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

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

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

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..

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

Tris-(nitroacetylacetonato) complexes as new high-energy materials

Recent advances in high-energy materials studies have shown that coordination compounds are promising energetic compounds with satisfactory detonation properties and moderate sensitivity. Earlier experimental studies found that the nitro-acetylacеtonato aluminum (III) complex easily ignites in the air when heated. Theoretical calculations performed on nitroaromatic explosives revealed that molecular electrostatic potential over the C-NO2 bonds is a good tool for determining the impact sensitivity of these molecules. Herein, we calculated the molecular electrostatic potential and bond dissociation energies for several nitro-tris(acetylacetonato) complexes. A rough estimation of the electrostatic potential predicts slightly positive electrostatic potentials above the C-NO2 bonds. These results show that the metal ion replacement may induce the fine adjustment of electrostatic potential above the C-NO2 bonds in the nitro-chelate complexes. The reported results agree with the calculated bond dissociation energies. These values indicate that introducing the transition metals in the nitro-chelate complexes may increase their sensitivity. However, we also synthesized and characterized the nitro-tris(acetylacetonato) cobalt(III) complex. The UV/VIS and FTIR tests confirmed that the synthesized complex was Co(acac-NO2)3. The obtained results agree with the experimental results that Collman et al. reported. The open flame test showed that this complex easily combusts when exposed to the open flame. Acknowledgments This research was supported by the Science Fund of the Republic of Serbia, PROMIS, #6066886,CD-HEM

Strong hydrogen bonds involving carbon atom as hydrogen atom acceptor

Pyramidane (tetracyclo[2.1.0.01,3.02,5]pentane, C5H4) and its derivates fall into the class of high-energy molecules with nonclasicall cage geometries [1]. Althoug pyrmidane itself has not been synthetized yet, cage molecules with strained triangular rings and an apex carbon atom were synthetized and their structures were determined. This provides an opportunity for the assessment of noncovalent bonding of the apex carbon atom in highly strained systems. Here, we analysed crystal stractures and performed interaction energies calculations to evaluate possibility of the apex carbon atom from pyramidane and pyramidane-like molecules to act as hydrogen atom acceptors in hydrogen bonds. Analysis of crystal structures from Cambridge Structural Database (CSD) showed that there are short hydrogen-carbon contacts between apex carbon atom from pyramidane-like structures and hydrogen atoms from X-H fragments. Results of quantum chemical calculations performed on MP2/DEF2-TZVP level showed that pyramidane molecules and its derivatives can form strong hydrogen bonds involving apex carbon atom as hydrogen atom acceptor. Calculated energy of O-H•••C hydrogen bond between apex carbon atom of tetramethyl derivate of pyramidine and water was ΔE = -6.86 kcal/mol. This is significantly stronger than hydrogen bond between two water molecules (ΔE = 5.02 kcal/mol). Results of this study can by of greate importance for the recognition of nonclasical hydrogen bonds involving highly strained molecules. In addition, results presented here may help in the assessment of high-energy properties of strained cage molecules