Abstract: This paper examines the concept of strain balance in alternate tensile and compressively strained layers using classical elasticity theory and clarifies a number of issues associated with the definition of strain and misfit. The strain-balance criteria are derived from a zero average in-plane stress condition and compared against two commonly used thickness weighted models, based on strain and lattice parameter respectively. The zero-stress condition fully accounts for differences in the elastic properties of the layers, and establishes the true definition for a strain-balanced structure, within the confines of linear elastic theory. The validity of the thickness weighted models is discussed in the context of epitaxial growth tolerance, showing that for some device designs, the choice of strain-balance model is important for successful growth. The differences in the strain-balance models have consequences for characterization. For example, a comparison between simulated X-ray rocking curves from structure...

Abstract: The structures and molecular packing of tribromo- and triiodomesitylene are reported and compared to that of trichloromesitylene. Attractive triangular X3 interactions dominate the molecular packing in all three structures. The nonspherical atomic charge distribution on the halogens results in the formation donor−acceptor interactions in which each halogen atom is simultaneously a donor and an acceptor. These triangular X3 (X = Br or I) interactions result in the formation of 2-dimensional sheetlike structures.

Abstract: A new approach has been proposed for the ab initio crystal structure prediction of small organic molecules. This exercise forms a part of the recent blind test on crystal structure prediction condu...

Abstract: Crystallization of 1,3,5-cyclohexanetricarboxylic acid (CTA) from EtOH affords the 1:1 hydrate, CTA.H 2 O, with 4-fold inclined interpenetrated (6,3) hydrogen-bonded networks. Crystallization of CTA with 4,4'-bipyridine (bipy) furnishes the complex, CTA.bipy.H 2 O (2:3:1), that has 3-fold interweaving (6,3) networks with parallel interpenetration. The striking similarity of these hydrogen bond networks to those found in the crystal structure of trimesic acid and its complex with bipy suggests that such interpenetrated networks may be engineered using retrosynthetic strategies.

Abstract: Peptides carried by filamentous phages with potential affinity to calcium carbonate were selected experimentally from a phage display library. The isolated phage were employed to affect the precipitation of calcium carbonate from aqueous solution. SEM, FTIR, and confocal microsopy techniques were used to monitor the morphology and polymorph development of calcium carbonate crystallization. Hollow spheres consisting of nanoscale vaterite crystallites were obtained, which may be due to the template effect of the phage. These spherical crystals transformed into rhombic calcite crystals with time, a process that was slowed by the presence of phage. It is proposed that this phase transformation is a solution-mediated process.

Abstract: In situ Raman spectroscopy was used to determine the rate of polymorph turnover for MK-A, a multipolymorphic compound in development at Merck Research Laboratories. The known crystal forms of MK-A include four anhydrous polymorphs, two hydrates, and numerous solvates. The penultimate and pure steps of this process involve a coupling reaction to generate a mixture of crystal forms followed by turnover to the desired polymorph, form A. This paper summarizes experiments to measure the kinetics of polymorph turnover from all relevant MK-A crystal forms to form A. Additionally, the turnover kinetics for polymorph reversion from form A to undesired forms were measured under simulated process upset conditions. The use of thermodynamic data to establish process boundaries and kinetic data to establish process time cycles resulted in the definition of a highly robust, cycle time efficient slurry turnover process to produce form A from any combination of other MK-A crystal forms.

Abstract: The temperature profile applied during batch cooling crystallization affects the supersaturation level, which in turn affects the crystal size distribution. It is possible, in principle, to calculate the optimal cooling profile; however, the nucleation and growth kinetics are rarely known to the degree of accuracy necessary for this calculation. The current study demonstrates an alternative approach to determination of the optimal cooling profile without any prior knowledge of kinetic data or subsequent modeling. An attenuated total reflectance−Fourier transform infrared (ATR-FTIR) spectrometer was used to monitor the supersaturation level during batch cooling crystallization. The ATR-FTIR was interfaced to a LABMAX automatic reactor system that was used in a feedback mode to control the cooling rate so that the supersaturation level remained close to the solubility throughout the cooling process. The resulting temperature profile corresponds to the optimal operating conditions for the maximum in the mean...

Abstract: Supramolecular complexes of tetra-p-sulfonated calix[4]arene and racemic (alanine, histidine, and phenylalanine) and chiral ((S)-alanine, (S)-histidine, and (S)-tyrosine) amino acids have been isolated in the solid state and their molecular structures elucidated by X-ray diffraction studies. For alanine, histidine, and phenylalanine, racemic pairs of molecules are confined in capsules of tetra-p-sulfonated calix[4]arene in an overall bilayer arrangement. The (S)-amino acid isomers for alanine and histidine, however, formed 1:1 complexes within the bilayer arrangement found for many tetra-p-sulfonated calix[4]arene complexes. For (S)-tyrosine, a π-stacked chiral pair of isomers was encapsulated by tetra-p-sulfonated calix[4]arene.

Abstract: Mach−Zender optical interferometry was used to measure the solute concentration profile in solution near the ice/solution interface under quasi-steady state conditions in order to gain a quantitative understanding of freeze concentration. At low ice growth velocities, the freeze concentration behavior of a range of solutes, including sucrose, a globular protein, and some low molecular weight polymers, was accurately described by the quasi-steady state approximation to the diffusion equation. Increasing deviations from this approximation occurred at higher growth speeds and for larger macromolecules, where diffusion was presumably inhibited by chain entanglement that led to the development of significant concentration gradients parallel to the ice/solution interface. In mixtures of noninteracting solutes, the concentration profiles of the individual components could be distinguished separately. The behavior of a helical antifreeze glycopeptide could not be explained in terms of its diffusion behavior, howe...

Abstract: This paper explores the crystallization of glycine from aqueous solution within a variety of colloidal systems in which the dimension of the crystallization environment varies from micrometers to nanometers. The study focuses on the polymorphic outcome of crystallization experiments and the extent to which crystal size can be controlled. The appearance of the β and γ polymorphic forms is found to be related to the organization and functionality of the surfactants utilized as well as the supersaturation. Overall, it is noted that while macroemulsions may be used to generate particulates of controlled size, crystal growth in microemulsion and lamellar phases is not restricted to the dimensions of the aqueous domains.

Abstract: A series of novel silver-thioether metal-organic supramolecular architectures forming different frameworks are constructed by the direct reactions of Ag I perchlorate with a series of di- or trithioether ligands which are closely related in structure. In the crystal structures of the four complexes, a variety of coordination modes of the Ag I centers due to the conformation freedom or steric hindrance have been observed, indicating that the nature of the ligands is a determining factor in controlling the structural topology of the metal-organic supramolecular architectures.

Abstract: Crystals of cubic GaN (c-GaN) were grown ammonothermally using hexagonal gallium nitride as a nutrient. h-GaN was sealed in a quartz tube with anhydrous ammonia, an acid (NH4X; X = Cl, Br, I), and in some cases a lithium halide (LiX). The bottom of the tube was heated to 470−510 °C in a vertically oriented pressure vessel containing a hydrostatic pressure of 30000−40000 psi. The thermal gradient was approximately −10 °C/cm. h-GaN dissolved in the hot zone and GaN crystals deposited in the cooler zone near the top of the tube. Most (>80%) of the deposit was c-GaN for most of the experimental conditions studied, but the hexagonal form was a persistent contaminant. When LiX was used as a co-mineralizer triangular prisms of c-GaN often grew. Triangular prismatic needles of c-GaN grew in a (111) direction in experiments containing a low concentration (0.28 mol %) of NH4Cl, a larger concentration (2.0 mol %) of LiCl, and a 55% fill factor. The crystals were tapered, becoming wider as they grew, and crystals of...

Abstract: In the crystal structures of the two organic salts, namely, pyrimethamine hydrogen glutarate (1:1) 1 and pyrimethamine formate (1:1) 2, the pyrimethamine moieties are protonated at one of the nitrogen atoms of the pyrimidine rings. The carboxylate group of the respective anions (hydrogen glutarate and formate) interacts with the protonated pyrimidine moiety in a near linear fashion through a pair of N−H···O hydrogen bonds. The dihedral angle between the diaminopyrimidine and the p-chlorophenyl plane is 74.8(1)° in compound 1, and the corresponding value in compound 2 is 76.7(1)°. In both compounds, the pyrimidine moieties are centrosymmetrically paired through a pair of N−H···N hydrogen bonds. The 2-amino group of the one member of the pair and the 4-amino group of the other member are bridged by an O atom of the carboxylate group, using a pair of N−H···O hydrogen bonds. This combination of hydrogen bonds results in the complementary DADA (D = donor and A = acceptor in hydrogen bonds) arrays of quadruple ...

Abstract: The growth morphology of monoclinic paracetamol as a function of the supersaturation is determined using Monte Carlo simulations based on the crystal structure. The results are compared with experimental results reported recently on both the morphology and the relevant growth mechanisms. The change of an elongated to a more bulky habit with increasing supersaturation is reproduced well by the simulations. The method used opens ways to predict the crystal morphology for real crystal structures in dependence of supersaturation once information on the relevant growth mechanism for the various faces is known.

Abstract: Two novel cobalt(II) coordination polymers, (H 4 hpz)[Co 3 (BTEC) 2 (H 2 O) 12 ].11H 2 O (1) and (H 4 hpz)[Co(BTEC)(H 2 O) 3 ].3H 2 O (2) (H 4 hpz = homopiperazonium; BTEC = 1,2,4,5-benzenetetracarboxylate), have been synthesized under aqueous conditions at room temperature and structurally characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic space group P1ο1 with a = 9.823(4) A, b = 11.587(4) A, c = 20.385(7) A, α = 95.10(2)°, β = 92.423(19)°, γ = 98.90(2)°, and Z = 2. Compound 2 also crystallizes in the triclinic space group P1 with a = 9.7755(17) A, b = 11.208(3) A, c = 11.224(2) A, α = 60.304(12)°, β = 73.687(12)°, γ = 84.311(14)°, and Z = 2. Both compounds have layered structures. In the case of 1, homopiperazonium cations and 1D anionic chains of [Co(BTEC)(H 2 O) 4 ] 2- n are sandwiched between 2D sheets of [Co 2 (BTEC)(H 2 O) 8 ] n . In the case of 2, homopiperazonium cations alone are sandwiched between 2D sheets of [Co(BTEC)(H 2 O) 3 ] 2- n .

Abstract: The productivity and quality of SiC bulk crystal grown from vapor phase depend strongly on the temperature distribution in a SiC growth chamber. An analytical formulation is proposed to correlate the growth rate with process parameters such as pressure, temperature, and temperature gradient. A growth kinetic model is also developed to predict the growth rate and examine the transport effects on the growth rate and dislocation formation. Simulation and analytical results show that the growth rate increases when the growth temperature increases, argon pressure decreases, and/or the temperature gradient between the source and seed increases. An anisotropic thermoelastic stress model is proposed to study the influence of thermal stress on dislocation density. The method to attach the seed is observed to play an important role in stress distribution in an as-grown silicon carbide ingot.

Abstract: In this work, the formation of unusual flowerlike structures with 10-petals composed of BaSO 4 single crystalline platelets is described. The structures are obtained at pH 5 in an aqueous solution in the presence of a double hydrophilic block copolymer poly(ethylene oxide)-block-sulfonated poly(ethylene imine) (PEO-b-PEI-SO 3 H) by site-specific polymer adsorption. The exposed faces are identified, the atomar surface structures of these faces are calculated, and preferred faces for polymer adsorption are found. A model for the growth of the unusual 10-petal BaSO 4 structures is presented which is based on the nucleation of primary particles, secondary growth of the petals, and finally layer wise petal overgrowth.

Abstract: Subtle anion effects have been observed for the cyclization of AgX (X - = BF 4 - vs ClO 4 - ) with bis(3-pyridyl)-dimethylsilane. For the two similar anions, BF 4 - affords a cyclic tetramer with two independent spaces, while ClO 4 - affords a dimer of cyclic dimer via an unusual intercyclic argentophilic interaction. For BF 4 - , the specific X - ...H-C interactions seem to play an important role in the formation of the cyclic tetramer.

Abstract: Model systems (of up to 116 atoms) for molecular crystals and mismatched pairs of DNA bases have been studied using GGA density functional theory (DFT) at BP86/TZ2P. In line with previous studies, we find that our approach is adequate for accurately describing the present model systems all of which involve hydrogen bonding. For example, our DFT bond energies for 17 DNA base pairs involving adenine (A), thymine (T), guanine (G), and cytosine (C) agree excellently with ab initio MP2 results (root-mean-square deviation = 1.1 kcal/mol). Our main purpose is to clarify the relative importance of electrostatic attraction versus orbital interaction in the hydrogen bonds involved in our model systems, using a quantitative bond energy decomposition scheme. At variance with widespread belief, the orbital interaction component in these hydrogen bonds is found to contribute about two-fifths (36-43%) of the attractive interactions and is thus of the same order of magnitude as the electrostatic component. Interestingly, we find a similarly prominent role for orbital interaction in the hydrogen bonds that are responsible for the cohesion within a layer of the molecular crystal of Watson-Crick pairs of 9-ethylguanine and 1-methylcytosine.

Abstract: The readily available sodium chlorate is an interesting ionic compound because, although achiral, it forms optically active crystals. When unperturbed, an aqueous solution of sodium chlorate yields a random distribution of + and − crystals on evaporation. Some chiral perturbations profoundly alter this distribution, however. These include seeding, the addition of the optically active cosolutes d-mannitol and d-sorbitol, and the energetic and chiral beta particles and positrons. The chiral weak interaction inherent in all atomic nuclei and thus atoms and molecules does not alter the distribution of + and − crystals. Stirring during evaporation, an achiral perturbation, affects the distribution of crystals in a given crystallization; when crystals from a large number of experiments are considered, however, the distribution of + and − crystals is random.

Abstract: In the present study, K2Ti2O5·0.5H2O, K2Ti2O5, K2Ti4O9, K2Ti6O13(I), and K2Ti6O13(II) were synthesized by calcination from TiO2·nH2O hydrate at 650, 820, 920, 1080, and 1123 °C, respectively. K2Ti2O5·0.5H2O and K2Ti2O5 are composed of grain aggregates and single crystals, respectively. K2Ti4O9, K2Ti6O13(I), and K2Ti6O13(II) all have whisker morphology. The K2Ti4O9 whiskers and hydrosoluble surface wrappage occurred simultaneously in the K2Ti2O5 single crystals at 920 °C during calcination. Subsequently, K2Ti6O13(I) whiskers, coated by more hydrosoluble wrappage generated from both the K2Ti2O5 single crystals and the K2Ti4O9 whiskers, evolved in the K2Ti4O9 whiskers at 1080 °C. K2Ti6O13(I) whiskers converted into K2Ti6O13(II) whiskers through a crystal lattice deformation occurring at 1123 °C. The sinters of K2Ti4O9, K2Ti6O13(I), and K2Ti6O13(II) are all composed of the axial-array whisker sheaves.

Abstract: The field of crystal engineering is rapidly expanding. As our understanding of the mechanism of construction and relationship between structure and function of molecular crystals increases, it is important to recognize that this field offers significant toxicological and environmental benefits. The processes of molecular recognition and self-assembly are inherently benign in terms of its impact on human health and the environment. These benefits must be articulated and exploited.

Abstract: We present here two different topologies that result from the bis-bidentate ligand bis(pyridine-4,4‘-diaminodiphenyl)methane, L, upon coordination to Cu(I) or Cu(II), namely, a metallo-cyclophane or “molecular-box” [Cu2L2(ClO4)2]·4(MeCN)·2(EtOH), 1, and a helicate [Cu2L3(ClO4)4]·3(MeCN), 2, and show that metal ion coordination preference is the major determinant in defining which topology results.

Abstract: Ultrasonic attenuation spectroscopy was successfully applied for in-situ determination of particle size during the crystallization of a molecular crystal in two different polymorphic forms. The crystallization of l-glutamic acid was carried out under different cooling conditions by which the α- or β-polymorphic form of l-glutamic was obtained preferentially. It is shown that each polymorph yields a characteristic acoustic attenuation due to the different habits of the two polymorphs. While it was found that ultrasonic attenuation measurements were less sensitive than turbidometric measurements for the determination of the onset of crystallization, ultrasonic attenuation measurements proved to be well behaved and provided particle sizing data for the prismatic crystals of the α-form of l-glutamic acid and an estimation of the primary dimensions of the β-form needles. Growth rate and supersaturation data were derived from particle size and solid concentration results and correlated.

Abstract: When cocrystallized with calix[5]arene, C60 arranges to form linear, 5-fold, Z-shaped columns consisting of molecular spheres that are in van der Waals contact with one another. The fullerene molecules are present in three completely different environments with regard to their supramolecular association with the calixarene molecules.

Abstract: Reaction of CdCl2·0.5H2O with 2,5-bis(4-pyridyl)-1,3,4-oxodiazole (bpo) and NH4SCN in a 1:1:2 molar ratio under CH3CN−H2O medium afforded a novel neutral three-dimensional (3D) coordination polymer {[Cd(bpo)(SCN)2]·CH3CN}n (1) [monoclinic, space group P21/c, a = 7.680(2) A, b = 10.029(3) A, c = 25.786(7) A, β = 93.779(5)°, Z = 4]. The crystal structure reveals that 1 has a 3D noninterpenetrating open framework with guest CH3CN molecules in the cavities, in which the CdII centers (with CdN4S2 octahedral geometry) are bridged by the bpo molecules and SCN- groups. It is interesting that the two-dimensional sheet in this 3D network consists of 16-membered [Cd4(μ-SCN-N,S)4] rings, and the bpo molecules extend these layers to a 3D structure, which is further stabilized by C−H···N hydrogen-bonding and strong π−π-stacking interactions. Thermogravimetric analysis and X-ray powder diffraction technique measurements illustrate that the framework of 1 is retained upon removal of the uncoordinated guest acetonitrile m...

Abstract: The correlation between morphology and polarity was investigated for GaN single crystals synthesized by the Na flux method. The polarity was identified by using anomalous X-ray dispersion. Colorless transparent prismatic single crystals were classified into three types. The first had a smooth basal plane face and no hexagonal pyramidal faces, the second had smooth pyramidal faces, and the third had a rough basal plane face and rough pyramidal faces. The prismatic crystals with smooth surfaces had N-polarity and grew in the −c direction, whereas the crystals having rough surfaces had Ga-polarity and grew in the +c direction. In colorless transparent platelet single crystals, one side of the basal planes had a mirror smooth surface, while the other side had many step edges and hexagonal pits. The smooth basal plane and the rough basal plane were the (0001) N-face and (0001) Ga-face, respectively. Black pyramidal crystals had a smooth (0001) basal plane face corresponding to the Ga-face.

Abstract: The first oxalato and isonicotinato mixed-ligand guest-inclusion open-framework coordination polymer {[(H2O)2(oxa)Zn2(IN)2]·2(H2O)} was synthesized from a chemical rearrangement of isonicotinate to oxalate under hydrothermal conditions: space group, P21/c; a = 8.302(1), b = 15.557(2), c = 7.344 (1) A, β = 94.351(1)°, U = 945.8(1) A3, Z = 2.