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Recently, great advances have been made in the mechanochromic luminescence (MCL) of organic crystals that can switch their emission colors upon exposure to mechanical stimuli. Although several polymorphic crystals and solvates have exhibited multicolor MCL properties, a further deep understanding of the relationship between crystal structures and stimuli-responsive properties is required for rationally generating multicolor-emissive polymorphic crystals and solvates from a single luminescent compound. Herein, multicolor luminescence switching has been achieved for solvates of a phenanthroimidazolylbenzothiadiazole derivative with dianisyl groups. Four types of solvates with different luminescence properties changed their emission colors upon amorphization induced by mechanical stimuli. The amorphous state was recrystallized into solvates when exposed to solvent vapors. Furthermore, the solvate containing pyridine molecules showed a bathochromic shift in emission wavelength upon exposure to acid vapor. Typical acid-responsive luminescence switching is characterized by the protonation of the basic moiety of luminescent molecules, whereas in this study, the change in luminescence color could be induced by protonating non-luminescent pyridine molecules in the solvate. The present study potentially provides useful insights for the development of smart luminescent sensors. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) facilitate the stabilization and isolation of highly reactive and almost "naked" cations. Alkoxyaluminate-based WCAs such as [Al(OC(CF3)3)4]− ([pf]−) are widely used due to their synthetic accessibility and their high stability. However, small cations are still able to coordinate the oxygen atoms of the [pf]− anion or even to abstract an alkoxy ligand. The novel WCA [Al(OC10F15)4]− ([pfAd]−; OC10F15 = perfluoro-1-adamantoxy) is characterized by a very rigid core framework, thus indicating a higher stability towards fluoride-ion abstraction (DFT calculations) and providing hope to generate less disordered crystal structures. The [pfAd]− anion was generated by the reaction of the highly acidic alcohol perfluoro-1-adamantanol C10F15OH with LiAlH4 in o-DFB. Li[pfAd] could not be synthesized free of impurities (and still contains unreacted alcohol). Yet, starting from contaminated Li[pfAd], the very useful pure salts Ag[pfAd], [Ph3C][pfAd] and [H(OEt2)2][pfAd] could be synthesized. The salts were characterized by NMR spectroscopy, single-crystal X-ray diffraction and IR spectroscopy. Additionally, [NO][pfAd] could be synthesized containing alcohol impurities but nonetheless enabled the synthesis of the salt P9+[pfAd]−. The synthesis of Tl[pfAd] in a mixture of H2O/acetone/o-DFB demonstrated the water stability of the [pfAd]− anion. [ABSTRACT FROM AUTHOR]

Ferroelectric epitaxial films of Pb1−xSrx TiO3 (PST) with nominal compositions of x = 0, 0.33, 0.39, and 0.43, supported by (100) SrTiO3 (STO) substrates, have been successfully grown by liquid phase epitaxy (LPE). Energy dispersive X-ray measurements performed on selected films reveal an increase in the Sr-content for each nominal increase in the growth solution. Structural and spectroscopic investigations, from X-ray diffraction and Raman spectroscopy, unveil that all of the PST films possess a tetragonal structure at room temperature, and with increasing Sr-content, the tetragonality and Curie temperature decrease accordingly with values approaching those of reference bulk compound materials. These results confirm we achieved full control of the composition, structure, and transition temperature of the ferroelectric films, by adapting the nominal composition of the LPE growth solution, performing epitaxial growth while maintaining the bulk-like properties. Finally, using piezoresponse force microscopy, various nanoscale polar domain configurations for the PST epitaxial films were disclosed. This indicates that films having a higher Sr content can have polar domain configurations compatible with different a/c and c nanodomains. This work underlines the usefulness of the LPE method for controlling tetragonal ferroelectric PST film growth, in order to tune the nanoscale polarisation landscape in films having bulk-like structures and ferroelectric transition temperatures. This opens a path to new investigations fully exploiting the combined advantages of multiple nanoscale electrical boundary configurations within bulk-like ferroelectric films. [ABSTRACT FROM AUTHOR]

In this study, the complicated solvation behaviors of arbutin were studied from both experiment investigations and theoretical calculations. Six solid forms of arbutin, namely the anhydrous form I and five solvates, were successfully obtained. The structures of form I, solvate S1, solvate S4, and solvate S5 are reported for the first time. The obtained forms of arbutin were thoroughly characterized and distinguished by PXRD, PLM, DSC, TGA, Raman, and FTIR spectroscopy techniques. It was found that solvate S4 and solvate S5 were isostructural solvates. Further, the packing arrangements and pore structures were analyzed to illustrate the formation of the isostructural solvates. Moreover, analyses of the crystal structures showed that arbutin exhibited flexible conformations in various solid forms, and there were strong correlations between the crystal lattice energy and the thermal stability of various solvates. Finally, the formation mechanism of arbutin solvates was proposed and rationalized and the conversion relationship between different solid forms was also established. [ABSTRACT FROM AUTHOR]

Based on Krivovichev information measures for crystal structures and the universal partitioning scheme for different sources of information described previously by Hornfeck, a ladder of information for crystal structures with primary motifs of different dimensionalities (0D, 1D, or 2D) is proposed. Ethanol (0D), SnIP (1D), and TlOH (2D) are discussed as examples of the introduced concept. The proposed calculation technique allows to explicitly obtain contributions of substructures of ordered structures into the information content of a structure conforming to the rule of strong additivity, thus giving a simple assessment of complexity at different hierarchical levels of organization, and takes into account partitioning contacts formed by structural units into equivalence classes, which is poorly dependent on that of the structural units themselves. The technique is a complementation to the multilevel topological analysis performed in the ToposPro program package. [ABSTRACT FROM AUTHOR]

Shape-persistent macrocycles have been of interest for many years to researchers due to their potential in synthesis and materials chemistry. They are regarded as reasonably rigid and in many cases they are able to spontaneously aggregate forming supramolecular assemblies. The dependence of a steric hindrance located on oxygen atoms in 2,6-bis-acetylenephenolates on the structure of macrocycles obtained from these precursors by Eglinton homocoupling has been investigated. A small library of crystal structures of arylene butadiynylene species has been obtained and analyzed in detail. Our results showed that regardless of the steric hindrance usually a wide range of macrocycles is formed (starting from tetramers) even though the smaller derivatives are significantly deviated from planarity, which might result from avoiding too much strain in these macrocyclic, cross-conjugated molecules. [ABSTRACT FROM AUTHOR]

We describe the synthesis, crystal structure and semiconducting properties of a number of hexacyanidometallates with the formula A2[MFe(CN)6]·xH2O (A = Na, K; M = Mg, Ca, Sr and Ba). All crystal structures were studied via single-crystal or powder X-ray diffraction. The unexpectedly low-symmetric structures in these ferrocyanides are described and contrasted with analogous transition-metal compounds which have been reported to be strictly or nearly cubic. The amount of crystal water in the structure for powder samples was determined by the thermogravimetric analysis (TGA), supported by IR and Raman spectroscopy. Electronic-structure calculations of K2[MgFe(CN)6] and K2[CaFe(CN)6] are compared with experimental UV-Vis measurements. The large band gaps by advanced theory indicate that the smaller experimental band gaps are due to surface effects of impurity states. Mott–Schottky curves of K2[MgFe(CN)6], K2[CaFe(CN)6] and K2[BaFe(CN)6]·3H2O exhibit positive slopes, which characterizes these compounds as n-type semiconductors. [ABSTRACT FROM AUTHOR]

Described herein are the synthesis, structure, and photophysics of the iodo-substituted cyclic trinuclear copper(I) complex, Cu3[4-I-3,5-(CF3)2Pz]3 supported by a highly-fluorinated pyrazolate in comparison with its previously reported 4-Br/4-Cl analogues. The crystal structure is stabilised by multiple supramolecular interactions of Cu3⋯I and hydrogen/halogen bonding. The photophysical properties and supramolecular interactions are investigated experimentally/computationally for all three 4-halo complexes vis-à-vis relativistic effects. [ABSTRACT FROM AUTHOR]

Peptidases are regulated by latency and inhibitors, as well as compatibilization and cofactors. Ulilysin from Methanosarcina acetivorans, also called lysargiNase, is an archaeal metallopeptidase (MP) that is biosynthesized as a zymogen with a 60-residue N-terminal prosegment (PS). In the presence of calcium, it self-activates to yield the mature enzyme, which specifically cleaves before basic residues and thus complements trypsin in proteomics workflows. Here, we obtained a low-resolution crystal structure of proulilysin, in which 28 protomers arranged as 14 dimers form a continuous double helix of 544 Å pitch that parallels cell axis b of the crystal. The PS includes two α-helices and obstructs the active-site cleft of the catalytic domain (CD) by traversing it in the opposite orientation of a substrate, and a cysteine blocks the catalytic zinc according to a "cysteine-switch mechanism". Moreover, the PS interacts through its first helix with an "S-loop" of the CD, which acts as an "activation segment" that lacks one of two essential calcium cations. Upon PS removal during maturation, the S-loop adopts its competent conformation and binds the second calcium ion. Next, we found that in addition to general MP inhibitors, ulilysin was competitively and reversibly inhibited by 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF; Ki = 4 μM). This is a compound that normally forms an irreversible covalent complex with serine peptidases but does not inhibit MPs. A high-resolution crystal structure of the complex revealed that the inhibitor penetrates the specificity pocket of ulilysin. A primary amine of the inhibitor salt-bridges an aspartate at the pocket bottom, thus mimicking the basic side chain of substrates. In contrast, the sulfonyl fluoride warhead is not involved and the catalytic zinc ion is freely accessible. Thus, the usage of inhibitor cocktails of peptidases, which typically contain AEBSF at ∼25-fold higher concentrations than the determined Ki, should be avoided when working with ulilysin. Finally, the structure of the complex, which occurred as a crystallographic dimer recurring in previous mature ulilysin structures, unveiled an N-terminal product fragment that delineated the non-primed side of the cleft. These results complement prior structures of ulilysin with primed-side product fragments and inhibitors. [ABSTRACT FROM AUTHOR]

The synthesis of novel phosphine palladium PEPPSI and dimer complexes bearing RuPhos, SPhos and XPhos phosphines is reported. The crystal structures of XPhos Pd PEPPSI with pyridine, SPhos Pd PEPPSI with 3-chloropyridine as throw-away ligands and the RuPhos palladium dimer were obtained and compared with previously reported congeners. The catalytic activity of these novel complexes was examined via a C–N coupling reaction involving 4-chloroanisole and morpholine. RuPhos complex 2b proved most active, leading to 97% yield with a low (0.2 mol%) catalyst loading, while phosphine palladium dimers showed significantly lower catalytic activity. However, the addition of 3-pentanone as an activator/stabilizer significantly improved the yields of phosphine dimers and PEPPSI complexes when the reactions were performed in THF. [ABSTRACT FROM AUTHOR]

We report the synthesis of single crystals of the quaternary sulfide, BaCeCuS3, for the first time by heating a polycrystalline sample of BaCeCuS3 with an excess of KCl flux inside a vacuum-sealed fused silica tube. The crystal structure of the compound is determined by a single-crystal X-ray diffraction study which shows that it crystallizes in the primitive orthorhombic crystal system (space group: Pnma) with cell constants of a = 10.6740(13) Å, b = 4.1200(6) Å, and c = 13.409(2) Å. The structure is best described as a pseudo-two-dimensional structure where tetrahedral CuS4 and octahedral CeS6 units serve as the main building blocks. The polyanionic layers in the structure are separated by the presence of electropositive Ba2+ cations. The optical absorption study on the polycrystalline sample of BaCeCuS3 shows a semiconducting nature with a direct bandgap of 1.8(2) eV consistent with the green color of the sample. The temperature-dependent thermal conductivity (ktot) measurements on the polycrystalline BaCeCuS3 sample reveal an extremely low value of ktot (0.32 W m−1 K−1) at 773 K. DFT calculations were carried out to obtain the electronic structure of the title compound. Our theoretical studies predict a high value of the thermoelectric figure of merit (>1) for BaCeCuS3 by optimization of the charge carriers. To also explore a practical application of BaCeCuS3, a liquid junction solar cell was fabricated: TiO2/CdS/BaCeCuS3/Sn2−/S2−/MWCNTs@Ni, and the cell delivered an efficiency enhanced by ∼45% compared to the one without the sulfide. The performance improvement is affected by the hole conducting properties of BaCeCuS3, which allows facile hole transfer from CdS to the polysulfide, increases the charge separation, and hence increases the efficiency. [ABSTRACT FROM AUTHOR]

Mononuclear oxovanadium(V) complexes [V(O)XL (1: X = Ot-Bu, 2: X = Cl)] [H2L: 2,2′-methylene bis(4,6-di-tert-butylphenol)(4′-tert-butyl-6′-(1-adamantyl)phenol)] directed towards asymmetric catalysis have been synthesised as racemic compounds using an unsymmetric and achiral phenolic bidentate ligand (H2L), and NMR and UV-vis absorption spectroscopies, single-crystal X-ray diffraction, and IR spectroscopy revealed their racemic chiral-at-vanadium structures in solution and in the crystal. In addition, theoretical calculations revealed that the HOMO–LUMO energy gap is smaller for unsymmetric ligands, which promotes d-orbital splitting of the metal centre. [ABSTRACT FROM AUTHOR]

Single crystals of Fe[SeO4]OH have been synthesized by hydrothermal treatment. The Fe[SeO4]OH structure was investigated using the superspace approach. It is shown that the structure belongs to a family of compounds including kieserite-like and pauflerite-like structure types. All these structures consist of topologically identical layers interconnected either by a mirror plane (m) or by an inversion centre (1¯). The sequence of these local elements of symmetry, m and 1¯, determines each member of the family. We used the (3 + 1)-dimension superspace group Pnam(00γ)000 applied to an average structure to be able to reproduce known polytypes and predict new ordered and partially or completely disordered structures in the R[MO4]Z structural family. [ABSTRACT FROM AUTHOR]

A series of new heteroleptic copper(I) complexes [Cu(N^N)(P^P)][BF4] (1–6), where N^N is a pyrazole-substituted 2,2′-bipyridine (5-(1H-pyrazol-4-yl)-2,2′-bipyridine (5-pzbpy, L1), 4,4′-di(1H-pyrazol-4-yl)-2,2′-bipyridine (4,4′-pz2bpy, L2), 5,5′-di(1H-pyrazol-4-yl)-2,2′-bipyridine (5,5′-pz2bpy, L3), and 3,8-di(1H-pyrazol-4-yl)-1,10-phenanthroline (3,8-pz2phen, L4)) and P^P is either oxybis(2,1-phenylene)bis(diphenylphosphane) (POP) or 1,3-bis(diphenylphosphanyl)propane (dppp), were successfully prepared and investigated. The crystal structures of 1, 2, 3 and 6 were determined by single X-ray diffraction. The novel copper(I) complexes 1, 2 and 3 show turn-on emission sensing for halogen ions. The fluorescence enhancement of the copper(I) complexes increases in the order of F− < I− < Br− < Cl−, and the differences in fluorescence intensity could be easily distinguished with the naked eye under UV light illumination. The 1H NMR titration indicated that the interaction involves hydrogen-bond formation between the halide (Cl−, Br− and I−) and the acidic H of the pyrazole group, with N–H deprotonation occurring at increasing F− concentrations. The result was further confirmed by carrying out theoretical calculations. [ABSTRACT FROM AUTHOR]

The entanglement of cyclic polymers is an open issue. Cyclic poly(ε-caprolactone)s (PCLs) with a number-average molar mass (Mn) ranging from 8 to 37 kg mol−1 were synthesized using a protocol without linear precursors to avoid the influence of linear contaminants. The crystallization and melting behaviors of the synthesized unconcatenated and unknotted cyclic PCLs were investigated by DSC, POM and X-ray. The DSC and POM characterized crystallization behaviors of the cyclic PCLs showed that the half-time of crystallization and spherulite growth rate related to the molecular weights. The rheological results showed that the critical molecular weight of cyclic PCLs is 11 kg mol−1, which is about two times that of the linear PCLs. The coupling effect of ring topology and entanglement leads to the maximum crystallization rate and minimum lamellar thickness at the medium molecular weight. In situ simultaneous SAXS/WAXS probe in heating was performed on the samples after isothermal crystallization, and the results indicated that the ring topology did not change the crystal of PCL, but the evolution of nano-scale crystalline structure is different from that of the linear PCLs. The evolution of metastable crystalline structure of cyclic PCLs is discussed based on the SAXS results, and the entanglements were found to reduce the rate of structural evolution. [ABSTRACT FROM AUTHOR]

Non-metallic η²-H2 complexes are extremely rare; moreover in the case of boranes (with the exception of the BH5 molecule) the existence of such structures was only indicated by computational studies. In a recent paper we have demonstrated that external electron donor groups can stabilize the η²-H2 complexes, similar to the backdonation in the case of transition metals. In this paper we present evidence of a new stabilizing effect: electron donation from the B-R bonds to the H2 σ* orbital. The stability and electronic structure of several mono-, di-, and trisubstituted borane-H2 complexes were investigated by ab initio calculations. SiR3 groups were found to facilitate the σ(B-R)σ*(H-H) interaction, increasing the stability of the η² complexes. Furthermore in the case of tris(trimethyl)silylborane, the exceptional stability of a novel neutral pentavalent borane structure is shown. [ABSTRACT FROM AUTHOR]

Silver bismuth diselenide (AgBiSe2) has attracted much attention as an efficient thermoelectric material, owing to its intrinsically low lattice thermal conductivity. While samples synthesized using a solid-state reaction showed n-type conductivity and their dimensionless figure of merit (ZT) reached ∼1 by electron doping, theoretical calculations predicted that a remarkably high thermoelectric performance can be achieved in p-type AgBiSe2. In this paper, we present the effect of Te substitution on the crystal structure and thermoelectric properties of AgBiSe2, expecting p-type conductivity due to the shallowing of the energy potential of the valence band. We found that all AgBiSe2−xTex (x = 0–0.8) prepared using a solid-state reaction exhibits n-type conductivity from 300 to 750 K. The room-temperature lattice thermal conductivity decreased to as low as 0.3 W m−1 K−1 by Te substitution, which was qualitatively described using the point defect scattering model for the solid solution. We show that ZT reaches ∼0.6 for x = 0.8 at a broad range of temperatures, from 550 to 750 K, due to the increased power factor, although the carrier concentration has not been optimized yet. [ABSTRACT FROM AUTHOR]

Two cyclometalated complexes [Ir(dfppy)2(aip)](PF6) (1) and [Ir(ppy)2(aip)](PF6) (2) have been synthesized based on a photoactive anthracene-based ligand aip and cyclometalating ligands dfppyH and ppyH [dfppyH = (2-(2,4-difluorophenyl)-pyridine), ppyH = 2-phenyl-pyridine]. Their crystal structures indicate that an aip ligand uses its phenanthroline moiety to chelate an {Ir(dfppy)2}+ unit in 1, while an {Ir(ppy)2}+ unit in 2. In CH2Cl2, the anthracene units in aip, 1 and 2 underwent photo-oxidation upon irradiation with 365 nm light, forming species aip-O, 1-O and 2-O, respectively. This photo-oxidation resulted in luminescence switching, from a luminescent state (emission at 493 nm) to a non-luminescent state for aip, while from a non-luminescent state to a luminescent state with an emission at 519 nm for 1 and 578 nm for 2. Additionally, the luminescence of aip, 1-O and 2-O in CH2Cl2 can be modulated by using TFA to protonate the imidazole units and/or non-coordinated phenanthroline moiety in these compounds. Upon adding TFA, aip showed luminescence quenching, while species 1-O and 2-O revealed both luminescence-intensity decrease and emission-wavelength increase (Δλ = 9 nm for 1-O, and Δλ = 4 nm for 2-O). In this paper, we discuss the luminescence switching/modulation of aip, 1 and 2 by light-irradiation-induced photo-oxidation of their anthracene units and by TFA treatment. [ABSTRACT FROM AUTHOR]

Two novel Ba(ii) complexes [Ba(TCPA)2(H2O)4] 1 and [Ba(H2O)8]·2(o-FcCOC6H4COO)·6H2O 2 [HTCPA = 2,4,6-trichlorophenoxyacetic acid and o-HOOCC6H4-COFc = o-ferrocenylcarbonyl benzoic acid] have been synthesized by a facile microwave method. The solid-state structures were well established by means of X-ray crystallography as well as routine analysis of the infrared spectrum (FTIR), elemental analysis, field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TG). Different polyhedra of tricapped triangular prisms for 1 and dodecahedra for 2 were present. It is worth noting that the central Ba(ii) ion in 1 is nine-coordinated by two carboxylate oxygen atoms from TCPA ligands and seven oxygen atoms from coordinated water molecules. By contrast, the eight-coordinated Ba(ii) in 2 forms barium-water clusters assembled by O–H…O hydrogen-bonds contributed by coordinated water molecules. The uncoordinated o-OOCC6H4-COFc ligands in 2 play a key role in the process of charge balance. FESEM images exhibited different surface appearances between the ligand and barium complexes, that is: flower-like HTCPA, branch-like o-HOOCC6H4-COFc, block-like complex 1 and corner-truncated cubes for complex 2. The allelopathic activity of the complexes and their corresponding ligands was evaluated against two herbaceous plants of barnyard grass and turnip (Raphanus sativus). All the tested compounds showed certain activity with good RI values. An antifungal bioassay was also carried out in vitro on three strains of Botrytis cinerea Pers., Glomerella cingulata Schr and Cytospora sp. Complex 1 and HTCPA can work against all three tested fungi, whereas o-HOOCC6H4-COFc and 2 only worked for Botrytis cinerea Pers. The complex presented in this paper has potential applications in weed control, and this work provides an experimental basis for future studies on Ba-based pesticides. [ABSTRACT FROM AUTHOR]

At multianvil high-pressure/high-temperature conditions of 10 GPa and 1273 K, the first ternary tungsten tellurate WTe2O7 is formed, starting from a stoichiometric mixture of WO3 and TeO2. The compound crystallizes triclinic in a hitherto unknown crystal structure type with the space group P1¯; (no. 2), and was refined from single-crystal X-ray diffractometer data: a = 538.3(1), b = 687.5(1), c = 802.3(1) pm, α = 72.4(1)°, β = 85.7(1)°, γ = 68.1(1)°, wR2 = 0.0323, GooF = 1.048, 3157 F2 values, and 106 variables. The main motifs of the crystal structure are pairs of edge-linked [WO6]6− octahedra and fourfold oxygen-coordinated Te4+ atoms. The oxidation state of W6+ and Te4+ was further verified by measuring the characteristic binding energy values for the W 4f and the Te 3d core levels via X-ray photoelectron spectroscopy (XPS). In addition, DFT calculations of the structure, the associated electron localisation functions (ELF) and vibrational spectra have been carried out. The theoretical data clearly demonstrates the impact of the residual electron density located at the Te4+ ions, which can be directly interpreted as the presence of lone electron pairs within the solid structure. [ABSTRACT FROM AUTHOR]

We present a comprehensive experimental study of the crystal structure of calcium vanadate (Ca3V2O8) under systematic temperature and pressure conditions. The temperature evolution (4–1173 K) of the Ca3V2O8 structural properties is investigated at ambient pressure. The pressure evolution (0–13.8 GPa) of the Ca3V2O8 structural properties is investigated at ambient temperature. Across all pressures and temperatures used in the present work, the Ca3V2O8 crystal structure was determined by Rietveld refinement of powder X-ray diffraction data. The experimental high-pressure data are also supported by density-functional theory calculations. According to the high-pressure results, Ca3V2O8 undergoes a pressure-induced structural phase transition at a pressure of 9.8(1) GPa from the ambient pressure trigonal structure (space group R3c) to a monoclinic structure (space group Cc). The experimentally determined bulk moduli of the trigonal and monoclinic phases are, respectively, B0 = 69(2) GPa and 105(12) GPa. The trigonal to monoclinic phase transition appears to be prompted by non-hydrostatic conditions. Whilst the trigonal and monoclincic space groups show a group/subgroup relationship, the discontinuity in the volume per formula unit observed at the transition indicates a first order phase transition. According to the high-temperature results, the trigonal Ca3V2O8 structure persists over the entire range of studied temperatures. The pressure-volume equation of state, axial compressibilities, Debye temperature (264(2) K), and thermal expansion coefficients are all determined for the trigonal Ca3V2O8 structure. [ABSTRACT FROM AUTHOR]

The crystal structure of substituted formamidine salts has been modeled on the basis of a combination of quantum chemistry methods and atom–atom potentials. Based on the new author's method (MICCM) for calculating the enthalpies of formation of salts, which is based on the model of a cocrystal consisting of a mixture of cations and anions and a "quasi-salt" of the neutral components of the salt itself, the formation enthalpy is calculated as the average between the enthalpies of formation of these two structural components for salts various formamidines and the contributions of the corresponding cations to the calculation scheme are given. The results are in good agreement with the experimental data obtained by combustion calorimetry. [ABSTRACT FROM AUTHOR]

Active pharmaceutical ingredients (APIs) and selected coformers were studied in crystalline self-environment, in selected co-crystal structures, and gas phase. To obtain comparable geometries from experimental crystal structures, we rely on fast quantum mechanical GFN2-XTB molecule-in-cluster optimizations. Optimized crystal structures are first analysed in terms of molecule-pair interaction energies, by subdividing a cluster generated from asymmetric unit content through space-group symmetry into pairs of molecules. Accurate energies are then obtained by single-point molecular orbital (MO/MO) two layer "ONIOM" energy partitioning, comparing the same molecules in different crystal environments. Clusters approximate the local environment of a crystal structure for ONIOM. The pre-processor program BAERLAUCH (Acta. Cryst. A 2012) was used to set up all cluster computations. Solid-state computations using dispersion-corrected density functional theory provide reference results. ONIOM partitioned energies shed light on the driving force of co-crystal formation, with the energy gain from the complementarity of molecule-pair wavefunctions in such structures being the main driving force. It follows that improving prediction of co-crystal structure formation beyond current approaches, e.g. COSMO-RS excess enthalpies, statistics from structural databases or full crystal structure prediction is possible by finding complementary molecule-pairs through conformational sampling, as ultimately exemplified. [ABSTRACT FROM AUTHOR]

Accurate and efficient computation of relative energies of molecular crystal polymorphs is of central importance for solid-state pharmaceuticals and in other technologically relevant fields. In recent years, dispersion-corrected density-functional theory (DFT) has emerged as the pre-eminent energy ranking method for crystal structure prediction (CSP). However, planewave implementations of these methods are hindered by poor scaling for large unit cells and are limited to semi-local functionals that suffer from delocalisation error. In this work, we demonstrate that a recent implementation of the exchange-hole dipole moment (XDM) dispersion correction in the Fritz Haber Institute ab initio materials simulation (FHI-aims) package provides excellent performance for the energy ranking step of CSP. Thanks to its use of highly optimized numerical atom-centred orbitals, FHI-aims provides effectively linear scaling with system size and allows efficient use of hybrid density functionals with minimal basis-set incompleteness errors. We assess the performance of this methodology for the 26 compounds that formed the first 6 CSP blind tests. The hybrid results show significant improvements for 4/26 compounds, where delocalisation error affects the quality of predicted crystal energy landscapes. [ABSTRACT FROM AUTHOR]

The current study shows that Schiff base HL, (Z)-2,4-dibromo-6-(((piperidin-2-ylmethyl)imino)methyl)phenol, can be used successfully as a selective chemosensor for Zn(II) and Ni(II) among several competing cations in purely aqueous and semi-aqueous media. Under UV light in methanol–water (9 : 1) HEPES buffer, the receptor gives its response by changing its color to cyan color in the presence of Zn(II) and to bluish cyan color in the presence of Ni(II). Surprisingly, the chemosensor can only reliably identify Zn(II) in a hundred percent aqueous medium by changing its color to light yellow. UV and fluorescence studies in both aqueous and semi-aqueous media are used to further investigate this Zn(II) and Ni(II) recognition phenomenon. The high values of the host–guest binding constants, obtained by electronic and fluorescence titration, ensure that a strong bond exists between HL and Ni(II)/Zn(II). As anticipated, two highly luminescent mononuclear, crystalline compounds, complexes 1 and 2, have been developed by a separate reaction of HL and Zn(II)/Ni(II), and the high luminous properties are due to the occurrence of Chelation Enhanced Fluorescence (CHEF). According to the single crystal structure, the asymmetric units of both complexes consist of two deprotonated chemosensor units and one Zn(II)/Ni(II), leading to the formation of an octahedral complex. For Ni(II) and Zn(II) sensing, the predicted LOD is in the nanomolar range. Both complexes 1 and 2 are fluorescence active and studies to check their ATP detection ability, but intriguingly, only complex 2 is capable of detecting ATP in a fully aqueous solution. Finally, the live cell imaging study validates the two sensors' biosensing functionality. [ABSTRACT FROM AUTHOR]

Using a dicarboxylic acid, [1,1′-biphenyl]-4,4′-dicarboxylic acid (H2L1) and an exobidentate ligand, (1E,1′E)-N,N′-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) (L2), two 3D interpenetrated networks, {[Zn3(L1)3(L2)]·9H2O}n (Zn-MOF) and {[Co3(L1)3(L2)(DMF)]·0.5DMF}n (Co-MOF), have been prepared in good yields. The crystal structure analysis of Zn-MOF and Co-MOF revealed that both have a 3D pillared-layer structure based on pinwheel trinuclear metal–carboxylate clusters as secondary building units (SBUs). Furthermore, the structures also exhibited three-fold interpenetration. Although the overall networks in Zn-MOF and Co-MOF showed significant resemblances, there are marked differences in their crystal structures, which are associated with the coordination environment of the metal centre and the binding modes of the carboxylates. Gas adsorption studies (N2 at 77 K and 1 bar) indicated that Co-MOF is more porous than Zn-MOF. Magnetic measurements on Co-MOF indicate a significant antiferromagnetic interaction (45 K to 303 K) between trimeric Co(II) S = 3/2 spins through syn–syn carboxylato bridges. Both MOFs were studied for the Lewis acid catalyzed Knoevenagel condensation reactions between benzaldehydes and malononitrile with an active methylene group, where Zn-MOF was found to be a better catalyst than Co-MOF. This was supported by the Monte Carlo simulations indicating the better substrate binding ability of Zn-MOF than Co-MOF. [ABSTRACT FROM AUTHOR]

A new polymorph of 5-nitrobenzo[c][1,2,5]thiadiazole, polymorph II, has been discovered. This polymorph is obtained by crystallization from solutions containing Cu(II) ions, which inhibit the formation of the already known polymorph I. The packings of the two polymorphs (actual crystal structures) are compared between each other and also with seven virtual polymorphs generated from the crystal structures of similar compounds retrieved from the CSD and optimized by ab initio calculations with periodic boundary conditions. The comparison is based on the analysis of the synthons present in the different crystal structures, and on calculated lattice energy and density. For the specific case examined, our analysis suggests that among crystal structures containing a given synthon, or a given combination of synthons, only the one with the lowest Ulat is observed; crystal structures with slightly higher Ulat (within 2 kcal mol−1) can be observed, but they must be based on different synthons. [ABSTRACT FROM AUTHOR]

A new hydrazone ligand, HL [(1-methylimidazol-2-yl)methylene]isonicotinohydrazide, has been synthesized and characterized by several spectroscopic methods. The ligand (HL) was then utilized for the preparation of two new complexes, namely, [Zn(L)2]·2H2O (complex 1) and [Zn(H2L)Cl3]·H2O (complex 2). The crystal structures of these complexes have been established by single-crystal X-ray analysis. The non-covalent interactions and supramolecular assemblies observed in the crystal packing of both complexes have been described focusing on π⋯π (for 1) and O⋯π–hole (for 2) interactions along with various hydrogen bonding interactions. A DFT study has been carried out to analyse their non-covalent interactions with rationalization using molecular electrostatic potential (MEP) surfaces and the combined QTAIM/NCI plot computational tools. In addition, the in vitro biological activities of the synthesized ligand (HL) and the water-soluble complex 2 were evaluated against Escherichia coli and Staphylococcus aureus. [ABSTRACT FROM AUTHOR]

The pure phase syntheses of three novel organic charge transfer complexes, obtained by combining the polyaromatic hydrocarbon triphenylene with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its fluorinated derivatives, are reported together with their crystal structures determined by 3D electron diffraction. The degree of charge transfer is estimated via examining intramolecular vibrational mode displacements between neutral TCNQFn and its complexes with triphenylene using infrared spectroscopy. The direct optical band gaps of 1.87, 1.76 and 1.70 eV for triphenylene–TCNQFn (n = 0, 2, 4) respectively, are determined via diffuse reflectance spectroscopy. The application of advanced structure determination techniques in combination with spectroscopic methods has allowed us to shed light on compelling charge transfer systems and to gain indications for the design of improved electrical organic conductors. [ABSTRACT FROM AUTHOR]

A series of twelve selenourea compounds with fluorinated fragments were synthesized and characterized. The influence of fluorine atoms in the chemical shift of the 77Se NMR was studied. The more fluorine atoms in the structure produced a downfield shift of the 77Se signal, indicating a higher π-acidity character in the N-heterocycle. The relative position of the fluorine atom also affects the chemical shift of the 77Se. It can be seen that a fluorine atom at 3-position, following by 4- and 2-position, respectively, produced a higher downfield shift. Interestingly, the opposite effect was observed for the –CF3 group. The crystal structure of six selenourea compounds revelead that the predominant interactions were three: Se⋯H, F⋯F and F⋯H. The latter was corroborated by Hirshfeld surface analysis and 2D dimensional fingerprint plots of each crystal structure. [ABSTRACT FROM AUTHOR]

The 6p orbit coupling of bismuth ions and the magnetism of iron ions endow bismuth–iron compounds with magnetic, optical and electrical properties. In this paper, non-rare-earth bismuth–iron crystals, KBa8Fe12(Bi6−xFex)O38 (x = 0.2, 1.1, 2.0, 2.9, and 3.8), with a large magnetocaloric effect were prepared by a hydrothermal method. The structure–function relationship is discussed. With the increase of the Fe content, the lattice parameters and unit cell volume decrease, while the magnetization intensity shows an increase on the whole and a fluctuation at the same time. The increase of the Fe content can improve the magnetocaloric effect. Importantly, the maximum magnetic entropy change (ΔSM) of KBa8Fe12(Bi4.9Fe1.1)O38 is as high as 1.54 J kg−1 K−1 at the low temperature of 2 K. [ABSTRACT FROM AUTHOR]

Sm3+-doped and Sm3+/Eu3+ co-doped CaTiO3 phosphor samples were synthesized by solid-state reaction method and characterized using XRD, FE-SEM, FTIR, XPS, UV visible absorption, and photoluminescence techniques. All the compounds showed a crystalline structure with an orthorhombic phase and Pnma(62) space group. The diffuse reflectance spectra showed an absorption band due to the host along with peaks for Sm3+ and Eu3+ ions. The photoluminescence emission spectra of Sm3+-doped CaTiO3 phosphor showed orange-red and deep red emissions on excitation with 407 nm in which the peak at 599 nm was of maximum intensity. Similarly, Eu3+ ions showed a maximum intensity peak at 613 nm on excitation with 398 nm wavelength. The Sm3+/Eu3+ co-doped CaTiO3 phosphor showed an energy transfer from Sm3+ to Eu3+ ions on excitation with 407 nm and the nature of interaction between them was found to be dipole–dipole type. The CIE color coordinates and the correlated color temperature (CCT) calculations of the phosphors were performed, which showed an orange-red color emission useful for LED applications. The lifetime of Sm3+ ions decreases in the presence of Eu3+ ions and this was due to energy transfer from Sm3+ to Eu3+ ions. The temperature-dependent PL spectra of the phosphors showed thermal quenching behaviour. The activation energy of CaTiO3:2Sm3+, CaTiO3:2.5Eu3+, and CaTiO3:2Sm3+/2.5Eu3+ phosphors were found to be 0.27, 0.22, and 0.17 eV, respectively. [ABSTRACT FROM AUTHOR]

Herein we report on the preparation, spectroscopic and thermal characterization, structural study, and magnetic investigation of a new heterobimetallic coordination polymer (CP) of formula {[Na(H2O)2][Cu2(bpca)2(CO3)(HCO3)]}n (1) [Hbpca = bis(2-pyridylcarbonyl)amide], which was isolated through the fixation of aerial carbon dioxide by the preformed [Cu(bpca)]+ complex in basic water/DMSO solvent mixtures. Compound 1 is made up of neutral heterobimetallic zigzag chains growing parallel to the crystallographic c axis where carbonate, bicarbonate, and bpca anions act as bridges with regular alternation of a pair of [Cu(bpca)]+ units and one [Na(H2O)2]+ fragment. The two crystallographically independent copper(II) ions (Cu1 and Cu2) are five-coordinate in somewhat distorted square pyramidal surroundings with three nitrogen atoms from the bpca ligand and either one bicarbonate-oxygen (Cu1) or a carbonate-oxygen (Cu2) in the basal plane and a shared carbonate-oxygen atom (Cu1 and Cu2) in the apical position. Each sodium(I) ion is also five-coordinate in a distorted trigonal bipyramidal environment, with two oxygen atoms from a bpca ligand and a water molecule building the trigonal plane and a bicarbonate-oxygen and another water molecule in the axial sites. The intrachain copper–copper separation across the bridging carbonate is 4.109(1) Å. The cryomagnetic study of 1 reveals the occurrence of a weak ferromagnetic interaction between the copper(II) ions through the bridging carbonate [J = +0.17(4) cm−1, the spin Hamiltonian being defined as H = −J S Cu1· S Cu2]. Density functional theory (DFT) calculations on the [{Cu(bpca)}2(μ-CO3)] fragment of 1 in the gas phase and solid state were used to estimate the magnetic coupling constant (J = +0.42 cm−1) and to describe the electronic structure and magnetic topology of the system. [ABSTRACT FROM AUTHOR]

High-performance anode materials are essential for the realization of sodium-ion batteries. In this work, nanostructured orthorhombic β-NaVO3 was prepared by a simple solution method and investigated as an anode material for sodium-ion batteries. β-NaVO3 exhibits an initial discharge capacity of 356 mA h g−1 at a low current density. Enhanced performance was realized with the β-NaVO3/Gr composite with an initial discharge capacity of 576 mA h g−1 at a low current density and an excellent cycle stability of 83% capacity retention after 400 cycles at a current density of 500 mA g−1. The sodium diffusion coefficients of β-NaVO3/Gr and β-NaVO3 calculated by the galvanostatic intermittent titration technique vary from 10−13 to 10−10 cm2 s−1. Ex situ XRD, TEM and Raman results reveal that the orthorhombic crystal structure of β-NaVO3 transforms into an amorphous phase after the initial charging–discharging process. The detailed pseudocapacitive behavior in β-NaVO3 was investigated by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The crystallization of poly(lactic acid) (PLA) homo-crystallites (HCs) and stereocomplex crystallites (SCs) is quite complicated for the inducing and competing effects of SCs on HCs. Furthermore, carbon dioxide (CO2) would simultaneously influence the H-bond interactions of SCs, and molecular chain mobility and supercooling of SCs and HCs, which might further affect the crystallization process of SC-induced HCs and the competing crystallization of homogeneous HCs and SCs. This manuscript revealed the effect of CO2 on the crystallization of HCs and SCs via influencing the crystallization kinetics and spherulite morphology for the first time. The results showed that CO2 accelerated the crystallization of SCs due to the increased chain mobility and restrained the crystallization of HCs because of the decreased supercooling. HCs could only form in the crystalline assembly of SCs under CO2 while in air, they could be generated at the growth front of SCs. Due to the increased chain diffusion, the development of branches of SCs was more adequate under CO2, resulting in less space on the surface of SCs for HC crystallization. Therefore, under CO2, the heterogeneous HC crystallization was shown as "bundles" and "dendritic" crystals, which was imperfect. Homogeneous and heterogeneous HCs exhibited different pressure dependencies on crystallization behaviors. [ABSTRACT FROM AUTHOR]

A novel high-pressure molybdenum nitride phase, Mo3N5, was synthesized at above 45 GPa via a nitridation reaction of molybdenum with nitrogen under high pressure using a laser-heated diamond anvil cell. Mo3N5, having an N–N dimer and 7-coordinated Mo sites, crystallizes in an orthorhombic structure with a space group of Cmcm (No. 63) without other prototype structures. The refined lattice parameters for Mo3N5 were a = 2.86201(2) Å, b = 7.07401(6) Å, and c = 14.59687(13) Å. The DFT enthalpy calculation suggested that Mo3N5 is a high-pressure stable phase, which is also consistent with an increasing coordination number compared to ambient- and low-pressure phases. The zero-pressure bulk modulus of Mo3N5 was determined to be K0 = 328(4) GPa with K′0 = 10.1(6) by the fitting for the compression curve, which is almost consistent with the theoretical E–V curve and elastic stiffness constants. The compressibility of Mo3N5 has axial anisotropy corresponding to the N–N dimer direction in the crystal structure. [ABSTRACT FROM AUTHOR]

This contribution reports the thermally induced spin crossover (SCO) in the titled series of hybrid solids from the magnetic (SQUID), DSC, IR, Raman, and Mössbauer data. The onset temperature for the high-to-low spin transition follows the order Cl (217 K) > Br (210 K) > I (155 K). This order is inverse to the one known for the halogen-bond propensity, Cl < Br < I. Their crystal structure for the high-spin (HS) phase was solved and refined from the powder XRD data, complemented with the IR spectra and TG curves. For the low-spin (LS) phase, the crystal structure was obtained by periodic DFT calculations, relaxing the room temperature (HS) structure. At room temperature, the CN–ON distance for these dangling ligands in the interlayer region follows the order Cl (5.03 Å) < Br (5.08 Å) < I (5.70 Å). The repulsive electrostatic interaction between these charge centers is responsible for a certain kinetic effect observed in the recorded magnetic data. This interaction was also detected in the recorded Mössbauer spectra. For the 3X-pyridine analogs, the thermally induced spin-crossover was observed only for X = F. This study discusses the nature of that difference in the behavior between the two subseries from three probes for the stabilization energy (SE) of the LS phase. Notably, (1) the effect of the substituent position on the deformation of the iron atom coordination environment; (2) the Mössbauer quadrupole splitting (ΔQS) value; and (3) the onset of the a1g → eg(eg) band absorption in the UV-vis-NIR spectrum. For a non-distorted octahedron, the value of SE coincides with 10Dq (the energy splitting between eg and t2g orbitals for the iron atom). This study is part of an effort to rationalize those structural features affecting the SCO in 2D ferrous nitroprussides. [ABSTRACT FROM AUTHOR]

X-ray structure analysis of a series of 1,3,5-trisubstituted 2,4,6-triethylbenzene derivatives, the structures of which differ in the nature, position and number of halogen atoms attached to the arene rings of the functionalized side-arms, provide information about how these structural differences affect the modes of molecular interactions and the conformations of the tripodal molecules. The crystal structures are characterized by the presence of dimers, which are constructed differently for compounds 1–6 than for 7, the only compound with ortho-substituted halogenophenoxy groups. Compounds 1–6 show an aab arrangement of the halogenophenoxy groups and a pronounced tendency to form pairs of closely nested molecules held together by C–H⋯O and/or C–H⋯π interactions. In the case of compound 7, which adopts the aaa orientation of the functionalized side-arms, the dimeric structures are stabilized by Br⋯Br and Br⋯O interactions. The association of the molecular dimers of 1–7 occurs via halogen bonds (Hal⋯Hal and Hal⋯π) and C–H⋯Hal hydrogen bonds. [ABSTRACT FROM AUTHOR]

Single crystal X-ray diffraction analysis was employed to investigate the supramolecular properties of five 5-brominated pyrazoles in order to evaluate the role of the Br atom in the formation of halogen bonding duly recognizing that the Br atom is less polarizable than the iodine atom. Hirshfeld analysis was employed to conceive a more descriptive image of the halogen bond propensity of 5-bromopyrazoles. The compounds display Br⋯O contacts or Br⋯Br as type I or type II halogen contacts. The structural analyses revealed the isostructurality of compounds 2 and 3 while compound 5 was found to be isostructural with its iodo-analogue, suggesting the importance of the halogen contacts even if they are considered weak in nature. [ABSTRACT FROM AUTHOR]

Three enantiomeric pairs consisting of copper(II) complexes with tridentate Schiff bases have been synthesized for employing in biological assessments: 1∞ [Cu2(R/S-salmet)2(H2O)] (1-R/S·H2O), 1∞ [Cu(R/S-3-HOMe-5-Me-salmet)] (2-R/S), and 1∞ [Cu(R/S-3-MeO-salmet)] (3-R/S) (where R/S-salmetH2, R/S-3-HOMe-5-Me-salmetH2, and R/S-3-MeO-salmetH2 result from the condensation of R/S-methionine with salicylaldehyde, 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde, and 3-methoxy-salicylaldehyde, respectively, in a 1 : 1 molar ratio). The crystal structures of 1-R·H2O and 2-R/S are reported. Moreover, the 1-R/S·H2O enantiomers have been subjected to a single-crystal-to-single-crystal (SC–SC) transformation by heating at 160 °C to afford their dehydrated forms, 1∞ [Cu2(R/S-salmet)2] (1-R/S), whose structures have also been crystallographically determined. The coordination polyhedra of the metal centers, the binding modes of the ligands, and the 1-D double chain assemblies generated by the chiral mononuclear units are comparatively described. The diffuse reflectance UV-Vis and circular dichroism (CD) spectra of compounds 1-R/S·H2O , 1-R/S , and 2-R/S are analysed with respect to their structural peculiarities and compared to those of 3-R/S. The UV-Vis and CD spectra of solutions of 1-R/S , 2-R/S , and 3-R/S point to the collapse of the double chains via dissolution. Biological tests performed on the model eukaryote Saccharomyces cerevisiae indicated low toxicity for 1-R/S , 2-R/S , and 3-R , and moderate toxicity for 3-S. The S-type complexes were accumulated by cells in higher quantity compared to their R-type counterparts due to selective transport via the high-affinity S-methionine transporter, Mup1. A chemogenomic analysis of 3-S toxicity performed on a collection of yeast knockout mutants revealed that most of the deleted genes identified in the screen were involved in the cell response to oxidative stress, calcium-mediated response, or metal homeostasis. Altogether, it was concluded that 3-S accumulation may perturb the redox state of the cell, also interfering with the calcium-mediated response to oxidative stress or metal-related oxidative stress. [ABSTRACT FROM AUTHOR]

We present several multicomponent crystalline species formed by zwitterionic GABA analogues pregabalin and phenibut. These compounds are evaluated based on their crystal structure in congruence with properties such as melting behaviour, solubility, and lattice energies. Furthermore, it is discussed how major property distinctions between a homo- and heterochiral co-crystalline system enable enantiopurification of pregabalin. [ABSTRACT FROM AUTHOR]

Silanones (O＝SiR2) are highly reactive species that readily convert to oligomeric siloxane (O–SiR2)n. The coordination of silanones to transition metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Herein, a pyridine-stabilized silanone molybdenum complex Cp*(OC)2Mo{O＝SiMes2(py)}(SiMe3) (2b, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2, and py: pyridine) was synthesized by reacting the silyl(silylene) complex Cp*(OC)2Mo(＝SiMes2)(SiMe3) (4b) with pyridine-N-oxide in pyridine. X-ray crystal structure analysis revealed that the geometry of complex 2b is similar to those of the previously synthesized DMAP-stabilized analogue Cp*(OC)2Mo{O＝SiMes2(DMAP)}(SiMe3) (2a, DMAP: 4-(dimethylamino)pyridine). The Si＝O and Mo–O bond distances in 2b are similar to those observed in 2a, but the N–Si coordination bond of 2b is slightly longer (approximately 0.05 Å) than that of 2a, indicating weaker pyridine coordination than that of DMAP. The reaction of 2a with excess PMe3 in C6D6 at room temperature for 28 h afforded Cp*(OC)2Mo(PMe3)(SiMe3) (5c) in a 43% NMR yield. In contrast, reacting 2b with excess PMe3 in C6D6 at room temperature for 9 h afforded 5c and the five-membered metallacyclic carbene complex Cp*(OC)Mo(＝C(SiMe3)OSiMes2O)(PMe3) (6) in 10% and 41% NMR yields, respectively. The reactions of pyridine-stabilized silanone complexes Cp*(OC)2M(O＝SiMes2(py))(SiMe3) (M = Mo (2b) and W (1b)) with acetone proceeded via pyridine elimination, coordination of acetone to the Si center in the silanone ligand, and elimination of HSiMe3 to give Cp*(OC)2M{OSiMes2OC(Me)＝CH2} (M = Mo (8) and W (9)) in high yields. [ABSTRACT FROM AUTHOR]

Identifying whether two experimental crystal structures determined under different experimental conditions correspond to the same polymorph is a challenging problem in crystallography, and its solution has practical (and even legal) implications for various technological fields as well as for molecular crystal structure prediction. In this work, we assess the popular COMPACK method vis a vis powder X-ray diffraction (PXRD)-based comparison methods using a dataset of 44 939 structure pairs employed in a previous study [CrystEngComm, 2020, 22, 7170–7185]. We propose a new PXRD-based similarity index and comparison method (VC-PWDF, variable-cell powder difference) that substantially improves the agreement with COMPACK (2.84% total disagreement), compared to the CCDC packing similarity PXRD-based comparison tool (12.35%). By analysing the structure pairs for which COMPACK and VC-PWDF disagree, we evaluated the strengths and weaknesses of each method. COMPACK has a counter-intuitive dependence on its tolerance parameters, by which structures that are considered the same at a given tolerance are viewed as different at a looser tolerance. COMPACK's RMSD(N) can also increase with increasing tolerance values at fixed number of matching molecules (N). We demonstrated a few additional weaknesses of COMPACK: a) extremely costly or incorrect comparisons in molecules with highly-branched substituents (possibly due to its use of Ullmann's method), b) failure to match structures when the molecular connectivity is incorrectly determined, c) difficulties with molecules presenting helical chirality, and d) very large cluster sizes (up to 50 molecules) are sometimes needed to correctly identify unequal polymorphs. In turn, VC-PWDF has difficulty differentiating structures with similar packings, such as polytypes, and conformational and isomorphous phases. It is shown that the proposed VC-PWDF is at least as robust as COMPACK for comparing molecular crystal structures. Although a grey area of difficult-to-compare structures still exists, using both COMPACK and VC-PWDF in combination may be successful at narrowing it. [ABSTRACT FROM AUTHOR]

One open tetra-benzimidazolium salt (1) and one cyclic tetra-imidazolium salt (2) based on tetramethylbenzene were synthesized and characterized. The single crystal structure of 1 was determined by X-ray diffraction. The recognition performance of compounds 1 and 2 for guests (1 for o-phenylenediamine (OPD) and 2 for F−) was investigated via fluorescent spectra, UV/vis spectra, 1H NMR, HRMS and IR spectra. In particular, a remarkable color change (from colorless to pale brown) was observed in the recognition process of 2 for F−, which indicated that this recognition can not only be carried out by using an instrument but also by the naked eye, and this had great convenience in practice. [ABSTRACT FROM AUTHOR]

The reactivity between 2-(p-tolyl)selenopheno[2,3-b]pyridine (L) and ICl in MeCN is presented. Single crystal structure analysis revealed the formation of two distinct crystalline materials both featuring the protonated 2-(p-tolyl)selenopheno[2,3-b]pyridinium cation [HL]+. Colourless crystals were identified as the dihydrate salt [HL]Cl·2H2O (1), and dark-red crystals as compound {[HL]+[I2Cl]−}3·1/2I2 (2) that features the peculiar presence of the rare non-classical [I2Cl]− interhalide. Halogen Bonds (XBs) between the cocrystallized I2 molecule and [I2Cl]− anions led to the novel overall discrete [I10Cl4]4−H-shaped polyinterhalide formation, which is stabilized through hydrogen bonds (HBs) with the templating [HL]+ cations. The experimental observations are supported by extensive theoretical calculations at the DFT level that were employed to study the role played by non-covalent interactions in the formation of the presented unique polyinterhalide. [ABSTRACT FROM AUTHOR]

Near-infrared-emitting quantum dots (QDs) are very interesting for (bio)medical uses because they penetrate biological tissues more deeply and emit light in the biological diagnostic window, that is, the region from 650 to 1450 nm. Among the semiconductors with appropriate band gaps to provide photoluminescence at wavelengths longer than 650 nm, silver chalcogenides are distinguished mainly by being environmentally friendly. This work proposes the use of experimental design techniques to optimize a one-pot aqueous procedure to synthesize photoluminescent silver selenide (Ag2Se) QDs capped with mercaptosuccinic acid (MSA). The best conditions found were Ag/Se and MSA/Ag molar ratios of 8 : 1 and 6 : 1, respectively, pH 5.0, and stirring for 20 minutes at 60 °C. The Ag2Se nanocrystals synthesized under those experimental parameters showed a photoluminescence quantum yield of 16.3%, absorption edge at 583 nm, and emission within the biological diagnostic window, at 789 nm, with orthorhombic crystal structure and an average diameter of 5.7 nm. [ABSTRACT FROM AUTHOR]