Synthesis, structure and Hirshfeld surface analysis of 2-oxo-2H-chromen-6-yl 4-tert-butyl-benzoate: work carried out as part of the AFRAMED project.

In the title compound, C20H18O4, the dihedral angle between the 2H-chromen-2-one ring system and the phenyl ring is 89.12 (5)°. In the crystal, the mol-ecules are connected through C-H⋯O hydrogen bonds to generate [010] double chains that are reinforced by weak aromatic π-π stacking inter-actions. The unit-cell packing can be described as a tilted herringbone motif. The H⋯H, H⋯O/O⋯H, H⋯C/C⋯H and C⋯C contacts contribute 46.7, 24.2, 16.7 and 7.6%, respectively, to its Hirshfeld surface.

Investigation of the Binary System of Proxyphylline Enantiomers: Structural Resolution and Phase Diagram Determination.

The solid-state landscape of proxyphylline (PXL), a chiral derivative of theophylline crystallizing as a racemic compound, was extensively investigated by means of thermal analyses and diffraction techniques. This study revealed the presence of five distinct polymorphic forms that were characterized: two polymorphs of the racemic mixture and three polymorphs of the pure enantiomer. The nature of each solid phase was confirmed by combining the different analytical techniques, revealing the presence of a thermodynamically stable racemic compound, RI (TFus= 134 °C), in equilibrium with the stable enantiopure crystal form, EI (TFus = 148.3 °C). Additionally, other crystal forms could be evidenced: a polymorph of the racemic compound, RII (TFus= 111.5 °C), as well as two metastable conglomerates, cEI and cEII, and two other polymorphs of the pure enantiomer, EII and EIII. The crystal structures of RI and EI are reported and discussed, highlighting the diversity of molecular conformations that can be adopted by the PXL molecule, which accounts for the versatility of the crystallization behaviors observed in this system. These findings enhance our understanding of the crystallization behavior of chiral pharmaceutical compounds and have implications for optimizing their crystallization processes in the pharmaceutical industry.

Role and Effect of Meso-Structuring Surfactants on Properties and Formation Mechanism of Microfluidic-Enabled Mesoporous Silica Microspheres.

We have shown in a previous work that the combination of the emulsion solvent evaporation technique and droplet-based microfluidics allows for the synthesis of well-defined monodisperse mesoporous silica microcapsules (hollow microspheres), whose size, shape and composition may be finely and easily controlled. In this study, we focus on the crucial role played by the popular Pluronic® P123 surfactant, used for controlling the mesoporosity of synthesised silica microparticles. We show in particular, that although both types of initial precursor droplets, prepared with and without P123 meso-structuring agent, namely P123+ and P123- droplets, have a similar diameter (≃30 µm) and a similar TEOS silica precursor concentration (0.34 M), the resulting microparticles exhibit two noticeably different sizes and mass densities. Namely, 10 µm and 0.55 g/cm3 for P123+ microparticles, and 5.2 µm and 1.4 g/cm3 for P123- microparticles. To explain such differences, we used optical and scanning electron microscopies, small-angle X-ray diffraction and BET measurements to analyse structural properties of both types of microparticles and show that in the absence of Pluronic molecules, P123- microdroplets divide during their condensation process, on average, into three smaller droplets before condensing into silica solid microspheres with a smaller size and a higher mass density than those obtained in the presence of P123 surfactant molecules. Based on these results and on condensation kinetics analysis, we also propose an original mechanism for the formation of silica microspheres in the presence and in the absence of the meso-structuring and pore-forming P123 molecules.

Structural Properties of Metal-Organic Frameworks at Elevated Thermal Conditions via a Combined Density Functional Tight Binding Molecular Dynamics (DFTB MD) Approach.

The performance of different density functional tight binding (DFTB) methods for the description of six increasingly complex metal-organic framework (MOF) compounds have been assessed. In particular the self-consistent charge density functional tight binding (SCC DFTB) approach utilizing the 3ob and matsci parameter sets have been considered for a set of four Zn-based and two Al-based MOF systems. Moreover, the extended tight binding for geometries, frequencies, and noncovalent interactions (GFN2-xTB) approach has been considered as well. In addition to the application of energy minimizations of the respective unit cells, molecular dynamics (MD) simulations at constant temperature and pressure conditions (298.15 K, 1.013 bar) have been carried out to assess the performance of the different DFTB methods at nonzero thermal conditions. In order to obtain the XRD patterns from the MD simulations, a flexible workflow to obtain time-averaged XRD patterns from (in this study 5000) individual snapshots taken at regular intervals over the simulation trajectory has been applied. In addition, the comparison of pair-distribution functions (PDFs) directly accessible from the simulation data shows very good agreement with experimental reference data obtained via measurements employing synchrotron radiation in case of MOF-5. The comparison of the lattice constants and the associated X-ray diffraction (XRD) patterns with the experimental reference data demonstrate, that the SCC DFTB approach provides a highly efficient and accurate description of the target systems.

X-ray scattering study of water confined in bioactive glasses: experimental and simulated pair distribution function.

Temperature-dependent total X-ray scattering measurements for water confined in bioactive glass samples with 5.9 nm pore diameter have been performed. Based on these experimental data, simulations were carried out using the Empirical Potential Structure Refinement (EPSR) code, in order to study the structural organization of the confined water in detail. The results indicate a non-homogeneous structure for water inside the pore, with three different structural organizations of water, depending on the distance from the pore surface: (i) a first layer (4 Å) of interfacial pore water that forms a strong chemical bond with the substrate, (ii) intermediate pore water forming a second layer (4-11 Å) on top of the interfacial pore water, (iii) bulk-like pore water in the centre of the pores. Analysis of the simulated site-site partial pair distribution function shows that the water-silica (Ow-Si) pair correlations occur at ∼3.75 Å. The tetrahedral network of bulk water with oxygen-oxygen (Ow-Ow) hydrogen-bonded pair correlations at ∼2.8, ∼4.1 and ∼4.5 Šis strongly distorted for the interfacial pore water while the second neighbour pair correlations are observed at ∼4.0 and ∼4.9 Å. For the interfacial pore water, an additional Ow-Ow pair correlation appears at ∼3.3 Å, which is likely caused by distortions due to the interactions of the water molecules with the silica at the pore surface.

Unprecedented Reverse Volume Expansion in Spin-Transition Crystals.

The current craze for research around the spin crossover phenomenon can be justified to some extent by the mechanical properties due to the decrease of volume associated with the transition of the metal ion from the HS state to the LS state. As demonstrated here, the molecular complex [Fe(PM-pBrA)2 (NCS)2 ] exhibits, on the contrary, an increase of the unit-cell volume from HS to LS. This counter-intuitive and unprecedented behavior that concerns both the thermal and the photoexcited spin conversions is revealed by a combination of single-crystal and powder X-ray diffraction complemented by magnetic measurements. Interestingly, this abnormal volume change appears concomitant with the wide rotation of a phenyl ring which induces a drastic modification, though reversible, of the structural packing within the crystal. In addition, the light-induced HS state obtained through the Light-Induced Excited Spin-State Trapping shows a remarkably high relaxation temperature, namely T(LIESST), of 109 K, one of the highest so far reported. The above set of quite unusual characteristics opens up new fields of possibilities within the development of spin crossover materials.

Crystal structure of a new phen-yl(morpholino)methane-thione derivative: 4-[(morpholin-4-yl)carbothioyl]benzoic acid.

4-[(Morpholin-4-yl)carbothioyl]benzoic acid, C12H13NO3S, a novel phen-yl(morpholino)methane-thione derivative, crystallizes in the monoclinic space group P21/n. The morpholine ring adopts a chair conformation and the carb-oxy-lic acid group is bent out slightly from the benzene ring mean plane. The mol-ecular geometry of the carb-oxy-lic group is characterized by similar C-O bond lengths [1.266 (2) and 1.268 (2) Å] as the carboxyl-ate H atom is disordered over two positions. This mol-ecular arrangement leads to the formation of dimers through strong and centrosymmetric low barrier O-H⋯O hydrogen bonds between the carb-oxy-lic groups. In addition to these inter-molecular inter-actions, the crystal packing consists of two different mol-ecular sheets with an angle between their mean planes of 64.4 (2)°. The cohesion between the different layers is ensured by C-H⋯S and C-H⋯O inter-actions.

Photoinduced Mo-CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping.

The photoinduced properties of the octacoordinated complex K4 MoIV (CN)8 ⋅2 H2 O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)7 species originating from the light-induced cleavage of one Mo-CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)]3 [MoIV (CN)7 ]⋅3 CH3 CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution.

Nonlinear optical organic-inorganic crystals: synthesis, structural analysis and verification of harmonic generation in tri-(o-chloroanilinium nitrate).

The structural and nonlinear optical properties of a new anilinium hybrid crystal of chemical formula (C6H7NCl+·NO3-)3 have been investigated. The crystal structure was determined from single-crystal X-ray diffraction measurements performed at a temperature of 100 K which show that the compound crystallizes in a noncentrosymmetric space group (Pna21). The structural analysis was coupled with Hirshfeld surface analysis to evaluate the contribution of the different intermolecular interactions to the formation of supramolecular assemblies in the solid state that exhibit nonlinear optical features. This analysis reveals that the studied compound is characterized by a three-dimensional network of hydrogen bonds and the main contributions are provided by the O...H, C...H, H...H and Cl...H interactions, which alone represent ∼85% of the total contributions to the Hirshfeld surfaces. It is noteworthy that the halogen...H contributions are quite comparable with those of the H...H contacts. The nonlinear optical properties were investigated by nonlinear diffuse femtosecond-pulse reflectometry and the obtained results were compared with those of the reference material LiNbO3. The hybrid crystals exhibit notable second (SHG) and third (THG) harmonic generation which confirms its polarity is generated by the different intermolecular interactions. These measurements also highlight that the THG signal of the new anilinium compound normalized to its SHG counterpart is more pronounced than for LiNbO3.

Very Long-Lived Photogenerated High-Spin Phase of a Multistable Spin-Crossover Molecular Material.

The spin-crossover compound [Fe( n-Bu-im)3(tren)](PF6)2 shows an unusual long relaxation time of 20 h after light-induced excited spin state trapping when irradiating at 80 K. This is more than 40 times longer than when irradiating at 10 K. Optical absorption spectroscopy, magnetometry, and X-ray diffraction using synchrotron radiation were used to characterize and explain the different relaxation behaviors of this compound after irradiation below and above 70 K. Rearrangement of the butyl chains of the ligands occurring during the relaxation after irradiation above 70 K is thought to be responsible for the unusually long relaxation time at this temperature.

Conducting Anilate-Based Mixed-Valence Fe(II)Fe(III) Coordination Polymer: Small-Polaron Hopping Model for Oxalate-Type Fe(II)Fe(III) 2D Networks.

The mixed-valence FeIIFeIII 2D coordination polymer formulated as [TAG][FeIIFeIII(ClCNAn)3]·(solvate) 1 (TAG = tris(amino)-guanidinium, ClCNAn2- = chlorocyanoanilate dianionic ligand) crystallized in the polar trigonal space group P3. In the solid-state structure, determined both at 150 and at 10 K, anionic 2D honeycomb layers [FeIIFeIII(ClCNAn)3]- establish in the ab plane, with an intralayer metal-metal distance of 7.860 Å, alternating with cationic layers of TAG. The similar Fe-O distances suggest electron delocalization and an average oxidation state of +2.5 for each Fe center. The cation imposes its C3 symmetry to the structure and engages in intermolecular N-H···Cl hydrogen bonding with the ligand. Magnetic susceptibility characterization indicates magnetic ordering below 4 K and the presence of a hysteresis loop at 2 K with a coercive field of 60 Oe. Mössbauer measurements are in agreement with the existence of Fe(+2.5) ions at RT and statistic charge localization at 10 K. The compound shows semiconducting behavior with the in-plane conductivity of 2 × 10-3 S/cm, 3 orders of magnitude higher than the perpendicular one. A small-polaron hopping model has been applied to a series of oxalate-type FeIIFeIII 2D coordination polymers, providing a clear explanation on the much higher conductivity of the anilate-based systems than the oxalate ones.

In-house time-resolved photocrystallography on the millisecond timescale using a gated X-ray hybrid pixel area detector.

With the remarkable progress of accelerator-based X-ray sources in terms of intensity and brightness, the investigation of structural dynamics from time-resolved X-ray diffraction methods is becoming widespread in chemistry, biochemistry and materials science applications. Diffraction patterns can now be measured down to the femtosecond time-scale using X-ray free electron lasers or table-top laser plasma X-ray sources. On the other hand, the recent developments in photon counting X-ray area detectors offer new opportunities for time-resolved crystallography. Taking advantage of the fast read-out, the internal stacking of recorded images, and the gating possibilities (electronic shutter) of the XPAD hybrid pixel detector, we implemented a laboratory X-ray diffractometer for time-resolved single-crystal X-ray diffraction after pulsed laser excitation, combined with transient optical absorption measurement. The experimental method and instrumental setup are described in detail, and validated using the photoinduced nitrosyl linkage isomerism of sodium nitroprusside, Na2[Fe(CN)5NO]·2H2O, as proof of principle. Light-induced Bragg intensity relative variations ΔI(hkl)/I(hkl) of the order of 1%, due to the photoswitching of the NO ligand, could be detected with a 6 ms acquisition window. The capabilities of such a laboratory time-resolved experiment are critically evaluated.

Elastic Frustration Triggering Photoinduced Hidden Hysteresis and Multistability in a Two-Dimensional Photoswitchable Hofmann-Like Spin-Crossover Metal-Organic Framework.

We report a two-dimensional Hofmann-like spin-crossover (SCO) material, [Fe(trz-py)2{Pt(CN)4}]·3H2O, built from [FePt(CN)4] layers separated by interdigitated 4-(2-pyridyl)-1,2,4,4H-triazole (trz-py) ligands with two symmetrically inequivalent FeII sites. This compound exhibits an incomplete first-order spin transition at 153 K between fully high-spin (HS-HS) and intermediate high-spin low-spin (HS-LS) ordered states. At low temperature, it undergoes a bidirectional photoswitching to HS-HS and fully low-spin (LS-LS) states with green and near-IR light irradiation, respectively, with associated T(LIESST = Light-Induced Excited Spin-State Trapping) and T(reverse-LIESST) values of 52 and 85 K, respectively. Photomagnetic investigations show that the reverse-LIESST process, performed from either HS-HS or HS-LS states, enables access to a hidden stable LS-LS state, revealing the existence of a hidden thermal hysteresis. Crystallographic investigations allowed to identify that the strong metastability of the HS-LS state originates from the existence of a strong elastic frustration causing antiferroelastic interactions within the [FePt(CN)4] layers, through the rigid NC-Pt-CN bridges connecting the inequivalent FeII sites. The existence of the stable LS-LS state paves the way for a multidirectional photoswitching and allows potential applications for electronic devices based on ternary digits.

Characterization of multifunctional ß-NaEuF4/NaGdF4 core-shell nanoparticles with narrow size distribution.

The properties of ß-NaEuF4/NaGdF4 core-shell nanocrystals have been thoroughly investigated. Nanoparticles with narrow size distribution and an overall diameter of ∼22 nm have been produced with either small ß-NaEuF4 cores (∼3 nm diameter) or large ß-NaEuF4 cores (∼18 nm diameter). The structural properties and core-shell formation are investigated by X-ray diffraction, transmission electron microscopy and electron paramagnetic resonance, respectively. Optical luminescence measurements and X-ray photoelectron spectroscopy are employed to gain information about the optical emission bands and valence states of the rare earth constituents. Magnetic characterization is performed by SQUID and X-ray magnetic circular dichroism measurements at the rare earth M(4,5) edges. The characterization of the core-shell nanoparticles by means of these complementary techniques demonstrates that partial intermixing of core and shell materials takes place, and a significant fraction of europium is present in the divalent state which has significant influence on the magnetic properties. Hence, we obtained a combination of red emitting Eu(3+) ions and paramagnetic Gd(3+) ions, which may be highly valuable for potential future applications.

Photocrystallography and IR spectroscopy of light-induced linkage NO isomers in [RuBr(NO)2(PCyp3)2]BF4.

One single photo-induced linkage NO isomer (PLI) is detected and characterized in the dinitrosyl pentacoordinated compound [RuBr(NO)2(PCyp3)2]BF4 by a combination of photocrystallographic and IR analysis. In the ground state, the molecule adopts a trigonal-bipyramidal structure with the two NO ligands almost linear with angles Ru-N1-O1 = 168.92 (16), Ru-N2-O2 = 166.64 (16)°, and exactly equal distances of Ru-N = 1.7838 (17) and O-N = 1.158 (2) Å. After light irradiation of 405 nm at T = 10 K, the angle of Ru-N2-O2 changes to 114.2 (6)° by rotation of the O atom towards the Br ligand with increased distances of Ru-N2 = 1.992 (6) and N2-O2 = 1.184 (8) Å, forming a bent κN bonded configuration. Using IR spectroscopy, the optimal wavelength and maximum population of 39 (1)% of the PLI is determined. In the ground state (GS), the two symmetric νs(NO) and asymmetric νas(NO) vibrations are measured at 1820 and 1778 cm(-1), respectively. Upon photo-irradiation, the detection of only one new vibrational ν(NO) stretching band at 1655 cm(-1), assigned to the antisymmetric coupled vibration mode and shifted to lower wavenumbers by -123 cm(-1), supports the photocrystallographic result. These experimental results are supported by additional DFT calculations, which reproduce the structural parameters and vibrational properties of both the ground state and the photo-induced linkage isomer well. Especially the experimentally characterized molecular structure of the PLI state corresponds to an energy minimum in the calculations; the stabilization of the bent κN bonded configuration of the PLI state originates from specific intramolecular orbital overlap.

Multiple light-induced NO linkage isomers in the dinitrosyl complex [RuCl(NO)2(PPh3)2]BF4 unravelled by photocrystallographic and IR analysis.

Multiple light-induced reversible metastable NO linkage isomers (PLIs) have been detected in the dinitrosyl compound [RuCl(NO)2(PPh3)2]BF4 by a combination of photocrystallographic and IR analysis. The IR signature of three PLI states has been clearly identified, with estimated populations of 59% (PLI-1), 8% (PLI-2) and 5% (PLI-3) for a total population of the metastable state of 72%. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. In the ground state, the structure is characterized by a bent and a linear nitrosyl, the bent one being oriented towards the linear equatorial nitrosyl with an Ru-N-O angle of 133.88 (9)°. X-ray Fourier difference maps indicate a selectivity of the photo-isomerization process in PLI-1: only the bent NO ligand changes its position, while the linear NO is unaffected. After irradiation at 405 nm, the orientation is changed by rotation towards the Cl ligand opposite the linear NO, with an Ru-N-O angle in this new position of 109 (1)°. The photocrystallographic analysis provides evidence that, in the photo-induced metastable state, the bent NO group is attached to the Ru atom through the N atom (Ru-N-O), rather than in an isonitrosyl Ru-O-N binding mode. In the IR spectra, the asymmetric NO vibrational band shifts by -33 cm(-1) to a lower value, whereas the symmetric band splits and shifts by 5 cm(-1) to a higher value and by -8 cm(-1) to a lower value. The down shift is a clear indication of the structural change, and the small upward shift in response to the new electronic configuration of the metastable structure. Variable-temperature IR kinetic measurements in the range 80-114 K show that the decay of the PLI-1 state follows an Arrhenius behaviour with an activation energy of 0.22 eV.

A comparative study of two polymorphs of L-aspartic acid hydrochloride.

Two polymorphs of L-aspartic acid hydrochloride, C4H8NO4(+)·Cl(-), were obtained from the same aqueous solution. Their crystal structures have been determined from single-crystal data collected at 100 K. The crystal structures revealed three- and two-dimensional hydrogen-bonding networks for the triclinic and orthorhombic polymorphs, respectively. The cations and anions are connected to one another via N-H···Cl and O-H···Cl interactions and form alternating cation-anion layer-like structures. The two polymorphs share common structural features; however, the conformations of the L-aspartate cations and the crystal packings are different. Furthermore, the molecular packing of the orthorhombic polymorph contains more interesting interactions which seems to be a favourable factor for more efficient charge transfer within the crystal.

The structural properties of a noncentrosymmetric polymorph of 4-aminobenzoic acid.

The crystal structure of a polymorph of 4-aminobenzoic acid (PABA), C7H7NO2, at 100 K is noncentrosymmetric, as opposed to centrosymmetric in the structures of the other known polymorphs. The two crystallographically independent PABA molecules form pseudocentrosymmetric O-H...O hydrogen-bonded dimers that are further linked by N-H...O hydrogen bonds into a three-dimensional network. The benzene rings stack in the b direction. The CO2 moieties are bent out slightly from the benzene ring plane.

Structural reinvestigation of the photoluminescent complex [NdCl2(H2O)6]Cl.

The structure of the photoluminescent compound hexaaquadichloridoneodymium(III) chloride has been redetermined from single-crystal X-ray diffraction data at 100 K, with the aim of providing an accurate structural model for the bulk crystalline material. The crystal structure may be described as a network of [NdCl2(H2O)6](+) cations with distorted square-antiprism geometry around the Nd(III) centre. The Nd(III) cation and the nonbonded Cl(-) anion are both located on twofold symmetry axes. The crystal packing consists of three different neodymium pairs linked by a three-dimensional network of O-H···Cl intermolecular interactions. The pair distribution function (PDF) calculated from the experimentally determined structure is used for the discussion of the local structure.

Light-induced bistability in the 2 D coordination network {[Fe(bbtr)3][BF4]2}∞ : wavelength-selective addressing of molecular spin states.

Whereas the neat polymeric Fe(II) compound {[Fe(bbtr)3 ][ClO4 ]2 }∞ (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) shows an abrupt spin transition centered at 107 K facilitated by a crystallographic symmetry breaking, in the covalently linked 2D coordination network of {[Fe(bbtr)3 ][BF4 ]2 }∞ , Fe(II) stays in the high-spin state down to 10 K. However, strong cooperative effects of elastic origin result in reversible, persistent, and wavelength-selective photoswitching between the low-spin and high-spin manifolds. This compound thus shows true light-induced bistability below 100 K. The persistent bidirectional optical switching behavior is discussed as a function of temperature, irradiation time, and intensity. Crystallographic studies reveal a photoinduced symmetry breaking and serve to establish the correlation between structure and cooperative effects. The static and kinetic behavior is explicated within the framework of the mean-field approximation.