Geometrical Bond Research Articles

Hexa-peri-hexabenzocoronene as a vector sensing and delivery of Carmustine anticancer drug: A density functional theory study

We conducted research on the adsorption of carmustine (BCNU) on the surface of pristine, N-doped, and BN-doped Hexa-peri-hexabenzocoronene (HBC) nanographene using density functional theory calculations. We used the B3LYP functional in conjunction with 6-31+G(d) and 6-311+G(d,p) basis sets to perform geometrical optimization calculations, vibrational frequencies, and natural bond orbitals (NBO) analysis. The dispersion correction term of Grimme-D3 was incorporated to account for the dispersion interactions. We found that the geometry of the nanographenes remains unchanged after the drug molecule adsorption. The calculated adsorption energies (Eads) were −17.1 kcal.mol−1 for HBC-BCNU, −17.0 kcal.mol−1 for NHBC-BCNU, and −17.9 kcal.mol−1 for BNHBC-BCNU when using the 6-31+G(d) basis set. The corresponding values calculated employing the 6-311+G(d,p) basis set were −17.9, −17.3, and −19.1 kcal.mol−1, respectively. Analysis of frontier molecular orbitals (HOMO and LUMO) showed that the electronic properties of NHBC were significantly affected by the presence of BCNU. We used NBO analysis to investigate the distribution of partial atomic charges in different systems. Finally, using the transition state equation and the smaller basis set, we found that the required time for BCNU to release from HBC, NHBC, and BNHBC is approximately 3.3, 1.8, and 13.0 s, respectively. The obtained values are 13.0, 4.6, and 96.0 s, respectively, for the higher level of calculations. The recovery time for all nanographenes is within a reasonable range, while NHBC exhibits the highest sensitivity for drug detection.

NCoV-19 therapeutics using cucurbitacin I structural derivatives: an in silico approach

BackgroundCucurbitacins are present in some common vegetables as secondary metabolites and are used by the plants against harmful microbes. Exploration of this capability of natural product based substances against wide variety of microbes seems relevant due to the ease of availability of the resources and safety. In this regard, considering the current pandemic, the antiviral properties of these molecules with a subset of Cucurbitacin I structural derivatives have been screened. The inhibition potential of the phytochemicals was assessed by the stability of the protein–ligand complex formed with the nucleocapsid protein (PDB ID: 7CDZ) of SARS-CoV-2 by computational methods. The proposition of an alternate antiviral candidate that is cost-effective and efficient relative to existing formulations is the main objective of this work.ResultsServer-based molecular docking experiments revealed CBN19 (PubChem CID: 125125068) as a hit candidate among 101 test compounds, a reference molecule (K31), and 5 FDA-approved drugs in terms of binding affinities sorted out based on total energies. The molecular dynamics simulations (MDS) showed moderate stability of the protein-CBN19 complex as implied by various geometrical parameters RMSD, Rg, RMSF, SASA and hydrogen bond count. The ligand RMSD of 3.0 ± 0.5 Å, RMSF of Cα of protein with less than 5 Å, and smooth nature of SASA and Rg curves were calculated for the adduct. The binding free energy (− 47.19 ± 6.24 kcal/mol) extracted from the MDS trajectory using the MMGBSA method indicated spontaneity of the reaction between CBN19 and the protein. The multiple ADMET studies of the phytochemicals predicted some drug-like properties with minimal toxicity that mandate experimental verification. ConclusionsBased on all the preliminary in silico results, Cucurbitacin, CBN19 could be proposed as a potential inhibitor of nucleocapsid protein theoretically capable of curing the disease. The proposed molecule is recommended for further in vitro and in vivo trials in the quest to develop effective and alternate therapeutics from plant-based resources against COVID-19.

Geometrical Optimization and Natural Bond Orbital Analysis of Relevant Structures in the Diastereoselective Cuprate Conjugate Addition Reaction of α,β-Unsaturated Lactams using Density Functional Theory

In this study, density functional theory calculations at the wB97XD/Def2TZVPP level were performed to analyze the mechanism underlying the cuprate conjugate addition reaction of α,β-unsaturated lactams. The calculation results were well-aligned with those obtained experimentally–the keto-aminal and aldo-aminal, i.e. 2 and 1a, yield the syn- and anti-products, respectively. The diastereoselectivity reversal originates from the small differences in the structure of the reactants. The pyramidalization and C7N3C2 angle between the aminal carbon, nitrogen and carbonyl carbon are large in 2. The dihedral angle of the aminal oxygen, aminal carbon, nitrogen and carbonyl carbon, O8C7N3C2, is closer to 180º in 2 than in 1a. The NBO analysis revealed string interactions between the lone pair of N3 and carbonyl π*(O1–C2) bond. These results validate the assumption—the planarity around nitrogen in molecule 2 increases the nucleophilicity of the carbonyl oxygen, thereby driving the reaction between molecule 2 and trimethylsilyl chloride (TMSCl), which yields a siloxyiminium cation 5b and this 5b propels the syn addition of dimethylcuprate, leading to the formation of complex 7. The π(C5–C6) (HOMO) and π*(C2–N3) (LUMO) interactions in the siloxyiminium cation explain the increased C5–C6 double bond electrophilicity. The aldo-aminal 1a directly reacts with dimethylcuprate under steric control and yields the anti complex 6a, whose π character is stronger than that of the syn complex 7 and this weak π characteristics of 7 increases its stability to compensate for the trimethylsilyl disturbance. The bicyclic α,β-unsaturated lactam 8 does not contain aminal oxygen and thus remains unreactive during the cuprate conjugate addition reaction. Moreover, its pyramidalization is higher than that of the keto-aminal 2 and its dihedral angle of C8C7N3C2 is closer to 180º. Finally, a thermodynamic anti product is obtained, which is more stable than the syn- product because of less torsional strain.

Deeper insights into the density functional theory of structural, optical, and photoelectrical properties using 5-[(4-oxo-4H-chromen-3-yl) methylidene]-4-oxo (thioxo)-6-thioxo-2-sulfido-1, 3, 2-diazaphosphinanes

The structure–activity relationship studied by DFT calculations and contacted with practical antimicrobial results for compounds 1–4 is discussed in detail. In light of this compounds 1–4 have been studied by using DFT/B3LYB/6-311++G (d,p) at the level of theory, the geometrical parameters, bond lengths and bond angles have been discussed. The results of quantum mechanical calculations showed that the presence of phosphorus and sulfur atoms changed the planarity of the parent compound 1 by the range from − 11 to 125°. The electronic parameter and dipole moment of these compounds in the ground state theoretically is analyzed by computing HOMO and LUMO pictures. Using frontier molecular orbital analysis, various spectroscopic and quantum chemical parameters are evaluated. Besides, absorption energies, oscillator strength, and electronic transitions of 1,3,2-diazaphosphinines 1–4 molecules have been derived at TD-DFT/CAM-B3LYP/6-311++G (d,p) computations utilizing, then the CAM-B3LYP method is “the Coulomb-attenuating method bases” set studied the electronic absorption spectra theoretically in the gas phase (TD-DFT) with the polarized split-valence 6-311++G (d, p) basis sets, in addition, the corrected linear response polarizable continuum model and measured experimentally in methanol and cyclohexane indicate a good agreement with the observed spectra (practically) in UV–Vis spectra. The molecular electrostatic potential surfaces plots have been computed to understand reactivity points.

Structural vibrational analysis (FT-IR, FT-Raman), electronic studies based on solvents (UV–Vis, non-linear optics, frontier molecular orbitals, molecular electrostatic potential, natural bond orbital and Fukui evaluation) and Hirshfeld surface analysis on 4-chloroacetophenone

The quantum mechanical DFT method is used to analyze spectral study for the title compound 4-chloroacetophenone (4CAPN) and the observations are compared with experimental results. The geometrical parameters bond lengths and bond angles are generated by DFT method with 6–311++G(d,p) basis set. Using solvents water, DMSO, ethanol and methanol, NLO properties are calculated, global descriptors are computed from HOMO-LUMO orbitals, the reactivity sites are analyzed from Molecular Electrostatic Potential (MEP) studies. From UV spectral analysis, UV–Vis spectra of 4CAPN are simulated and analyzed using the represented solvents. From Fukui function analysis, the electrophilic and nucleophilic spots are acknowledged. Using Multiwave function, the wave functional properties such as ELF, LOL and RDG are investigated in gas phase. Using Hirshfeld analysis, the molecular interactions are predicted.

Synthesis, Computational and cytotoxicity studies of aryl hydrazones of β-diketones: Selective Ni2+ metal Responsive fluorescent chemosensors

A new fluorescent sensor 2-(2-(3-chloro-4-fluorophenyl)hydrazono)-5,5-dimethyl cyclohexane-1,3-dione (A) and 2-(2-(4-chloro-2-nitrophenyl)hydrazono)-5,5-dimethyl cyclohexane-1,3-dione (B) composed of a β-diketones of aryl hydrazones synthesized by simple and cost-effective method. Various analytical tools analyzed the structural investigations of the synthesized substituted β-diketones of aryl hydrazones like FT-IR, 1H, 13C NMR and UV–Vis techniques, Single-crystal X-ray diffraction studies (SCXRD) (for A), Scanning electron microscopy (SEM), and fluorescence spectroscopy. SEM also investigates surface morphology modifications of aryl hydrazones and Ni2+ complex. Furthermore, the metal sensing (Chemo sensing) behavior of newly prepared aryl hydrazones of β-diketones derivatives was further studied by fluorescence spectroscopy. The aryl hydrazones sensor materials show admirable fluorescence selectivity with enrichment to Ni2+ over different cations in an aqueous ethanol solution with a recognition extremity of 4 μM–7 μM. A joint experimental and theoretical investigation was led on the chemical structure employing a density functional theory (DFT) (B3LYP), engaging a 6-31G basis set. The DFT technique's enhanced geometrical bond angles and lengths exhibited great covenant with the experimental results. The highest occupied molecular (HOMO) orbital and lowest unoccupied (LUMO) molecular orbital energy has been concluded. The cytotoxicity studies show these compounds impede the growth of KB cells highly and from the studies to evaluate their capability to accurately dock aryl hydrazones to antibodies of cancer protein such as 4LRH, 4L9K, 4 EKD and 4GIW cancer proteins.

Statistical Assessment of In-Plane Masonry Panels Using Limit Analysis with Sliding Mechanism

Historical masonry structures have a great interest in civil engineering because they constitute a large part of the world’s building heritage. In this paper, the effects that different geometrical (panel ratio, block ratio, and bond type) and mechanical (friction ratio) parameters have on the in-plane structural response of brick masonry panels are investigated. A discrete modeling approach, based on a limit analysis and capable of reproducing sliding mechanisms, formulation by one of the authors has been adopted, enhanced, and implemented. Results, in terms of collapse multipliers and collapse mechanisms, are presented and analyzed following a systematic statistical approach. Statistically significant effects have been found for each factor considered. Furthermore, the statistical model adopted included nonlinear terms that allowed the identification of whether the effect of one parameter on the response depends on the level of any other parameters. Thus, it was observed that two-way factor interactions played an important role in the in-plane response of masonry panels. The panel ratio-friction ratio two-way factor interaction was the one with a more significant effect.

Computational Study of Hydrogen Bonding in CH3CN•••H-X (X=OH, F, Cl, NH2) Complexes

In this work, first principles study of acetonitrile complexes (acetonitrile•••H-X, X=F, Cl, NH2, OH) has been carried out using electrostatic potential analysis, ab initio (MP2/6-311++g(2d, 2p), B3LYP/6-311++g(2d, 2p) and AIM theoretical calculations and these calculations confirm the hydrogen bonding interaction for these complexes. The geometrical parameters, binding energy and (3, -1) bond critical points confirm that HF donor is found to form strong hydrogen bond and NH3 donor is found to form weaker hydrogen bond for these complexes.

Mono-, di-, tri- and tetra-silacyclobutenes: Strain energy, hyperconjugation and ring-opening reaction

The ring strain, π-σ hyperconjugation and ring-opening reaction of silicon-substituted cyclobutenes (monosilacyclobutenes, disilacyclobutadienes, trisilacyclobutenes and tetrasilacyclobutene) are systemically studied at the level of B3LYP/6–311 + G(d,p). The strengths of the ring strains are characterized by the bond angle deviation from the normal angle of hybrid orbitals of the silicon and carbon atoms. A reasonable correlation is found between the strain energy and the departure of the bond path length from a linear geometrical bond. The positions of strongly-bent σ bonds are regarded as an important factor that causes different strains in silacyclobutenes. The π-σ hyperconjugation is directly estimated using the second order perturbation energy from the NBO analysis and we found that hyperconjugation is responsible for relaxing the ring strain in silacyclobutenes. The thermal ring opening reactions of silacyclobutenes are predicted to possess a symmetry-allowed conrotatory mechanism. The contribution of the bond energy is the main factor that dictates the ring-opening process to be either endothermic or exothermic.

Comparing the adhesion strength of 316L stainless steel joints after laser surface texturing by CO2 and fiber lasers

This paper focuses on the effects of the laser surface texturing process and joint configuration of stainless steel adherends on the adhesive tensile bond strength. Two different sources, a CO2 and a fiber laser, were used and compared. In particular, proper choice of laser parameters was explored with the aim of producing different roughness and peak-to-valley distance and different textures on the bonding area, which could increase the real contact surface. Furthermore, to more thoroughly understand the effect of the laser parameters on joint fracture load, the experimental campaign was conducted according to a Design of Experiment (DoE) framework and the results were analyzed with this methodology. The creation of particular textures and roughness levels were related to the resulting joint geometrical configuration and bond strengths. In particular, significant increases in joint bond strength were achieved using both laser sources. Furthermore, by optimizing the laser parameters, smaller laser spot scan path overlaps can be achieved as well as a more refined scale of surface texture and surface roughness. This thereby enables the joining of thinner sections of different materials.

Mesoscopic computational model of covalent cross-links and mechanisms of load transfer in cross-linked carbon nanotube films with continuous networks of bundles

An “effective bond model” of covalent cross-links between carbon nanotubes (CNTs) is developed for mesoscopic simulations of CNT materials. The cross-links are represented by discrete stretchable bonds between mesoscopic nanotube elements. These bonds induce forces in both the normal and tangential directions to the CNT surfaces. A general approach for fitting the model parameters based on results of atomistic simulations describing the pullout of a nanotube from a bundle is suggested. This approach is used to obtain sets of the best-fit parameters, recommended for simulations with (26,0) CNTs when cross-links are predominantly formed by single interstitial atoms. It is shown that quantitative agreement between the atomistic and mesoscopic simulations can be achieved if the equilibrium length of the mesoscopic cross-link bond is smaller than the equilibrium gap between pristine CNTs and an additional fitting parameter, which controls the direction of the cross-link force with respect to the geometrical bond, is introduced into the model. The developed model is used to simulate stretching and compression of a thin CNT film with a continuous network of bundles and to reveal the microscopic mechanisms of the mechanical load transfer. It is found that during stretching the cross-links create a transient percolating “load transfer network” that includes relatively small number of strained CNT segments, participating in the load transfer, while bending modes of CNTs are not activated. The structure of this network evolves with increasing strain, when breaking of certain cross-links irreversibly activates new paths of load transfer. During compression, mechanical response of the nanotube network is determined by the trade-off between stretching and bending of individual nanotubes, while growing correlations between motions of large bundles eventually result in the collective bending of the whole film.

Molecular Structure of Monomeric Cadmium-Dihalides, CdCl2, CdBr2, CdF2, CdI2

The geometrical parameters, namely, bond lengths and bond angles of cadmium dihalides were calculated from different levels of computation and experimentally. Several ab initio studies have been carried out. Most of them were assuming linearity for CdCl2. On the other hand, computational studies show that the monomeric cadmium dihalides were assigned linear geometries [1, 2]. In this work we have calculated the equilibrium structure of the Cadmium dihalides using the interionic force model. The computed bond lengths and bond angles are in a good agreement with measured values from electron diffraction (ED) and quantum chemical calculations such as, LDF and QCISD. Supposing linearity of the molecules their 3  bending frequencies were estimated from electron diffraction, except cadmium diiodide molecule that was fitted to 1  mode frequency. We have made use of the simplifying features that have previously been established in similar studies of other ionic compounds which are the transferability of parameters describing the halogen ion [3, 4, 5]. It has been shown that the interionic force model is capable of the molecular structures of cadmium dihalides. Keywords: Cadmium Dihalides, Interionic Force Model, chloride, fluoride, bromide, iodide DOI: 10.7176/JSTR/5-8-10

Life prediction of copper wire bonds in commercial devices using principal component analysis (PCA)

Copper has been widely adopted as a viable alternative to gold for wire bonding, due to its lower cost, better electrical and thermal conductivity, lower tendency for wire sweep due to a higher modulus and slower intermetallic compound (IMC) formation with aluminum bond-pad. However, these IMCs can cause an increase in resistance and separation between bonding interface which causes an open circuit. Wire bond and component reliability must consider all factors in combination with the change of wire bond materials and processes. How can users of off-the-shelf components determine the effects of wire bond material changes on the reliability of the components in their systems? How will these changes affect high reliability applications such as automotive, military and harsh environments?Although physics-of-failure based models can represent the failure mechanisms individually, the complex nature of the mixed failure mechanism has inhibited development of an analytical equation to represent it. In addition, geometrical and material characteristics of the entire package along with bonding process parameters play a crucial role in magnitude of stress experienced by these bonds, portraying difficulty in developing one such equation for use to all copper wire bonded devices. This study has aimed to develop a data-based predictive method based on the principal component analysis technique to provide an estimate of the wire bond time to failure for plastic encapsulate components. Extensive thermal cycling experiments have been performed on multiple commercial devices to obtain training data for the model. This method of wire bond fatigue and failure prediction is an adaptive technique which can achieve greater accuracy as more data is added. This method aims to provide a life-time estimate of copper wire bonded component with inputs such as initial geometrical, material properties, and wire bond related attributes for a specific package.

Revisiting the ionic diffusion mechanism in Li3PS4 via the joint usage of geometrical analysis and bond valence method

Inorganic solid electrolytes have obvious advantages on safety and electrochemical stability compared to organic liquid electrolytes, but the advance on high ionic conductivity of typical electrolytes is still undergoing. Although the first-principles calculation in the ion migration simulation is an important strategy to develop high-performance solid electrolyte, the process is very time-consuming. Here, we propose an effective method by combining the geometrical analysis and bond valance sum calculation to obtain an approximate minimum energy path preliminarily, in parallel to pave the way for the interoperability of low-precision and high-precision ion transport calculation. Taking a promising electrolyte Li3PS4 as an example, we revisit its Li-ionic transport behavior. Our calculated Li-ion pathways and the activation energies (the corresponding values: 1.09 eV vs. 0.88 eV vs. 0.86 eV) in γ-, β- and α-Li3PS4 are consistent with the ones obtained from the first-principles calculations. The variations of the position of P-ions lead the rearrangement of the host PS4 tetrahedron, affecting the diffusion positions of Li-ions and further enabling high Li+ conductivity in β-Li3PS4.

Theoretical study of the mechanism of 2,5-diketopiperazine formation during pyrolysis of proline

ABSTRACT In biomass pyrolysis reactions, the wide range of products obtained (some of them environmentally harmful) usually depends on the temperature and the content of amino acids, this fact results in general interest in studying the involved mechanisms of reaction which, in many cases, are poorly understood. In this work, the mechanism of formation of 2,5-diketopiperazine upon pyrolysis of proline at 300°C was theoretically studied by means of DFT calculations (B97XD/6-311G(d,p)). All transition states and minimum energy structures involved were optimised, and thermodynamic parameters were theoretically estimated. A mechanism of four steps was proposed, and the most influential step was analysed by using the reaction force formalism, and an analysis of geometrical parameters, charge distributions and bond orders. Results show that the transition state correspond to a dehydration process, and its preceding intermediate, are the most important rate-controlling states of the overall reaction. Reaction force analysis shows a high dominance of geometrical rearrangements (75% of the activation energy), while charge transfer was not an important factor for the analysed reaction step. Finally, from the bond order analysis, it was determined that the rate-controlling transition state is early formed and that the process is asynchronous.

Synthesis, molecular modeling and antioxidant activity of new phenolic bis-azobenzene derivatives

New phenolic bis-azobenzene derivatives have been synthesized through reaction of 4-((2,4-dihydroxyphenyl)azo)-2-hydroxybenzoic acid with various diazotized anilines. The chemical structures of the prepared compounds were characterized by elemental and spectral analyses (IR, NMR and UV–Visible). The DFT geometry optimization of the bis-azobenezenes was carried out at B3LYP/6–311++G (d,p) level to indicate that they have a planar structure. The geometrical parameters, bond length and bond angle were in good agreement with those obtained from x-ray crystal structure of analogue compounds. The TD-DFT is used to obtain λmax and compared with the experimental UV–Visible absorption spectra. The HOMO-LUMO energy gap and other chemical reactivity descriptors were calculated. The antioxidant activity of the investigated compounds was screened. The data indicated that the methoxy derivative 5c exhibited higher activity than their corresponding derivatives with IC50 = 23.01 μg/mL which close to the reference (Ascorbic acid, IC50 = 22.03 μg/mL).

Different Donor-Acceptor Interactions of Carbene Ligands in Heteroleptic Divalent Group 14 Compounds, LEL' (E=C-Sn; L=N-Heterocyclic Carbene; L'=Cyclic Alkyl(Amino) Carbene).

The electronic structure and reactivity of heteroleptic divalent group 14 compounds, 1E (E=C-Sn) with NHC and cAAC ligands have been studied at the BP86/TZ2P level of theory and compared with homoleptic group 14 compounds. The EDA-NOCV (energy decomposition analysis-natural orbitals for chemical valence) analysis indicates that the interaction between the two carbene ligands and the central C-atom in 1C can be best represented as one 3c-2e electron sharing σ-bond and one 3c-2e donor-acceptor σ-bond. There exists an electron sharing interaction between the π-type orbital on the central C-atom and the C-N π* orbital of cAAC and a π-back-donation from the σ-type lone pair on the central C-atom to the π*-MO of NHC. This bonding description is equivalent to the localized bonding representation, where the central C-atom forms two electron sharing bonds and two donor-acceptor bonds with cAAC and NHC ligands. However, the bonding between the carbene ligands and the heavier group 14 element can be best represented as two 2c-2e donor-acceptor σ-bonds and a π-back-donation from group 14 element to C-N π* orbital of cAAC. This bonding description is well supported by the geometrical and Natural Bond Orbital (NBO) analyses. Hence, 1C can be best described as a carbene and the heavier analogues can be best described as tetrylones. However, the high first (287.6-274.3 kcal mol-1 ) and second proton affinities (162.0-158.5 kcal mol-1 ) suggest that 1E (E=C-Sn) behave as tetrylones.

Molecular structure, vibrational spectra, NBO, Fukui function, HOMO-LUMO analysis and molecular docking study of 6-[(2-methylphenyl)sulfanyl]-5-propylpyrimidine-2,4(1H,3H)-dione

Theoretical and experimental FT-IR and FT-Raman vibrational spectral analysis of 6-[(2-methylphenyl)sulfanyl]-5-propylpyrimidine-2,4(1H,3H)-dione have been recorded in the region 4000-400 cm-1 and 4000-100 cm-1 insolid phase. The molecular geometrical parameters, bond length, bond angle and vibrational wave numbers, harmonic vibrational frequency were investigated using the density functional theory B3LYP method with the 6-311++G(d,p) basis set. The stability of the molecule has been investigated using the natural bond orbital (NBO) analysis. The electronic properties such as HOMO-LUMO energies were determined by the time-dependent DFT approach. The thermodynamical properties and the first order hyperpolarizability and molecular electrostatic potential (MEP) of the title compound were also studied. The electron density-based local reactivity descriptors such as the Fukui functions were calculated to explain the chemical selectivity or reactivity site in the molecule. The molecule orbital contributions were investigated using the total density of states (TDOS), the sum of 𝛼 and 𝛽 electron density of states (𝛼𝛽DOS). The molecular docking (ligand-protein) simulations have been performed using the SWISSDOCK server. The full fitness (FF) score and hydrogen bonding interaction and binding affinity values revealed that title compound can act as potential inhibitor against HIV-1 protease.

Magnetic Phase Diagram of the Breathing Pyrochlore Antiferromagnet LiGa1−xInxCr4O8

The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation. We show here that the solid solutions LiGa1-xInxCr4O8 between these two 'breathing' pyrochlore compounds display (i) rapid suppression of magnetic and structural transitions upon doping the end members, (ii) spin-glass-like freezing above 2 K in the range 0.1 $\lesssim$ x $\lesssim$ 0.6, and (iii) apparent spin-gap behavior for x $\gtrsim$ 0.7. Furthermore, no transitions are observed above 2 K at x ~ 0.9, where magnetic susceptibility remains finite at 2 K and magnetic heat capacity shows a quadratic temperature dependence at 1-5 K. Our work shows that breathing pyrochlore compounds provide a unique opportunity for studying both geometrical frustration and bond alternation.

Observation of neutral, ionic and intermediate states in lamotrigine-acid complexes- inference from crystallographic bond geometries

The anticonvulsant and antiepileptic drug lamotrigine was crystallized with three aromatic acids viz., 2,5-dihydroxybenzoic acid (I), para-toluenesulfonic acid (II) and 4-bromobenzoic acid (III), with the objective of understanding the formation of a salt or co-crystal in the solid state. Single crystal X-ray diffraction and FT-infrared spectroscopic measurements were carried out for all of them. The asymmetric units of I and II contain two lamotriginium cations and two anions (2,5-dihydroxybenzoate in I and para-toluenesulfonate in II), respectively, and additionally II contains one water molecule. The asymmetric unit of III comprises one lamotriginium cation, one 4-bromobenzoate anion and one dimethylformamide (DMF) solvate. In all three complexes the protonation occurs at the N2 atom of the triazine ring. In I and II, the complete proton transfer is observed. However in III, only partial proton transfer is inferred from O to N because of the acidic H atom disorder. The protonation of lamotrigine is also confirmed by the unambiguous location of H atom from the difference Fourier map and as well as from the geometrical bond analysis. Further, various lamotrigine-acid complexes from the CSD were analyzed to establish a correlation between different ionization states (neutral, intermediate and ionic) and changes in the geometrical parameters. The bond angles of triazine ring in lamotrigine and bond distances of carboxylic acid are found to be the best descriptors for distinguishing all three ionization states, whereas, the bond angles of carboxylic acid have to failed to distinguish intermediate state from ionic. From hydrogen bonding point of view, only the lamotrigine-acid heterosynthon is observed in I and II, whereas in III, both lamotrigine-lamotrigine homosynthon and lamotrigine-acid heterosynthon are observed. In I, the cation–anion and anion–anion interactions form a supramolecular two-dimension hydrogen-bonded square grid network, while the water molecule of II cross-link the two-dimensional cation–anion hydrogen-bonded layers. In III, a pseudo-quadruple hydrogen bonding is formed with aid of DMF solvate.