Structural Transformations in Organic Crystals During Photochemical Reactions

Crystallization is a kinetic phenomenon and the experimental conditions like solvents, concentration, pH, temperature and time have greater influence on the nature of products in the synthesis of coordination network structures. During crystallization, the solvents and ligands bind to the metal ions reversibly and hence, the least soluble polymer will crystallize first, independent of the metal-ligand ratio used in the crystallization. The kinetic products quite often contain solvents bonded to the metal ions. The removal of these coordinated solvents is likely to transform the kinetically formed coordination polymers (CPs) into thermodynamically stable products. In these structural conversions, supramolecular interactions play a major role. Such structural transformations as well as [2+2] cycloaddition reactions have been demonstrated in many coordination polymeric network structures aided by the directional hydrogen bonding interactions. A number of structural transformations involving the loss of solvent molecules and use of photodimerization reactions in the solid state will be presented in this talk.

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Monitoring structural transformations in crystals. 12. Course of an intramolecular [4 + 4] photocycloaddition in a crystal

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768108009853 ◽

2008 ◽

Vol 64 (3) ◽

pp. 375-382 ◽

Cited By ~ 13

Author(s):

Elżbieta Trzop ◽

Ilona Turowska-Tyrk

Keyword(s):

Hydrogen Bonds ◽

Cell Volume ◽

Molecular Shape ◽

Structural Transformations ◽

Photochemical Reactions ◽

Molecular Structures ◽

X Ray Diffraction ◽

X Ray ◽

Crystal And Molecular Structures ◽

Orientation Of Molecules

Variations in crystal and molecular structures, brought about by the intramolecular [4 + 4] photocycloaddition of bi(anthracene-9,10-dimethylene), were monitored using X-ray diffraction. The cell volume increased by 0.8% until the reaction was ca 40% complete, and afterwards decreased by 1.6% during the remainder of the photoreaction. The changes of the a and b lattice parameters were correlated with the changes of the molecular shape and packing. The distance between the directly reacting C atoms varied in a manner not observed for other photochemical reactions in crystals. It was constant until ca 20% photoreaction progress, then decreased, and later stabilized from ca 40% photoreaction progress. This phenomenon was explained by interplay between stress resulting from the presence of product molecules and the rigidity of reactant molecules. Changes of the orientation of molecules during the photoreaction were smaller than in the case of other monitored photochemical reactions in crystals owing to similarities in the shape and packing of reactant and product molecules. Weak C—H...π hydrogen bonds exist among reactant molecules in the pure reactant and partly reacted crystals.

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Structural transformations in crystals induced by radiation and pressure. Part 1. How pressure influences the intramolecular photochemical reactions in crystals

CrystEngComm ◽

10.1039/c4ce00320a ◽

2014 ◽

Vol 16 (27) ◽

pp. 6039-6048 ◽

Cited By ~ 7

Author(s):

Julia Bąkowicz ◽

Ilona Turowska-Tyrk

Keyword(s):

Structural Transformations ◽

Photochemical Reactions ◽

Pressure Part

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Structure–reactivity correlation of photochemical reactions in organic crystals: intramolecular hydrogen abstraction in an aromatic nitro compound

Journal of the Chemical Society Perkin Transactions 2 ◽

10.1039/p29870001153 ◽

1987 ◽

pp. 1153-1158 ◽

Cited By ~ 8

Author(s):

Kaillathe Padmanabhan ◽

Kailasam Venkatesan ◽

Vaidyanathan Ramamurthy ◽

Rolf Schmidt ◽

Dietrich Döpp

Keyword(s):

Nitro Compound ◽

Hydrogen Abstraction ◽

Photochemical Reactions ◽

Organic Crystals ◽

Aromatic Nitro Compound ◽

Aromatic Nitro ◽

Intramolecular Hydrogen

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Interpretation of irradiation-induced changes in electron diffractograms and images of extinction contours at low temperatures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100111458 ◽

1984 ◽

Vol 42 ◽

pp. 268-269

Author(s):

E. Knapek ◽

H. Formanek ◽

G. Lefranc ◽

I. Dietrich

Keyword(s):

Low Temperatures ◽

Carbon Films ◽

Organic Crystals ◽

Wide Spread ◽

Lens System ◽

Preparation Conditions ◽

Thin Carbon ◽

Electron Diffractograms ◽

Diffraction Patterns ◽

Induced Changes

A few years ago results on cryoprotection of L-valine were reported, where the values of the critical fluence De i.e, the electron exposure which decreases the intensity of the diffraction reflections by a factor e, amounted to the order of 2000 + 1000 e/nm2. In the meantime a discrepancy arose, since several groups published De values between 100 e/nm2 and 1200 e/nm2 /1 - 4/. This disagreement and particularly the wide spread of the results induced us to investigate more thoroughly the behaviour of organic crystals at very low temperatures during electron irradiation.For this purpose large L-valine crystals with homogenuous thickness were deposited on holey carbon films, thin carbon films or Au-coated holey carbon films. These specimens were cooled down to nearly liquid helium temperature in an electron microscope with a superconducting lens system and irradiated with 200 keU-electrons. The progress of radiation damage under different preparation conditions has been observed with series of electron diffraction patterns and direct images of extinction contours.

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Structural Transformation of a Germanium Σ=13 (510) [001] Tilt Grain Boundary under the Electron Beam

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179014 ◽

1990 ◽

Vol 48 (1) ◽

pp. 52-53 ◽

Cited By ~ 1

Author(s):

Jean-Luc Rouvière ◽

Alain Bourret

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Grain Boundary ◽

Structural Transformation ◽

Mirror Symmetry ◽

High Resolution Electron Microscopy ◽

Structural Transformations ◽

Covalent Bonds ◽

Resolution Electron ◽

Tilt Grain Boundary

The possible structural transformations during the sample preparations and the sample observations are important issues in electron microscopy. Several publications of High Resolution Electron Microscopy (HREM) have reported that structural transformations and evaporation of the thin parts of a specimen could happen in the microscope. Diffusion and preferential etchings could also occur during the sample preparation.Here we report a structural transformation of a germanium Σ=13 (510) [001] tilt grain boundary that occurred in a medium-voltage electron microscopy (JEOL 400KV).Among the different (001) tilt grain boundaries whose atomic structures were entirely determined by High Resolution Electron Microscopy (Σ = 5(310), Σ = 13 (320), Σ = 13 (510), Σ = 65 (1130), Σ = 25 (710) and Σ = 41 (910), the Σ = 13 (510) interface is the most interesting. It exhibits two kinds of structures. One of them, the M-structure, has tetracoordinated covalent bonds and is periodic (fig. 1). The other, the U-structure, is also tetracoordinated but is not strictly periodic (fig. 2). It is composed of a periodically repeated constant part that separates variable cores where some atoms can have several stable positions. The M-structure has a mirror glide symmetry. At Scherzer defocus, its HREM images have characteristic groups of three big white dots that are distributed on alternatively facing right and left arcs (fig. 1). The (001) projection of the U-structure has an apparent mirror symmetry, the portions of good coincidence zones (“perfect crystal structure”) regularly separate the variable cores regions (fig. 2).

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