金属Xchiff碱配合物的研究 II: 三价铁自旋变异晶态配合物的磁学和谱学表征

本文对五种组成为[Fe(3-EtO-SalAPA)2]ClO4.S的Fe(III)自旋变异晶态配合物进行了磁学和谱学表征, 所有溶剂合物的变温磁化率和EPR数据证示它们的自旋态转变性质均属渐变型, 在110-300K范围内的Mossbauer谱都只显示单一的四极分裂双峰. 实验结果还表明, 在所有晶态配合物中, Fe(III)自旋态的转变速率小于EPR谱学的时间标度(~10^1^0s^-^1), 而大于Mossbauer谱学的时间标度(~10^7s^-^1). 随着溶剂分子体积由C6H5F至o-C5H4Cl2的依次增大, 相应溶剂合物的μeff-T曲线的Tc值向低温方向位移.特别在单卤代苯系列中, 溶剂的分子体积与Tc值呈线性关系, 但氯苯溶剂合物是例外:后者的反常现象主要是由晶格内部的Tc≈185K时伴随发生了与自旋变异协同的一级相变所造成, 这个相变过程已为示差扫描量热测定和Mossbauer中心位移对温度的曲线呈现的不连续性所证实.     

Solid state of a new flavonoid derivative DA-6034

DA-6034 is a new synthetic flavonoid known to possess anti-inflammatory activity. The objective of this work was to investigate the existence of polymorphs and pseudopolymorphs of DA-6034. Six crystal forms, one hydrate form and five solvates, of DA-6034 have been isolated by recrystallization and characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and powder X-ray diffractometry (PXRD). From the DSC and TG data it was confirmed that Form 1 is monohydrate; Form 2 is DMSO solvate; Form 3 is 1/2 DMSO solvate; Form 4 is 1/2 methyl ethyl ketone solvate; Form 5 is 1.5 H₂O, 1/2 acetic acid solvate; Form 6 is 1/2 H₂O, 1/4 butanol solvate. The PXRD patterns of the six crystal forms were different respectively. In the dissolution studies in pH 6.8 ± 0.05 buffer at 37 ± 0.5 °C, the solubility of solvates was higher than that of Form 1.     

Role of structural and macrocrystalline factors in the desolvation behaviour of cortisone acetate solvates

A combined analysis of structural data and experimental results (DSC, temperature-resolved XRPD and hot stage optical microscopy) revealed that the dehydration mechanism of cortisone acetate monohydrate (CTA·H₂O) involves a collective and anisotropic departure of water molecules followed by a cooperative structural reorganization toward the anhydrous polymorph CTA (form 2). In spite of the lack of crystal structure data, it can be postulated from experimental data that thermal decomposition of the dihydrated form (CTA·2H₂O) and of the tetrahydrofuran solvate (CTA·THF) toward another polymorph (CTA (form 3)) also proceeds according to a cooperative mechanism, thus giving rise to probable structural filiations between these crystalline forms of CTA. The crystal structure determination of two original solvates (CTA·DMF and CTA·DMSO) indicates that these phases are isomorphous to the previously reported acetone solvate. However, their desolvation behaviour does not involve a cooperative mechanism, as could be expected from structural data only. Instead, the decomposition mechanism of CTA·DMF and CTA·DMSO starts with the formation of a solvent-proof superficial layer, followed by the partial dissolution of the enclosed inner part of crystals. Hot stage optical microscopy observations and DSC measurements showed that dissolved materials (resulting from a peritectic decomposition) is suddenly evacuated through macroscopic cracks about 30°C above the ebullition point of each solvent. From this unusual behaviour, the necessity to investigate rigorously the various aspects (thermodynamics, kinetics, crystal structures and physical factors) of solvate decompositions is highlighted, including factors related to the particular preparation route of each sample.     

The thermodynamic solvate difference rule: solvation parameters and their use in interpretation of the role of bound solvent in condensed-phase solvates

Our earlier-established thermodynamic solvate difference rule encompasses thermodynamic relationships for the quantities P=DeltafH degrees, DeltafG degrees, DeltafS degrees, S degrees, Vm, and UPOT for pairs of condensed-phase solvates (including hydrates) having n and m moles, respectively, of bound solvent (including water, i.e., L=H2O), and can be written as P{MpXq.nL,p} approximately P{MpXq.mL,p}+(n-m).thetaP{L,p-p} (with m=0 for the corresponding thermodynamic quantity of the condensed-phase unsolvated parent, P{MpXq,p}), where thetaP{L,p-p} is the incremental contribution per mole of the bound solvent, L, to the property, P, of the solvate in condensed phase, p (where p=solid or liquid). We find that this rule can be extended to supercooled NaOH (and, probably, even more generally). Once established, the parameter thetaP{L,p-p} provides approximate values of the thermodynamic property, P, for the remaining solvates (hydrates) for which data are unknown. The difference rule is here further extended to heat-capacity data, Cp, for both hydrates and other solvates. For solid-phase hydrates, thetaCp{H2O,s-s} is determined to be 42.8 J K(-1) mol(-1). Further, the method is shown to apply also to the organic solvates, DMSO and DMF (the latter is based on a single example), leading to the (tentative) values thetaCp{DMSO,s-s} approximately 105 J K(-1) mol(-1) (at 255 K); approximately 161 J K(-1) mol(-1) (at 350 K), illustrating typical temperature dependence of the thetaCp values. thetaCp{DMF,s-s} approximately 84 J K(-1) mol(-1). For supercooled NaOH, thetaCp{NaOH,l-l}=77 J K(-1) mol(-1). The values of the solvate difference rule parameters provide us with insight into the bonding condition of the solvent molecule, leading to the conclusion that bound solvent water in an ionic environment is ice-like. The situation is more complex within zeolites because water may enter the solvate in a variety of ways. These latter considerations are also briefly discussed with respect to fullerenes.     

Relationship between the thermally induced reorientations of aromatic solvate molecules in Cu(hfac)2-nitroxide breathing crystals and the character of the magnetic anomaly

A new group of "breathing" crystals has been synthesized. These are aromatic solvates of the copper(II) hexafluoroacetylacetonate complex with spin-labeled pyrazole Cu(hfac)(2)L·0.5Solv, where L is 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and Solv is benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, styrene, o-xylene, m-xylene, p-xylene, 1,4-bis(trifluoromethyl)benzene, 1-methyl-4-ethylbenzene, 1-methyl-4-vinylbenzene, 1,4-diethylbenzene, 1,2,3-trimethylbenzene, or 1,2,4-trimethylbenzene. The main feature of Cu(hfac)(2)L·0.5Solv single crystals is their remarkable mechanical stability and ability to undergo thermally induced structural rearrangements accompanied by spin-crossover-like phenomena. The structures of Cu(hfac)(2)L·0.5Solv solvates are similar and based on mutually parallel {Cu(hfac)(2)L}(∞) heterospin chains with a "head-to-head" motif. The localization of voids with guest molecules being the same in all crystals, the temperature dependence of the effective magnetic moment (μ(eff)) for Cu(hfac)(2)L·0.5Solv is determined by the structure of the guest molecules, along which the polymer chains are "gliding" when the temperature changes. When the temperature decreased from 300 to 100-50 K, μ(eff) decreased, abruptly or gradually, from 2.7-2.4 to ~1.8 β for the majority of Cu(hfac)(2)L·0.5Solv except the solvates with benzene, toluene, and 1,4-bis(trifluoromethyl)benzene. When Cu(hfac)(2)L·0.5C(6)H(6) and Cu(hfac)(2)L·0.5CH(3)-C(6)H(5) were cooled to 50 K, μ(eff) decreased to ~2.1-2.2 β. When Cu(hfac)(2)L·0.5(1,4-(CF(3))(2)-C(6)H(4)) was cooled to 50 K, μ(eff) initially decreased from ~2.7 to 1.9 β and then abruptly increased to ~2.4 β. A single-crystal X-ray diffraction analysis of each solvate within a temperature range wider than the range of magnetic anomaly temperatures revealed a complex interrelated dynamics of the aromatic solvent guest molecules and heterospin chains. The dynamics largely depended on the orientation of the solvent guest molecules relative to the polymer chains. An analysis of the thermally induced phase transformations revealed a relationship between the structural rearrangement of Cu(hfac)(2)L·0.5Solv and the form of the magnetic anomaly on the μ(eff)(T) curve and between the structural rearrangement of the solvate and the temperature of the magnetic effect.     

Structure prediction, disorder and dynamics in a DMSO solvate of carbamazepine

We have applied crystal structure prediction methods to understand and predict the formation of a DMSO solvate of the anti-convulsant drug carbamazepine (CBZ), in which the DMSO molecules are disordered. Crystal structure prediction calculations on the 1:1 CBZ:DMSO solvate revealed the generation of two similar low energy structures which differ only in the orientation of the DMSO molecules. Analysis of crystal energy landscapes generated at 0 K suggests the possibility of solvent disorder. A combined computational and experimental study of the changes in the orientation of the DMSO within the crystal structure revealed that the nature of the disorder changes with temperature. At low temperature, the DMSO disorder is static whilst at high temperature the DMSO configurations can interconvert by a 180° rotation of the DMSO molecules within the lattice. This 180° rotation of the DMSO molecules drives a phase change from a high temperature dynamically disordered phase to a low temperature phase with static disorder. Crystallisation of a DMSO solvate of the related molecule epoxycarbamazepine resulted in a different degree of DMSO disorder in the crystal structure, despite the similarity of the carbamazepine and epoxycarbamazepine molecules. We believe consideration of disorder and its contribution to entropy and crystal free energies at temperature other than 0 K is fundamental for the accuracy of future energy rankings in crystal structure prediction calculations of similar solvated structures.     

"Venetian blinds" mechanism of solvation/desolvation in palladium(II) wheel-and-axle organic-inorganic diols

A family of organic-inorganic wheel-and-axle diols (Pd(LOH)(2)Cl(2), Pd(LOH)(2)(CH(3))Cl, Pd(LOH)(2)(CH(3)COO)(2), LOH = alpha-(4-pyridyl)benzhydrol) and several corresponding solvates are synthesized and characterized by single-crystal X-ray diffraction analysis. Their structures are compared to investigate the factors governing the modes of solid state association, the propensity to clathration, and the structural basis of guest inclusion. In all the complexes, the palladium coordination is a slightly distorted square. The LOH ligands coordinate Pd(2+) by means of the 4-pyridyl ring. In the chloride complexes solvation occurs with a 1:2 host/guest ratio by hydrogen bonding between the terminal -OH groups of the complex diol and one acceptor atom on the guest, and it is further assisted by guest stacking between host aryl rings. All solvates are organized in layers with practically invariant metrics, while the layers may be assembled in different arrangements. The structures of the nonsolvate compounds are related to the metrics of the solvate forms by rotation of the complex molecules within the layer plane. In all cases the nonsolvates are completely converted into the corresponding crystalline solvate forms by exposure to the vapor of the guest, and conversely they are quantitatively recovered from the solvate upon removal of the guest by mild conditions. On the basis of the structural data, it is proposed that the solvation/desolvation process proceeds by a concerted rotation of the complex molecules in the layer plane. The structural analysis of Pd(LOH)(2)(CH(3)COO)(2) and of its tetrahydrofuran monosolvate form suggests that the first step of the solid/gas solvation process may imply the clathration of 1 mol of guest between the aryl rings, which successively triggers the collective reorientation of the host molecules.     

Structures and properties of solvated and unsolvated isopropyl functionalised calix[4]arenes

The tetra-isopropyl ethers of calix[4]arene and p-t-butylcalix[4]arene have been isolated in the cone conformation, and structurally characterised as chloroform solvates. Thermogravimetric analysis demonstrated that the parent isopropylcalix[4]arene solvate is significantly more stable than the p-t-butylcalix[4]arene analogue, retaining the solvent up to a temperature of 125°C. It was found that the calix[4]arene ether sublimes at atmospheric pressure, and solvent-free crystals appropriate for structure determination were produced at reduced pressure. The p-t-butylcalix[4]arene ether was also isolated without solvent in the lattice, but in this case the calixarene was crystallised from acetone, as sublimation did not produce crystals of sufficient quality.     

Three solvates of a bis‐mesoionic fluorescent yellow pigment

p‐Phenylenebis(2‐oxo‐3‐phenyl‐1,2‐dihydropyrido[1,2‐a]pyrimidin‐5‐ium‐4‐olate), C₃₄H₂₂N₄O₄, is a bis‐mesoionic yellow pigment that shows fluorescence in the solid state. During a polymorph screening, single crystals of three solvates were grown and their crystal structures determined. Solvent‐free crystals were not obtained. A solvate with N‐methylpyrrolidone (NMP) and propan‐2‐ol, C₃₄H₂₂N₄O₄·2C₅H₉NO·C₃H₈O, (Ia), and an NMP trisolvate, C₃₄H₂₂N₄O₄·3C₅H₉NO, (Ib), crystallize with pigment molecules on inversion centres. The NMP/propan‐2‐ol mixed solvate (Ia) forms O—H...O hydrogen bonds between the different solvent molecules. In both structures, at least one of the solvent molecules is disordered. A third solvate structure, C₃₄H₂₂N₄O₄·0.5C₅H₉NO·C₄H₁₀O, (Ic), was obtained by crystallization from NMP and butan‐1‐ol. In this case, there are two symmetry‐independent pigment molecules, both situated on inversion centres. The solvent molecules are heavily disordered and their contribution to the scattering was suppressed. This solvate displays a channel structure, whereas the other two solvates form layer structures.     

Zinc paddlewheel dimers containing a strong π···π stacking supramolecular synthon: designed single-crystal to single-crystal phase changes and gas/solid guest exchange

The ligand 4-(1,8-naphthalimido)benzoate, L(C4)(-), containing a linear link between the strong π···π stacking 1,8-naphthalimide supramolecular synthon and the carboxylate donor group, reacts with Zn(O(2)CCH(3))(2)(H(2)O)(2) in the presence of dimethylsulfoxide (DMSO) to yield [Zn(2)(L(C4))(4)(DMSO)(2)]·2(CH(2)Cl(2)). This compound contains the "paddlewheel" Zn(2)(O(2)CR)(4) secondary building unit (SBU) that organizes the rigid phenylene and naphthalimide rings of the carboxylate ligands in a square arrangement. The supramolecular architecture is dominated by π···π stacking interactions between naphthalimide rings of one dimer with four adjacent dimers, essentially at right angles, forming an open three-dimensional network structure. Two symmetry equivalent networks of this type interpenetrate generating overall a densely packed three-dimensional, 2-fold interpenetrated architecture in which the CH(2)Cl(2) solvate molecules are trapped in isolated pockets. Upon cooling, single crystals of [Zn(2)(L(C4))(4)(DMSO)(2)]·2(CH(2)Cl(2)) undergo two distinct crystallographic phase transitions, as characterized by X-ray diffraction at different temperatures, without loss of crystallinity. These two new phases have supramolecular structures very similar to the room temperature structure, but changes in the ordering of the CH(2)Cl(2) solvate cause shifting of the naphthalimide rings and a lowering of the symmetry. Crystals of [Zn(2)(L(C4))(4)(DMSO)(2)]·2(CH(2)Cl(2)) undergo a single-crystal to single-crystal gas/solid guest exchange upon exposure to atmospheric moisture, or faster if placed under vacuum or heated under dry gas to 100 °C, followed by atmospheric moisture, to yield [Zn(2)(L(C4))(4)(DMSO)(2)]·3.9(H(2)O). The molecular and supramolecular structures of this new compound are very similar to the dichloromethane adduct, with now the water molecules encapsulated into the framework. The remarkable feature of both the phase changes and exchange of solvates is that this robust network is not porous; local distortions (ring slippage and tilting changes) of the π···π stacking interactions of the naphthalimide rings that organize these structures allow these changes to take place without the loss of crystallinity. The complexes [Zn(2)(L(C4))(4)(DMSO)(2)]·2(CH(2)Cl(2)) and [Zn(2)(L(C4))(4)(DMSO)(2)]·3.9(H(2)O) show green emission in the solid state.     

Concerted molecular displacements in a thermally-induced solid-state transformation in crystals of DL-norleucine

Martensitic transformations are of considerable technological importance, a particularly promising application being the possibility of using martensitic materials, possibly proteins, as tiny machines. For organic crystals, however, a molecular level understanding of such transformations is lacking. We have studied a martensitic-type transformation in crystals of the amino acid DL-norleucine using molecular dynamics simulation. The crystal structures of DL-norleucine comprise stacks of bilayers (formed as a result of strong hydrogen bonding) that translate relative to each other on transformation. The simulations reveal that the transformation occurs by concerted molecular displacements involving entire bilayers rather than on a molecule-by-molecule basis. These observations can be rationalized on the basis that at sufficiently high excess temperatures, the free energy barriers to concerted molecular displacements can be overcome by the available thermal energy. Furthermore, in displacive transformations, the molecular displacements can occur by the propagation of a displacement wave (akin to a kink in a carpet), which requires the molecules to overcome only a local barrier. Concerted molecular displacements are therefore considered to be a significant feature of all displacive transformations. This finding is expected to be of value toward developing strategies for controlling or modulating martensitic-type transformations.     

Dehydration Mechanism and Crystallisation Behaviour of Lactose

The dehydration mechanism of α-lactose monohydrate was investigated by several techniques and interpreted on the basis of structural data. Whatever the dehydration conditions (heating or use of hygroscopic organic solvents), the departure of water molecules occurs cooperatively in channels parallel to the c axis of the initial structure. Subsequently, the reorganization leads to the closest packing (hygroscopic metastable form, Lα_H) under heating or to the stable anhydrous form (Lα_S), probably via a nucleation and growth process in ethanol. The use of acetone as dehydrating solvent on single crystals of α-lactose monohydrate led to the unexpected formation of single crystals of the anomeric β-lactose at room temperature, from which the crystal structure of β-lactose could be accurately re-determined. Recrystallization experiments of anhydrous lactose allowed to prepare N-methylpyrrolidinone and DMSO solvates of α-lactose. This revised version was published online in August 2006 with corrections to the Cover Date.     

Niclosamide methanol solvate and niclosamide hydrate: structure,solvent inclusion mode and implications for properties

Structural studies have been carried out of two solid forms of niclosamide [5‐chloro‐N‐(2‐chloro‐4‐nitrophenyl)‐2‐hydroxybenzamide, NCL], a widely used anthelmintic drug, namely niclosamide methanol monosolvate, C₁₃H₈Cl₂N₂O₄·CH₃OH or NCL·MeOH, and niclosamide monohydrate, denoted H_A. The structure of the methanol solvate obtained from single‐crystal X‐ray diffraction is reported for the first time, elucidating the key host–guest hydrogen‐bonding interactions which lead to solvate formation. The essentially planar NCL host molecules interact viaπ‐stacking and pack in a herringbone‐type arrangement, giving rise to channels along the crystallographic a axis in which the methanol guest molecules are located. The methanol and NCL molecules interact via short O—H...O hydrogen bonds. Laboratory powder X‐ray diffraction (PXRD) measurements reveal that the initially phase‐pure NCL·MeOH solvate readily transforms into NCL monohydrate within hours under ambient conditions. PXRD further suggests that the NCL monohydrate, H_A, is isostructural with the NCL·MeOH solvate. This is consistent with the facile transformation of the methanol solvate into the hydrate when stored in air. The crystal packing and the topology of guest‐molecule inclusion are compared with those of other NCL solvates for which the crystal structures are known, giving a consistent picture which correlates well with known experimentally observed desolvation properties.     

Studies on the Conversions of Diols and Cyclic Ethers. Part 48. Dehydration of alcohols and diols on the action of dimethylsulfoxide

The transformations of 13 alcohols and 13 diols in the presence of a small amount dimethylsulfoxide (1/16 mol) were studied. Relationships were found between the type of the hydroxy compound and the selectivity of the transformation, and conclusions were drawn regarding the transformation mechanism. The ether formation observed with certain alcohols proceeds via a carbenium cation. The reaction conditions applied were found suitable for inducing water elimination from the ditertiary 1,2- and 1,3-diols (pinacol rearrangement, 1,2-elimination). From the 1,4- and 1,5-diols the corresponding oxacycloalkanes can be obtained in good yield. Cyclodehydration occurs by intramolecular nucleophilic substitution, via a concerted mechanism. The effect of DMSO is exerted directly, and protoncatalysis occurs simultaneously.     

Crystal structure of three solvated Alpinumisoflavones

Single crystals of alpinumisoflavone, C₂₀H₁₆O₅, {systematic name: 5-hydroxy-7-(4 hydroxyphenyl)-2, 2-dimethyl-2H, 6H-benzo [1, 2-b: 5, 4-b′]-dipyran-6-one}, solvated with water, methanol, and ethanol, have been obtained. The incorporation of the solvent molecules into the crystal structure creates a new short inter-molecular O–H···O and C–H···O contacts between the alpinumisoflavone moiety and its solvate molecule. The temperatures at which the solvated molecules lose their solvent molecules are 53, 54, and 65 °C for water, methanol, and ethanol, respectively. The observed temperatures at which the solvates efflorescence are reflective of the progressive increase in mass of the solvates from water to ethanol in the series. The benzopyrone moiety shows the usual planar conformation with the pyran ring deformed into a half-chair conformer as seen previously in the other analogous compounds with puckering parameters [Å], 0.2656(8), 0.3703(8), and 0.3957(9), respectively, for the water, ethanol, and methanol solvates. These are higher than the non-solvated alpinumisoflavone compound previously studied. The size of a substituent group proximal to the keto group has a more pronounced effect on the degree of puckering than substitution on the terminal phenyl ring. The attached phenyl ring shows consistent out-of-plane twist from the mean plane of the benzopyrone system as observed previously for this class of compounds. The observed dihedral angles are 30.26(3), 37.75(3), and 34.00(3)°, respectively, for the water, methanol, and ethanol solvates.     

The solvation of the mercury(II) ion-a 199Hg NMR study

The solvation of the mercury(II) ion in solvents with different solvation properties, water, dimethylsulfoxide, N,N-dimethylthioformamide, and liquid ammonia, has been studied by means of (199)Hg NMR. The (199)Hg chemical shift shows a pronounced dependence on the coordination number of the mercury(II) ion in the solvates resulting in a difference of over 1200 ppm between basically tetrahedral and octahedral complexes. The chemical shifts can furthermore be associated with electron-pair donor properties of the solvents. The spin-lattice relaxation times of the (199)Hg nucleus in the solvates have been measured at different applied magnetic fields, concentrations, temperatures, and isotope substitutions. Possible mechanisms for the (199)Hg relaxation were proposed and the chemical shielding anisotropy in the solvates has been estimated. The (199)Hg relaxation rates and the anisotropy are correlated with the structure of the solvate complexes in solution obtained from recent LAXS and EXAFS studies.     

Crystallization of Pseudopolymorphs of Some Gamboge Pigments. Pyridine,Dimethylformamide and Dimethylsulfoxide Solvates of Morellic Acid,Gambogic Acid and Guttiferic Acid

Abstract

Morellic acid, gambogic acid and guttiferic acid are related naturally-occurring xanthone pigments that yield X-ray quality crystals only from solvents like pyridine, dimethylformamide (dmf) and dimethyl sulfoxide (dmso). The structures of four of these crystals have been determined and are found to contain solvents of crystallization. The solvents hydrogen bond to the carboxyl groups with O—H…O/N motifs previously seen in other carboxylic acids. Distinctive, however, is the presence of an extended though somewhat diffuse array of C—H…O hydrogen bonds that aggregates the entire solute-solvent assemblage in a multi-point manner. Pyridine and dmf are able to mimic each other with respect to their hydrogen bond donating and accepting characteristics and in this respect play equivalent roles in their solvates with morellic acid and gambogic acid. Dmso is seen to self-associate in its guttiferic acid solvate. It is possible that these solvents with multiple hydrogen bonding donor and acceptor capability can act as hydrogen bond nucleators, providing just enough rigidity to the solutes to ensure crystallization.     

Thermal analyses (TGA and DSC) of some spironolactone solvates

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies have been performed on a commercial preparation of spironolactone and on five solvates (acetonitrile, ethyl acetate, ethanol, methanol, and benzene) prepared from it by recrystallization at room temperature. The results of these studies are discussed and compared with those recently reported in the literature for similar preparations. The variable behaviour of these solvates in their release (and partial retention) of solvent before the onset of melting, meant that their stoichiometry had to be measured by elemental microanalyses. Solvent loss from solvate decomposition was followed by thermogravimetric analysis (TGA). Solvate decomposition and spironolactone melting temperatures and enthalpies were determined by differential scanning calorimetry (DSC). The parent substance and two of the solvates (methanol and ethanol) exhibited small exotherms in addition to the expected endotherms.