Polymorphie bei CsTlBr4

Polymorphism of CsTlBr₄ . CsTlBr₄ which is synthesized either by bromation of a 1:1 mixture of CsBr/TlBr or by dehydration of CsTlBr₄ · H₂O, shows trimorphism. The phase transitions α-CsTlBr₄ β-CsTlBr₄ γ-CsTlBr₄ were characterized by thermal analysis, X-ray diffraction and Raman spectroscopy. α-CsTlBr₄ crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 677.78(10), b = 760.77(9), c = 1 768.99(44) pm; Z = 4. In the structure the Cs cations are coordinated by 11 bromines which belong to seven TlBr₄ anions. The structure of β-CsTlBr₄ is unknown. γ-CsTlBr₄ crystallizes in the orthorhombic baryt-type (a = 1 243,5; b = 1029,5; c = 782,5 pm).     

Polymorphie und Mischkristallbildung bei Sulfonamiden und verwandten Verbindungen

Zusammenfassung Im zweiten Teil unserer Untersuchungen an Sulfonamiden und verwandten Verbindungen wurden etwa 70 Zweistoffsysteme mit der Kontaktmethode auf Isomorphie und Mischbarkeit geprüft. Zehn Zustandsdiagramme wurden quantitativ aufgenommen. Es zeigte sich, daß Sulfapyridin und Sulfathiazol den größten Verwandtschaftsgrad aufweisen; in diesem System konnten drei isomorphe Mischkristallreihen realisiert werden. Besonderes Interesse verdienen die beiden Systeme Sulfapyridin—Sulfametin und Sulfathiazol—Sulfametin, da sie Pseudomolekülverbindungen bilden. Diese kommen durch Stabilisierung des Maximums einer von äußerst instabilen Modifikationen gebildeten Mischkristallreihe nach Typ. II Roozeboom zustande und ihre Liquiduskurve gleicht einer echten Molekülverbindung.

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Polymorphism and formation of mixed crystals in sulfonamides and related compounds

Summary In the second part of our investigations of sulfonamides and related compounds about 70 binary systems were studied for isomorphism and miscibility by the contact method. Ten phase diagrams were taken up quantitatively. It was found that sulfapyridine and sulfathiazole exhibit the greatest degree of relationship; three isomorphous mixed crystals series were realized in this system. Special interest resides in the two systems sulfapyridine-sulfametine and sulfathiazole-sulfametine because they yield pseudomolecular compounds. These arise through stabilization of the maximum of one of the unstable modifications of the mixed crystals formed according to Type II Roozeboom and its liquidus curve resembles a genuine molecular compound.

     

Zur Polymorphie von In5Br7

On the Polymorphism of In₅Br₇ The existence of two polymorphs of In₅Br₇ has been proved by single crystal structure determinations. In₅Br₇ (tP192) crystallizes with the tetragonal space group P4₁2₁2 and lattice parameters a_t = 1318.9(5) pm and c_t = 3723.8(9) pm (293 K). Concerning monoclinic In₅Br₇ (mC192), the centrosymmetric space group C2/c with lattice parameters a_m = 1867.3(4) pm, b_m=1867.0(5) pm, c_m = 1918.0(7) pm, and β_m = 103.96(2)° (293 K) has been confirmed. Both modifications of In₅Br₇ are built up from layers of the same type. These layers with a thickness of about 930 pm consist of structure fragments [InBr₂]⁴⁺ and [InBr₁₂]^4–. The anion is composed of two ethan‐like [InBr₆]^2– units, which contain In–In bonds. The stacking sequence of the layers with symmetry C 1 2 (1) differs for the two modifications of In₅Br₇. The tetragonal form is generated by applying a 4₁ screw axis; the monoclinic polymorph is formed by introducing inversion centers between the layers. The adequate name of In₅Br₇ = In[InBr₆]Br is triindium(I)‐hexabromodiindate(II)(In–In)‐bromide.     

Polymorphie bei APd2X2-Verbindungen (A = Sr,Ba; X = As,Sb)

Polymorphism of APd₂X₂-Compounds (A = Sr, Ba; X = As, Sb) SrPd₂Sb₂ crystallizes at room temperature in the CaBe₂Ge₂-type structure (lattice constants see “Inhaltsübersicht”); a high-temperature modification with ThCr₂Si₂-type structure was obtained by quenching samples from above 730°C. The same structure was found for the high-temperature modification of BaPd₂As₂ which can be prepared by quenching from above 720°C. For (ThCr₂Si₂-structure) no phase transition could be observed.     

Röntgenstrukturanalyse von 2,4,6-Tri(tert-butyl)phenyl-lithium · N,N,N′,N′-Tetramethylpropan-1,2-diamin: Eine monomere Organolithium-Verbindung

X-Ray Crystal-Structure Analysis of 2,4,6-Tri(tert-butyl)phenyllithium · N,N,N′,N′-Tetramethylpropane-1,2-diamine: a Monomeric Organolithium Compound Tri(tert-butyl)phenyllithium is an important reagent for the preparation of derivatives of main-group elements with low coordination state as well as a highly hindered base for the generation of amine-free Li-enolates. Its monomeric nature in solution was previously deduced from NMR measurements. While Et₂O, THF, and N,N,N′,N′-tetramethylethylene-1,2-diamine (tmen) led to crystalline samples which were not suitable for structure analysis, the N,N,N′,N′-tetramethylpropane-1,2-diamine (tmpn) gave good single crystals of the title compound from Et₂O/hexane (disorder along the two-fold crystallographic axis running through Li? C(1) and C(4) of the Ph ring. The structure (Fig. 1, Table 1) has some remarkable features: (i) it is one of the very few monomeric organolithium compounds so far, (η¹-Li on aromatic ring); (ii) it has the rare trigonal-planar coordination of the Li-atom; iii) there are close contacts between the Li-atom arid one of the Me groups in each ortho-position (Fig. 3). The internal angle on the Ph-ring ipso-C-atom is 114°. This angle as well as those of the other known phenyllithium (Table 2), -magnesium, and -aluminum structures are included in a plot of ipso-angles against Pauling electronegativities (Fig. 2).     

Polymorphie: Fast ein kristallographisches Wintermärchen

A closer look at stories of polymorphic crystals that “appear, ” then “disappear, ” and then ”reappear” again shows that there are no magical mysteries involved. Instead it is the complex interaction between thermodynamics and kinetics that makes the process of crystallization so complex that the experimental results can be almost unbelievable. Clearly the chemists' work is not finished with the pure synthesis, as polymorphic crystals of a new compound have properties which are so different that they might be quite promising one time or undesirable the next. As is true for all fields of chemistry, growing the 'right' crystal form is both a science and an art. Sometimes, though, the mystery that remains is like magic itself.     

Polymorphie von SrTa2O6

Polymorphism of SrTa₂O₆ Orthorhombic SrTa₂O₆ is a new low temperature modification related to orthorhombic CaTa₂O₆. SrTa₂O₆(orh.) was obtained when the wellknown modification SrTa₂O₆(TTB) which is related to the tetragonal tungsten bronzes was heated in the presence of a transporting agent (chlorine) or a mineralizer (melt of B₂O₃) at temperatures below 1150°C. It could be prepared by the reaction of a 1:1 mixture of Sr(NO₃)₂ or SrCO₃ with Ta₂O₅ in a sealed quartz glass tube as well. SrTa₂O₆(orh.) also occurred as an intermediate phase of the reaction of the corresponding 1:2 mixture at temperatures below 900°C (e. g. 840°C). Indexing of Guinier powder patterns led to the following unit cell: a = 11.006 Å, b = 7.638 Å, c = 5.622 Å. At temperatures above 1220°C SrTa₂O₆(orh.) changes (in air) to SrTa₂O₆(TTB). A reversal of this transition could not be achieved without the presence of a mineralizer or a transporting agent. Ca_xSr_1?xTa₂O₆ solid solutions of the low temperature form could not definitely be established. However, at 1300°C solid TTB solutions of Ca_xSr_1?xTa₂O₆ were formed. For x > 0.05 the TTB unit cells are orthorhombically distorted. For x ≥ 0.85 the x-ray powder patterns of the solid solutions looked like the one of CaTa₂O₆(orh.) and no TTB-structure was observed at 1300°C.     

Über die Polymorphie der Wolframperowskite Ba2SE0,67WO6

Polymorphism of Tungsten Perovskite Compounds Ba₂SE_0,67WO₆ The compounds Ba₂SE_0,67WO₆ with SE = Gd? Lu are polymorphic. Above 1200°C the instable cubic modification (ordered perovskit with 4 formula units Ba₂SE_0,67□_0,33WO₆ per cell) transforms irreversibly into a hexagonal modification with completely filled cationic lattice. For Ba₂Eu_0,67WO₆ the transformation is incomplete. With SE = Nd and Sm only the cubic modification is formed.