Pub Date : 2017-02-01DOI: 10.1107/S2052520616019181
A. Vegas, H. Jenkins
The structure of (NH4)2Ge7O15 recently described as being a microporous material containing rings, in which GeO6 octahedra coexist with GeO4 tetrahedra, is re-examined in the light of the Extended Zintl–Klemm Concept as applied to cations in oxides. The Ge[6] atoms together with the NH4+ groups act as true cations, transferring their 6 valence electrons to the acceptor Ge2O5 moiety, so converting it into the [Ge6O15]6−≡3(Ψ-As2O5) ion (where Ψ refers to a pseudo-lattice) and yielding threefold connectivity. The tetrahedral Ge network shows similarities with the Sb2O3 analogue. At the same time, the Ge[6] atoms are connected to other Ge[4] atoms forming blocks that are part of a rutile-type GeO2 structure. Such an analysis shows that both substructures (the Zintl polyanion and the rutile fragments) must be satisfied simultaneously as has already been illustrated in previous articles which considered stuffed-bixbyites [Vegas et al. (2009). Acta Cryst. B65, 11–21] as well as the compound FeLiPO4 [Vegas (2011). Struct. Bond. 138, 67–91]. This new insight conforms well to previous (differential thermal analysis) DTA–TGA (thermogravimetric analysis) experiments [Cascales et al. (1998). Angew. Chem. Int. Ed. 37, 129–131], which show endothermic loss of NH3 and H2O to give rise to the metastable structure Ge7O14, which further collapses to the rutile-type GeO2 structure. We analyze the stability change in terms of ionic strength, I, and so provide a means of rationalizing the driving force behind this concept capable of explaining the atomic arrangements found in these types of crystal structures. Although the concept was formulated in 2003, later than the publication of the germanate structure, it was not used or else ignored by colleagues who solved this crystal structure.
最近描述的(NH4)2Ge7O15的结构是一种含有环的微孔材料，其中GeO6八面体与GeO4四面体共存，根据扩展的Zintl-Klemm概念应用于氧化物中的阳离子重新检查。Ge[6]原子与NH4+基团一起充当真正的阳离子，将它们的6个价电子转移到受体Ge2O5部分，从而将其转化为[Ge6O15]6−≡3(Ψ-As2O5)离子(其中Ψ指的是伪晶格)并产生三重连接。四面体Ge网络与Sb2O3类似物有相似之处。同时，Ge[6]原子与其他Ge[4]原子连接，形成块体，成为金红石型GeO2结构的一部分。这样的分析表明，两个子结构(Zintl聚阴离子和金红石碎片)必须同时得到满足，这在之前的文章中已经说明了，这些文章考虑了填充璧石[Vegas et al.(2009)]。Acta结晶。B65, 11-21]以及化合物FeLiPO4 [Vegas(2011)]。结构体。[j].地理学报，2008,27(2):387 - 391。这一新发现与之前的(差热分析)DTA-TGA(热重分析)实验[Cascales et al.(1998)]很好地吻合。Angew。化学。Int。编37,129-131]，表明NH3和H2O的吸热损失产生亚稳结构Ge7O14，进一步坍缩为金红石型GeO2结构。我们从离子强度的角度分析了稳定性的变化，从而提供了一种解释这种概念背后的驱动力的方法，这种概念能够解释在这些类型的晶体结构中发现的原子排列。虽然这个概念是在2003年提出的，晚于日耳曼结构的发表，但它没有被解决这种晶体结构的同事使用或忽视。
{"title":"A revised interpretation of the structure of (NH4)2Ge7O15 in the light of the Extended Zintl–Klemm Concept","authors":"A. Vegas, H. Jenkins","doi":"10.1107/S2052520616019181","DOIUrl":"https://doi.org/10.1107/S2052520616019181","url":null,"abstract":"The structure of (NH4)2Ge7O15 recently described as being a microporous material containing rings, in which GeO6 octahedra coexist with GeO4 tetrahedra, is re-examined in the light of the Extended Zintl–Klemm Concept as applied to cations in oxides. The Ge[6] atoms together with the NH4+ groups act as true cations, transferring their 6 valence electrons to the acceptor Ge2O5 moiety, so converting it into the [Ge6O15]6−≡3(Ψ-As2O5) ion (where Ψ refers to a pseudo-lattice) and yielding threefold connectivity. The tetrahedral Ge network shows similarities with the Sb2O3 analogue. At the same time, the Ge[6] atoms are connected to other Ge[4] atoms forming blocks that are part of a rutile-type GeO2 structure. Such an analysis shows that both substructures (the Zintl polyanion and the rutile fragments) must be satisfied simultaneously as has already been illustrated in previous articles which considered stuffed-bixbyites [Vegas et al. (2009). Acta Cryst. B65, 11–21] as well as the compound FeLiPO4 [Vegas (2011). Struct. Bond. 138, 67–91]. This new insight conforms well to previous (differential thermal analysis) DTA–TGA (thermogravimetric analysis) experiments [Cascales et al. (1998). Angew. Chem. Int. Ed. 37, 129–131], which show endothermic loss of NH3 and H2O to give rise to the metastable structure Ge7O14, which further collapses to the rutile-type GeO2 structure. We analyze the stability change in terms of ionic strength, I, and so provide a means of rationalizing the driving force behind this concept capable of explaining the atomic arrangements found in these types of crystal structures. Although the concept was formulated in 2003, later than the publication of the germanate structure, it was not used or else ignored by colleagues who solved this crystal structure.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"1 1","pages":"94-100"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84063843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616017558
P. Coppens, A. Makal, Bertrand Fournier, K. Jarzembska, R. Kamiński, K. Basuroy, E. Trzop
In picosecond and slower pump–probe diffraction experiments, collection of response–ratio correlation sets prior to full data collection provides an invaluable confirmation of the existence of a light-induced signal prior to full data collection. If a response to light exposure is observed, the quality of the data being collected can be assessed. A number of such correlation plots both for synchrotron and in-house pump–probe data collection are presented.
{"title":"A priori checking of the light-response and data quality before extended data collection in pump–probe photocrystallography experiments","authors":"P. Coppens, A. Makal, Bertrand Fournier, K. Jarzembska, R. Kamiński, K. Basuroy, E. Trzop","doi":"10.1107/S2052520616017558","DOIUrl":"https://doi.org/10.1107/S2052520616017558","url":null,"abstract":"In picosecond and slower pump–probe diffraction experiments, collection of response–ratio correlation sets prior to full data collection provides an invaluable confirmation of the existence of a light-induced signal prior to full data collection. If a response to light exposure is observed, the quality of the data being collected can be assessed. A number of such correlation plots both for synchrotron and in-house pump–probe data collection are presented.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"59 1","pages":"23-26"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82336713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616018308
N. Thomas
The method of Ionic Network Analysis (INA) is defined by reference to the known crystal structures of olivine minerals. It is based on a reversible transformation between two alternative representations of ionic crystal structures: (a) the crystallographic and (b) the interactional. Whereas the former encompasses unit-cell parameters and atomic coordinates, the latter consists of selected interaction vectors between ions. Since the lengths and orientations of these vary only slightly between crystal structures obtained under systematically varying (p, T, X) conditions, they may be used to predict the crystal structures at intermediate (p, T, X) values by interpolation. Two interactional networks are constructed, one for the anions and the other for cations. As both networks lead to independent calculated values of the unit-cell parameters, it is possible to exploit the known, continuous (p, T, X) variations of cell parameters as normative constraints for the prediction of atomic coordinates within a predictive structural refinement procedure. Continuously varying structurally based parameters such as the volumes of cation coordination polyhedra may likewise be used. The choice of olivines for developing the method has been guided by the availability of pressure, temperature and compositional structural data for them. However, the ideas are expounded sufficiently generally for the method to be applied to other minerals.
{"title":"Crystal structure prediction by ionic network analysis: the example of (p–T–X)-structure relationships in olivines","authors":"N. Thomas","doi":"10.1107/S2052520616018308","DOIUrl":"https://doi.org/10.1107/S2052520616018308","url":null,"abstract":"The method of Ionic Network Analysis (INA) is defined by reference to the known crystal structures of olivine minerals. It is based on a reversible transformation between two alternative representations of ionic crystal structures: (a) the crystallographic and (b) the interactional. Whereas the former encompasses unit-cell parameters and atomic coordinates, the latter consists of selected interaction vectors between ions. Since the lengths and orientations of these vary only slightly between crystal structures obtained under systematically varying (p, T, X) conditions, they may be used to predict the crystal structures at intermediate (p, T, X) values by interpolation. Two interactional networks are constructed, one for the anions and the other for cations. As both networks lead to independent calculated values of the unit-cell parameters, it is possible to exploit the known, continuous (p, T, X) variations of cell parameters as normative constraints for the prediction of atomic coordinates within a predictive structural refinement procedure. Continuously varying structurally based parameters such as the volumes of cation coordination polyhedra may likewise be used. The choice of olivines for developing the method has been guided by the availability of pressure, temperature and compositional structural data for them. However, the ideas are expounded sufficiently generally for the method to be applied to other minerals.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"77 1","pages":"74-86"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84654112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616017844
R. N. Devi, C. Jelsch, S. Israel, E. Aubert, C. Anzline, Amar A. Hosamani
The experimental charge density analysis of the anti-hyperglycemic agent metformin chloride with high-resolution X-ray diffraction data at low temperature (100 K) has been performed and these experimental results were compared with that derived from the corresponding periodic theoretical calculations at the B3LYP/6-31G** level of theory. The experimental and theoretical multipolar charge-density analyses of metformin chloride have been accomplished in order to understand its structural and electronic properties. The C and N atoms of the molecular backbone adopt a near trigonal geometry due to the occurrence of extensive delocalization/resonance of C—N bonds, as confirmed by topological analysis and also found by Natural Resonance Theory calculations performed in the isolated metformin cation. The molecule contains six C—N bonds and the topological bond order analysis shows that four bonds have bond orders close to 4/3 and two bonds can be considered as single. The analysis of numerical parameters of the valence shell charge concentration reports that the N3 atom, which forms two bonds with C atoms, possesses one non-bonding valence-shell charge concentration (VSCC) in the direction of the electron lone pair. Among the intermolecular interactions of the chloride atom with the H—C and H—N atoms, eight have been found to be shorter than the sum of van der Waals radii. The analysis of contacts on the Hirshfeld surface reveals that the H—N⋯Cl hydrogen bonds are enriched (over-represented) and act as the driving force in the crystal packing formation. The metformin cations form favorable electrostatic interactions with the chloride anions which have globally a stronger energy than the unfavorable cation/cation interactions.
{"title":"Charge density analysis of metformin chloride, a biguanide anti-hyperglycemic agent","authors":"R. N. Devi, C. Jelsch, S. Israel, E. Aubert, C. Anzline, Amar A. Hosamani","doi":"10.1107/S2052520616017844","DOIUrl":"https://doi.org/10.1107/S2052520616017844","url":null,"abstract":"The experimental charge density analysis of the anti-hyperglycemic agent metformin chloride with high-resolution X-ray diffraction data at low temperature (100 K) has been performed and these experimental results were compared with that derived from the corresponding periodic theoretical calculations at the B3LYP/6-31G** level of theory. The experimental and theoretical multipolar charge-density analyses of metformin chloride have been accomplished in order to understand its structural and electronic properties. The C and N atoms of the molecular backbone adopt a near trigonal geometry due to the occurrence of extensive delocalization/resonance of C—N bonds, as confirmed by topological analysis and also found by Natural Resonance Theory calculations performed in the isolated metformin cation. The molecule contains six C—N bonds and the topological bond order analysis shows that four bonds have bond orders close to 4/3 and two bonds can be considered as single. The analysis of numerical parameters of the valence shell charge concentration reports that the N3 atom, which forms two bonds with C atoms, possesses one non-bonding valence-shell charge concentration (VSCC) in the direction of the electron lone pair. Among the intermolecular interactions of the chloride atom with the H—C and H—N atoms, eight have been found to be shorter than the sum of van der Waals radii. The analysis of contacts on the Hirshfeld surface reveals that the H—N⋯Cl hydrogen bonds are enriched (over-represented) and act as the driving force in the crystal packing formation. The metformin cations form favorable electrostatic interactions with the chloride anions which have globally a stronger energy than the unfavorable cation/cation interactions.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"29 1","pages":"10-22"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89613026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616018412
M. R. Jørgensen, P. Piccoli, V. R. Hathwar, Xiaoping Wang, C. Hoffmann, A. Yakovenko, G. J. Halder, J. Schlueter, B. Iversen, A. Schultz
The structural phase transition accompanied by a Jahn-Teller switch has been studied over a range of H/D ratios in (NH4)2[Cu(H2O)6](SO4)2 (ACTS). In particular, single-crystal neutron diffraction investigations of crystals with deuteration in the range 50 to 82% are shown to be consistent with previous electron paramagnetic resonance (EPR) experiments exhibiting a phase boundary at 50% deuteration under ambient pressure. Polycrystalline samples show that the two phases can co-exist. In addition, single-crystal neutron and polycrystalline X-ray diffraction pressure experiments show a shift to lower pressure at 60% deuteration versus previous measurements at 100% deuteration. (Less)
{"title":"Neutron and X-ray investigations of the Jahn–Teller switch in partially deuterated ammonium copper Tutton salt, (NH4)2[Cu(H2O)6](SO4)2","authors":"M. R. Jørgensen, P. Piccoli, V. R. Hathwar, Xiaoping Wang, C. Hoffmann, A. Yakovenko, G. J. Halder, J. Schlueter, B. Iversen, A. Schultz","doi":"10.1107/S2052520616018412","DOIUrl":"https://doi.org/10.1107/S2052520616018412","url":null,"abstract":"The structural phase transition accompanied by a Jahn-Teller switch has been studied over a range of H/D ratios in (NH4)2[Cu(H2O)6](SO4)2 (ACTS). In particular, single-crystal neutron diffraction investigations of crystals with deuteration in the range 50 to 82% are shown to be consistent with previous electron paramagnetic resonance (EPR) experiments exhibiting a phase boundary at 50% deuteration under ambient pressure. Polycrystalline samples show that the two phases can co-exist. In addition, single-crystal neutron and polycrystalline X-ray diffraction pressure experiments show a shift to lower pressure at 60% deuteration versus previous measurements at 100% deuteration. (Less)","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"42 1","pages":"87-93"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85739560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S205252061601917X
O. Siidra, E. Nazarchuk, S. Bocharov, W. Depmeier, A. Zadoya
Four new inorganic uranyl chromates were obtained by evaporation and hydrothermal methods: [(CH3)2NH2]2[(UO2)2(CrO4)3(H2O)](H2O) (1), K(Rb0.6K0.4)[(UO2)2(CrO4)3(H2O)](H2O)3 (2) [(CH3)3CNH3]2[(UO2)2(CrO4)3H2O] (3), [(CH3)2NH2]4[(UO2)2(CrO4)3H2O]2(H2O) (4). Their structures are based on two-dimensional chiral or achiral units with the composition [(UO2)2(CrO4)3(H2O)]2− and two types of topologies (A or/and B). The structural architecture of (4) is unique amongst all known uranyl-based structures, and unusual among hybrid organic/inorganic structures in general as it contains layers of identical composition, but of different topology. The unique structural configurations and non-centrosymmetry in (1) and (4) is governed by selective formation of hydrogen bonding rather than by the formation of hydrophobic and hydrophilic zones in the organic interlayer. It is shown that chiral architectures in uranyl systems may form from achiral building units as observed in (3) and (4). This is somewhat analogous to certain organic compounds, where achiral molecules are also able to form chiral layers. Within the concept of such an interpretation the structure of (3) can then be described as a racemate consisting of two A and A′ chiral layers. In a similar approach the structure of (4) can be interpreted as being formed by four chiral layers. Layer pairs AA′ and BB′ can then be considered as racemic pairs and the whole structure is a co-racemate built by a combination of two racemates. Two-stage formation can be suggested for (4).
{"title":"Formation of co-racemic uranyl chromate constructed from chiral layers of different topology","authors":"O. Siidra, E. Nazarchuk, S. Bocharov, W. Depmeier, A. Zadoya","doi":"10.1107/S205252061601917X","DOIUrl":"https://doi.org/10.1107/S205252061601917X","url":null,"abstract":"Four new inorganic uranyl chromates were obtained by evaporation and hydrothermal methods: [(CH3)2NH2]2[(UO2)2(CrO4)3(H2O)](H2O) (1), K(Rb0.6K0.4)[(UO2)2(CrO4)3(H2O)](H2O)3 (2) [(CH3)3CNH3]2[(UO2)2(CrO4)3H2O] (3), [(CH3)2NH2]4[(UO2)2(CrO4)3H2O]2(H2O) (4). Their structures are based on two-dimensional chiral or achiral units with the composition [(UO2)2(CrO4)3(H2O)]2− and two types of topologies (A or/and B). The structural architecture of (4) is unique amongst all known uranyl-based structures, and unusual among hybrid organic/inorganic structures in general as it contains layers of identical composition, but of different topology. The unique structural configurations and non-centrosymmetry in (1) and (4) is governed by selective formation of hydrogen bonding rather than by the formation of hydrophobic and hydrophilic zones in the organic interlayer. It is shown that chiral architectures in uranyl systems may form from achiral building units as observed in (3) and (4). This is somewhat analogous to certain organic compounds, where achiral molecules are also able to form chiral layers. Within the concept of such an interpretation the structure of (3) can then be described as a racemate consisting of two A and A′ chiral layers. In a similar approach the structure of (4) can be interpreted as being formed by four chiral layers. Layer pairs AA′ and BB′ can then be considered as racemic pairs and the whole structure is a co-racemate built by a combination of two racemates. Two-stage formation can be suggested for (4).","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"26 1","pages":"101-111"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89928664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616017935
Piotr Fabrykiewicz, M. Stekiel, I. Sosnowska, R. Przeniosło
High-resolution synchrotron radiation powder diffraction patterns of α-Fe2O3 measured between room temperature and 1100 K, i.e. above the Neel temperature TN = 950 K, have been analyzed. The integral breadths of the Bragg peaks show a hkl-dependent anisotropy, both below and above TN. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). J. Appl. Cryst. 32, 281]. Model calculations show that the rhombohedral α-Fe2O3 lattice is deformed and the deformation leads to a monoclinic lattice with the unique monoclinic axis along the hexagonal [110] direction both below and above TN. The monoclinic symmetry of bulk α-Fe2O3 is compatible with α-Fe2O3 nanowire growth along the [110] direction reported in Fu et al. [Chem. Phys. Lett. (2001), 350, 491].
{"title":"Deformations of the α-Fe2O3 rhombohedral lattice across the Néel temperature","authors":"Piotr Fabrykiewicz, M. Stekiel, I. Sosnowska, R. Przeniosło","doi":"10.1107/S2052520616017935","DOIUrl":"https://doi.org/10.1107/S2052520616017935","url":null,"abstract":"High-resolution synchrotron radiation powder diffraction patterns of α-Fe2O3 measured between room temperature and 1100 K, i.e. above the Neel temperature TN = 950 K, have been analyzed. The integral breadths of the Bragg peaks show a hkl-dependent anisotropy, both below and above TN. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). J. Appl. Cryst. 32, 281]. Model calculations show that the rhombohedral α-Fe2O3 lattice is deformed and the deformation leads to a monoclinic lattice with the unique monoclinic axis along the hexagonal [110] direction both below and above TN. The monoclinic symmetry of bulk α-Fe2O3 is compatible with α-Fe2O3 nanowire growth along the [110] direction reported in Fu et al. [Chem. Phys. Lett. (2001), 350, 491].","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"27 1","pages":"27-32"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81072413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616018801
D. Goossens, E. Chan
Terephthalic acid (TPA, C8H6O4) is an industrially important chemical, one that shows polymorphism and disorder. Three polymorphs are known, two triclinic [(I) and (II)] and one monoclinic (III). Of the two triclinic polymorphs, (II) has been shown to be more stable in ambient conditions. This paper presents models of the local order of polymorphs (I) and (II), and compares the single-crystal diffuse scattering (SCDS) computed from the models with that observed from real crystals. TPA shows relatively weak and less-structured diffuse scattering than some other polymorphic materials, but it does appear that the SCDS is less well modelled by a purely harmonic model in polymorph (I) than in polymorph (II), according to the idea that the diffuse scattering is sensitive to anharmonicity that presages a structural phase transition. The work here verifies that displacive correlations are strong along the molecular chains and weak laterally, and that it is not necessary to allow the —COOH groups to librate to successfully model the diffuse scattering – keeping in mind that the data are from X-ray diffraction and not directly sensitive to H atoms.
{"title":"Synchrotron X-ray diffuse scattering from a stable polymorphic material: terephthalic acid, C8H6O4","authors":"D. Goossens, E. Chan","doi":"10.1107/S2052520616018801","DOIUrl":"https://doi.org/10.1107/S2052520616018801","url":null,"abstract":"Terephthalic acid (TPA, C8H6O4) is an industrially important chemical, one that shows polymorphism and disorder. Three polymorphs are known, two triclinic [(I) and (II)] and one monoclinic (III). Of the two triclinic polymorphs, (II) has been shown to be more stable in ambient conditions. This paper presents models of the local order of polymorphs (I) and (II), and compares the single-crystal diffuse scattering (SCDS) computed from the models with that observed from real crystals. TPA shows relatively weak and less-structured diffuse scattering than some other polymorphic materials, but it does appear that the SCDS is less well modelled by a purely harmonic model in polymorph (I) than in polymorph (II), according to the idea that the diffuse scattering is sensitive to anharmonicity that presages a structural phase transition. The work here verifies that displacive correlations are strong along the molecular chains and weak laterally, and that it is not necessary to allow the —COOH groups to librate to successfully model the diffuse scattering – keeping in mind that the data are from X-ray diffraction and not directly sensitive to H atoms.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"106 1","pages":"112-121"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74879517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616019028
N. Sabalisck, C. Guzmán-Afonso, C. González-Silgo, M. Torres, J. Pasán, J. del-Castillo, D. Ramos-Hernández, A. Hernández-Suárez, L. Mestres
In order to clarify the polymorphism in the lithium sulfate family, LiREx(NH4)1 − xSO4 (0.5 ≤ x ≤ 4.0 mol%, nominal value; RE = Er3+, Yb3+ and Dy3+) crystals were grown from aqueous solution by slow evaporation between 298 and 313 K. The doping of the samples allowed us to obtain two polymorphic forms, α and β, of LiNH4SO4 (LAS). By means of X-ray diffraction (XRD) in single crystals, we determined the crystal structures of two new α-polytypes, which we have named α1- and α2-LAS. They present the same space group P21/c and the following relation among their lattice parameters: a2 = −c1, b2 = −b1, c2 = −2a1 − c1. In order to evaluate the stability of the new α-polytypes, we performed thermal analysis, X-ray diffraction and dielectric spectroscopy on single crystals and polycrystalline samples over the cyclic temperature range: 190 → 575 → 190 K. The results obtained by all the techniques used in this study demonstrate that α-polytypes are stable across a wide range of temperatures and they show an irreversible phase transition to the paraelectric β-phase above 500 K. In addition, a comparative study of α- and β-polytypes shows that both polymorphic structures have a common axis, with a possible intergrowth that facilitates their coexistence and promotes the reconstructive α → β transition. This intergrowth was related to small anomalies detected between 240 and 260 K, in crystals with an α-habit.
{"title":"Structures and thermal stability of the α-LiNH4SO4 polytypes doped with Er3+ and Yb3+","authors":"N. Sabalisck, C. Guzmán-Afonso, C. González-Silgo, M. Torres, J. Pasán, J. del-Castillo, D. Ramos-Hernández, A. Hernández-Suárez, L. Mestres","doi":"10.1107/S2052520616019028","DOIUrl":"https://doi.org/10.1107/S2052520616019028","url":null,"abstract":"In order to clarify the polymorphism in the lithium sulfate family, LiREx(NH4)1 − xSO4 (0.5 ≤ x ≤ 4.0 mol%, nominal value; RE = Er3+, Yb3+ and Dy3+) crystals were grown from aqueous solution by slow evaporation between 298 and 313 K. The doping of the samples allowed us to obtain two polymorphic forms, α and β, of LiNH4SO4 (LAS). By means of X-ray diffraction (XRD) in single crystals, we determined the crystal structures of two new α-polytypes, which we have named α1- and α2-LAS. They present the same space group P21/c and the following relation among their lattice parameters: a2 = −c1, b2 = −b1, c2 = −2a1 − c1. In order to evaluate the stability of the new α-polytypes, we performed thermal analysis, X-ray diffraction and dielectric spectroscopy on single crystals and polycrystalline samples over the cyclic temperature range: 190 → 575 → 190 K. The results obtained by all the techniques used in this study demonstrate that α-polytypes are stable across a wide range of temperatures and they show an irreversible phase transition to the paraelectric β-phase above 500 K. In addition, a comparative study of α- and β-polytypes shows that both polymorphic structures have a common axis, with a possible intergrowth that facilitates their coexistence and promotes the reconstructive α → β transition. This intergrowth was related to small anomalies detected between 240 and 260 K, in crystals with an α-habit.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"21 1","pages":"122-133"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90750031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-01DOI: 10.1107/S2052520616017534
A. Udovenko, Alexander A. Karabtsovb, Natalia M. Laptasha
A classical elpasolite-type structure is considered with respect to dynamically disordered ammonium fluoro-(oxofluoro-)metallates. Single-crystal X-ray diffraction data from high quality (NH4)3HfF7 and (NH4)3Ti(O2)F5 samples enabled the refinement of the ligand and cationic positions in the cubic Fm bar 3 m (Z = 4) structure. Electron-density atomic profiles show that the ligand atoms are distributed in a mixed (split) position instead of 24e. One of the ammonium groups is disordered near 8c so that its central atom (N1) forms a tetrahedron with vertexes in 32f. However, a center of another group (N2) remains in the 4b site, whereas its H atoms (H2) occupy the 96k positions instead of 24e and, together with the H3 atom in the 32f position, they form eight spatial orientations of the ammonium group. It is a common feature of all ammonium fluoroelpasolites with orientational disorder of structural units of a dynamic nature.
考虑了动态无序氟-(氧氟-)金属酸铵的典型斜长石型结构。高质量(NH4)3HfF7和(NH4)3Ti(O2)F5样品的单晶x射线衍射数据使立方Fm bar 3 m (Z = 4)结构中的配体和阳离子位置得以细化。电子密度原子谱显示配体原子分布在混合(分裂)位置，而不是24e。其中一个铵基在8c附近无序，因此它的中心原子(N1)在32f处形成一个四面体。然而，另一个基团(N2)的中心仍然在4b位，而它的H原子(H2)占据了96k位而不是24e位，与位于32f位的H3原子一起形成了铵基的8个空间取向。具有动态性质的结构单元取向紊乱是所有氟化铵石的共同特征。
{"title":"Crystallographic features of ammonium fluoroelpasolites: dynamic orientational disorder in crystals of (NH4)3HfF7 and (NH4)3Ti(O2)F5","authors":"A. Udovenko, Alexander A. Karabtsovb, Natalia M. Laptasha","doi":"10.1107/S2052520616017534","DOIUrl":"https://doi.org/10.1107/S2052520616017534","url":null,"abstract":"A classical elpasolite-type structure is considered with respect to dynamically disordered ammonium fluoro-(oxofluoro-)metallates. Single-crystal X-ray diffraction data from high quality (NH4)3HfF7 and (NH4)3Ti(O2)F5 samples enabled the refinement of the ligand and cationic positions in the cubic Fm bar 3 m (Z = 4) structure. Electron-density atomic profiles show that the ligand atoms are distributed in a mixed (split) position instead of 24e. One of the ammonium groups is disordered near 8c so that its central atom (N1) forms a tetrahedron with vertexes in 32f. However, a center of another group (N2) remains in the 4b site, whereas its H atoms (H2) occupy the 96k positions instead of 24e and, together with the H3 atom in the 32f position, they form eight spatial orientations of the ammonium group. It is a common feature of all ammonium fluoroelpasolites with orientational disorder of structural units of a dynamic nature.","PeriodicalId":6887,"journal":{"name":"Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry","volume":"21 1","pages":"1-9"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84933721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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