Structure and stoichiometry of resorcinarene solvates as host–guest complexes – NMR, X-ray and thermoanalytical studies

Accepted Manuscript Title: Structure and Stoichiometry of Resorcinarene Solvates as Host-Guest Complexes - NMR, X-ray and thermoanalytical studies Author: Przemyslaw Ziaja Agnieszka Krogul Tomasz S. Pawłowski Grzegorz Litwinienko PII: DOI: Reference:

S0040-6031(15)00424-4 http://dx.doi.org/doi:10.1016/j.tca.2015.10.018 TCA 77377

To appear in:

Thermochimica Acta

Received date: Revised date: Accepted date:

4-9-2015 27-10-2015 28-10-2015

Please cite this article as: P. Ziaja, A. Krogul, T.S. Pawlowski, G. Litwinienko, Structure and Stoichiometry of Resorcinarene Solvates as Host-Guest Complexes - NMR, X-ray and thermoanalytical studies, Thermochimica Acta (2015), http://dx.doi.org/10.1016/j.tca.2015.10.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

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Structure and Stoichiometry of Resorcinarene Solvates as Host-Guest Complexes - NMR, X-ray and thermoanalytical studies.

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Przemyslaw Ziaja, Agnieszka Krogul, Tomasz S. Pawłowski, and Grzegorz Litwinienko*

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University of Warsaw, Faculty of Chemistry, Pasteura 1, 02-093 Warsaw, Poland.

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Fax: +48228222380

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*Corresponding author, E-mail: [email protected]

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ABSTRACT

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Controlled release of a guest from inclusion host-guest complexes is an important aspect of design and synthesis of advanced materials for sensing, purification, chromatography, and storage of wide variety of molecules. In this work, host-guest complexes of Cmethylcalix[4]resorcinarene (RES1) and C-undecylcalix[4]resorcinarene (RES2) with four solvents were examined by NMR, X-ray and thermoanalytical techniques in order to compare their stoichiometries, solvent effects, the role of water during solubilisation / complexation process. The phenomena of poor solubility of some resorcinarenes in dry solvents versus their good solubility in wet solvents is explained on example of resorcinarene / dioxane / water complex. An asymmetric unit contains RES1 macrocycle in C2v symmetry which adopts a boat-like conformation and RES1 is a rccc isomer with four axial methyl groups. Water is a molecular linker that organizes the whole network in RES1 2dioxane 3H2O solvate.

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Keywords: calixarenes, resorcinarenes, solvates, supramolecular complexes, inclusion compounds, thermal analysis

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1. Introduction

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Cyclic polyphenols (calixarenes) are convenient templates employed in design of functional materials for selective and reversible sorption of gases and vapors [1-2]. This feature is also expected from different class of calixarenes called calix[n]resorcinarenes or, simply, resorcinarenes (see Chart 1) [3-10]. Calix[n]resorcinarenes can adopt crown, boat, chair, saddle or diamond conformations (see Chart 1) depending on the methodology of crystallization and on the presence of template molecules [11]. A change of conformation from crown into boat is facilitated by the ability of a host to be both a HB donor and acceptor [12,13]. For C-methylcalix[n]resorcinarene (RES1) a presence of strong HB acceptor competes with intramolecular hydrogen bond and promotes the interconversion between conformations of RES1 to form boat [14-16], chair [17-19], scoop [19], or T-shape [20] structures of the macrocycle.

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OH R

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Chart 1. A) General structure of the investigated calix[4]resorcinarenes, R=CH3 for C-methylcalix[4]resorcinarene, abbreviated RES1 in the text, and R=C11H23 for C-undecylcalix[4]resorcinarene, abbreviated RES2 in the text. Conformations of RES1: chair (B), crown ( bowl) (C), boat (D), saddle (E), and diamond (F), from ref. [3c].

A relatively large number of studies on inclusion compounds of resorcinarenes and amine derivatives contrasts with rather limited number of works on structure and stability of resorcinarenes containing small molecules like water and simple organic solvents. In RES1 4DMSO 3H2O complex RES1 adopts a boat conformation [21]. Hydrothermal method of crystallization at 150°C applied by Ma et al. [22] allowed to obtain RES1 nH2O (n=1-3) complexes with scoop, chair and boat conformations, depending on the crystallization 2 Page 2 of 16

conditions. Complexes of RES1 with alcohols are described in few works. According to Momose and Bosch [23] simple crystallization of RES1 from methanol had been failed. However, slow evaporation of CH2Cl2:CH3OH (9:1) solution of RES1 resulted in the formation of RES1 2CH3OH complex including diamond conformer [24]. Strong intermolecular hydrogen bonds between neighbouring RES1 macrocycles and relatively strong π-π interactions between the opposite resorcinol rings was described for RES1 3CH3OH 5H2O solvates [25] and resorcinarene complexes with alcohols and organic cations [26]. The results of X-ray analysis of RES1 crystallized from ethanol have not been reported, but crystallographic data for C-ethylcalix[4]resorcinarene crystallized from ethanol indicated a host : guest stoichiometry1:3, presenting the resorcinarene in a slightly “pinched” crown conformation [12].

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RES1 adopts crown conformation if methanol is replaced with other small molecules. In wet acetonitrile two solvates with crown conformation are formed: RES1 2.5CH3CN 3H2O, where extensive hydrogen bonds link RES1 with water molecules [27] and RES1 3CH3CN 2H2O, where water forms intermolecular hydrogen bonds with resorcinarene macrocycle and with acetonitrile [28]. Structurally similar but having longer C-alkyl chains C-undecylcalix[4]resorcinarene (RES2) adopts a crown conformation in majority of known inclusion complexes as it was observed for RES2 4C2H5OH [29], RES2 4dioxane [30], RES2 5DMA [19] (DMA denotes dimethylacetamide). C-nonylcalix[4]resorcinarene crystallized from methanol and ethanol forms solvates where host macrocyle adopts crown conformation [31]. A crown conformation of macrocycle is formed in spontaneously selfassembled hexameric capsules of RES1 [23,32-35]. Formation of hexamers of RES1 (as well as RES2) requires the use of wet solvents [33-36]. Water, being a HB donor and acceptor, plays at least three important functions in host-guest assembles: water can be a part of a building block of the hexameric capsules [34,36], it can be also incorporated in a multicomponent framework as a molecular linker (resulting in an increase of cavity size) [16,18,22,37]. Third function of water is described as solubility improving agent when a host compound is practically insoluble in anhydrous solvent [41,37].

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Thermodynamics and kinetics of formation / decomposition of these host-guest complexes have capital meaning for their future applications and thermoanalytical methods like thermogravimetry (TG) and differential scanning calorimetry (DSC) are very helpful in these studies [38-42]. In some reports a qualitative estimation of stability of inclusion complexes has been proposed [38,39,43] as a simple comparison of decomposition temperature (from TG curve) of host-guest complex with normal boiling point of a guest. DSC in non-isothermal mode has also been successfully applied for the investigation of thermal stability of host-guest complexes of calixarenes [41,43-45], and as a validation technique in theoretical studies [46], TG was successfully applied for studies on stoichiometry of C-undecylcalix[4]resorcinarene clathrates with secondary and tertiary amines [40,41]. Herein we analysed several complexes of RES1 and RES2 (see Chart 1) with organic solvents (methanol, ethanol, acetonitrile and dioxane) by thermoanalytical methods, i.e., thermogravimetry (TG) and differential scanning calorimetry (DSC) and the results were confronted with NMR and X-ray data.

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2. Results and discussion 3 Page 3 of 16

Our experimental results are divided into three main sections: structure of solvates, NMR analysis, and thermal analysis.

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2.1. Structure of solvates

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Taking into account all the data described in the Introduction it can be stated that RES1 forms boat conformation with strong HB acceptors (Cl- anions, amines, and DMSO), scoop conformation with water, and crown conformation with acetonitrile. Resorcinarenes with longer C-alkyl chains (like RES2) usually adopt crown conformation even in complexes with strong HB acceptors like dioxane or dimethylacetamide. According to our knowledge, the structure of RES1 solvate with dioxane/water has not been reported yet and such RES1/dioxane/water system is interesting in spite of flexibility of RES1 conformation depending on the presence of HB donor and acceptor. Several attempts to crystallize RES1 from dioxane/water caused formation of solid complexes that were not reproducible. After careful recrystallization from wet dioxane with traces of acetic acid (to shift back the ionization equilibria of resorcinarene in the presence of water, see Supplementary material), we obtained the crystals suitable for X-ray analysis. An asymmetric unit contains RES1 macrocycle in C2v symmetry which adopts a boat-like conformation (Figure 1), thus, the network of four intramolecular hydrogen bonds typical for a crown conformer with C4v symmetry is broken. Because of spatial orientation of methyl groups RES1 is a rccc isomer with four axial methyl groups. There are two molecules of dioxane (solvent marked as “s” in Figure 1) and three molecules of water (symbols “w” in Fig. 1) in the asymmetric unit, hence the stoichiometry of the solid state solvate RES1/dioxane/water is 1:2:3.

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Figure 1. An asymmetric unit of the host-guest complex formed during crystallization of RES1 from wet dioxane (ORTEP drawing where thermal ellipsoids are presented at 50% probability level). Hydrogen atoms are omitted. Dioxane molecule above RES1’s cavity and one of the three water molecules are disordered. Crystallographic date for the host-guest complex formed during crystallization of RES1 from wet dioxane is deposited the Cambridge Crystallographic Data Centre (CCDC 838124) and can be obtained free of charge from www.ccdc.cam.ac.uk/data_request/cif.

The packing of RES1 2dioxane 3H2O presented in Figure 2 shows head-to-tail arrangement of macrocycles along the Z (c) axis (Figure 2C) and there are linear ribbons formed along the Y (b) axis, as indicates the XZ projection (Figure 2B). Such structural organization is greatly facilitated by intermolecular hydrogen bonds and this specific arrangement with ribbons was 4 Page 4 of 16

also reported for RES1 complex crystallized from methanol/dichloromethane mixture in the presence of 1,2-bis(5’-pyrimidyl)ethene [16]. Molecules of water and dioxane form solvent channels that intersperse the linear ribbons, see Figure 2B.

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Hydrogen bonds between RES1 macrocycles and water molecules are also observed but, surprisingly, not between RES1 and dioxane. The lack of interactions between dioxane and RES1 and the presence of strong dioxane-water and water-RES1 interactions leads to intriguing conclusion that water is a molecular linker that organizes the whole network of RES1 2dioxane 3H2O solvate. This kind of indirect interactions (RES1 with dioxane via water molecules) can explain good solubility of RES1 in wet dioxane against its low solubility in anhydrous dioxane. Weak C-H···π and H···π interactions are also observed, however, on this level of analysis and without further theoretical calculations they can be interpreted as caused by packing. RES1 interactions with dioxane and acetonitrile are too weak and addition of small amount of water is substantial during solubilization of RES1 in these two HB accepting solvents.

Figure 2. Packing of the solid state host-guest complex formed between RES1 and wet dioxane. Left Panel: YZ projection. Middle Panel: XZ projection. Right Panel XY projection. Full size pictures are placed in Supporting Information.

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2.2. NMR analysis of solvated and desolvated resorcinarenes.

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H NMR analysis of RES1 and RES2 (see Experimental Section and Supplementary material) is in excellent agreement with the literature data reported for RES1 [47] and for RES2 [27]. To be sure that observed TG and DSC effects are due to guest release and not by decomposition / dehydration of a host molecule, we did additional 1H NMR analyses of solvates heated from ambient temperature to 220°C in the calorimetric cell under the same conditions as in typical DSC measurements. We also analyzed the solvates kept isothermally at 220°C in vacuum during 3 hours. Analysis of NMR spectra of solvates before heating and after heating, regardless the method (static or dynamic) gave perfect agreement of the signals from cyclic polyphenols and the only difference was the signals from solvents that disappeared after the heating (see Supplementary material including examples of NMR spectra of the samples). Therefore, the results of our experiments gave a proof that the change 5 Page 5 of 16

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Additional and quite unexpected results of these NMR experiments is that even prolonged heating was not enough to completely remove the water included in RES1 and RES2 macrocycle (see Supplementary material) – this observation confirmed similar reports given by Kuzmicz et al. [28]. The persistent presence of water in resorcinarenes was described by Aoyama et al. [48] who observed that solid RES2 tetrahydrate heated at 80 ºC in vacuum decomposed gradually giving RES2 3H2O (signal at 3.40 ppm from OH in H2O), dihydrate RES2 2H2O (3.75 ppm) and monohydrate RES2 H2O (4.95 ppm) [48]. The same authors reported the spontaneous formation of RES2 4H2O when solid RES2 was exposed to air. In our studies RES1 and RES2 contain water molecules included during synthesis (in methanol with water coming from aqueous HCl) and before preparation of solvates we dried RES1 and RES2, but even prolonged isothermal drying in reduced pressure at 50°C (and during 3 hours at 220°C), was not sufficient to remove this residual water, see Experimental section and Supplementary material. Moreover, samples of RES2 exposed to air absorb water to give RES2 : water 1:4 (calculated from NMR spectra), fully confirming the observations described by Aoyama et al [48].

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of mass during the heating up to 220°C is caused by decomposition of host-guest complex and that the basic chemical structure of resorcinarenes survives at temperatures below 220°C without damage.

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2.3. Thermal properties of the solvates

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TG curves recorded at extended temperature range 0 - 500°C for eight complexes are presented in Figure 3 for RES1 (left panel) and RES2 (right panel). For all solvates (with one exception, RES1/dioxane) the first release of solvent occurs below 100°C. The common feature of the complexes formed by both resorcinarenes is that their decomposition can be distinguished into two stages, below and above 250°C. In order to prove that desolvation is the only process causing a weight loss recorded during the first step of decomposition, we did 1 H NMR measurements to compare chemical structures of RES1 and RES2 before and after heating in that range of temperatures.

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On the basis of NMR experiments (see previous section) we can state that weight loss observed at 50-220°C for RES1 and RES2 complexes is connected with thermal decomposition of solvates and is neither connected with decomposition of resorcinarene skeleton nor the elimination of hydroxyl groups. Samples heated above 250°C indicated irreversible decomposition with charred residue, thus, temperature 280-300°C can be considered as boundary between solvent loss and macrocycle decomposition (above 300°C).

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Figure 4. TG and DSC curves of thermal decomposition of C-methylcalix[4]resorcinarene (RES1) complexes with: A) methanol, B) ethanol, C) wet acetonitrile, D) wet dioxane. Heating rate was 5 K/min.

Figure 4 presents TG and DSC curves from 0 to 250°C recorded for RES1. Complex RES1/methanol (Figure 4A) is the only sample with single endothermal peak of decomposition while for other complexes at least two peaks of decomposition are observed. For the RES1solvates with ethanol and with wet acetonitrile the first thermal decomposition below 100°C leads to an intermediate that decomposes at temperature higher than 180°C. Thermal behavior of RES1/wet dioxane complex (showed on Fig. 4D) is somewhat different the sample is stable until 116°C and then decomposes in three steps with two last steps partially overlapping. The stoichiometries of the solvates calculated on the basis of TG curves are presented in Table 1, together with temperatures of each step of decomposition. Stoichiometry of RES1/methanol (1:6.3) is not consistent with the literature value 1:2 obtained by X-ray analysis. It seems that our RES1/methanol complex has different conformation (and, thus, stoichiometry), whereas the literature value 1:2 was reported for 7 Page 7 of 16

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specifically isolated diamond conformer [24]. Another possible explanation of different stoichiometry is a presence of small amount of acetic acid that increases the HB donor ability of the host. The RES1/EtOH stoichiometry 1:3.6 is slightly different if compared with 1:3 reported for EtOH solvates of C-ethylcalix[4]resorcinarene and C-nonylcalix[4]resorcinarene. The second peak at DSC curve starting at 163°C is accompanied by a 5.1% decrease of sample weight. NMR analysis (discussed in previous section) indicates no decomposition of resorcinarene skeleton or elimination of functional groups.

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Thus, we assigned the 5.1% weight loss at 163-192°C as water release. The presence of water was detected by NMR (see previous section). The stoichiometries of complexes obtained for RES1 in wet solvents, acetonitrile and dioxane, are (RES1 / solvent / water) 1:2.7:2.1 and 1:1.8:2.7, respectively, and the TG results are in reasonable (±10%) agreement with the results of X-ray analysis (see Table 1). As described in experimental section, during crystallization of RES1 from dioxane/water system we experienced some difficulties because the samples were not reproducible (see Supplementary material to compare the examples of various DSC curves). The reproducible (by X-ray, TG and DSC) results, i.e. well defined RES1•2dioxane•3H2O samples were obtained when recrystallization procedure was modified

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In parentheses: (Boiling point of organic solvent in ˚C/ permittivity),from CRC Handbook of Chemistry and Physics, 89th ed. 2008-2009; Lide, D. R. Ed. CRC Press: Boca Raton, FL, 2008. b Temperature range of decomposition determined from DSC curves. c Stoichiometric ratio expressed as calix[4]resorcinarene : solvent ratio. For solvent containing water the ratio is expressed as resorcinarene: solvent : H2O. d Results of X-ray analysis for solvate formed between diamond RES1 and methanol (orthorhombic, Pnma) by evaporation from CH2Cl2:MeOH (9:1), Ref. 24. Other conditions of crystallization gave complexes of different stoichiometries resulted in RES1·3MeOH·5H2O (orthorhombic, Pnam) as reported by Åhman et al. Ref. 25. For Cpropylcalix[4]resorcinarene (triclinic, P1) and C-nonylresorcinarene (triclinic, P1) crystallized from MeOH the stoichiometry of the complexes were 1:5 – Ref. 23, 31. For C-pentylcalix[4]resorcinarene (monoclinic, C2/c) the asymmetric units included half of C-pentylcalix[4]resorcinarene and two methanol molecules – Ref. 23. e The results of X-ray analysis have not been reported according to our knowledge. However, for two other resorcinarenes: C-ethylcalix[4]resorcinarene (triclinic, P1) and C- nonylcalix[4]resorcinarene (triclinic, P1) crystallized from ethanol the stoichiometry equals 1:3 (Ref. 12,29). f General structure of complex is presented as RES1 3CH3CN 2H2O (monoclinic, P21/n) – Ref. 28. g There is also reported crystal structure RES1 2.5CH3CN 3H2O (triclinic, P1) – Ref. 27. h The result of our X-ray study: RES1 2C4H8O2 3H2O (orthorhombic, Pnma).

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by addition of minute amount of diluted aqueous acetic acid to wet dioxane. X-ray analysis did not indicate the presence of acetic acid in crystal structure and we suppose that the role of traces of acid was to shift back the acid/base equilibria. Since resorcinarenes are polyphenols, this kind of equilibrium might affect the crystallization process in a medium being a mixture of polar (water) and non-polar (dioxane) solvent. Spectrophotometric titration of 10-4 M RES1 solution in water/methanol (1:1) allowed us to determine pKa parameters 8.82 ± 0.03, 10.8 ± 0.4, and 11.7 ± 0.4 for first, second and third deprotonation step, respectively. Taking into account the RES1 acidity and anomalous microscopic properties of dioxane/water mixtures in cybotactic region [49], we suppose that neutral (non-deprotonated) RES1 is more prone to self-organize around the molecule and addition of traces of acetic acid can be helpful in formation of well defined self-assembled structures of RES1•2dioxane•3H2O complex. This intriguing hypothesis needs to be further studied for other cyclic polyphenols. 102 100

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Thermal behavior of the RES2 complexes (Figure 5) differs from RES1 solvates. In general, all RES2 complexes start to decompose at temperature similar to temperature of RES1 decomposition but (with exception for RES2/acetonitrile for which one decomposition step is observed, see Figure 5C) the second endothermic effect is much closer to first decomposition - all processes occur at temperatures below 150°C, that is, the complexes of RES2 with methanol, ethanol and dioxane are less thermally stable than RES1 complexes are. All thermal effects are connected with weight loss, therefore, we assume that detected endotherms are caused by decomposition of RES2 solvates. Complex RES2/methanol shows at least three endothermic effects on DSC curve (Figure 5A). Third endotherm (100-120°C) 9 Page 9 of 16

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can be elucidated as a phase transition, because no weight loss is observed in that temperature range. Similar thermal effects without mass loss were observed for calixarene and thiacalixarene derivatives and were interpreted as phase transitions or formation of molecular glass after removal of included guest molecule [50].

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Table 2. Temperatures of decomposition, mass changes and stoichiometries of the RES2 complexes with four solvents. Literature data were taken from crystallographic studies. Solvent No of Temp. b Stoichiometric ratioc ∆m steps /˚C /% this work literature methanol (64.7) a 2 6.9 25-100 1:2.6 1:5d 1.8 101-128 1:0.7 1:1d a ethanol (78.3) 1 9.8 35-81 1:2.0 1:4e 1:2.0(H2O) acetonitrile (81.5) a 1 3.8 45-86 1.1:1 1:1d

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Table 2 presents the stoichiometries for RES2 complexes (including a presence of water, see footnote c) showing excellent agreement between TG data and literature values for acetonitrile and dioxane molecules, however, some differences between crystallographic data and TG are observed for complexes with alcohols. Our attempts to obtain RES2/methanol suitable for X-ray analysis were unsuccessful – during re-crystallization from methanol we experienced the same difficulties as described and discussed for C-alkylresorcinarenes (Cpropyl, butyl, pentyl) by Momose and Bosch [23]. TG data indicate release of 2.6 molecules of methanol per one molecule of RES2. Better, but still far from satisfactory, are the results for RES2/ethanol complex (Table 2). We exclude the explanation that differences between TG and literature stoichiometries of RES2 with methanol and ethanol might result from different conformations of resorcinarene macrocycles because, regardless the kind of solvate (methanol, ethanol, acetonitrile and dioxane) after all solvent molecules are released, the remaining compounds start to decompose at the same temperature 300°C (see Fig. 3B). We also exclude the possibility that water molecules could give erroneous results of RES2: alcohols stoichiometries, because NMR experiments showed that water molecules are not released from RES2/methanol and, for RES2/Ethanol, only one molecule of water is released below 200°C (see footnote c to Table 2). As discussed by Nassimbeni [38], inclusion

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35-92 1:4 1:4f 93-143 a Boiling point in ˚C. b Temperature range of decomposition estimated on the basis of peaks on DSC curves. c For explanation of stoichiometric ratio see fotnote c to Table 1. Water was not included, however, NMR experiments indicate presence of 4 molecules of H2O in RES2 complexes with MeOH, CH3CH and dioxane, and presence of two H2O molecules in RES2/EtOH. With exception of RES2/EtOH complex, these water molecules are not released from RES2 below 200°C(see NMR in Supporting Material) . d When C-propylcalix [4]resorcinarene (triclinic, P1) and C-nonylcalix[4]resorcinarene (triclinic, P-1) were crystallized from MeOH the stoichiometries were 1:5 – Refs. 23,31. The lack of suitable data is discussed in Ref. 23. However, the stoichiometry calculated on the basis of thermogravimetric study equals 1:1 for both RES2•MeOH and RES2•acetonitrile solvates – Ref. 40. e Results of X-ray analysis: RES2•4C2H6O (triclinic, P1)– Ref. 29. f Results of X-ray analysis: RES2 4C4H8O2 (triclinic, P-1) – Ref. 30. 2

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compounds have often non-stoichiometric host / guest ratio and the same system crystallized at various temperatures can result in different stoichometries. Another cause might be connected with low stability of a solvate - a slow release of solvent molecules can occur during thermal equilibration of a sample. Comparing data collected in Table 1 and Table 2 one can conclude that thermal stability of RES1 and RES2 solvates is not correlated with such parameters of the four solvents as permitivity or ability of a solvent to form a hydrogen bond.

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3. Conclusions

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We discussed interactions of calix[4]resorcinarenes with four solvents. Two of them, acetonitrile and dioxane, were not able to dissolve C-methylcalix[4]resorcinarene and addition of water greatly enhanced the solubility.X-ray studies in solid phase demonstrated that water is a hydrogen bond mediator between non-polar organic solvent (like dioxane) and solute molecules. Solvates formed by calixresorcinarenes (and other cyclic polyphenols) can be explored by means of thermal analysis techniques working together with other analytical methods like X-ray analysis and NMR. TG and DSC experiments carried out for typical RES1 and RES2 complexes with methanol, ethanol, acetonitrile and dioxane resulted in determination of their stoichiometries in relatively simple way as alternative for time consuming crystallographic analysis. We recommend these fast and efficient thermoanalytical methods as giving first (but sometimes approximate) knowledge on complex stoichiometry and very precise knowledge on thermal stability of inclusion host-guest complexes.

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4. Experimental Section

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Solvents were of highest purity and were used without further purification. Macrocyclic polyphenols: C-methylcalix[4] resorcinarene (RES1) and C-undecylcalix[4]resorcinarene (RES2) were prepared according to the procedure proposed by Weinelt and Schneider [51] by condensation of resorcinol and appropriate aldehyde (acetaldehyde or lauryl aldehyde, respectively) in methanol containing aqueous HCl [51] and dried in vacuum. The crystals of supramolecular complexes were obtained as results of cooling and slow evaporation (at room temperature) of the hot solutions of the two resorcinarenes in appropriate solvents (methanol, ethanol, acetonitrile, dioxane). C-methylcalix[4]resorcinarene is soluble in wet acetonitrile and wet dioxane and, therefore, during preparation of those solutions addition a few drops of water was needed (the role of water is discussed in the Results and Discussion section). Prolonged (overnight) drying of the crystals under vacuum caused desolvation, therefore, fresh crystals were dried in air at room temperature until their mass was stable (± 1 %) and the samples were kept in closed small vials (during long storage in closed vials no decomposition of the complexes was observed).

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Acidity of C-methylcalix[4]resorcinarene was determined by spectrophotometric titration analogously to method applied by us to polyphenolic compounds [52]. Briefly, small volumes of titrant (1M KOH in water) were subsequently added to 200 ml of RES1 solution at a

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concentration of 10-4 M in methanol:water (1:1), thus, the pKa value is referred to 1:1 watermethanol scale. A precision pH meter was used with a combined pH glass electrode calibrated on primary pH standards for mixed methanol : water as recommended by IUPAC [53]. After each addition of titrant and when pH value was stable, small 0.5 ml samples of titrated solution were transferred to quartz cuvettes (optical path 10 mm), and UV-vis spectra in the range 200-400 nm were recorded. Each time the samples were returned to the main titrated solution. The pKa’s were calculated using DATAN 3.1 (MultiD Analyses).

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X-ray measurements were carried out on a Bruker KAPPA APEX II ULTRA diffractometer controlled by APEXII software [54], equipped with MoKα rotating anode X-ray source (λ = 0.71073 A, 50.0 kV, 22.0 mA) monochromatized by multi-layer optics and APEX-II CCD detector. The experiments were carried out at 100K using the Oxford Cryostream cooling device. Indexing, integration and initial scaling were performed with SAINT [55] and SADABS software [56]. The data collection and processing statistics are reported in tables for according structures (see ESI, Tables S1 and S2). 940 frames were measured at 0.5o intervals with a counting time of 10 sec. The structures were solved by direct methods approach using the SHELXS [57] program and refined with the SHELXL [58]. Multi-scan absorption correction have been applied in the scaling procedure. The refinement was based on F2 for all reflections except those with negative intensities. Weighted R factors wR and all goodness-offit S values were based on F2, whereas conventional R factors were based on the amplitudes, with F set to zero for negative F2. The F02 > 2σ( F02) criterion was applied only for R factors calculation was not relevant to the choice of reflections for the refinement. Most of hydrogen atoms were located in idealised geometrical positions. Hydrogen atoms engaged in hydrogen bonds, were located from a differential map and their temperature factors were refined isotropically. Scattering factors were taken from Tables 4.2.6.8 and 6.1.1.4 from the International Crystallographic Tables Vol. C [59]. Formula: C32H32O8, 3C4H8O2, 5H2O, pale yellow crystals, 0.28x0.11x011 mm (grown from wet dioxane), Mr= 898.97, orthorhombic, Pnma, a= 12.620(3) Å, b= 20.771(6) Å, c= 17.141(4) Å, V= 4493(2) Å3, Z=4, d= 1.329 dcm3 , The collected data range: 1.54<Θ<26.58 (-15
405 406 407 408 409 410 411 412 413

All DSC measurements were performed by means of DuPont 910 Differential Scanning Calorimeter equipped with a DuPont 9900 Thermal Analyzer. Normal pressure cell was calibrated by means of high-purity indium standard. TA Instruments software (General 4.0) was applied in data analysis. In typical DSC measurement a small sample (5 mg) placed in an aluminum pan in calorimetric cell and was heated with linear heating rate (β) from ambient temperature to 250ºC under nitrogen flow (6 dm3/h). As a reference material an empty aluminum pan was used. Thermogravimetric measurements were performed with a thermobalance DuPont 951 (precision ± 0.4%, minimal mass 0.02 mg) under nitrogen flow (6 dm3/h), employing platinum vessels. Two points temperature calibration was performed.

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Tests with decomposition of standard material (calcium oxalate monohydrate) were successful. All TG measurements were analyzed by means of TGA V5.1 program in order to determine the temperatures of decomposition.

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Proton NMR spectra were recorded on a Varian UnityPlus spectrometer at 199,96 MHz and 298K. The spectra were done in acetone-d6 or in CDCl3 (for complexes with acetonitrile) and are listed as δ values in ppm (versus TMS). RES1/ethanol solvate: 1.76 (d, 12 H, CH3, J = 7.2 Hz), 4.52 (q, 4H, methine CH, 7.4 Hz), 6.21 (s, 4H, aromatic CH in ortho position), 7.64 (s, 4H, aromatic CH in meta position), 8.50 (bs, 8H, OH), 1.12 (t, CH3 from ethanol, J = 6.9 Hz), 3.58 (q, CH2 from ethanol, J = 7.0 Hz), 2.95 (bs, water).

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RES1/ethanol complex after non-isothermal heating at DSC chamber from ambient temperature to 220ºC: 1.76 (d, 12 H, CH3, J = 7.4 Hz), 4.52 (q, 4H, methine CH, 7.2 Hz), 6.21 (s, 4H, aromatic CH in ortho position), 7.65 (s, 4H, aromatic CH in meta position), 8.46 (bs, 8H, OH), 2.95 (bs, water). RES1/ethanol complex after a sample was heated isothermally during 3 hours in 220ºC under vacuum: 1.76 (d, 12 H, CH3, J = 7.4 Hz), 4.52 (q, 4H, methine CH, 7.2 Hz), 6.21 (s, 4H, aromatic CH in ortho position), 7.65 (s, 4H, aromatic CH in meta position), 8.47 (bs, 8H, OH), 2.95 (bs, water).

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H NMR spectra of complexes with acetonitrile were recorded in CDCl3 to avoid acetone-d6 residual signals overlapping with CH3CN signals. RES2/acetonitrile solvate (in CDCl3): 0.88 (t, 12H, CH3, J = 6.2 Hz), 1.27 (bs, 72H, CH2(CH2)9CH3), 2.21 (m, 8H, CH2(CH2)9), 4.30 (t, 4H, CH), 6.11 (s, aromatic CH in ortho position), 7.20 (s, aromatic CH in meta position overlaps with the solvent residual peak), 9.29 and 9.60 (bs, 8H, OH), 2.01 (bs, CH3 acetonitrile), and 2.88 (s, water). RES2/acetonitrile after non-isothermal heating at DSC chamber from ambient temperature to 220ºC: (200 MHz, CDCl3, 298 K): 0.89 (t, 12H, CH3, J = 6.3 Hz), 1.30 (bs, 72H, CH2(CH2)9CH3), 2.30 (m, 8H, CH2(CH2)9), 4.31 (t, 4H, methine CH 7.9 Hz), 6.23 CH (s, 4H, aromatic CH in ortho position), 7.55 (s, 4H, aromatic CH in meta position), 8.50 (bs, 8H, OH), 2.86 (bs, water). RES2/acetonitrile complex after a sample was heated isothermally during 3 hours in 220ºC under vacuum: 0.88 (t, 12H, CH3, J = 6.5 Hz), 1.27 (bs, 72H, CH2(CH2)9CH3), 2.22 (m, 8H, CH2(CH2)9) 4.30 (t, 4H, CH), 6.11 (s, aromatic CH in ortho position), 7.20 (s, aromatic CH in meta position overlaps with the solvent residual peak), 9.30 (t, 4H, OH) and 9.60 (t, 4H, OH), 3.11 (bs, water).

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We thank Malgorzata Szewczyk for performing some thermoanalytical experiments. The project was financially supported by the Ministry of Science and Higher Education of Poland (research grant No. N N204 029936) and by National Science Center of Poland (NCN grant Opus No. 2011/03/B/ST4/ 00629).

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Supplementary material available: thermal decomposition of RES1/dioxane solvate (Figure S1), proton NMR spectra for RES1/ethanol, RES2/acetonitrile solvates and for desolvated samples (Figures S2-S16), UV-VIS absorption spectrum of RES1 in water/methanol (Figure S17), as well as detailed crystallographic data for CAL1/dioxane/water solvate (Table S1) including bond lengths, angles (Table S2), the asymmetric unit (Figures S18-S20), packing (Figures S22-S24). 13 Page 13 of 16

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[57] Sheldrick, G. Acta Crystallogr. Sect. A 1990, 46, 467. [58] Sheldrick, G. M.; SHELXL93. Program for the Refinement of Crystal Structures., Univ. Gottingen. [59] Wilson, A. J. C. International Tables for Crystallography; Kluwer: Dordrecht, 1992; Vol. C.

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Solvates of calix[4]resorcinarenes with 4 solvents were studied.

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Stoichiometry and thermal stability of inclusion host-guest complexes were determined.

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Water is a hydrogen bond mediator between non-polar solvent and resorcinarene.

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TG and DSC are alternative methods for time consuming crystallographic analysis.

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TA is a convenient tool for studies of complexes with volatile, small guest molecules.

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