Quaternary semiconductor materials of the Pb₄Ga₄GeS(Se)₁₂ composition have attracted the attention of researchers due to possible use as active elements of optoelectronics and nonlinear optics. The Pb₄Ga₄GeS(Se)₁₂ phases belong to the solid solution ranges of the Pb₃Ga₂GeS(Se)₈ compounds which form in the quasi-ternary systems PbS(Se)−Ga₂S(Se)₃−GeS(Se)₂ at the cross of the PbGa₂S(Se)₄−Pb₂GeS(Se)₄ and PbS(Se)−PbGa₂GeS(Se)₆ sections. The quaternary sulfide melts congruently at 943 K. The crystallization of the Pb₄Ga₄GeSe₁₂ phase is associated with the ternary peritectic process L_p + PbSe ↔ PbGa₂S₄ + Pb₃Ga₂GeSe₈ at 868 K. For the single crystal studies, Pb₄Ga₄GeS(Se)₁₂ were pre-synthesized by co-melting high-purity elements. X-ray diffraction results confirm that these compounds possess non-centrosymmetric crystal structure (trigonal symmetry, space group ). The crystals were grown by the vertical Bridgman method in a two-zone furnace. The starting composition was stoichiometric for Pb₄Ga₄GeS₁₂, and the solution-melt method was used for the selenide Pb₄Ga₄GeSе₁₂. Obtained value of the bandgap energy for the Pb₄Ga₄GeS₁₂ and Pb₄Ga₄GeSе₁₂ crystals is 1.86 and 2.28 eV, respectively. Experimental measurements of the spectral distribution of photoconductivity for the Pb₄Ga₄GeS₁₂ and Pb₄Ga₄GeSе₁₂ crystals exhibit the presence of two spectral maxima. The first lies in the region of 570 nm (2.17 eV) and 680 nm (1.82 eV), respectively, and matches well the optical bandgap estimates. The locations of the admixture maxima at about 1030 nm (1.20 eV) and 1340 nm (0.92 eV), respectively, agree satisfactorily with the calculated energy positions of the defects V_S and V_Se.

Investigation of sulfur- and selenium-containing quasi-ternary systems Tl₂X–M^IIX–M^IVX₂ (M^II = Cd, Hg; M^IV = Si, Ge, Sn) by DTA and XRD methods at 520 K found the formation of twelve quaternary compounds, Tl₂HgSi(Ge,Sn)S₄, Tl₂PbSiS₄, Tl₂CdSi(Ge,Sn)Se₄, Tl₂HgSi(Ge,Sn)Se₄, Tl₂PbSi(Ge)Se₄, at the vertical sections Tl₂M^IVX₃–M^IIX, and seven compounds, Tl₂CdGe₃Se₈, Tl₂HgSi(Ge)₃S₈, Tl₂PbSi(Ge)₃S₈, Tl₂HgSi(Ge)₃Se₈, at the Tl₂M^IIM^IVX₄–M^IVX₂ sections. Additionally, series of analogous compounds Tl₂Cd(Hg)SiTe₄ of the 2-1-1-4 type and Tl₂Mg(Mn,Zn)Ge₃Se₈ of the 2-1-3-8 type, were obtained. The compounds of both 2-1-1-4 and 2-1-3-8 groups that form in the A^I₂Х–В^IIХ–D^IVX₂ system possess non-centrosymmetric crystal structure making them potential candidates for optical and other properties valuable for materials science. Similar quasi-ternary systems A^I₂Х–В^IIХ–D^IVX₂ feature quaternary phases, individual known representatives of which such as Li₂CdGeSe₄, Li₂CdSnSe₄, Cu₂CdGeSe₄, Cu₂CdSnSe₄, belong to diamond-like semiconductors and have already found use in non-linear optics and other fields of semiconductor applications. The structure of all quaternary compounds Tl₂M^IIM^IVX₄, except Pb-containing ones, was determined in isotropic approximation with the Tl₂HgGeTe₄ structure as model (tetragonal symmetry, space group I-42m), as well as six other tellurides Tl₂Mn(Cd,Hg)Ge(Sn)Te₄. Tl₂PbSiS₄ and Tl₂PbGeS₄ are isostructural and crystallize in the monoclinic symmetry, space group Р2₁/а. A family of compounds of the general formula Tl₂M^IIM^IV₃X₈ (M^II = Mg, Zn, Cd, Hg, Mn; M^IV = Ge; X = Se, Te) are analogous to the quaternary phases with alkaline metals α-K₂ZnSn₃S₈ and Cs₂M^IIM^IV₃Se₈ which crystallize in the orthorhombic symmetry, space group P2₁2₁2₁.

Stone is one of the most durable construction materials used in historic buildings all over the world. However, over time, the stone can be subject to various degradation processes leading to physical and chemical modifications. Although these effects may be limited to the surface and negligible to the structural stability of the affected buildings, they can represent a major problem in decorative elements of artistic value, where any detail should be preserved [1]. The challenge for conservators and material scientists involved in stone conservation has always been to find a way to stop or delay the effects of these degradation processes. The basic principle of the patrimony is that the cultural heritage is an incalculable and integral legacy to our future: observing and knowing the past, will help next generations to better challenge the future. Thus, conservation of stone heritage is always a delicate and complex task, due to the multiple variables that have to be taken into account to identify the problems, and to define the necessary conservation actions and to select materials and best procedures to be used. The variety of factors to be analyzed includes the intrinsic stone properties (from geological features up to mechanical behavior), the state of conservation, the degradation mechanisms and the environmental factors.

One of the most promising technology employed for lowering the previously described degradation processes, is that of nanomaterials, nowadays largely applied in the maintenance of the world cultural heritage, with the aim of improving the consolidation and protection treatments of damaged stone materials they are made of [2]. Such nanomaterials display important advantages that could solve many problems found in the traditional interventions, that often showed the serious bias of the lack the vital compatibility with the original substrate and a durable performance: application of nanotechnology in the cultural heritage conservation is characterized by the possibility to design consolidant products strongly compatible with the original stone substrate. Moreover, when particles have dimensions of about 100 nanometers, the material properties change significantly from those at larger scales. The nanoparticles must show: stability and sustained photoactivity; biological and chemical inactivity nontoxicity, as well as antimicrobial properties for lowering ecotoxicological impact on animals and plants [3]; low cost suitability towards visible or near UV light; high conversion efficiency and high quantum yield. In addition, these treatments can also have water repellent properties which favor this self-cleaning action and prevent the generation of damage caused by water. The most commonly used inorganic consolidant agents are the products based on Ca(OH)₂ calcium hydroxide nanoparticles [4], due to their compatibility with a large part of the built and sculptural heritage. As well as other hydroxides (Mg(OH)₂, Sr(OH)₂), metal oxides (TiO₂, ZnO), and metal nanoparticles (Au, Ag, Pt)) have been reported in the literature, focusing on their potential as consolidants on different artifacts of cultural heritage [2, 5]. But one of the most challenging nanomaterial is Ca₁₀(PO₄)₆(OH)₂ hydroxyapatite (HAP), already applied in a large variety of technological and biomedical applications, mainly due to its close relationship with mineral component of hard human tissues [6-7], and in cultural heritage conservation used for carbonate stone consolidation [2]. HAP can be applied for the consolidation of limestones, marbles and sandstones with different carbonate contents. This product is not introduced directly into stone material, but it comes from the reaction between phosphate ions from an aqueous solution of diammonium hydrogen phosphate applied to the stone and calcium ions coming from substrate. Among its advantages, HAP has a similar crystal structure and close lattice parameters of CaCO₃ calcite, the main constituents of marbles and limestone. Thanks to its low viscous nature, this aqueous consolidant product is able to penetrate deeply into the stone, generating a significant improvement in mechanical properties of the same stone. The HAP has been tested as a protective treatment for marble against acid rain corrosion [8]. The study of compatibility and adaptability requires that the physical and chemical properties of both consolidator products and stone substrate are well known. Such a knowledge plays a very important role for the good outcome of the present project. Materials of interest, synthesized in our labs has been analysed by using: 1) X-ray diffraction (XRD), effective on crystalline materials and able to carry out information on chemical composition, size, shape and atomic structure, 2) small- and/or wide-angle scattering (SAXS/WAXS), powerful tool to investigate the domain of phosphate particles as a function of their optical properties; in the case of SAXS the technique can be applied to HAp nanoparticles characterization; 3) Fourier-Transform Infrared (FTIR) spectroscopy, reliable techniques for investigating hydroxyl anions and variations within anionic and cationic groups in the obtained materials; 4) scanning electron microscopy for checking morphologies of nanonparticles; 5) biological evaluation of the antimicrobial properties of obtained HAp materials, through direct contact and disc diffusion methods versus most common gram + and gram - bacteria present in human or animal biosystems 6) Laser Induced Breakdown Spectroscopy (LIBS), a non-destructive technique able to get quali-quantitative informations on museal artifacts.

1 - Pesce C., Moretto L.M., Orsega E.F., Pesce G.L., Corradi M., Weber J. Effectiveness and Compatibility of a Novel Sustainable Method for Stone Consolidation Based on Di-Ammonium Phosphate and Calcium-Based Nanomaterials. Materials 12 (2019) 3025.

2 - David, M.E., Ion, R.-M., Grigorescu, R.M., Iancu, L., Andrei, E.R. Nanomaterials Used in Conservation and Restoration of Cultural Heritage: An Up-to-Date Overview. Materials 13 (2020) 2064.

3 - Reyes-Estebanez, M., Ortega-Morales, B.O., Chan-Bacab, M., Granados-Echegoyen, C., Camacho-Chab, J.C., Pereanez-Sacarias J.E., Gaylarde C. Antimicrobial engineered nanoparticles in the built cultural heritage context and their ecotoxicological impact on animals and plants: a brief review. Heritage Science 6 (2018) 52.

4 - El Bakkari M, Bindiganavile V, Boluk Y. Facile Synthesis of Calcium Hydroxide Nanoparticles onto TEMPO-Oxidized Cellulose Nanofibers for Heritage Conservation. ACS Omega 4 (2019) 20606-20611.

5 - Dida B., Siliqi D., Baldassarre, F., Karaj D., Hasimi A., Kasemi V., Nika V., Vozga I. “Nanomaterialet për Konservimin e Trashëgimisë Kulturore”, SHLBSH, Tirana (2020), ISBN 978-99943-2-468-2

6 - Rakovan J.R., Pasteris J.D. A technological gem: Materials, Medical, and Environmental Mineralogy of Apatite. Elements 11 (2015) 195-200.

7 - Baldassarre F., Altomare A., Corriero N., Mesto E., Lacalamita M., Bruno G., Sacchetti A., Dida B., Karaj D., Della Ventura G.D., Capitelli, F., Siliqi, D. Crystal Chemistry and Luminescence Properties of Eu-Doped Polycrystalline Hydroxyapatite Synthesized by Chemical Precipitation at Room Temperature. Crystals 10 (202) 250.

8 - Graziani G., Sassoni E., Franzoni E., Scherer G.W. Hydroxyapatite Coatings for Marble Protection: Optimization of Calcite Covering and Acid Resistance. Applied Surface Science 368 (2016) 241-257.

Crystals of linear oligophenyls p-nP (n is the number of phenyl groups) are of interest for organic electronics and photonics as effective blue emitters and scintillators. The surface properties and external conditions of the growth medium are the determining factors in the nucleation and formation of crystals. However, the crystallization processes of conjugated linear molecules are still understudied and there is practically no experimental data on the surface properties of solutions and crystals. At the same time, there are few studies in the literature on modeling the surface energy of the crystal faces of these substances [1].

This work presents the results of studying of the linear oligophenyls (n = 2..6) crystals growth from solutions and the vapor phase. In the approximation of the OPLS atomic force field method, the values of the surface energy of the (100), (010), (110), and (001) faces of the crystals are determined. Based on the data on the crystal structure and the obtained values of the surface energy of the faces, the morphology of the crystals is analyzed and their equilibrium shapes are predicted. Within the framework of the classical nucleation theory, the parameters of crystal nucleation under experimental conditions of growth from solutions and physical vapor transport are studied.

References

1. Nabok D., Puschnig P. and Ambrosch-Draxl C. Phys. Rev. B 2008, B 77, 245316.

Studies in part on crystals growth from solution and modeling the surface energy of crystal faces were made with financial support from the Ministry of Science and Higher Education of the Russian Federation within the State assignment FSRC “Crystallography and Photonics” RAS using the equipment of Collaborative Access Center “Structural diagnostics of materials” (project # RFMEF162119X0035); studies in part on crystals growth by the PVT method, their crystal structure and nucleation thermodynamic analysis were made under the support of the Russian Foundation for Basic Research (grant no. 19-32-90145); development of the approaches to purification of the conjugated oligomers was supported by the Russian Science Foundation (grant no. 18-73-10182).

Recrystallization from ethanol of mixtures of various substituted nitrobenzoic acid derivatives and their isomers, and as a result preparation of ansolvated crystalline phases, in order to ensure that solid solutions can form between them. Crystalline phases that were obtained during the work were identified using X-ray powder diffraction and thermal analysis methods, in addition using the resulting nuclear magnetic resonance spectrum, obtained information about the ratio of mixtures of various nitrobenzoic acid derivatives and their isomers in crystallization products. Further, using quantum chemical calculations, the structural analysis of crystal structures, molecular properties, interaction strength – including Hirschfield surface 2D fingerprint graphs and electrostatic potential maps, in addition, the crystalline lattice parameters of the obtained solid solutions were determined, and also energetic aspects – intermolecular interaction and crystal lattice energy, are studied and described, for possibility to predict formation of solid solution of the studied compounds.

Polymorphism is the phenomenon of the existence of different arrangements of molecules in the crystal phase. Molecules can differ in conformations (conformational polymorphism) and / or in intermolecular interactions between them in the crystal (orientational polymorphism). The influence of molecular packing on the properties of materials cannot be overestimated, thus, the choice of the most suitable polymorphic form is crucial for manufacture. However, a lot of crystal structures are not stable and can undergo polymorphic transformation due to different reasons.

We present a multistage method for the analysis of mechanisms of polymorphic transformations based on shear slips of strongly bound fragments in structures that differ mainly in packing on the example of pharmaceutical compounds aspirin, piracetam and ibuprofen. The first stage consists in the computation of pairwise interaction energies between molecules in a crystal using quantum chemical methods. It reveals the most strongly bound structural fragments (building units and basic structural motifs) and the planes between which the binding of structural fragments is the least. In the second stage, parts of two adjacent structural motifs are displaced in different directions within the planes separated out earlier. The most probable shift directions are chosen based on a geometric estimate of minimum distances during translations and, further, shift energy profiles and barriers inherent to them are calculated. Inexpensive and efficient, our method allows to determine probabilities of molecular translations with high accuracy.

While metal-organic frameworks (MOFs) have been investigated intensively throughout the last decades, only a fraction of the published articles on MOFs feature heterobimetallic structures. Combining two metallic centers in a rigid framework could lead to interesting effects, such as magnetic coupling, collaborating fluorescence or catalytic properties; however, its synthesis is more sophisticated than for monometallic MOFs. We utilize ditopic ligands which coordination sites differ in their Pearson hardness (HSAB). This enables a stepwise selective formation of heterobimetallic MOFs: first, a monometallic building block is synthesized. In a second step the framework can be achieved by crosslinking with a second metal ion. In this work we present our newest ligand as a candidate for this purpose: 3-(1,3,5-trimethyl-1H-pyrazol-4-yl)acetylacetone. Its synthesis is straightforward and inexpensive. The O,O’ coordination was accomplished with a variety of hard cations like Fe(III) or Ga(III). First crosslinking attempts with N coordination of the Fe(III) building block to Ag(I) lead to a one-dimensional coordination polymer with high porosity.

Octahedral tris(bidentate) coordination complexes demonstrate helicoidal chirality due to the arrangement of the ligands around the metal core. The enantiomers of the nitrate salts [Ni(en)₃](NO₃)₂ and [Zn(en)₃](NO₃)₂ (en = ethylenediamine) spontaneously resolve to form a mixture of conglomerate crystals, which present a reversible phase transition from space group P6₃22 to enantiomorphic P6₅22 or P6₁22, with the latter depending on the handedness of the enantiomer. To extend the family of such compounds, we have investigated [Mn(en)₃](NO₃)₂ and [Co(en)₃](NO₃)₂, which were found to be isostructural to the Zn(II) and Ni(II) derivatives. The Mn(II) analogue undergoes the same phase transition centered at 149(2) K, as determined by single-crystal X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. The Co(II) derivative does not demonstrate a phase transition down to 2 K, as evidenced by powder diffraction and heat capacity measurements.¹

From the perspective of chirality, although conglomerate formation allows crystals of only one or the other enantiomer to be effortlessly obtained, spontaneous resolution can only truly be considered accomplished after the identification and triage of the two forms of crystals. For this, we have implemented an original method for determining the handedness of individual crystals in a mixture using a tightly-focused, circularly polarized X-ray beam.² The X-ray natural circular dichroism (XNCD) spectra measured at the metal K-edge on selected crystals of [Co(en)₃](NO₃)₂ and [Ni(en)₃](NO₃)₂ show maxima at the metal pre-edge. A mapping of a collection of crystals was performed, by setting the X-ray energy to the peak maximum and determining the sign of the difference in absorption for the two polarizations, which then directly yielded the handedness of the crystal. Furthermore, the mapping resolution (~150 mm) allowed us to evidence that while the majority of the crystals form a conglomerate as expected, a few individuals present opposite handedness domains, and in two cases we found unexpectedly fully racemic crystals.

1) M. Cortijo, A. Valentin-Perez, M. Rouzières, R. Clérac, P. Rosa, E.A. Hillard, Crystals, 2020, 10(6), 472 https://doi.org/10.3390/cryst10060472.

2) M. Cortijo, A. Valentin-Perez, A. Rogalev, F. Wilhelm, Ph. Sainctavit, P. Rosa, E.A. Hillard, Chem. Eur. J., 2020, https://doi.org/10.1002/chem.202001783

In the rich field of metal-organic frameworks (MOFs) there is a vast number of results revolving around ligands based on oxygen and nitrogen donors, but little to no work on ligands containing phosphorus donors. A few reasons for this lack of research are obvious: the lower stability of phosphorus(III), the more elaborate syntheses, and the nonexistent availability of commercially suitable candidate molecules. Nevertheless, the usage of phosphorus can enable a much greater variety of structural possibilities for MOF synthesis, as it can stabilize metal cations in low oxidation states, among other advantages.

Thus, we intend to compare the abilities of the three donors by preparing the ligand 4-(3-(4-(diphenylphosphino)phenyl)-3-oxopropanoyl)benzonitrile. This multifunctional ligand contains a chelating beta-diketone and a nitrile group as O and N donors, as well as a triarylphosphine donor group. The results show that its coordination behavior very much depends on reaction conditions. We have selectively prepared mononuclear complexes on both the O and P side, but no purely N coordinated complexes could be obtained. Furthermore, we have crystallized a bimetallic supramolecular cube in the rare cubic space group P-43n. Finally, the formation of a porous bimetallic MOF. with an interesting topology, could be achieved by the simultaneous coordination of all three donors.

Two model substances were used in the study – 2,6-dimethoxybenzoic acid (2,6MeOBA) and 3-hydroxybenzoic acid (3OHBA), each having two polymorphic forms, including a form without carboxylic acid homodimers in their crystal structure. For each polymorph 2-3 largest crystal faces were selected for MD simulations and the crystal was cut along these planes by preparing simulation box with these planes facing towards solution. In the performed study it was determined which additives potentially can influence the crystal morphology (based on the selected planes) and possibly also the obtained polymorph achieved by significantly changing crystal growth rate by adsorbing on the surface. For the study 4-5 additives providing different intermolecular interaction possibilities were selected. Growth of both explored surfaces of 2,6MeOBA form I are best inhibited by urea in 1,4-dioxane, while in methanol all explored additives act almost equally. All the studied surfaces of form II dissolved, indicating the very low stability of this. A different effect of urea and para-aminobenzoic acid (PABA) on the morphology of 3OHBA form I was found. In 1,4-dioxane different sorption results were observed for both additives. The growth of {011} surface could be inhibited by urea, but the {020} surface by PABA. The simulations showed that urea could not play a decisive role in the discrimination of 3OHBA polymorphic forms, as it was well sorbed on surfaces of both forms. Meanwhile the simulations showed that trans-stilbene has the potential to inhibit the formation of {110} surface of 3OHBA form II in methanol due to a strong π-π interactions. It was also observed that solvent has notable effect on the sorption of additives. The sorption of the studied additives was notably different in 1,4-dioxane, but in the methanol sorption of all additives was rather similar. Based on the results 1,4-dioxane is probably a better solvent for inhibition of growth of surfaces where hydrogen bonds are the dominant type of interactions. Among the studied additives urea showed the mot complete sorption and the longest residence time on surfaces for both substances with the exceptions of some specific planes. Meanwhile, complete and irreversible adsorption on crystal could also indicate on the possibility of formation of a mixed phase (co-crystal) in the presence of these additives.