Ueber physikalische Isomerie

Lehmann, O.

doi:10.1524/zkri.1877.1.1.97

Cited by 17 publications

(7 citation statements)

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“…A similar pair of solubility curves for Zn7 (orthorhombic and monoclinic varieties) were measured by Bury (1924). Crystallisation of an orthorhombic form of Fe7 is described by Volger (1855)-who named it tauriscite-and by Lehmann (1877) in his landmark paper on isomorphism. Perhaps the most interesting studies on this matter, however, are those made by De Boisbaudran (1867a, b, 1868a, b), which report efforts to seed various highly concentrated (and supersaturated) solutions with crystals belonging to other hydrates.…”

Section: Discussionmentioning

confidence: 75%

Cation substitution in synthetic meridianiite (MgSO4·11H2O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

2012

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Meridianiite, MgSO 4 Á11H 2 O, is the most highly hydrated phase in the binary MgSO 4 -H 2 O system. Lower hydrates in the MgSO 4 -H 2 O system have end-member analogues containing alternative divalent metal cations (Ni 2? , Zn 2? , Mn 2? , Cu 2? , Fe 2? , and Co 2? ) and exhibit extensive solid solution with MgSO 4 and with one another, but no other undecahydrate is known. We have prepared aqueous MgSO 4 solutions doped with these other cations in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate ? ice by rapid quenching in liquid nitrogen. The solid products have been characterised by X-ray powder diffraction, and the onset of partial melting has been quantified using a thermal probe. We have established that of the seven end-member metal sulfates studied, only MgSO 4 forms an undecahydrate; ZnSO 4 forms an orthorhombic heptahydrate (synthetic goslarite), MnSO 4 , FeSO 4 , and CoSO 4 form monoclinic heptahydrates (syn. mallardite, melanterite, bieberite, respectively), and CuSO 4 crystallises as the well-known triclinic pentahydrate (syn. chalcanthite). NiSO 4 forms a new hydrate which has been indexed with a triclinic unit cell of dimensions a = 6.1275(1) Å , b = 6.8628(1) Å , c = 12.6318(2) Å , a = 92.904(2)°, b = 97.678(2)°, and c = 96.618(2)°. The unit-cell volume of this crystal, V = 521.74(1) Å 3 , is consistent with it being an octahydrate, NiSO 4 Á8H 2 O. Further analysis of doped specimens has shown that synthetic meridianiite is able to accommodate significant quantities of foreign cations in its structure; of the order 50 mol. % Co 2? or Mn 2? , 20-30 mol. % Ni 2? or Zn 2? , but less than 10 mol. % of Cu 2? or Fe 2? . In three of the systems we examined, an 'intermediate' phase occurred that differed in hydration state both from the Mg-bearing meridianiite end-member and the pure dopant end-member hydrate. In the case of CuSO 4 , we observed a melanterite-structured heptahydrate at Cu/ (Cu ? Mg) = 0.5, which we identify as synthetic alpersite [(Mg 0.5 Cu 0.5 )SO 4 Á7H 2 O)]. In the NiSO 4 -and ZnSO 4 -doped systems we characterised an entirely new hydrate which could also be identified to a lesser degree in the CuSO 4 -and the FeSO 4 -doped systems. The Ni-doped substance has been indexed with a monoclinic unit-cell of dimensions a = 6.7488(2) Å , b = 11.9613(4) Å , c = 14.6321(5) Å , and b = 95.047(3)°, systematic absences being indicative of space-group P2 1 /c with Z = 4. The unit-cell volume, V = 1,176.59(5) Å 3 , is consistent with it being an enneahydrate [i.e. (Mg 0.5 Ni 0.5 )SO 4 Á9H 2 O)]. Similarly, the new Zn-bearing enneahydrate has refined unit cell dimensions of a = 6.7555(3) Å , b = 11.9834(5) Å , c = 14.6666(8) Å , b = 95.020(4)°, V = 1,182.77(7) Å 3 , and the new Febearing enneahydrate has refined unit cell dimensions of a = 6.7726(3) Å , b = 12.0077(3) Å , c = 14.6920(5) Å , b = 95.037(3)°, and V = 1,190.20(6) Å 3 . The observation that synthetic meridianiite can form in the pres...

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Section: Discussionmentioning

confidence: 75%

Cation substitution in synthetic meridianiite (MgSO4·11H2O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

2012

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“…This may be because the reverse rate is too slow, or because the G surfaces of the phases concerned do not intersect and the one and same phase remains thermodynamically stable throughout right up to its melting point. If the latter is the cause, then the transformation is referred to as monotropic, in contrast to thermodynamically reversible transformations which are called enantiotropic [48,49]. Monotropic transformations are not subject to a transition temperature, but are controlled by kinetic factors.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Polymorphic phase transitions: Macroscopic theory and molecular simulation

Anwar

Zahn

2017

Advanced Drug Delivery Reviews

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Transformations in the solid state are of considerable interest, both for fundamental reasons and because they underpin important technological applications. The interest spans a wide spectrum of disciplines and application domains. For pharmaceuticals, a common issue is unexpected polymorphic transformation of the drug or excipient during processing or on storage, which can result in product failure. A more ambitious goal is that of exploiting the advantages of metastable polymorphs (e.g. higher solubility and dissolution rate) while ensuring their stability with respect to solid state transformation. To address these issues and to advance technology, there is an urgent need for significant insights that can only come from a detailed molecular level understanding of the involved processes. Whilst experimental approaches at best yield time- and space-averaged structural information, molecular simulation offers unprecedented, time-resolved molecular-level resolution of the processes taking place. This review aims to provide a comprehensive and critical account of state-of-the-art methods for modelling polymorph stability and transitions between solid phases. This is flanked by revisiting the associated macroscopic theoretical framework for phase transitions, including their classification, proposed molecular mechanisms, and kinetics. The simulation methods are presented in tutorial form, focusing on their application to phase transition phenomena. We describe molecular simulation studies for crystal structure prediction and polymorph screening, phase coexistence and phase diagrams, simulations of crystal-crystal transitions of various types (displacive/martensitic, reconstructive and diffusive), effects of defects, and phase stability and transitions at the nanoscale. Our selection of literature is intended to illustrate significant insights, concepts and understanding, as well as the current scope of using molecular simulations for understanding polymorphic transitions in an accessible way, rather than claiming completeness. With exciting prospects in both simulation methods development and enhancements in computer hardware, we are on the verge of accessing an unprecedented capability for designing and developing dosage forms and drug delivery systems in silico, including tackling challenges in polymorph control on a rational basis.

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“…[10][11][12][13][14][15][16] For instance, the first issue of Zeitschrift fur Kristallographie, founded in 1877 by the legendary P. von Groth, 12 contained a paper by his student, Otto Lehmann, with a diagram of a hot stage microscope and a ''time versus temperature'' curve, clearly indicating the four polymorphs of ammonium nitrate. 17 Although the subject was not a molecular crystal, the study is a classic example of the recording of thermal events associated with transitions between polymorphic crystal forms.…”

Section: Introductionmentioning

confidence: 99%

Facts and fictions about polymorphism

2015

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We present new facts about polymorphism based on (i) crystallographic data from the Cambridge Structural Database (CSD, a database built over 50 years of community effort), (ii) 229 solid form screens conducted at Hoffmann-La Roche and Eli Lilly and Company over the course of 8+ and 15+ years respectively and (iii) a dataset of 446 polymorphic crystals with energies and properties computed with modern DFT-d methods. We found that molecular flexibility or size has no correlation with the ability of a compound to be polymorphic. Chiral molecules, however, were found to be less prone to polymorphism than their achiral counterparts and compounds able to hydrogen bond exhibit only a slightly higher propensity to polymorphism than those which do not. Whilst the energy difference between polymorphs is usually less than 1 kcal mol(-1), conformational polymorphs are capable of differing by larger values (up to 2.5 kcal mol(-1) in our dataset). As overall statistics, we found that one in three compounds in the CSD are polymorphic whilst at least one in two compounds from the Roche and Lilly set display polymorphism with a higher estimate of up to three in four when compounds are screened intensively. Whilst the statistics provide some guidance of expectations, each compound constitutes a new challenge and prediction and realization of targeted polymorphism still remains a holy grail of materials sciences.

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Ueber physikalische Isomerie

Cited by 17 publications

References 0 publications

Cation substitution in synthetic meridianiite (MgSO4·11H2O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

Cation substitution in synthetic meridianiite (MgSO4·11H2O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

Polymorphic phase transitions: Macroscopic theory and molecular simulation

Facts and fictions about polymorphism

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