Calculated Bond Lengths Research Articles

Uranium-Incorporated Pyrochlore La2(UxMgxZr1-2x)2O7 Nuclear Waste Form: Structure and Phase Stability.

As efficient and stable nuclear waste forms, single-phase uranium (U6+)-incorporated La2Zr2O7 nanoparticles were designed and synthesized in an air atmosphere. To obtain a high U loading, divalent magnesium (Mg2+) was introduced to balance the extra charge from the substitution of tetravalent zirconium (Zr4+) by U6+ with a minimized impact to the lattice. There is a composition-driven phase transition from order pyrochlore to defect fluorite as the U concentration increases from 10 to 30 mol %, demonstrating both good solubility and stability of the La2Zr2O7 host for U and potentially for other actinides. La2(UxMgxZr1-2x)2O7 (x = 0-0.3) nanoparticles showed good dispersity and crystallinity with an average particle size of ∼48 nm. Furthermore, X-ray photoelectron spectroscopy, Raman spectroscopy, and emission spectroscopy revealed that U was stabilized in the hexavalent state in the form of a UO22+ ion. Spectroscopic methods also demonstrated that our samples caused a scintillating response with an orange emission (597 nm) by 230 nm excitation. In addition, density functional theory simulations were employed to investigate the atomic structures and electronic properties of the U-incorporated pyrochlores. The calculated bond lengths, atomic charges, and charge density confirm the existence of UO22+ ions. Supported by both experimental and computational results, a novel geometrical structure was proposed to explain the Mg2+-U6+ substitution. This work demonstrated the successful development of U-incorporated La2Zr2O7 nanoparticles and provided an efficient way to immobilize U in these ceramic waste matrixes.

Relationship between the Relative Dielectric Constant and the Monomer Sequence of Acrylonitrile in Rubber.

Acrylonitrile-butadiene rubbers (NBRs) have a lower glass transition temperature (Tg) and a higher dielectric constant than other rubbers. To understand how a low Tg and a high dielectric constant are compatible, we focused on the acrylonitrile (AN) monomer sequence in rubber and synthesized random and alternating copolymers to evaluate the effect of the sequence. The AN monomer sequence dependence of the relative dielectric constant was investigated by the C–N stretching vibration of the nitrile group through Fourier transform infrared spectroscopy and internal rotation potential energy measurements around the C–C bond within the nitrile group based on dimer model calculations. The alternating copolymers, including NBR, showed a higher dielectric constant than random copolymers. The alternating copolymer shifted from ∼2243 cm–1 for polyAN to ∼2236 cm–1 for NBRs, while the random copolymer only shifted to ∼2239 cm–1. The peak of the C–N stretching vibration was correlated with the AN sequence. The sequence dependence of the shift can be explained by the C–N bond length calculation. The internal rotation potential energy between gauche and trans of the NBR model was the lowest, indicating that the NBR main chain is flexible and that AN in the main chain rotates easily. Therefore, NBR has a high dielectric constant and a low Tg because of the presence of an alternating sequence and the flexibility of the NBR main chain.

DFT Prediction of Factors Affecting the Structural Characteristics, the Transition Temperature and the Electronic Density of Some New Conjugated Polymers.

Conjugated polymers are promising materials for various cutting-edge technologies, especially for organic conducting materials and in the energy field. In this work, we have synthesized a new conjugated polymer and investigated the effect of distance between bond layers, side-chain functional groups (H, Br, OH, OCH3 and OC2H5) on structural characteristics, phase transition temperature (T), and electrical structure of C13H8OS using Density Functional Theory (DFT). The structural characteristics were determined by the shape, network constant (a, b and c), bond length (C–C, C–H, C–O, C–S, C–Br and O–H), phase transition temperatures, and the total energy (Etot) on a base cell. Our finding shows that the increase of layer thickness (h) of C13H8OS–H has a negligible effect on the transition temperature, while the energy bandgap (Eg) increases from 1.646 eV to 1.675 eV. The calculation of bond length with different side chain groups was carried out for which C13H8OS–H has C–H = 1.09 Å; C13H8OS–Br has C–Br = 1.93 Å; C13H8OS–OH has C–O = 1.36 Å, O–H = 0.78 Å; C13H8OS–OCH3 has C–O = 1.44 Å, O–H =1.10 Å; C13H8OS–OC2H5 has C–O = 1.45 Å, C–C = 1.51Å, C–H = 1.10 Å. The transition temperature (T) for C13H8OS–H was 500 K < T < 562 K; C13H8OS–Br was 442 K < T < 512 K; C13H8OS–OH was 487 K < T < 543 K; C13H8OS–OCH3 was 492 K < T < 558 K; and C13H8OS–OC2H5 was 492 K < T < 572 K. The energy bandgap (Eg) of Br is of Eg = 1.621 eV, the doping of side chain groups H, OH, OCH3, and OC2H5, leads to an increase of Eg from 1.621 eV to 1.646, 1.697, 1.920, and 2.04 eV, respectively.

Synthesis of the Three Mixed-Ligand Metal Complexes and One Organic Salt of 3,5-Dinitrobenzoic Acid for Biopharmaceutical Optimization Through Monoethanol-Amine. Structures and Dft Studies of Complexes

The simplest derivatives of benzoic acid show a wide spectrum of the biological action mostly being poor water soluble. In order to demonstrate on example of 3,5-dinitrobenzoic acid (DNBA) a possibility of the simultaneous enhancement of water solubility and antimicrobial activity the complexation (salt formation and metal coordination) approach has been examined. Monoethanolamine (MEA) is selected as the complexing agent. Three isomorphic mixed-ligand complexes of Cu, Ni, Co with DNBA and MEA as well one organic salt in the polymorphic form have been synthesized and their structures are characterized by the element analysis, FTIR and X-ray crystallography. Measurements of water solubility and determination of the antimicrobial activity attest that a solubility of the copper mixed-ligand complex and organic salt is increased about 4 and 8 times with simultaneous enhancement of the bioactivity. The DFT studies by B3LYP/def2-TZVP and B3LYP/6-311G(d,p) showed that Cu, Ni, and Co complexes with DNBA and MEA have high-spin ground electronic states as a doublet, triplet and quartet, respectively. Calculated bond lengths and bond angles of all metal complexes in higher-spin ground electronic states are in good agreement (about R 2 =0.97) with X-ray data. Additionally, the energies of the frontier MOs and frontier electron densities and also electrostatic potential of isostructural complexes have been analyzed by the DFT/6-311G(d,p) method.

Effect of SnO2/SeO2 on Au nano-particles doped silicate glasses: a structural study using XAS and EXAFS refinements

Au LIII edge X-ray absorption spectroscopic measurements were carried out over a series of Au nanoparticles embedded glasses with SnO2 and SeO2. The results obtained from EXAFS and XANES confirms the typical characteristics and structure of gold nanoparticles in these glasses. Raman analysis was performed to understand the structure of the glass. XANES data reveal that these glasses show Au0 and Au+1 oxidation state depending on reducing agent. EXAFS refinements were performed using ARTEMIS software to calculate bond lengths, R-factor and Debye–Waller factor on these glasses.

Quantum Chemical Determination of the Molecular Structure of 1,2,4-Triazole and the Calculation of its Infrared Spectrum

The molecular structure of 1,2,4-triazole is calculated by the density functional theory method in the B3LYP/6–31G approximation using the Gaussian program package. The calculated bond lengths and bond angles are well consistent with their experimental values. The results of the calculation show that triazole has a planar structure. Normal vibrational frequencies of triazole are calculated and these normal vibrations are assigned. Absorption band intensities are calculated and the IR spectrum of triazole is constructed. When compared, the theoretical spectrum qualitatively reproduces the experimental one.

Structural, electronic, electrical, and magnetic properties of Rhn (1 ≤ n ≤ 13) clusters

Douglas-Kroll-Hess calculations of bond lengths, binding energies, HOMO-LUMO energy gaps, vertical ionization potentials and electron affinities, dissociation energies, second-order difference of total energies, polarizabilities, and spin magnetic moments of small rhodium cluster are carried out using the BLYP functional along with the all-electron TZP+1d-DKH basis set. Our results agree well with the experimental values available in the literature. Overall, the spin magnetic moments computed in this work are the best published to date. These findings certainly add credibility to the ground state geometrical structures reported by us, which do not always coincide with the structures found earlier. Rh8 and Rh12 are the most stable clusters, while Rh5 and Rh7 are the most reactive. Mean dipole polarizabilities and polarizability anisotropies are also reported. It is the first time that these electrical properties are calculated and they are useful for understanding the electronic structures of the Rhn clusters.

Density functional theory studies of Hypaphorine from Erythrina mildbraedii and Erythrina addisoniae: structural and biological properties

This study was aimed at isolating hypaphorine from Erythrina mildbraedii Harms (Fabaceae) and Erythrina addisioniae Hutch. & Datziel (Fabaceae) in order to determine its structural and antibacterial effects. Density functional theory (DFT) calculations and X-ray crystallographic analysis of the isolated hypaphorine was determined. The antibacterial effects of hypaphorine against a number of Gram positive and Gram negative bacterial strains were investigated. The root mean square deviation between the experimental and calculated bond lengths and bond angles of hypaphorine were found to be 0.046 A and 1.5° respectively. The highest occupied molecular orbital (HOMO) of hypaphorine was delocalised on the indole moiety whereas the lowest occupied molecular orbital (LUMO) was delocalised on the –N(CH3)3 group and the HOMO–LUMO gap of hypaphorine was 4.65 eV. Hypaphorine inhibited the growth of the Gram-positive bacteria tested, namely Bacillus cereus, B. subtilis, Staphylococcus aureus and S. epidermidis. The lowest minimum inhibitory concentration (MIC) value of 2 mg/mL was exhibited against Mycobacterium smegmatis, Staphylococcus aureus and B. subtilis. The theoretical and experimental results from this study showed that hypaphorine is capable of forming quadrupole moments thus explaining its antibacterial effects on Gram positive bacteria.

Experimental and computational evidence for C=O π-bonding in [CH2OH]+ and related oxonium ions.

The question of whether [CH2OH]+ should be described as the hydroxymethyl cation, +CH2OH, or protonated formaldehyde, CH2=OH+, is reconsidered in the light of experimental information and new computational evidence. Previous arguments that the charge distribution in [CH2OH]+ may be probed by considering the incremental stabilisation of [CH2OH]+ induced by homologation on carbon (to give [CH3CHOH]+) or oxygen (to produce [CH2OCH3]+) are critically examined. Cation stabilisation energies are shown to be better indicators of the nature of these oxonium ions. Further insight into the structure of larger CnH2n+1O+ oxonium ions is obtained by considering the site of protonation of enol ethers and related species. Computational information, including AIM (Atoms and Molecules) and NBA (Natural Bond Analysis) charges on the carbon and oxygen atoms in [CH2OH]+ and related species, is considered critically. Particular attention is focused on the calculated bond lengths and barriers to rotation about the C-O bond(s) in [CH2OH]+, [CH3CHOH]+, [(CH3)2COH]+, CH3OH and [CH2OCH3]+ and the C-N bond in [CH2NH2]+. Trends in these data are consistent with appreciable π-bonding only in the C-O connections which correspond to the C=O bond in the parent aldehyde or ketone from which the oxonium ion may be considered to be derived by protonation or alkyl cationation.

A motif for heteronuclear C[triple bond, length as m-dash]E (E = Si, Ge, Sn, Pb) bonding: Lewis acid-base pair strategy.

The design and characterization of the heteronuclear group 14 C[triple bond, length as m-dash]E (E = Si, Ge, Sn, Pb) triple bonds have attracted intensive interest in the past few decades. In the current work, utilizing the advantages of N-heterocyclic carbenes (NHCs) and Lewis acid-base pair strategy, we theoretically designed a new class of compounds III-1, i.e., (NHCAR)C[triple bond, length as m-dash]E(Al(C6F5)3). Quantum chemical calculations showed that these singlet compounds possess very favourable isomerization, fragmentation and dimerization stabilities at the B3LYP/def2-TZVPP//B3LYP/def2-SVP level. The calculated bond lengths of CE in III-1 are 1.63 Å for Si, 1.70 Å for Ge, 1.91 Å for Sn and 2.01 Å for Pb, respectively, which are close to or even shorter than the known C[triple bond, length as m-dash]E bond lengths. In addition, the significant Mayer bond order values, two orthogonal π orbitals and one σ orbital between the C and E atoms also indicate the characteristics of triple bonds. Based on several bonding analyses, strong delocalization is found to exist between the C[triple bond, length as m-dash]E core and NHCAR forming a weak C[double bond, length as m-dash]C double bond. Hence, such obtained C[triple bond, length as m-dash]E species also can be described by their resonace structures as cunmulene analogs. In all, III-1 proposed here not only presents a universal C[triple bond, length as m-dash]E motif for all the heavier group 14 elements, but also provides a new strategy for the design and synthesis of heteronuclear group 14 triple bonds in the future.

Vibrational spectroscopic and Hirshfeld surface analysis of N,N'-(azanediylbis(2,1-phenylene))bis(2-chloropropanamide)

The title molecule, N,N'-(azanediylbis(2,1-phenylene))bis(2-chloropropanamide) (LNNN) was synthesized and characterized by means of Hirshfeld surface analysis and vibrational (FT-IR and RAMAN) studies. Ab-initio Hartree-Fock (HF) and density functional theory (DFT; BLYP, B3LYP, B3PW91 and mPW1PW91) calculations were accomplished using 6-31G(d,p) and 6-311G(d,p) basis sets. The comparison of calculated bond lengths and angles with X-ray crystal structure shows sufficient agreement. The solid phase FT-IR and FT-RAMAN spectra of LNNN have been recorded in the regions 4000-525 cm-1 and 4000-50 cm-1, respectively. A comparative analysis between the calculated and experimental vibrational frequencies was carried out and significant bands were assigned. The results indicated a good correlation between experimental and theoretical IR and RAMAN frequencies. A detailed analysis of the intermolecular interactions via Hirshfeld surface analysis and fingerprint plots revealed that supramolecular structure of the LNNN is stabilized mainly by the formation of H···H, C···H, Cl···H ve O···H intermolecular interactions.

Theoretical investigation of excited-state proton transfer (ESPT) for 2,5-bis(2-benzothiazolyl)hydroquinone: single or double?

ABSTRACT In this work, the single and double proton transfer dynamic process in the first excited state of 2,5-bis(2-benzothiazolyl)hydroquinone (BBTHQ) were theoretically investigated based on the time-dependent density functional theory (TD-DFT) method. The calculations of primary bond lengths, bond angles, IR vibrational spectra and NCI analysis reveal that two intramolecular hydrogen bonds of BBTHQ are strengthened in the first excited state, which provides a driving force for excited state proton transfer. The frontier molecular orbitals (FMOs) indicate the nature of intramolecular charge transfer. In addition, the potential energy surfaces (PESs) of the ground state and first excite state were also constructed to further elucidate the mechanism of intramolecular proton transfer of BBTHQ.

Mononuclear Hydroxo Carbonato Complexes of Np(V), Np(VI), and U(VI): A Density Functional Study

Mononuclear ternary actinide hydroxo carbonato complexes AnO2(OH)y(CO3)zq have been studied computationally for An = Np(V), Np(VI), and U(VI). Density functional calculations were carried out to examine complexes with up to two carbonate and two hydroxide ligands. This study focusses on ternary Np(V) complexes suggested by experiment. Geometry parameters of hydroxo carbonato complexes lie between the corresponding values of hydroxo and carbonato complexes with the same number of anionic ligands. We used calculated bond lengths to interpret an EXAFS experiment. We determined a tendency to decreasing complexation energies for series of complexes with a constant number of anionic ligands and increasing numbers of carbonate ligands. Our results suggest that mononuclear hydroxo carbonato complexes should also exist for An(VI). Complexation energy trends of An‐OH‐CO3 complexes also yield a new perspective on the open debate on complexation constants of Np(V) hydroxo complexes. The consistently calculated properties of the An‐OH‐CO3 system and their trends will be helpful for further experimental characterization.

The Site Occupancy Assessment in Beryl Based on Bond-Length Constraints

The site preference for each cation and site in beryl based on bond-length calculations was determined and compared with analytical data. Tetrahedral SiO4 six-membered rings normally have no substitutions which results from very compact Si4+–O bonds in tetrahedra. Any substitution except Be would require significant tetrahedral ring distortion. The Be tetrahedron should also be negligibly substituted based on the bond-valence calculation; the tetrahedral Li–O bond length is almost 20% larger than Be2+–O. Similar or smaller bond lengths were calculated for Cr3+, V3+, Fe3+, Fe2+, Mn3+, Mg2+, and Al3+, which can substitute for Be but also can occupy a neighboring tetrahedrally coordinated site which is completely vacant in the full Be occupancy. The octahedral site is also very compressed due to dominant Al with short bond lengths; any substitution results in octahedron expansion. There are two channel sites in beryl: the smaller 2b site can be occupied by Na+, Ca2+, Li+, and REE3+ (Rare Earth Elements); Fe2+ and Fe3+ are too small; K+, Cs+, Rb+, and Ba2+ are too large. The channel 2a-site average bond length is 3.38 Å which allows the presence of simple molecules such as H2O, CO2, or NH4 and the large-sized cations-preferring Cs+.

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches - differential electrochromic vs photochromic behavior.

Our undergraduate research group has long focused on the preparation and investigation of electron-deficient analogs of the perimidinespirohexadienone (PSHD) family of photochromic molecular switches for potential application as "photochromic photooxidants" for gating sensitivity to photoinduced charge transfer. We previously reported the photochemistry of two closely related and more reducible quinazolinespirohexadienones (QSHDs), wherein the naphthalene of the PSHD is replaced with a quinoline. In the present work, we report our investigation of the electrochemistry of these asymmetric QSHDs. In addition to the short wavelength and photochromic long-wavelength isomers, we have found that a second, distinct long-wavelength isomer is produced electrochemically. This different long-wavelength isomer arises from a difference in the regiochemistry of spirocyclic ring-opening. The structures of both long-wavelength isomers were ascertained by cyclic voltammetry and 1H NMR analyses, in concert with computational modeling. These results are compared to those for the symmetric parent PSHD, which due to symmetry possesses only a single possible regioisomer upon either electrochemical or photochemical ring-opening. Density functional theory calculations of bond lengths, bond orders, and molecular orbitals allow the rationalization of this differential photochromic vs electrochromic behavior of the QSHDs.

Structure-antioxidant activity relationships, QSAR, DFT calculation, and mechanisms of flavones and flavonols

DFT calculations were performed on nine flavones and flavonols to explain their high antioxidant activity and variations in their activity. Conformational analysis showed that only flavonols with 3-OH directed toward the B-ring are nonplanar; however, flavones and resulted radicals are planar. Hydroxyl group eligible for dissociation is the one with ortho OH directed toward it; otherwise, one of B-ring (in 2′ or 4′-position) hydroxyl group. There are two main factors responsible for stabilizing the resulted radicals and lowering the bond dissociation energy and hence there were found well correlated with the experimental activity. First, driving force resulted from the conversion of nonplanar flavonols to planar radicals accompanied by resonance toward the carbonyl group and H-bond formation with 3-OH and second, radical stabilization by H-bond with ortho hydroxyl group with resonance toward carbonyl or pyrone oxygen. All resonance and H-bonds were confirmed by spin density, bond length, and molecular orbital calculations.

Cyclization of chalcones into N-propionyl pyrazolines for their single crystal X-ray, computational and antibacterial studies

Abstract The chalcones have been cyclized into the N-propionyl-2-pyrazolines using propionic acid with hydrazine hydrate. The structures of pyrazolines were determined by FT-IR, NMR spectroscopy, and confirmed by single crystal X-ray diffraction (SC-XRD) study. Further, a combined experimental and density functional theory (DFT) based study of these pyrazolines has been reported. A comprehensive DFT investigation was performed with the level of theory as B3LYP/6-311 + G(d,p), investigating the electronic structure characteristics, FMOs and non-linear optical features of said compounds. However, the UV absorption spectra of 2a, 2b and 2c were calculated in acetone by Polarizable Continuum Model (PCM) at TD-B3LYP/6-311+G(d,p), and TD-Cam-B3LYP/6-311+G(d,p), levels. The AIM calculations were performed to explore the non-covalent interactions (NCIs). The calculated bond lengths and bond angles of said compounds are in good agreement with the SC-XRD determined parameters. The computed alignment of the frontier molecular orbitals of the derivatives with smaller energy gap provides additional information into the electronic features which enhancing the nonlinear optical (NLO) efficiency of the derivatives. Besides, synthesized compounds were applied for antibacterial activity and found compound 2c was most significant antibacterial agent. It has an antibacterial efficiency in the form of zone inhibition 20 ± 0.50 and 21 ± 0.25 mm against Gram-positive bacterial strains S. aureus and B. subtilis and 19 ± 0.35 and 18 ± 0.40 mm against Gram-negative bacterial strains E. coli and P. peli. Overall, antibacterial activity of synthesized compounds was significant against bacteria, though variable against Gram-positive and negative bacterial strains.

Bond length calculation of aniline and its reaction products by semi-empirical method

Bond length calculation of aniline and its reaction products by semi-empirical method

Origin of enhanced corrosion resistance of Ag and Au doped anatase TiO2

Anatase TiO2 is a promising corrosion resistance material due to the excellent corrosion resistance, order array structure and good adsorption stability. However, the fundamental mechanism of interaction between TiO2 and sulfur (S) is unclear. In particular, the nature of corrosion resistance of alloy-doped TiO2 is not understood. By using the first-principles calculations, we study the sulfuretted mechanism of TiO2 and explore the influence of Ag and Au on the corrosion resistance of TiO2. The results show that sulfur is favorable to occupy the tetrahedral interstitial site because sulfur occupied this position can improve the localized hybridization between S-3p state and O-2p state, which forms the SO bond. The calculated bond length of SO bond is 1.967 Å. In particular, Ag dopant and Au dopant enhance the localized hybridization between sulfur and oxygen. The calculated bond length of SO bond for Ag dopant (1.483 Å) and Au dopant (1.506 Å) is shorter than that of S-doped TiO2. As a result, those alloying elements improve the corrosion resistance of TiO2. Compared to Au dopant, Ag dopant improves the corrosion resistance of TiO2 because the bond strength of SO bond for Ag dopant is stronger than that of Au dopant.

Investigation of the structural, electrical, optical and magnetic properties of XMg4Mn6O15 (X = K, Rb, and Cs) compounds

Full-potential linearized augmented plane wave (FP-LAPW) method for an investigation of the structural, electrical, optical and magnetic properties of cubic manganese oxides in both spin channels was used. The calculated bond lengths and atomic positions for all the atoms are in good agreement with the recent experimental measurements. Electronic band structures calculations revealed that these materials have direct band gaps from the spin up case, while indirect band gaps from the spin down case, with the energy band gap of (Eg↑ = 0.06 eV, Eg↓ = 4.23 eV), (Eg↑ = 0.02 eV, Eg↓ = 4.28 eV) and (Eg↑ = 0.04 eV, Eg↓ = 4.27 eV) for KMg4Mn6O15, RbMg4Mn6O15 and CsMg4Mn6O15, respectively. Overall, the behavior of these compounds is semiconductor have close concurrence with the experimental data. Spin up band gap is much lower in comparison to the spin down results. Density of states showed that valence and conduction bands are dominated by the Mn-d and O-p states. We also analyzed and discussed the optoelectronic properties in the energy range 0–10 eV to describe the absorption capability of these compounds. From the calculated magnetic moments, it is observed that all these compounds have high magnetic moments. The major contributions to the magnetic moment come from the Mn atoms.