Binary and terenary titanium oxides for application in renewable energy technologies-controlling of structural properties

U disertaciji je dat pregled binarnih i ternarnih oksidi titana, počev od fundamen-talnih principa, preko sinteze, karakterizacije i procesiranja, do konkretne primene. Osnovni cilj istraživanja bilo je uspostavljanje zavisnosti između sinteze, svojstava i primene nestehiometrijskih binarnih oksida: titan-monoksida (TiOx) i Manjelijevih faza (TinO2n-1), kao i ternarnih oksida: Li4Ti5O12 spinela i α-Li2-xTiO3-x (OH)x · yH2O koji sadrže litijum. Dobijeni materijali su ispitivani za primenu kao strujni kolektori u olovnim, ili kao elektrode u Li-jonskim akumulatorima. Materijali su sintetisani mehanohemijskim postupkom, koji je u nekim slučajevima praćen termičkim tretmanom, zatim reakcijama u čvrstom stanju, ili hidrotermalnim tretmanom. Za karakterizaciju su korišćene: rendgenska difrakcija, termogravimetrija i diferencijalno-skenirajuća kalorimetrija, skenirajuća i transmisiona elektronska mikroskopija, spektroskopija kuplovana sa plazmom, metoda tri tačke za određivanje provodnosti i ciklična voltametrija. Mlevenjem smeša Ti i TiO2 sa različitim stehiometrijskim odnosima (1:1, 1,1:1 i 1,25:1) već na sobnoj temperaturi dobijen je TiOx, sa x = 0,92 – 1,19 sa veličinom kristalita oko 6 nm. Podešavanjem odnosa reaktanata moguće je diktirati fazni sastav krajnjih, žarenih proizvoda, čime se ostvaruje kontrola provodnosti ovog materijala. Uzorci Manjelijevih faza, TinO2n-1, sa n = 4 – 6, dobijeni su žarenjem mehanohemijski aktiviranih smeša TiO i TiO2 ili Ti2O3 i TiO2, pri čemu je pokazano da temperatura potrebna za dobijanje ovih faza može da se snizi za čak 30 % u odnosu na uobičajeni postupak. Dobijeni oksidi i smeše oksida, kao i originalni EBONEX® prah, prevedeni su u folije uz korišćenje polietilena. Na osnovu poređenja provodnosti i korozione stabilnosti, pokazano je da sintetisani novi materijali imaju bolje karakteristike od EBONEX®-a. Dobijeni su neporozni i elastični strujni kolektori, a neki od ispitanih uzoraka veoma obećavaju kao mogući strujni kolektori u veoma agresivnim sredinama kakva je H2SO4...Binary and ternary titanium oxides are studied, starting with the fundamental principles, through synthesis, characterization and processing, to the specific applications of these materials. The main goal of this work was to establish functional relations between synthesis, properties and application of nonstoichiometric binary oxides: titanium monoxide (TiOx) and Magneli phases (TinO2n-1), as well as ternary, Li-containing titanium oxides: Li4Ti5O12 spinel and α-Li2-xTiO3-x (OH)x · yH2O. The prapared materials were tested for application as bipolar plate in bipolar Pb-acid battery or as electrode in Li-ion batteries. The materials were prepared by mechanochemical method, in some cases followed by thermal treatment, as well as by solid state reactions and hydrothermal treatment. The products are characterized by X-ray powder diffraction, thermogravimetry and differential scanning calorimetry, scanning and transmission electronic microscopy, optical emission spectrometry coupled with plasma (ICP-OS), three point probe conductivity measurements and cyclic voltammetry. Nanocrystalline cubic titanium monoxide, TiOx (0.92 < x < 1.19), with the mean crystallite size of about 6 nm, was synthesized by mechanochemical treatment of Ti and TiO2 powder mixtures with molar ratios of 1:1, 1.10:1 and 1.25:1. The phase composition of the products after annealing can be directed by setting of the ratio of reactants, and in this way the conductivity of TiOx can be controlled. Some Magneli phases TinO2n-1, with n = 4 – 6, or their mixtures were prepared using mechanochemical procedure followed by thermal treatment from stoichiometric mixtures of TiO and TiO2 or Ti2O3 and TiO2 powders. The temperature needed for synthesis of Magneli phases is lowered for about 30 % in respect to common methods. The prepared oxides and mixtures identical or similar to the Ebonex® powder, and original Ebonex® powder have proceeded into plastic-bonded, non-porous and flexible foil electrodes using a low density polyethylene. The electrodes were tested for corrosion stability in real lead-acid battery conditions and their conductivities were compared. Some investigated samples iii iv are very promising for application as current collector in extremely aggressive H2SO4 surrounding..

Theoretical study of the influence of halogen substituents on sensitivity of polycyclic nitroaromatic explosives

Positive values of electrostatic potential on the surface of high-energy molecules are a good indicator of the high sensitivity towards detonation. Here we used Bond Dissociation Energy and Molecular Electrostatic Potential calculations to predict the influence of the halogen substituents on the detonation properties of selected halogen-containing dinitronaphthalenes. Results of ab initio calculations indicated that halogen substituents may affect the geometry of the nitro- groups and lead to decreased stability of the weakest C-N bonds. Presence of halogen substituents also affects the values of the electrostatic potentials in the central regions of the molecular surfaces

JIMP 2 Software as a teaching tool: Understanding orbitals using fenskee-hall method

Teaching molecular orbital concept to undergraduate students is known to be very challenging; analysis of examination data for undergraduate students reveals that they do not have a clear understanding of the concepts of atomic and molecular orbitals (Tsaparlis, 1997). Understanding of the orbital concept has been subject to considerable debate and research (Barradas-Solas and Sánchez Gómez, 2014). One of teaching strategies to deal with this problem is based on usage of different quantum chemical software to calculate shape, energy and to visualize molecular orbitals. The main downside of this approach is the fact that quantum chemical calculations are often very time-consuming, especially in the case of molecules that contain transition metal atoms. Fenske-Hall method is ab initio method mainly developed for molecular orbitals calculation of transition metal complexes and organometallic compounds (Hall and Fenske, 1972). It was shown that this method is very fast, and very accurate (results are similar to the results obtained by more rigorous and more time-consuming DFT methods). Here we present a series of computational laboratory exercises using Fenske-Hall method incorporated in Jimp2 software to calculate and visualize both atomic and molecular orbitals. Students will learn how to calculate energy and visualize molecular orbitals of simple molecules. Exercises provide deeper insight into relationship between atomic and molecular orbitals with special emphasis on calculation of contribution of atomic orbitals in particular molecular orbital. Using results of Fenske-Hall calculations, students will construct molecular-orbital diagrams for simple molecules

Study of sulfur-sulfur interactions in crystal structures of small molecules and proteins using informatics and quantum chemical methods

Сумпор-сумпор интеракције су препознате у многим молекулским системима, где су одговорне за молекулску структуру и функцију многих познатих неорганских и органских материјала као и протеина. У овој докторској дисертацији проучаване су геометрије и енергије сумпор-сумпор интеракција анализом података из кристалних структура и применом квантнохемијских прорачуна високог нивоа теорије...Sulfur-sulfur interactions have been recognized in various molecular systems, where they are responsible for the molecular structure and function of many well known inorganic and organic moleculs and proteins. This doctoral study investigates the geometries and energies of sulfur-sulfur interactions by analyzing data obtained from crystal structures and by high-level quantum chemical calculations..

Theoretical Study of σ-hole Bonding between Selenium Atoms in Crystal Structures of Organoselenium Compounds

Non-covalent interactions involving selenium atoms are of great importance in chemistry and biochemistry due to the prominent role of selenium-containing molecules (like Se-antioxidants and selenoenzymes) in different biochemical processes. In this work, we combined analysis of crystallographic data extracted from crystal structures of selenium-containing molecules with the quantum chemical calculations to reveal the energy and geometry of seleniumselenium interactions in crystal structures of organoselenium compounds. In addition, Energy Decomposition Analysis was performed on model systems to reveal the nature of selenium-selenium interactions. Results of analysis of crystal structures were in excelent agreement with the results of quantum chemical calculations performed on model systems. Results of Energy Decomposition Analysis calculations showed that although the dispersion is the most important component of energy of selenium-selenium interactions, electrostatic component is also very strong. Results also suggest that electrostatic component has crucial role in defining the geometry of selenium-selenium interactions. Reduced Density Gradient calculations on model systems showed that selenium-selenium interactions are often accompanied with additional C-H ...Se interactions.4th International Symposium on Halogen Bonding (ISXB-4 Virtual) held as a virtual event from 2 – 5 November 202

Tris(3-nitropentane-2,4-dionato-κ2 O,O′) Complexes as a New Type of Highly Energetic Materials: Theoretical and Experimental Considerations

Decreasing the sensitivity towards detonation of high-energy materials (HEMs) is the ultimate goal of numerous theoretical and experimental studies. It is known that positive electrostatic potential above the central areas of the molecular surface is related to high sensitivity towards the detonation of high-energy molecules. Coordination compounds offer additional structural features that can be used for the adjustment of the electrostatic potential values and sensitivity towards detonation of this class of HEM compounds. By a careful combination of the transition metal atoms and ligands, it is possible to achieve a fine-tuning of the values of the electrostatic potential on the surface of the chelate complexes. Here we combined Density Functional Theory calculations with experimental data to evaluate the high-energy properties of tris(3-nitropentane-2,4-dionato-κ2 O,O′) (nitro-tris(acetylacetonato)) complexes of Cr(III), Mn(III), Fe(III), and Co(III). Analysis of the Bond Dissociation Energies (BDE) of the C-NO2 bonds and Molecular Electrostatic Potentials (MEP) showed that these compounds may act as HEM molecules. Analysis of IR spectra and initiation of the Co(AcAc-NO2)3 complex in the open flame confirmed that these compounds act as high-energy molecules. The measured heat of combustion for the Co(AcAc-NO2)3 complex was 14,133 J/g, which confirms the high-energy properties of this compound. The results also indicated that the addition of chelate rings may be used as a new tool for controlling the sensitivity towards the detonation of high-energy coordination compounds

How aromatic system size affects the sensitivities of highly energetic molecules?

Positive values of electrostatic potentials above the central regions of the molecular surface are strongly related to the high sensitivities of highly energetic molecules. The influence of aromatic system size on the positive values of electrostatic potentials and bond dissociation energies of C–NO2 bonds was studied by Density Functional Theory (DFT) calculations on a series of polycyclic nitroaromatic molecules. Calculations performed at PBE/6-311G** level showed that with the increase of the aromatic system size, values of positive electrostatic potential above the central areas of selected energetic molecules decrease from 32.78 kcal mol−1 (1,2,4,5-tetranitrobenzene) to 15.28 kcal mol−1 (2,3,9,10-tetranitropentacene) leading to the decrease in the sensitivities of these molecules towards detonation. Results of the analysis of electrostatic potential maps were in agreement with the trends in bond dissociation energies calculated for C–NO2 bonds of studied nitroaromatic molecules. Bond dissociation energies values indicate that the C–NO2 bond in the molecule of 1,2,4,5-tetranitrobenzene (56.72 kcal mol−1) is weaker compared to the nitroaromatic molecules with the additional condensed aromatic rings and with a similar arrangement of –NO2 groups (59.75 kcal mol−1 in the case of 2,3,9,10-tetranitropentacene). The influence of the mutual arrangement of –NO2 groups on the sensitivity of nitroaromatic molecules was also analyzed. Results obtained within this study could be of great importance for the development of new classes of highly energetic molecules with lower sensitivity towards detonation.Supplementary material: [https://cherry.chem.bg.ac.rs/handle/123456789/4804

Supplementary data for the article: Veljković, I. S.; Kretić, D. S.; Veljković, D. Ž. Geometrical and Energetic Characteristics of Se⋯Se Interactions in Crystal Structures of Organoselenium Molecules. CrystEngComm 2021, 23 (18), 3383–3390. https://doi.org/10.1039/D1CE00129A.

Supplementary material for: [https://doi.org/10.1039/D1CE00129A]Related to published version: [https://cherry.chem.bg.ac.rs/handle/123456789/4430

The chelate complexes as an improved high-energy compounds

Recent studies in high-energy material design revealed that coordination compounds show excellent detonation performances. Earlier experimental studies found that the nitro-acetylacеtonato aluminum (III) complex easily combusts in the air when heated.1 These findings indicate that the nitro-acetylacetonato metal derivatives may act as potential energetic compounds. The intensive theoretical studies of classical explosives formerly revealed that the impact sensitivity of high-energy molecules could be predicted by analysis of molecular electrostatic potential over the C–NO2 bonds.2 This concept is applied here. In order to investigate their energetic properties, we calculated the molecular electrostatic potential and bond dissociation energies for the weakest C-NO2 bonds for several nitro-tris(acetylacetonato) complexes. The results show good agreement between bond dissociation energies calculated for the weakest C-NO2 bonds and a slightly positive electrostatic potential above the observed C-NO2 bonds. The bond dissociation energies for studied complexes are close to the BDE value calculated for the 1,3,5- triamino-2,4,6-trinitrobenzene classified as a significant low-sensitive explosive. We also noticed that the metal ion replacement may be used for fine-tuning of the electrostatic potential above the middle regions of the nitro-chelate rings. However, the presented results show that these compounds have moderate sensitivity, and that the positive electrostatic potential above the central area of the nitro-chelate rings could be used for the assessment of detonation properties of chelate energetic molecules. References 1. C. Đorđević, Croat. Chem. Acta 1963, 35, 129. 2. B.M. Rice, E.F.C. Byrd, J. Mater. Res. 2006, 10(21), 2444. Acknowledgments This research was supported by the Science Fund of the Republic of Serbia, PROMIS, #6066886, CD-HEM

Influence of the presence of halogen substituents on high-energy properties of nitroaromatic molecules

Sensitivity towards detonation of high energetic materials (HEMs) and the positive potential in the central regions of their molecular surfaces are directly related. The presence of halogen atoms in HEMs creates the possibility for halogen bonding which can be used for modifying of electrostatic potential values [1]. Also, it has been noticed that the substitution of hydrogen atoms by halogen atoms in molecules like nitromethane leads to a decrease of bond dissociation energy values (BDE) for the C–N bond [2]. In this paper, the geometries and potentials in the central regions of molecular surfaces of 1,4-dihalo-5,8-dinitronaphthalene and 2,3-dihalo-5,8-dinitronaphthalene were analyzed. Optimal geometries and maps of electrostatic potential (MEP) were calculated using PBEPBE/6-311G** level of theory. The WFA-SAS program was used to obtain MEP for the mentioned molecules. Bond dissociation energies for optimized geometries were calculated using SAPT program. Results showed that the potentials above the central regions of molecular sufaces in the 2,3-dihalo-5,8-dinitronaphthalene molecules are higher than in the case of 1,4-dihalo- 5,8-dinitronaphthalene analogues. The most significant difference was detected in the case of molecules with chlorine as a substituent (up to 3 kcal/mol). However, the dissociation energies of C–N bonds are higher for all 2,3-substituted dinitronaphthalenes compared to 1,4-substituted analogues. There is a decrease in BDE values in both cases, but it is more significant for the 1,4-substituted dinitronaphthalenes, where the BDE value for 1,4-difluoro-5,8-dinitronaphthalene is more than 7 kcal/mol higher compared to the BDE for iodine analogue. References 1. A. B. Đunović, D. Ž. Veljković, CrystEngComm. 2021, 23, 6915. 2. G. M. Khrapkovskii, A. G. Shamov, R. V. Tsyshevsky, D. V. Chachkov, D. L. Egorov, I. V. Aristov, Comput. Theor. Chem. 2012, 985, 80. Acknowledgments This research was supported by the Science Fund of the Republic of Serbia, PROMIS, #6066886, CD-HEM