Variable-temperature X-ray Diffraction Studies Research Articles

Switching On/Off of a Solvent Coordination in a Au(I)-Pb(II) Complex: High Pressure and Temperature as External Stimuli.

The benzonitrile solvate {[{Au(C6F5)2}2{Pb(terpy)}]·NCPh}n (1) (terpy = 2,2':6',2″-terpyridine) displays reversible reorientation and coordination of the benzonitrile molecule to lead upon external stimuli. High-pressure X-ray diffraction studies between 0 and 2.1 GPa reveal a 100% of conversion without loss of symmetry, which is totally reversible upon decompression. By variable-temperature X-ray diffraction studies between 100 and 285 K, a partial coordination is achieved.

Engineering Metal-Organic Frameworks for Selective Separation of Hexane Isomers Using 3-Dimensional Linkers.

Metal-organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo[1.1.1]pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different sizes and shapes of these isomers.

Synthesis and Characterization of Biodegradable Polymers Based on Glucose Derivatives.

Syntheses of two new monomers, namely the glucose derivatives 2,3,4,6-tetra-O-acetyl-1 methacryloyl-glucopyranose (MGlc) and 2,3,4,6 tetra-O-acetyl-1-acryloylglucopyranose (AGlc), are presented. Their chemical structures were determined by the FTIR, 1H and 13C NMR spectroscopies, the single-crystal X-ray analysis, supported by the powder X-ray diffraction, and the DSC analyses. Molecules of both monomers exist in the β-anomeric form in the solid state. The variable temperature X-ray diffraction studies, supported by the DSC analyses, revealed AGlc's propensity for polymorphism and temperature-induced phase transitions. MGlc and AGlc crystallised from methanol were polymerized or copolymerized with methyl methacrylate and N-vinylpyrrolidone. The biodegradabilities of polymers as well as thermal and optical properties were studied. The results show that some properties of the obtained homopolymers and copolymers resemble those of PMMA. The main difference is that the AGlc and MGlc homopolymers are biodegradable while PMMA is not. The ternary copolymers, i.e., MGlc/AGlc-MMA-NVP lose more than 10% of their weight after six months.

Preparation and Solid-State Characterization of Eltrombopag Crystal Phases.

Eltrombopag, of C25H22N4O4 chemical formula, is a drug used against thrombocytopenia, marketed worldwide under different tradenames in the form of its bis-olamine salt. The free acid (CAS no. 496775-61-2) is an intermediate species used for the final drug isolation and is reported to crystallize in more than 20 distinct crystal forms, including a large number of hydrates and solvates. Their identification, and, ultimately, their quantification in industrial lots require the usage of accurately measured X-ray powder diffraction pattern, as well as the assessment of the metrical features (crystal symmetry and lattice parameters), nowadays accessible by powerful crystallographic software. Here, the complete indexing of 13 monophasic samples, prepared using literature or newly tailored crystallization methods, jointly to simultaneous thermogravimetric and calorimetric analyses and to variable temperature X-ray diffraction studies, provide a clear picture of the stability fields of the different crystal phases and their mutual interconversion processes, leading, in a few cases, to new and unexpected crystalline polymorphs or solvates of the pristine unsolvated Form I.

Understanding stability relationships among three curcumin polymorphs

Understanding thermodynamic stability relationship among polymorphs of any active pharmaceutical ingredient (API) is a necessary step for drug formulation development. Knowledge of such relationship enables identification of a stable polymorphic form at the prevalent conditions. Curcumin, a pharmaceutically active ingredient found in herbal spice turmeric, exists in three polymorphic forms; a monoclinic form (Form 1) and two orthorhombic forms (Form 2 and Form 3). However, thermodynamic stability relationships among curcumin polymorphs have not been ascertained yet. This work therefore, was focused on understanding thermodynamic stability relationships among curcumin polymorphs. During purification of curcumin, the pressure applied for vacuum evaporation of organic solvent was found to significantly affect the polymorphic outcome. Form 1 was obtained at pressures ranging from 300 to 400 mbar whereas Form 2 was obtained at pressures ranging from 100 to 200 mbar. Form 3 was obtained by liquid antisolvent precipitation using ultrasound and Bovine Serum Albumin (BSA) as an additive. The obtained polymorphs were characterized by X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC) techniques. Relative stability of polymorphs was established by conducting solvent mediated transformation studies, thermal analysis through DSC and variable temperature X-ray diffraction studies (VT-XRD). It was observed that Form 2 and Form 3 irreversibly convert to Form 1 upon heating. Further, Form 2 and Form 3 convert to Form 1 in aqueous organic solutions at temperatures ranging from 0 °C to 50 °C. Thus, the curcumin polymorphs were found to be monotropically related to each other with the monoclinic form (Form 1) being the most stable form.

Influence of peripheral alkyl chain length on the mesomorphic behaviours of hexasubstituted triphenylene 2,3-dicarboxylic esters

ABSTRACTA comparative study of our established synthetic approaches to hexasubsituted triphenylenes 2,3-dicarboxylic esters containing four identical β-alkoxy and two adjacent β-alkoxycarbonyl side chains shows that the phase behaviours of small-sized discotic liquid crystals can be tailored over a wide range by simply varying the length of the peripheral alkyl chains. All the prepared esters in two series were observed to form a single hexagonal columnar phase, except for Tp4-1 having four β-butyloxy and two adjacent β-methoxycarbonyl chains which displays two columnar mesophase behaviours with a transition from the columnar plastic phase to hexagonal columnar phase. A significant difference between the two mesophase was observed in the variable temperature X-ray diffraction studies, and the mesophase assignment was also confirmed by polarising optical microscopy and differential scanning calorimetry. Moreover, the prepared esters in each series display the general trend of decreasing clearing temperature upon increasing alkoxy or alkoxycarbonyl chains length. The intermediate triphenylene 2,3-dicarboxylic acids were also found not only to exhibit columnar hexagonal mesophase over a narrower temperature range by maintaining high melting and clearing points but also to form organogel on mixing with toluene or dichloromethane with the assistance of hydrogen bonding.

Synthesis and ionic conductivity of new high Li ion content garnets, LnSr2Ta2Li7O12 (Ln = La, Pr, Nd, Sm, Gd)

In this paper we report the synthesis and Li ion conductivity of the new high Li content garnet phases LnSr2Ta2Li7O12 (Ln = La, Pr, Nd, Sm or Gd). Close inspection of the X-ray diffraction patterns indicate that these systems are mostly composed of the ordered tetragonal garnet phase, along with a small amount of cubic garnet. The presence of a small amount of cubic garnet phase can most likely be correlated with partial Li loss on synthesis as well as some degree of H+/Li+ exchange. The latter was supported by results from variable temperature X-ray diffraction studies and thermogravimetric analysis. The adoption of the tetragonal garnet structure by these new systems highlights further that in order to accommodate 7 Lithium ions within the garnet structure, then cation ordering must occur to prevent short Li–Li interactions. In line with other tetragonal garnet systems, the Li ion conductivity is shown to be low, as a result of this ordered Li distribution.

Probing the structural changes accompanying a spin crossover transition in a chiral [Fe(ii)(N3O2)(CN)2] macrocycle by X-ray crystallography

The preparation and characterization of a novel chiral macrocycle S,S-[FeII(PhCH2OCH2)2(N3O2)(CN)2] (4) is presented. Magnetic susceptibility studies reveal that this complex undergoes a gradual spin crossover in the solid state with no thermal hysteresis. Variable temperature X-ray diffraction studies on single crystals of 4 reveal that at 150 K the complex is comprised of two crystallographically independent octahedral Fe(II) centres. Warming the crystal to 300 K results in a subtle change in coordination geometry of one of the octahedral Fe(II) centers towards a 7-coordinate, pentagonal bipyramidal geometry that is accompanied by a conformation change in one of the PhCH2OCH2 substituents.

Common Packing Motif in Salts of H-Acid, and the Incommensurate Sodium Hydrate

"""H-Acid"" (4-ammonio-5-hydroxynaphthalene-2,7-disulfonate) is a coal tar derivative and important intermediate in the manufacture of hundreds of dyes. Despite the fact that on the order of one million metric tons of the sodium salt have been manufactured in the past century, no crystal structures incorporating this organosulfonate have been reported. Diffraction quality needles of the hydrated sodium salt are prepared by slow cooling a concentrated aqueous solution under anaerobic conditions. Variable temperature X-ray diffraction studies revealed the structure exhibits positional disorder of donor atoms around aqua-bridged Na+ dimers between room temperature and 180 K. Upon further cooling the structure undergoes a reversible phase transition to an ordered, incommensurately modulated structure with retention of crystal quality. Structure elucidation of over a dozen other salts of H-Acid revealed in all cases the adoption of a stacking motif reinforced by hydrogen bonds involving a ""keystone"" water molecule. This water molecule is also retained during in situ dehydration of the sodium salt at elevated temperature; surprisingly, a sodium-coordinated water molecule is the first to be released."

Novel organogelators based on pyrazine-2,5-dicarboxylic acid derivatives and their mesomorphic behaviors

A series of new low molecular organogelators (LMOGs) with thermotropic mesophase were synthesized via the reaction of 3,6-dimethyl-pyrazine-2,5-dicarboxylic acid with p-alkoxyl anilines. These compounds readily formed stable gels in a variety of organic solvents and their self-assembly behavior, structure–property relationship were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR) and ultra-violet–visible spectroscopy (UV). The results showed a combination of intra-hydrogen bonding, π–π stacking and van der Waals interaction resulted in the aggregation of the organogelators to form three-dimension fibrous networks. The gels formed were multi-responsive to environmental stimuli, such as temperature, fluorinion, and shear stress. More importantly, all the organogelators exhibited thermotropic hexagonal column mesophase as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and variable temperature XRD studies. A control compound was synthesized and its gelling ability was also checked.

Effect of Chelate Ring Expansion on Jahn–Teller Distortion and Jahn–Teller Dynamics in Copper(II) Complexes

The expanded ligand N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamine (ddpd) coordinates to copper(II) ions in a meridional fashion giving the dicationic complex mer-[Cu(ddpd)(2)](BF(4))(2) (1). In the solid state at temperatures below 100 K the cations of 1 localize in Jahn-Teller elongated CuN(6) polyhedra with the longest Cu-N bond pointing in the molecular x or y directions while the z axis is constrained by the tridentate ddpd ligand. The elongated polyhedra are ordered in an antiferrodistortive way giving an idealized zincblende structure. At higher temperature dynamically averaged (fluxional) polyhedra in the molecular x/y directions are observed by multifrequency variable temperature electron paramagnetic resonance (EPR) and by variable temperature X-ray diffraction studies. Compared to [Cu(tpy)(2)](2+) (tpy = 2,2';6',2″-terpyridine) the Jahn-Teller splitting 4δ(1) of 1 is larger. This is very probably caused by the much more favorable orbital overlap in the Cu-N bonds in 1 which results from the larger bite angle of ddpd as compared to tpy. The "freezing-in" of the Jahn-Teller dynamics of 1 (T ≈ 100 K) occurs at higher temperature than observed for [Cu(tpy)(2)](2+) (T < 77 K) which is also probably due to the larger Jahn-Teller distortion of 1 resulting in a larger activation barrier.

Synthesis and characterization of luminescent tricationic salts of mesitylene and stilbazolium moieties

A series of luminescent tricationic salts having mesitylene and stilbazolium moieties with various organic counterions were synthesized by using quaternization and metathesis reactions. Their chemical structures were characterized by 1H, 19F and 13C NMR spectroscopy, and elemental analysis. Their crystalline and amorphous properties were examined by differential scanning calorimetry, polarized optical microscopy, and variable-temperature X-ray diffraction studies. Their thermal stabilities were determined by thermogravimetric analyses, which were in the broad temperature ranges of 239–317°C in nitrogen. Their optical properties were studied by UV–Vis and photoluminescent spectroscopy. The light-emission properties were dependent on the polarity of organic solvents (positive solvatochromism) but independent on the chemical structures of organic counterions. They emitted blue light in various organic solvents in a broad range of wavelengths of 470–497nm, but emitted green light in a narrow range of wavelengths of 506–515nm in their solid states.

In situ variable temperature X-ray diffraction studies on the transformations of nano-precursors to La–Ni–O phases

In situ variable temperature XRD (VT-XRD) measurements on the transformation of nano-precursors to LaNiO phases are presented. Experimental results showed that LaNiO 3 and La 2NiO 4 phases were formed at ca. 700 °C via the reaction of La 2O 3 and NiO (from the initial nano-precursors), where a relatively low temperature of 700 °C was found for the synthesis of La 2NiO 4. The formation of La 3Ni 2O 7 at higher temperature (up to 1150 °C) appeared to proceed through a further reaction of La 2NiO 4 with unreacted NiO, whilst the formation of La 4Ni 3O 10 (at 1075 °C) proceeded via a further decomposition of LaNiO 3. Although phase pure La 3Ni 2O 7 and La 4Ni 3O 10 were not directly obtained under the processing conditions herein, the results of this study allow for a better understanding of formation pathways, particularly for the higher order La–Ni–O phases.

Remarkable structural similarities between organic co-crystals and a metal–organic coordination network—insights into hydrogen bonded aliphatic ammonium chlorides

The reaction of trans-1,4-diaminocyclohexane and piperazine with hydrochloric acid in dimethylsulfoxide or water led to new co-crystals and chloride salts, namely trans-1,4-diammoniocyclohexane dichloride dimethylsulfoxide 1, trans(ammonio-4-amino)cyclohexane monochloride 2, and piperazinium dichloride hemihydrate 3. The crystal structures show unexpected similarities to already noted organic and metal–organic derivatives. Furthermore, hot-stage microscopy, variable-temperature X-ray diffraction studies, and thermoanalytical measurements revealed decomposition reactions, solvent-free reaction pathways, and phase transition at temperatures between 160 and 210 °C.

Biomimetic Synthesis of Titanium Dioxide Utilizing the R5 Peptide Derived from Cylindrotheca fusiformis

Current approaches to the synthesis of metal oxides generally require harsh conditions. In contrast, many biological processes can produce intricate metal oxide nanostructures under ambient conditions. For example, the diatom Cylindrotheca fusiformis forms reproducible nanostructures from silicic acid using species specific peptides known as silaffins. Herein, we report that the R5 peptide a bioinspired analogue derived from the NatSil protein in C. fusiformis can form titanium dioxide (TiO2) in a concentration dependent manner from the non-natural substrate, titanium bis(ammonium lactato)dihydroxide. Additionally, the polypeptide poly(l-lysine) acts as a template for the biomimetic synthesis of TiO2. Subsequently, the nanoparticles were characterized using scanning electron microscopy, energy-dispersive X-ray spectrometry, and IR spectroscopy. A variable temperature X-ray diffraction study of the titanium dioxide phase transition from anatase to rutile was conducted. A delay in transition temperature was observed with titanium dioxide synthesized in the presence of phosphate buffer.

A new polymorph of terpyridine: variable temperature X-ray diffraction studies and solid state photophysical properties

The crystal structure of a new monoclinic polymorph of 2,2′ : 6′,2″ terpyridine (terpy) that contains two independent but structurally similar molecules, and crystallises in a space group P21/c, is reported. Variable-temperature single-crystal X-ray diffraction studies at 100, 150, 200 and 250 K show that the b-axis length increases significantly with increasing temperature. The molecules pack in a sandwich herringbone arrangement and the intermolecular non-bonded contacts are described in detail. All structural results are contrasted with those obtained for the previously reported polymorph of terpyridine, which crystallises in the orthorhombic space group P212121. Photophysical properties of the new polymorph of terpyridine are also reported. The solid-state room temperature UV/vis absorption and emission spectra were measured. The sample was found to phosphoresce on the millisecond timescale, this being measured as a function of temperature (100–280 K). Its long-lived phosphorescent nature also allowed a pseudo-steady-state to be built up by continuous laser pumping (at 10 Hz repetition rate), which was investigated as a function of temperature (100–280 K).

Hydrogen bond-directed aggregation of diazadibenzoperylene dyes in low-polarity solvents and the solid state.

The formation of complex superstructures via hydrogen bonding of two ditopic building blocks, diazadibenzoperylenes 1a,b and isophthalic acid 2, has been investigated. It was found that only the phenoxy-substituted diazadibenzoperylene 1a forms extended assemblies with 2 in complexes of a 1:1 stoichiometry, whereas for the 4-tert-butylphenoxy-substituted analogue 1b, no indications for superstructure formation with 2 were found. The different behavior is explained by the presence of additional pi-pi interactions, which are only observed for [1a x 2], as revealed by concentration-dependent optical absorption and fluorescence spectroscopy. Based on variable temperature x-ray diffraction studies, a lamellar structure for [1a x 2] is proposed that takes into account the concept of microphase-segregation.

Color of red mercuric iodide at cryogenic temperatures

We investigated a red to yellow color change observed in α-HgI2 when cooled below 150 K. A phase transformation to β-HgI2, which has a yellow color, was ruled out by a variable temperature x-ray diffraction study. Instead the color change at cryogenic temperatures is caused by a shift in the transmission edge to shorter wavelengths which we attribute to a widening band gap at low temperatures. Using optical transmission spectroscopy the width of the band gap was measured between 10 and 330 K. At room temperature the gap was 2.11±0.03 eV, which is significantly smaller than the most recently published values of ∼2.3 eV. This smaller band gap was further verified by measuring the thermoelectric current at elevated temperatures.

Mesomorphic behaviour, single crystal and low angle variable temperature X-ray diffraction studies of the chloro-bridged cyclopalladated dimer obtained from 4,4′-hexyloxyazobenzene

Abstract The newly synthesized palladium complex [(Azo-6)Pd(μu-C1)]2, 1, [H(Azo-6) = 4,4′-hexyloxyazobenzene] has been investigated by optical observations, calorimetric measurements, and single crystal and low angle variable temperature X-ray diffraction techniques. Two different mesophases appear from 210 to 220°C (nematic) and above 220 until 235°C (smectic E) where the compound eventually decomposes. The nematic phase is not in thermodynamic equilibrium and when subjected to an annealing process transforms into a smectic phase. The molecular structure of the dinuclear cyclopalladated complex 1 has an intramolecular Pd-Pd distance of 3.528(1) A. Moreover the molecules of 1 are arranged in pairs with an intermolecular Pd-Pd non-bonded interaction distance of 3.668(1) A. On the basis of this structural feature and of the variable temperature low-angle XRD studies, transitions involving dissociation of the molecular pairs (e.g. N(pair)⇌E(single), on heating; N(pair)→SE(pair), at constant temperature) are ...

Hydride atom location and atomic dispersion parameter analysis in trimetal clusters using variable temperature X-ray diffraction

Variable temperature X-ray diffraction studies were carried out on several μ-imidoyl clusters with the general formula, (μ-H)2M3(CO)9-(μ-imidoyl)(X) whereM=Ru or Os,X=Cl, Br, CF3COO, and imidoyl ligand is or CH3C=NCH2CH3, in order to analyze ligand atom motion in the solid state and to precisely locate the hydride ligands. An initial study on (μ-H)(μ3-η2-CH3C=NCH2CH3)Ru3(CO)8PPh3 indicates that the atomic (thermal) dispersion parameters (ADP) of the μ3-imidoyl ligand atoms can possibly be used to correlate solution ligand fluxionality with ligand-binding forces in the solid-state structures. Difference Fourier analysis techniques were used to locate hydride ligands in several triosmium clusters, and it was observed that if there was a nitrogen atom in the bridging ligand along a metal edge which also contained a hydride bridge then the hydride was asymmetrically bonded (ca. 0.1–0.7 A) and always closer to the nitrogen bonded metal. In addition, in dihydrido trimetallic clusters, the distance of separation of the two hydride ligands correlates with the tendency of those hydrides to exchange at room temperature. If the angle ϑ, which describes the angle between the planes relating the bridging hydride ligands and the two inclusive metal atoms, is less than about 55 degrees, then the hydrides can undergo site exchange at room temperature on the nmr time scale.