- Email: [email protected]
Reversible pressure-induced disordering in bis(dl -serinium) oxalate dihydrate
Journal of Molecular Structure xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Reversible pressure-induced disordering in bis(DL-serinium) oxalate dihydrate Boris A. Zakharov ⇑, Elena V. Boldyreva ⇑ Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze Street 18, Novosibirsk 630128, Russian Federation Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090, Russian Federation
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Bis(DL-serinium) oxalate dihydrate
was studied at high pressures. The crystal split into disordered
domains with pressure but was restored on decompression. The strain anisotropy correlates with the relative strength of different types of H-bonds.
a r t i c l e
i n f o
Article history: Received 31 December 2013 Received in revised form 25 March 2014 Accepted 22 April 2014 Available online xxxx Keywords: High pressure Phase transitions Amino acid salts X-ray diffraction Raman spectroscopy
a b s t r a c t We report the study of a reversible phase transition accompanied by pressure-induced disordering in bis(DL-serinium) oxalate dihydrate which was observed at hydrostatic pressures of 4 GPa. The disordering manifested itself as a strong diffuse scattering in diffraction patterns and as a similarity of low-wavenumber Raman spectra measured for different polarizations. Several domains were formed, though the single crystals remained intact. On releasing pressure, both the order in the crystal structure and the mono-domain single crystal were restored. Structural strain on increasing pressure prior to the phase transition was studied by single-crystal X-ray diffraction and Raman spectroscopy and compared with that on cooling, as well as with the pressure-induced strain of DL-serine, in which no pressure-induced disordering or structural transitions could be observed. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Molecular crystals are often used as active pharmaceutical ingredients, biomimetics and molecular materials. They are widely studied, in order to correlate the intermolecular interactions in the ⇑ Corresponding author at: Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze Street 18, Novosibirsk 630128, Russian Federation. Tel.: +7 3833634272; fax: +7 3833634132. E-mail addresses: [email protected] (B.A. Zakharov), eboldyreva@yahoo. com (E.V. Boldyreva).
crystal structures at ambient conditions with structural strain and phase transitions induced by varying temperature or pressure [1–7]. The intermolecular hydrogen bonds present in their crystal structures often account for the high stability of the crystal structure with respect to its amorphisation on changing temperature, pressure, or applying electric field, and act as ‘‘springs’’ damping stress. Phase transitions (reversible or not) are induced, but the samples remain crystalline. At the same time, some phase transitions preserve the single crystals intact, whereas other result in fragmentation to give powder. It is important to understand what helps to avoid the fragmentation of a crystal, in order to design the
http://dx.doi.org/10.1016/j.molstruc.2014.04.067 0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
2
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 1. Displacement ellipsoid plot of bis(DL-serinium) oxalate dihydrate showing the atom-numbering scheme and 50% probability displacement ellipsoids at ambient conditions. H atoms are shown as arbitrary spheres.
structures suitable to be used as materials in the devices undergoing multiple cycles of transformations on changing the external conditions without mechanical failure. In many molecular crystals molecules can change their conformation and/or rotate in the structure. These changes can accompany the changes in molecular packing. It is quite common that multiple molecular conformations or orientations are present in a structure, but the structure remains ordered, so that several crystallographically independent molecules (Z0 ) are present in the asymmetric unit. Increasing pressure may reduce the value of Z0 [8], or increase it [9], but both the ambient- and the high-pressure
phases remain ordered. The crystal is often preserved intact through the phase transition point, though multiple domains are formed through the phase transition in one direction and disappear on the reverse transformation [9]. Pressure-induced amorphisation is also known [1,2,10], but for molecular crystals with the hydrogen bonds networks it is usually observed at very high pressures, above 12 GPa [11,12]. Most high-pressure studies are dedicated to the crystals of individual compounds. Even more interesting effects can be expected if multi-component molecular crystals – salts, co-crystals, solvates are considered [13]. The salts or co-crystals of amino acids belong to such promising systems. Many of them are promising as molecular materials for optics (see as recent examples [14,15]. As compared with the individual amino-acids, their multicomponent crystals have a greater variety of functional groups which can be involved in intermolecular interactions to form the intermolecular hydrogen bonds of more different types. In this case the stability of a structure with respect to phase transitions can either increase as compared to that of the individual components by forming extra H-bonds [16], or decrease because of a change in the molecular packing [17,18]. In the present contribution we report a rather unusual behavior of the crystals of another amino acid salt, bis(DL-serinium) oxalate dihydrate, with increasing pressure. At 4 GPa the crystal structure gets disordered, the crystal splits into several domains, but is preserved intact. On reverse decompression the order in the crystal structure is restored completely. Moreover, the domains also disappear, to give a single crystal again.
Fig. 2. Photographs of different bis(DL-serinium) oxalate dihydrate crystals in two series of experiments: in methanol–ethanol mixture (a) in pentane–isopentane mixture (b). The photograph of the crystal at 6.2 GPa corresponds to the highest pressure achieved in the experiment. Transition pressures are the same for both liquids and are near 4 GPa, as was independently confirmed by X-ray diffraction.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
3
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 2 Parameters characterizing directions of principal axes of strain ellipsoid up to 4 GPa (before the phase transition) for bis(DL-serinium) oxalate dihydrate. Axes 1, 2, 3 are the directions of minimum, medium and maximum compression. Angle with (°)
Axis 1 Axis 2 Axis 3
+A
+B
+C
30.7 (0.8) 90 (0) 59.3 (0.8)
90 (0) 0 (0) 90 (0)
122.4 (0.8) 90 (0) 32.4 (0.8)
High-pressure generation and measurements
Fig. 3. Polarized Raman spectra of bis(DL-serinium) oxalate dihydrate. ll- and mmdefine polarizations of incident and scattered beam along the longest and the medium crystal dimensions, correspondingly. A mixture of methanol and ethanol (4:1 stoichiometric ratio) was used as pressure-transmitting medium.
Materials and methods Samples The crystals of bis(DL-serinium) oxalate dihydrate were grown by slow evaporation from a drop of an aqueous solution of DL-serine and oxalic acid (2:1 stoichiometric ratio) saturated at room temperature. The structure of the samples was confirmed using single-crystal X-ray diffraction. DL-serine and oxalic acid were purchased from ICN Biomedicals and Reakhim, respectively.
Hydrostatic pressure was generated in the diamond-anvil cells (DACs) without beryllium backing plates of ‘Almax–Boehler’ type [25]. Steel gaskets with the initial thickness of 200 lm were preindented to 100 lm with a hole size of 300 lm. The ruby fluorescence method was used for pressure calibration [26,27], precision ±0.05 GPa. For the first preliminary Raman experiment we used a mixture of methanol and ethanol (4:1 stoichiometric ratio) with a hydrostatic limit of 10 GPa [28] as the pressure-transmitting medium. The title compound dissolved slightly in this pressuretransmitting medium, and recrystallized in the DAC. Raman spectra measured for the recrystallized sample and compared with those previously measured at ambient conditions proved that the substance recrystallized to the same phase. To avoid dissolution and to save the initial sample while loading a DAC, for the subsequent X-ray diffraction experiment, a mixture of pentane with isopentane (in a 1:1 stoichiometric ratio) with a hydrostatic limit of 7 GPa [28] was used. Since pentane and isopentane boil at 309 and 301 K, respectively, a special chamber was used to facilitate the DAC loading [29]. Several facts confirm inertness of isopentane and pentane in relation to the title compound. First of all, no dissolution has been detected for the system studied. Second, all the structure-forming molecules of the title compound are hydrophilic and did not seem to interact actively with hydrophobic pentane. The last but not least, the size of pentane and isopentane molecules is too large for them to enter the crystal structure on increasing pressure without irreversible crystal structure distortions. Raman spectroscopy
Techniques A combination of the single-crystal X-ray diffraction and polarized Raman spectroscopy was used, since it was proven to be especially informative for studying individual amino-acids and their multicomponent crystals at low temperatures and high pressures [18–24].
Raman spectra were recorded using a LabRAM HR 800 spectrometer from HORIBA Jobin Yvon with a CCD detector. For spectral excitation a 488 nm line of an Ar+ laser was used with a beam size of 1 lm at the surface of the sample and 8 mW power. All data were collected using a Raman microscope in backscattering geometry. Spectral resolution was 3 cm1, but
Table 1 Cell refinement details and parameters of data collection for bis(DL-serinium) oxalate dehydrate before the phase transition. Pressure (GPa)
0.4
1.0
1.4
2.0
2.5
3.0
3.5
4.0
a (Å) b (Å) c (Å) b (°) V (Å3) Number of reflections for cell refinement hmin hmax hmin hmax kmin kmax lmin lmax
4.8472 (3) 17.0785 (13) 16.999 (5) 92.308 (12) 1406.1 (5) 1318 1.6875 27.9929 6 6 21 21 11 11
4.8320 (4) 16.9564 (14) 16.773 (6) 92.812 (14) 1372.6 (6) 1345 2.3974 28.1526 6 6 21 21 10 10
4.8217 (4) 16.8223 (14) 16.637 (6) 94.011 (14) 1346.1 (5) 1226 2.4165 28.1078 6 6 21 21 10 10
4.8110 (4) 16.7098 (14) 16.506 (6) 94.255 (14) 1323.3 (5) 1181 2.4328 28.1522 6 6 21 21 10 10
4.8044 (5) 16.6023 (17) 16.366 (8) 94.85 (2) 1300.7 (7) 958 2.4486 28.1145 6 6 21 21 10 10
4.8014 (4) 16.4937 (14) 16.263 (7) 95.477 (17) 1282.0 (5) 944 2.4647 28.0714 6 6 21 20 10 10
4.7912 (4) 16.3712 (14) 16.181 (8) 95.760 (17) 1262.8 (6) 889 1.7705 28.0377 6 6 20 20 10 10
4.7637 (17) 16.271 (7) 16.17 (4) 95.85 (9) 1247 (3) 436 2.4984 28.2556 6 6 20 20 10 10
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
4
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 4. Crystal structure fragments of bis(DL-serinium) oxalate dihydrate. 1P, 2P and 3P arrows show the directions of the least, medium and major compression, correspondingly.
Fig. 5. Relative volume changes for bis(DL-serinium) oxalate dihydrate (black symbols) and for DL-serine (open symbols).
actual broadening of the bands in the spectra was significantly higher due to an increase in the anharmonicity with increasing pressure [30]. The size of the crystal used for Raman measurements after its recrystallization from the pressure-transmitting medium was 0.040 0.020 0.015 mm, the structure of the sample was confirmed spectroscopically to be the same as before the recrystallization. The title compound was studied up to 5.3 GPa at multiple pressures with a 0.5 GPa interval between the measurements. At each pressure point two Raman spectra were recorded with the polarization of the incident and the scattered beam along the longest side of the crystal and along the medium side of the crystal (i.e. 90° to each other, ll- and mmpolarizations), correspondingly. This was done to facilitate the analysis of structural changes with pressure. Single-crystal X-ray diffraction Data were collected using an Oxford Diffraction Gemini R Ultra X-ray diffractometer with a CCD area detector and Mo Ka radiation. The title compound was studied up to 6.2 GPa. The following software was used: CrysAlis PRO [31] for data collection, cell refinement and data reduction; STRAIN [32] was used to calculate the anisotropy of lattice strain. Results and discussion Bis(DL-serinium) oxalate dihydrate, 2C3H8NO+3C2O2 4 2H2O (Fig. 1) crystallizes in space group P21/c [21,33]. As was mentioned in the Experimental, the crystals dissolved slightly in the
methanol–ethanol mixture and this resulted in the recrystallization of the crystals at the initial pressure increase. At the first pressure point a Raman spectrum from recrystallized sample was measured and compared with the spectrum of dry solid compound without any liquids. These spectra were identical and there were no reasons to suppose inclusion of the solvent molecules into the crystal structure. The microphotographs of recrystallized sample at several pressures are shown at Fig. 2a. Further increase in pressure did not result in any additional dissolution of the sample. Therefore, the changes in the Raman spectra were measured for these recrystallized samples. However, to avoid dissolution and to save the initial sample while loading a DAC, for the subsequent experiments a mixture of pentane with isopentane (in a 1:1 stoichiometric ratio) with a hydrostatic limit of 7 GPa [28] was used. The changes in the spectra observed in pentane–isopentane mixture were the same as in the mixture of alcohols, and the phase transition (see below) was observed in the same pressure range for either of the pressure-transmitting liquids. Both the photographs and the polarized Raman spectra of bis(DL-serinium) oxalate dihydrate measured at different pressures (Fig. 3) show clearly that a phase transition occurs between 3.8 and 4.3 GPa. The three translational bands merged into one high-intensity band at 140 cm1 (Raman shift at 4.3 GPa) and the intensity of a libration band at 217 cm1 (Raman shift at 3.8 GPa) decreased very strongly during the phase transition. In the higher wavenumbers range the most significant changes were observed for the bands related to the C–C and C–N stretching vibrations (between 800 and 1100 cm1). A strong increase of intensity was observed for the bands at 901 and 1038 cm1 as compared to the band at 870 cm1 (Raman shifts at 4.3 GPa). Importantly, when analyzing the spectra recorded with different polarization vectors one can see that the same picture was observed for different polarizations in the range between 100 and 220 cm1, and only two bands at 140 and 201 cm1 (Raman shifts at 4.3 GPa) were visible in the spectra. A mere visual inspection gave evidence that some process has occurred in the crystal at this pressure (Fig. 2a). Raman data suggested that the crystal of bis(DL-serinium) oxalate dihydrate underwent a phase transition accompanied by disordering, since the polarized Raman spectra measured for a ‘‘normal’’ (undisturbed) monoclinic crystal structure should not be so similar for different crystal orientations and light polarizations. To prove this hypothesis we have performed an additional single-crystal X-ray diffraction experiment. Crystal structure stability up to 4 GPa was completely confirmed by diffraction measurements, and it was possible to obtain cell parameters and to calculate the anisotropy of lattice strain for this pressure range. Unfortunately it was not possible to follow fine details of changing molecular geometry and hydrogen bonds at high pressure because of a relatively lower quality of high-pressure data and a higher number of parameters for refinement, as compared with the
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
5
Fig. 6. Reconstruction of layers containing vectors: (a) column – [0 1 0] and [0 0 1]), (b) column – [0 1 0] and [1 0 0] at selected pressures. Background and gasket reflections are subtracted for clarity. Strong stretched spots are diamond reflections.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
6
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
previously published high-pressure study of a related compound – DL-alaninium semi-oxalate monohydrate (the only detailed study of the changes in a crystal structure of an amino acid salt at high pressures up to now) [18]. Details of data collection, cell parameters and parameters characterizing directions of principal axes of strain ellipsoid up to 4 GPa are summarized in Tables 1 and 2. Directions of the principal axes of strain ellipsoid in relation to the main structural motifs are shown at Fig. 4. Comparing these data to the strain induced in the same structure on cooling [21], one can see an obvious similarity. The structure expands slightly in the direction of the C44(20) hydrogen-bonded chains formed by the strongest hydrogen bonds in the structure (principal axis 1). Medium compression (axis 2) coincides with the crystallographic axis b, and the largest compression is observed in the direction close to that along the hydrogen-bonded chains C33(9) formed by the weakest hydrogen bonds in the structure between water molecules. Thus, the anisotropy of lattice strain correlates well with the relative strength of different types of intermolecular hydrogen bonds in the crystal structure. It is also interesting to compare the compression of bis(DL-serinium) oxalate dihydrate with that of the corresponding individual amino acid, DL-serine. Relative volume changes for the salt (the present study) and the individual amino acid [30,34] are almost identical; only at pressures above 2.5 GPa bis(DL-serinium) oxalate dihydrate compressed slightly stronger, than DL-serine, although the salt hydrate has stronger hydrogen bonds in its crystal structure (Fig. 5). At the same time, DL-serine does not undergo phase transitions up to 8.6 GPa [34], in contrast to the oxalate hydrate. The compression of bis(DL-serinium) oxalate dihydrate on cooling down to 100 K [21] was significantly (3 times) stronger than that of the individual amino acid. This shows that high pressures and low temperatures influence the crystal structure in different ways, even though the directions of principal axes and the anisotropy of strain are similar. On increasing pressure above the phase transition point, the crystal significantly changed, so that the borderlines between domains could be detected visually using an optical microscope (Fig. 2b), confirming the occurrence of the phase transition. Remarkably, these changes were completely reversible, and this was additionally confirmed by single-crystal X-ray diffraction. Strong scattering of the X-rays in the plane containing [0 1 0] and [0 0 1] vectors was observed in the diffraction patterns measured above the phase transition point (Fig. 6). This provided evidence of a substantial degree of disorder in the high-pressure phase. At the same time, the scattering did not make it possible to integrate the intensities reliably and to find the cell parameters. As a result the crystal structure of the high-pressure phase could not be solved. Taking into account the reconstruction of the layers shown at Fig. 6, we could conclude that the crystal structure was disordered in the (b*c*) plane and this manifested itself as ‘‘layers’’ of reflections in the reciprocal space; b and c cell parameters could not be found correctly, while the third parameter related to the distance between these layers after the phase transition could be estimated roughly as 4.7 Å, what is close to a parameter before the transition. Attempts to model this disorder theoretically using DISCUS software [35] have so far been unsuccessful due to the complexity of this crystal structure and a very large number of parameters that can be varied.
Conclusions The reversible pressure-induced disorder in bis(DL-serinium) oxalate dihydrate is an interesting example of a process when the regular orientation of molecular fragments in a crystal structure can be first distorted by compressing the structure and
reducing the volume, but is then completely restored reversibly on decompression. Apparently, the strong hydrogen bonds present in the structure help in preserving the main structural framework and its reversible distortion, whereas the weak hydrogen bonds together with the ability of the molecular fragments and molecules to rotate account for disordering after the phase transition point. A somewhat similar process – with strong hydrogen bonds preserving the main structural framework and the integrity of a single crystal, and the weak ones ‘‘switching over’’ – was observed and studied in details in the crystals of DL-alaninium semi-oxalate monohydrate [18]. The peculiar feature of the system described in the present study is that the structure transforms reversibly not between two ordered crystalline phases, or between a crystalline and an amorphous state, but between an ordered and a partially disordered crystalline states, and the single crystal splits into multiple domains on compression, but is restored completely as a perfect crystal when pressure is released. Acknowledgements This work was supported by RFBR (Project 12-03-31541 mol_a), by Russian Academy of Sciences, by the Ministry of Education and Science of Russian Federation and by a Grant from the President of Russia for State support of Russian leading Scientific Schools (Project NSh-221.2012.3). We are very grateful to Prof. Boris A. Kolesov for discussing the results of Raman spectroscopy. References [1] A. Katrusiak, P. McMillan (Eds.), High Pressure Crystallography, Kluwer, Dordrecht, 2003. [2] E.V. Boldyreva, P. Dera (Eds.), High-pressure crystallography, From Novel Experimental Approaches to Applications in Cutting-Edge Technologies, Springer, Dordrecht, 2010. [3] S.K. Sikka, S.M. Sharma, Phase Transit. 81 (2008) 907–934. [4] E.V. Boldyreva, Herald Russ. Acad. Sci. 82 (2012) 423–431. [5] S.A. Moggach, S. Parsons, P.A. Wood, Crystallogr. Rev. 14 (2008) 143–184. [6] A. Katrusiak, Acta Cryst. A 64 (2008) 135–148. [7] E.V. Boldyreva, Acta Cryst. A 64 (2008) 218–231. [8] R.D.L. Johnstone, M. Ieva, A.R. Lennie, H. McNab, E. Pidcock, J.E. Warren, et al., CrystEngComm 12 (2010) 2520–2523. [9] Y.V. Seryotkin, T.N. Drebushchak, E.V. Boldyreva, Acta Cryst. B 69 (2013) 77– 85. [10] S.M. Sharma, S.K. Sikka, Prog. Mater. Sci. 40 (1996) 1–77. [11] N.P. Funnell, W.G. Marshall, S. Parsons, CrystEngComm 13 (2011) 5841– 5848. [12] A.K. Mishra, C. Murli, N. Garg, R. Chitra, S.M. Sharma, J. Phys. Chem. B 114 (2010) 17084–17091. [13] E.V. Boldyreva, Z. Kristallogr. 229 (2014) 236–245. [14] M. Fleck, A.M. Petrosyan, J. Cryst. Growth 312 (2010) 2284–2290. [15] V.V. Ghazaryan, M. Fleck, A.M. Petrosyan, J. Cryst. Growth 362 (2013) 182– 188. [16] V.S. Minkov, E.V. Boldyreva, T.N. Drebushchak, C.H. Görbitz, CrystEngComm 14 (2012) 5943–5954. [17] B.A. Zakharov, E.A. Losev, E.V. Boldyreva, CrystEngComm 15 (2013) 1693– 1697. [18] B.A. Zakharov, E.V. Boldyreva, Acta Cryst. B 69 (2013) 271–280. [19] B.A. Kolesov, E.V. Boldyreva, J. Phys. Chem. B 111 (2007) 14387–14397. [20] B.A. Kolesov, E.V. Boldyreva, Raman-spectroscopic study of L-alanine single crystals in the temperature range of 3–300 K, in: L. Champion, PM, Ziegler (Ed.), XXII Int. Conf. Raman Spectrosc., 2010, pp. 619–620. [21] B.A. Zakharov, B.A. Kolesov, E.V. Boldyreva, Phys. Chem. Chem. Phys. 13 (2011) 13106–13116. [22] E.V. Boldyreva, Phase Transit. 82 (2009) 303–321. [23] N.A. Tumanov, E.V. Boldyreva, B.A. Kolesov, A.V. Kurnosov, R. Quesada Cabrera, Acta Cryst. B 66 (2010) 458–471. [24] B.A. Zakharov, E.A. Losev, B.A. Kolesov, V.A. Drebushchak, E.V. Boldyreva, Acta Cryst. B 68 (2012) 287–296. [25] R. Boehler, Rev. Sci. Instrum. 77 (2006) 115103-1–115103-3. [26] R.A. Forman, G.J. Piermarini, J. Dean Barnett, S. Block, Science 176 (1972) 284– 285. [27] G.J. Piermarini, S. Block, J.D. Barnett, R.A. Forman, J. Appl. Phys. 46 (1975) 2774–2780. [28] G.J. Piermarini, J. Appl. Phys. 44 (1973) 5377–5382. [29] B.A. Zakharov, A.F. Achkasov, J. Appl. Crystallogr. 46 (2013) 267–269. [30] B.A. Zakharov, B.A. Kolesov, E.V. Boldyreva, Acta Cryst. B 68 (2012) 275–286.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx [31] OxfordDiffraction, CrysAlisPro, 2010. [32] Y. Ohashi, C.W. Burnham, Am. Miner. 58 (1973) 843–849. [33] M. Alagar, M. Subha Nandhini, R.V. Krishnakumar, S. Natarajan, Acta Cryst. E 58 (2002) o114–o116.
7
[34] E.V. Boldyreva, E.N. Kolesnik, T.N. Drebushchak, H. Sowa, H. Ahsbahs, Y.V. Seryotkin, Z. Kristallogr. 221 (2006) 150–161. [35] R.B. Neder, T. Proffen, Diffuse Scattering and Defect Structure Simulations. A Cook Book Using the Program DISCUS. IUCr, Oxford University Press, 2008.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Reversible pressure-induced disordering in bis(DL-serinium) oxalate dihydrate Boris A. Zakharov ⇑, Elena V. Boldyreva ⇑ Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze Street 18, Novosibirsk 630128, Russian Federation Novosibirsk State University, Pirogova Street 2, Novosibirsk 630090, Russian Federation
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Bis(DL-serinium) oxalate dihydrate
was studied at high pressures. The crystal split into disordered
domains with pressure but was restored on decompression. The strain anisotropy correlates with the relative strength of different types of H-bonds.
a r t i c l e
i n f o
Article history: Received 31 December 2013 Received in revised form 25 March 2014 Accepted 22 April 2014 Available online xxxx Keywords: High pressure Phase transitions Amino acid salts X-ray diffraction Raman spectroscopy
a b s t r a c t We report the study of a reversible phase transition accompanied by pressure-induced disordering in bis(DL-serinium) oxalate dihydrate which was observed at hydrostatic pressures of 4 GPa. The disordering manifested itself as a strong diffuse scattering in diffraction patterns and as a similarity of low-wavenumber Raman spectra measured for different polarizations. Several domains were formed, though the single crystals remained intact. On releasing pressure, both the order in the crystal structure and the mono-domain single crystal were restored. Structural strain on increasing pressure prior to the phase transition was studied by single-crystal X-ray diffraction and Raman spectroscopy and compared with that on cooling, as well as with the pressure-induced strain of DL-serine, in which no pressure-induced disordering or structural transitions could be observed. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Molecular crystals are often used as active pharmaceutical ingredients, biomimetics and molecular materials. They are widely studied, in order to correlate the intermolecular interactions in the ⇑ Corresponding author at: Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze Street 18, Novosibirsk 630128, Russian Federation. Tel.: +7 3833634272; fax: +7 3833634132. E-mail addresses: [email protected] (B.A. Zakharov), eboldyreva@yahoo. com (E.V. Boldyreva).
crystal structures at ambient conditions with structural strain and phase transitions induced by varying temperature or pressure [1–7]. The intermolecular hydrogen bonds present in their crystal structures often account for the high stability of the crystal structure with respect to its amorphisation on changing temperature, pressure, or applying electric field, and act as ‘‘springs’’ damping stress. Phase transitions (reversible or not) are induced, but the samples remain crystalline. At the same time, some phase transitions preserve the single crystals intact, whereas other result in fragmentation to give powder. It is important to understand what helps to avoid the fragmentation of a crystal, in order to design the
http://dx.doi.org/10.1016/j.molstruc.2014.04.067 0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
2
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 1. Displacement ellipsoid plot of bis(DL-serinium) oxalate dihydrate showing the atom-numbering scheme and 50% probability displacement ellipsoids at ambient conditions. H atoms are shown as arbitrary spheres.
structures suitable to be used as materials in the devices undergoing multiple cycles of transformations on changing the external conditions without mechanical failure. In many molecular crystals molecules can change their conformation and/or rotate in the structure. These changes can accompany the changes in molecular packing. It is quite common that multiple molecular conformations or orientations are present in a structure, but the structure remains ordered, so that several crystallographically independent molecules (Z0 ) are present in the asymmetric unit. Increasing pressure may reduce the value of Z0 [8], or increase it [9], but both the ambient- and the high-pressure
phases remain ordered. The crystal is often preserved intact through the phase transition point, though multiple domains are formed through the phase transition in one direction and disappear on the reverse transformation [9]. Pressure-induced amorphisation is also known [1,2,10], but for molecular crystals with the hydrogen bonds networks it is usually observed at very high pressures, above 12 GPa [11,12]. Most high-pressure studies are dedicated to the crystals of individual compounds. Even more interesting effects can be expected if multi-component molecular crystals – salts, co-crystals, solvates are considered [13]. The salts or co-crystals of amino acids belong to such promising systems. Many of them are promising as molecular materials for optics (see as recent examples [14,15]. As compared with the individual amino-acids, their multicomponent crystals have a greater variety of functional groups which can be involved in intermolecular interactions to form the intermolecular hydrogen bonds of more different types. In this case the stability of a structure with respect to phase transitions can either increase as compared to that of the individual components by forming extra H-bonds [16], or decrease because of a change in the molecular packing [17,18]. In the present contribution we report a rather unusual behavior of the crystals of another amino acid salt, bis(DL-serinium) oxalate dihydrate, with increasing pressure. At 4 GPa the crystal structure gets disordered, the crystal splits into several domains, but is preserved intact. On reverse decompression the order in the crystal structure is restored completely. Moreover, the domains also disappear, to give a single crystal again.
Fig. 2. Photographs of different bis(DL-serinium) oxalate dihydrate crystals in two series of experiments: in methanol–ethanol mixture (a) in pentane–isopentane mixture (b). The photograph of the crystal at 6.2 GPa corresponds to the highest pressure achieved in the experiment. Transition pressures are the same for both liquids and are near 4 GPa, as was independently confirmed by X-ray diffraction.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
3
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 2 Parameters characterizing directions of principal axes of strain ellipsoid up to 4 GPa (before the phase transition) for bis(DL-serinium) oxalate dihydrate. Axes 1, 2, 3 are the directions of minimum, medium and maximum compression. Angle with (°)
Axis 1 Axis 2 Axis 3
+A
+B
+C
30.7 (0.8) 90 (0) 59.3 (0.8)
90 (0) 0 (0) 90 (0)
122.4 (0.8) 90 (0) 32.4 (0.8)
High-pressure generation and measurements
Fig. 3. Polarized Raman spectra of bis(DL-serinium) oxalate dihydrate. ll- and mmdefine polarizations of incident and scattered beam along the longest and the medium crystal dimensions, correspondingly. A mixture of methanol and ethanol (4:1 stoichiometric ratio) was used as pressure-transmitting medium.
Materials and methods Samples The crystals of bis(DL-serinium) oxalate dihydrate were grown by slow evaporation from a drop of an aqueous solution of DL-serine and oxalic acid (2:1 stoichiometric ratio) saturated at room temperature. The structure of the samples was confirmed using single-crystal X-ray diffraction. DL-serine and oxalic acid were purchased from ICN Biomedicals and Reakhim, respectively.
Hydrostatic pressure was generated in the diamond-anvil cells (DACs) without beryllium backing plates of ‘Almax–Boehler’ type [25]. Steel gaskets with the initial thickness of 200 lm were preindented to 100 lm with a hole size of 300 lm. The ruby fluorescence method was used for pressure calibration [26,27], precision ±0.05 GPa. For the first preliminary Raman experiment we used a mixture of methanol and ethanol (4:1 stoichiometric ratio) with a hydrostatic limit of 10 GPa [28] as the pressure-transmitting medium. The title compound dissolved slightly in this pressuretransmitting medium, and recrystallized in the DAC. Raman spectra measured for the recrystallized sample and compared with those previously measured at ambient conditions proved that the substance recrystallized to the same phase. To avoid dissolution and to save the initial sample while loading a DAC, for the subsequent X-ray diffraction experiment, a mixture of pentane with isopentane (in a 1:1 stoichiometric ratio) with a hydrostatic limit of 7 GPa [28] was used. Since pentane and isopentane boil at 309 and 301 K, respectively, a special chamber was used to facilitate the DAC loading [29]. Several facts confirm inertness of isopentane and pentane in relation to the title compound. First of all, no dissolution has been detected for the system studied. Second, all the structure-forming molecules of the title compound are hydrophilic and did not seem to interact actively with hydrophobic pentane. The last but not least, the size of pentane and isopentane molecules is too large for them to enter the crystal structure on increasing pressure without irreversible crystal structure distortions. Raman spectroscopy
Techniques A combination of the single-crystal X-ray diffraction and polarized Raman spectroscopy was used, since it was proven to be especially informative for studying individual amino-acids and their multicomponent crystals at low temperatures and high pressures [18–24].
Raman spectra were recorded using a LabRAM HR 800 spectrometer from HORIBA Jobin Yvon with a CCD detector. For spectral excitation a 488 nm line of an Ar+ laser was used with a beam size of 1 lm at the surface of the sample and 8 mW power. All data were collected using a Raman microscope in backscattering geometry. Spectral resolution was 3 cm1, but
Table 1 Cell refinement details and parameters of data collection for bis(DL-serinium) oxalate dehydrate before the phase transition. Pressure (GPa)
0.4
1.0
1.4
2.0
2.5
3.0
3.5
4.0
a (Å) b (Å) c (Å) b (°) V (Å3) Number of reflections for cell refinement hmin hmax hmin hmax kmin kmax lmin lmax
4.8472 (3) 17.0785 (13) 16.999 (5) 92.308 (12) 1406.1 (5) 1318 1.6875 27.9929 6 6 21 21 11 11
4.8320 (4) 16.9564 (14) 16.773 (6) 92.812 (14) 1372.6 (6) 1345 2.3974 28.1526 6 6 21 21 10 10
4.8217 (4) 16.8223 (14) 16.637 (6) 94.011 (14) 1346.1 (5) 1226 2.4165 28.1078 6 6 21 21 10 10
4.8110 (4) 16.7098 (14) 16.506 (6) 94.255 (14) 1323.3 (5) 1181 2.4328 28.1522 6 6 21 21 10 10
4.8044 (5) 16.6023 (17) 16.366 (8) 94.85 (2) 1300.7 (7) 958 2.4486 28.1145 6 6 21 21 10 10
4.8014 (4) 16.4937 (14) 16.263 (7) 95.477 (17) 1282.0 (5) 944 2.4647 28.0714 6 6 21 20 10 10
4.7912 (4) 16.3712 (14) 16.181 (8) 95.760 (17) 1262.8 (6) 889 1.7705 28.0377 6 6 20 20 10 10
4.7637 (17) 16.271 (7) 16.17 (4) 95.85 (9) 1247 (3) 436 2.4984 28.2556 6 6 20 20 10 10
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
4
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 4. Crystal structure fragments of bis(DL-serinium) oxalate dihydrate. 1P, 2P and 3P arrows show the directions of the least, medium and major compression, correspondingly.
Fig. 5. Relative volume changes for bis(DL-serinium) oxalate dihydrate (black symbols) and for DL-serine (open symbols).
actual broadening of the bands in the spectra was significantly higher due to an increase in the anharmonicity with increasing pressure [30]. The size of the crystal used for Raman measurements after its recrystallization from the pressure-transmitting medium was 0.040 0.020 0.015 mm, the structure of the sample was confirmed spectroscopically to be the same as before the recrystallization. The title compound was studied up to 5.3 GPa at multiple pressures with a 0.5 GPa interval between the measurements. At each pressure point two Raman spectra were recorded with the polarization of the incident and the scattered beam along the longest side of the crystal and along the medium side of the crystal (i.e. 90° to each other, ll- and mmpolarizations), correspondingly. This was done to facilitate the analysis of structural changes with pressure. Single-crystal X-ray diffraction Data were collected using an Oxford Diffraction Gemini R Ultra X-ray diffractometer with a CCD area detector and Mo Ka radiation. The title compound was studied up to 6.2 GPa. The following software was used: CrysAlis PRO [31] for data collection, cell refinement and data reduction; STRAIN [32] was used to calculate the anisotropy of lattice strain. Results and discussion Bis(DL-serinium) oxalate dihydrate, 2C3H8NO+3C2O2 4 2H2O (Fig. 1) crystallizes in space group P21/c [21,33]. As was mentioned in the Experimental, the crystals dissolved slightly in the
methanol–ethanol mixture and this resulted in the recrystallization of the crystals at the initial pressure increase. At the first pressure point a Raman spectrum from recrystallized sample was measured and compared with the spectrum of dry solid compound without any liquids. These spectra were identical and there were no reasons to suppose inclusion of the solvent molecules into the crystal structure. The microphotographs of recrystallized sample at several pressures are shown at Fig. 2a. Further increase in pressure did not result in any additional dissolution of the sample. Therefore, the changes in the Raman spectra were measured for these recrystallized samples. However, to avoid dissolution and to save the initial sample while loading a DAC, for the subsequent experiments a mixture of pentane with isopentane (in a 1:1 stoichiometric ratio) with a hydrostatic limit of 7 GPa [28] was used. The changes in the spectra observed in pentane–isopentane mixture were the same as in the mixture of alcohols, and the phase transition (see below) was observed in the same pressure range for either of the pressure-transmitting liquids. Both the photographs and the polarized Raman spectra of bis(DL-serinium) oxalate dihydrate measured at different pressures (Fig. 3) show clearly that a phase transition occurs between 3.8 and 4.3 GPa. The three translational bands merged into one high-intensity band at 140 cm1 (Raman shift at 4.3 GPa) and the intensity of a libration band at 217 cm1 (Raman shift at 3.8 GPa) decreased very strongly during the phase transition. In the higher wavenumbers range the most significant changes were observed for the bands related to the C–C and C–N stretching vibrations (between 800 and 1100 cm1). A strong increase of intensity was observed for the bands at 901 and 1038 cm1 as compared to the band at 870 cm1 (Raman shifts at 4.3 GPa). Importantly, when analyzing the spectra recorded with different polarization vectors one can see that the same picture was observed for different polarizations in the range between 100 and 220 cm1, and only two bands at 140 and 201 cm1 (Raman shifts at 4.3 GPa) were visible in the spectra. A mere visual inspection gave evidence that some process has occurred in the crystal at this pressure (Fig. 2a). Raman data suggested that the crystal of bis(DL-serinium) oxalate dihydrate underwent a phase transition accompanied by disordering, since the polarized Raman spectra measured for a ‘‘normal’’ (undisturbed) monoclinic crystal structure should not be so similar for different crystal orientations and light polarizations. To prove this hypothesis we have performed an additional single-crystal X-ray diffraction experiment. Crystal structure stability up to 4 GPa was completely confirmed by diffraction measurements, and it was possible to obtain cell parameters and to calculate the anisotropy of lattice strain for this pressure range. Unfortunately it was not possible to follow fine details of changing molecular geometry and hydrogen bonds at high pressure because of a relatively lower quality of high-pressure data and a higher number of parameters for refinement, as compared with the
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
5
Fig. 6. Reconstruction of layers containing vectors: (a) column – [0 1 0] and [0 0 1]), (b) column – [0 1 0] and [1 0 0] at selected pressures. Background and gasket reflections are subtracted for clarity. Strong stretched spots are diamond reflections.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
6
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx
previously published high-pressure study of a related compound – DL-alaninium semi-oxalate monohydrate (the only detailed study of the changes in a crystal structure of an amino acid salt at high pressures up to now) [18]. Details of data collection, cell parameters and parameters characterizing directions of principal axes of strain ellipsoid up to 4 GPa are summarized in Tables 1 and 2. Directions of the principal axes of strain ellipsoid in relation to the main structural motifs are shown at Fig. 4. Comparing these data to the strain induced in the same structure on cooling [21], one can see an obvious similarity. The structure expands slightly in the direction of the C44(20) hydrogen-bonded chains formed by the strongest hydrogen bonds in the structure (principal axis 1). Medium compression (axis 2) coincides with the crystallographic axis b, and the largest compression is observed in the direction close to that along the hydrogen-bonded chains C33(9) formed by the weakest hydrogen bonds in the structure between water molecules. Thus, the anisotropy of lattice strain correlates well with the relative strength of different types of intermolecular hydrogen bonds in the crystal structure. It is also interesting to compare the compression of bis(DL-serinium) oxalate dihydrate with that of the corresponding individual amino acid, DL-serine. Relative volume changes for the salt (the present study) and the individual amino acid [30,34] are almost identical; only at pressures above 2.5 GPa bis(DL-serinium) oxalate dihydrate compressed slightly stronger, than DL-serine, although the salt hydrate has stronger hydrogen bonds in its crystal structure (Fig. 5). At the same time, DL-serine does not undergo phase transitions up to 8.6 GPa [34], in contrast to the oxalate hydrate. The compression of bis(DL-serinium) oxalate dihydrate on cooling down to 100 K [21] was significantly (3 times) stronger than that of the individual amino acid. This shows that high pressures and low temperatures influence the crystal structure in different ways, even though the directions of principal axes and the anisotropy of strain are similar. On increasing pressure above the phase transition point, the crystal significantly changed, so that the borderlines between domains could be detected visually using an optical microscope (Fig. 2b), confirming the occurrence of the phase transition. Remarkably, these changes were completely reversible, and this was additionally confirmed by single-crystal X-ray diffraction. Strong scattering of the X-rays in the plane containing [0 1 0] and [0 0 1] vectors was observed in the diffraction patterns measured above the phase transition point (Fig. 6). This provided evidence of a substantial degree of disorder in the high-pressure phase. At the same time, the scattering did not make it possible to integrate the intensities reliably and to find the cell parameters. As a result the crystal structure of the high-pressure phase could not be solved. Taking into account the reconstruction of the layers shown at Fig. 6, we could conclude that the crystal structure was disordered in the (b*c*) plane and this manifested itself as ‘‘layers’’ of reflections in the reciprocal space; b and c cell parameters could not be found correctly, while the third parameter related to the distance between these layers after the phase transition could be estimated roughly as 4.7 Å, what is close to a parameter before the transition. Attempts to model this disorder theoretically using DISCUS software [35] have so far been unsuccessful due to the complexity of this crystal structure and a very large number of parameters that can be varied.
Conclusions The reversible pressure-induced disorder in bis(DL-serinium) oxalate dihydrate is an interesting example of a process when the regular orientation of molecular fragments in a crystal structure can be first distorted by compressing the structure and
reducing the volume, but is then completely restored reversibly on decompression. Apparently, the strong hydrogen bonds present in the structure help in preserving the main structural framework and its reversible distortion, whereas the weak hydrogen bonds together with the ability of the molecular fragments and molecules to rotate account for disordering after the phase transition point. A somewhat similar process – with strong hydrogen bonds preserving the main structural framework and the integrity of a single crystal, and the weak ones ‘‘switching over’’ – was observed and studied in details in the crystals of DL-alaninium semi-oxalate monohydrate [18]. The peculiar feature of the system described in the present study is that the structure transforms reversibly not between two ordered crystalline phases, or between a crystalline and an amorphous state, but between an ordered and a partially disordered crystalline states, and the single crystal splits into multiple domains on compression, but is restored completely as a perfect crystal when pressure is released. Acknowledgements This work was supported by RFBR (Project 12-03-31541 mol_a), by Russian Academy of Sciences, by the Ministry of Education and Science of Russian Federation and by a Grant from the President of Russia for State support of Russian leading Scientific Schools (Project NSh-221.2012.3). We are very grateful to Prof. Boris A. Kolesov for discussing the results of Raman spectroscopy. References [1] A. Katrusiak, P. McMillan (Eds.), High Pressure Crystallography, Kluwer, Dordrecht, 2003. [2] E.V. Boldyreva, P. Dera (Eds.), High-pressure crystallography, From Novel Experimental Approaches to Applications in Cutting-Edge Technologies, Springer, Dordrecht, 2010. [3] S.K. Sikka, S.M. Sharma, Phase Transit. 81 (2008) 907–934. [4] E.V. Boldyreva, Herald Russ. Acad. Sci. 82 (2012) 423–431. [5] S.A. Moggach, S. Parsons, P.A. Wood, Crystallogr. Rev. 14 (2008) 143–184. [6] A. Katrusiak, Acta Cryst. A 64 (2008) 135–148. [7] E.V. Boldyreva, Acta Cryst. A 64 (2008) 218–231. [8] R.D.L. Johnstone, M. Ieva, A.R. Lennie, H. McNab, E. Pidcock, J.E. Warren, et al., CrystEngComm 12 (2010) 2520–2523. [9] Y.V. Seryotkin, T.N. Drebushchak, E.V. Boldyreva, Acta Cryst. B 69 (2013) 77– 85. [10] S.M. Sharma, S.K. Sikka, Prog. Mater. Sci. 40 (1996) 1–77. [11] N.P. Funnell, W.G. Marshall, S. Parsons, CrystEngComm 13 (2011) 5841– 5848. [12] A.K. Mishra, C. Murli, N. Garg, R. Chitra, S.M. Sharma, J. Phys. Chem. B 114 (2010) 17084–17091. [13] E.V. Boldyreva, Z. Kristallogr. 229 (2014) 236–245. [14] M. Fleck, A.M. Petrosyan, J. Cryst. Growth 312 (2010) 2284–2290. [15] V.V. Ghazaryan, M. Fleck, A.M. Petrosyan, J. Cryst. Growth 362 (2013) 182– 188. [16] V.S. Minkov, E.V. Boldyreva, T.N. Drebushchak, C.H. Görbitz, CrystEngComm 14 (2012) 5943–5954. [17] B.A. Zakharov, E.A. Losev, E.V. Boldyreva, CrystEngComm 15 (2013) 1693– 1697. [18] B.A. Zakharov, E.V. Boldyreva, Acta Cryst. B 69 (2013) 271–280. [19] B.A. Kolesov, E.V. Boldyreva, J. Phys. Chem. B 111 (2007) 14387–14397. [20] B.A. Kolesov, E.V. Boldyreva, Raman-spectroscopic study of L-alanine single crystals in the temperature range of 3–300 K, in: L. Champion, PM, Ziegler (Ed.), XXII Int. Conf. Raman Spectrosc., 2010, pp. 619–620. [21] B.A. Zakharov, B.A. Kolesov, E.V. Boldyreva, Phys. Chem. Chem. Phys. 13 (2011) 13106–13116. [22] E.V. Boldyreva, Phase Transit. 82 (2009) 303–321. [23] N.A. Tumanov, E.V. Boldyreva, B.A. Kolesov, A.V. Kurnosov, R. Quesada Cabrera, Acta Cryst. B 66 (2010) 458–471. [24] B.A. Zakharov, E.A. Losev, B.A. Kolesov, V.A. Drebushchak, E.V. Boldyreva, Acta Cryst. B 68 (2012) 287–296. [25] R. Boehler, Rev. Sci. Instrum. 77 (2006) 115103-1–115103-3. [26] R.A. Forman, G.J. Piermarini, J. Dean Barnett, S. Block, Science 176 (1972) 284– 285. [27] G.J. Piermarini, S. Block, J.D. Barnett, R.A. Forman, J. Appl. Phys. 46 (1975) 2774–2780. [28] G.J. Piermarini, J. Appl. Phys. 44 (1973) 5377–5382. [29] B.A. Zakharov, A.F. Achkasov, J. Appl. Crystallogr. 46 (2013) 267–269. [30] B.A. Zakharov, B.A. Kolesov, E.V. Boldyreva, Acta Cryst. B 68 (2012) 275–286.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067
B.A. Zakharov, E.V. Boldyreva / Journal of Molecular Structure xxx (2014) xxx–xxx [31] OxfordDiffraction, CrysAlisPro, 2010. [32] Y. Ohashi, C.W. Burnham, Am. Miner. 58 (1973) 843–849. [33] M. Alagar, M. Subha Nandhini, R.V. Krishnakumar, S. Natarajan, Acta Cryst. E 58 (2002) o114–o116.
7
[34] E.V. Boldyreva, E.N. Kolesnik, T.N. Drebushchak, H. Sowa, H. Ahsbahs, Y.V. Seryotkin, Z. Kristallogr. 221 (2006) 150–161. [35] R.B. Neder, T. Proffen, Diffuse Scattering and Defect Structure Simulations. A Cook Book Using the Program DISCUS. IUCr, Oxford University Press, 2008.
Please cite this article in press as: B.A. Zakharov, E.V. Boldyreva, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.067