. doi:10.1107/S0108768104020300.

[30]

H. Sun, S.G. DiMagno, Anhydrous Tetrabutylammonium Fluoride, J. Am. Chem. Soc. 127 (2005) 2050–2051. doi:10.1021/ja0440497.

[31]

T. Jaroń, W. Wegner, M.K. Cyrański, Dobrzycki, W. Grochala, Tetrabutylammonium cation in a homoleptic environment of borohydride ligands: [(n-Bu)4N][BH4] and [(n-Bu)4N][Y(BH4)4], J. Solid State Chem. 191 (2012) 279–282. doi:10.1016/j.jssc.2012.03.040.

[32]

W. Beichel, U.P. Preiss, B. Benkmil, G. Steinfeld, P. Eiden, A. Kraft, I. Krossing, Temperature dependent crystal structure analyses and ion volume determinations of organic salts, Zeitschrift Fur Anorg. Und Allg. Chemie. 639 (2013) 2153–2161. doi:10.1002/zaac.201300246.

[33]

L. Chen, V.S. Bryantsev, A density functional theory based approach for predicting melting points of ionic liquids, Phys. Chem. Chem. Phys. 19 (2017) 4114–4124. doi:10.1039/C6CP08403F.

[34]

T. Steiner, Hydrogen-Bond Distances to Halide Ions in Organic and Organometallic Crystal Structures: Up-to-date Database Study, Acta Crystallogr. Sect. B Struct. Sci. 54 (1998) 456– 463. doi:10.1107/S0108768197014821.

[35]

T. Steiner, The Hydrogen Bond in the Solid State, Angew. Chemie Int. Ed. 41 (2002) 48–76. doi:10.1002/1521-3773(20020104)41:1<48::AID-ANIE48>3.0.CO;2-U.

[36]

A. Kazakov, J. Magee, R.D. Chirico, E. Paulechka, V. Diky, C.D. Muzny, K. Kroenlein, M. Frenkel, NIST standard reference database 147: NIST ionic liquids database-(ILThermo), (2013).

[37]

Q. Dong, C.D. Muzny, A. Kazakov, V. Diky, J.W. Magee, J.A. Widegren, R.D. Chirico, K.N. Marsh, M. Frenkel, ILThermo: A free-access web database for thermodynamic properties of ionic liquids, J. Chem. Eng. Data. 52 (2007) 1151–1159. doi:10.1021/je700171f.

[38]

T.G. Coker, J. Ambrose, G.J. Janz, Fusion Properties of Some Ionic Quaternary Ammonium Compounds, J. Am. Chem. Soc. 92 (1970) 5293–5297. doi:10.1021/ja00721a001.

[39]

H. Elias, H. Strecker, Kinetik des homogenen Isotopenaustausches zwischen Isopropylchlorid und Chlorid-Ionen in Dimethylformamid, Chem. Ber. 99 (1966) 1019–1025. doi:10.1002/cber.19660990343.

[40]

I.Y. Kabachnik, M I, Zakharov L S, Kudryavtsev, No Title, Izv. Akad. Nauk SSSR, Ser. Khim. 12 (1989) 2789–2792.

[41]

Y.-L. Gu, F. Shi, Y.-Q. Deng, Room temperature ionic liquid as leaching reagent for separation of the solid mixture of taurine and sodium sulfate, Acta Chim. Sin. 62 (2004) 532–536.

[42]

J.J. Shim, D. Kim, S.R. Choon, Carboxylation of styrene oxide catalyzed by quaternary onium salts under solvent-free conditions, Bull. Korean Chem. Soc. 27 (2006) 744–746. doi:10.5012/bkcs.2006.27.5.744.

[43]

P.J. Linstrom, W.G. Mallard, The NIST Chemistry WebBook: A chemical data resource on the Internet, J. Chem. Eng. Data. 46 (2001) 1059–1063. doi:10.1021/je000236i.

12

• • • • •

[(n-C4H9)4N]Cl, and its novel toluene and water solvates have been investigated [(n-C4H9)4N]Cl and its solvates form puckered layers of trigonally coordinated ions The hydrate is stabilized by rather strong O–H…Cl hydrogen bond DFT optimization is required for more realistic position of water molecule [(n-C4H9)4N]Cl melts at 76.3 oC, vaporizes above 170 oC, forming smaller fragments

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: