Relaxed Potential Energy Surface Scans Research Articles

The effects of conformation and intermolecular hydrogen bonding on the structure and IR spectra of flutamide; a study based on the matrix isolation technique, ab initio and DFT calculations

In this study, stable conformers of flutamide referred to as an anticancer drug were searched through a relaxed potential energy surface scan carried out at the B3LYP/6-31G(d) level of theory. This was followed by geometry optimization and thermochemistry calculations performed with the HF-SCF, MP2, B3LYP methods and the 6-31G(d), 6–311++G(d,p), aug-cc-pvTZ basis sets for each of the determined minimum energy conformers. The results revealed that flutamide has at least five stable conformers and two of them provide the major contribution to the observed matrix isolation infrared (IR) spectra of the molecule. The effects of conformational variety and intermolecular hydrogen bonding interactions on the observed IR spectra of flutamide were interpreted in the light of the vibrational spectral data obtained for the most stable monomer and dimer forms of the molecule at the same levels of theory. Pulay’s “Scaled Quantum Mechanical-Force Field (SQM-FF)” method was used in the refinement of the calculated harmonic wavenumbers, IR intensities and potential energy distributions. This scaling method which proved its superiority to both anharmonic frequency calculations and other scaling methods helped us to correctly interpret the remarkable differences between the matrix IR spectra of flutamide in argon and the condensed phase IR spectra of the molecule in solvents such as KBr, H2O, D2O, ethanol and methanol.

A Reactive Molecular Dynamics Study of Chlorinated Organic Compounds. Part I: Force Field Development.

This work presents a novel parametrization for the ReaxFF formalism as a means to investigate reaction processes of chlorinated organic compounds. Force field parameters cover the chemical elements C, H, O, Cl and were obtained using a novel optimization approach involving relaxed potential energy surface scans as training targets. The resulting ReaxFF parametrization shows good transferability, as demonstrated on two independent ab initio validation sets. While this first part of our two-paper series focuses on force field parametrization, we apply our parameters to the simulation of chlorinated dibenzofuran formation and decomposition processes in Part II.

Hydrogen-bonding interactions involving the Imidazol-2‑ylidene and its Heavy-atom analogues

The hydrogen-bonded complexes formed between the imidazol-2‑ylidene and its heavier congeners C2H4N2T: (T = C, Si, Ge, Sn, Pb) and the three selected electron acceptors (HF, HCN and C2H2) have been optimized at the aug-cc-pVTZ level, and the nature of these complexes has been investigated by natural bond orbital (NBO), atoms in molecules (AIM) and energy decomposition analyses. The complexes can be classified into type-A structure and type-B structure according to the location of the electron acceptors. The electron acceptors are around T atoms of C2H4N2T: for the type-A complexes, and the electron acceptors are above the five-membered ring (π-system) of C2H4N2T: for the type-B complexes. The electron-donating ability of T atoms becomes weaker, and that of π-systems becomes stronger when T atoms become heavier for C2H4N2T:, which is consistent with the molecular electrostatic potentials (MEP) maps of C2H4N2T:. For a given C2H4N2T:, the Eint values of the type-A complexes go in the order HF > HCN > C2H2, and the Eint values of the type-B complexes go in the order HF ≈ HCN > C2H2. The contribution of electrostatic energy to the interaction energy of complexes becomes smaller for the type-A complexes when the T atoms become heavier. The interaction energies are dominated by the electrostatic energies for all the type-B complexes involving HF, and the interaction energies are dominated by the dispersion energies for most type-B complexes involving HCN and C2H2. The relaxed potential energy surface scans were performed for some selected complexes involving HF and HCN to examine the difference in binding behavior between HF and HCN.

Thermodynamics and Reaction Mechanisms for Decomposition of a Simple Protonated Tripeptide, H+GGA: From H+GGG to H+GAG to H+GGA.

We present a thorough characterization of fragmentations observed in threshold collision-induced dissociation (TCID) experiments of protonated glycylglycylalanine (H+GGA) with Xe using a guided ion beam tandem mass spectrometer. Kinetic energy dependent cross sections for nine ionic products were obtained and analyzed to provide 0 K barriers for the five primary products, [b2]+, [y1 + 2H]+, [b3]+, [y2 + 2H]+, and [a1]+; and four secondary products, [a2]+, [a3]+, high-energy [y1 + 2H]+, and CH3CHNH2+, after accounting for multiple ion-molecule collisions, the internal energy of reactant ions, unimolecular decay rates, competition between channels, and sequential dissociations. Relaxed potential energy surface scans performed at the B3LYP-GD3BJ/6-311+G(d,p) level of theory are used to identify transition states (TSs) and intermediates of the five primary and three secondary products (with the mechanism of the other secondary product previously established). Geometry optimizations and single point energy calculations of reactants, products, intermediates, and TSs were performed at several levels of theory. These theoretical energies are compared with experimental threshold energies and found to give reasonable agreement, with B3LYP-GD3BJ and M06-2X levels of theory performing slightly better than MP2 and better than B3LYP. The results obtained here are compared with previous results for decomposition of H+GGG and H+GAG to probe the effect of changing the amino acid sequence. Methylation in H+GGA has a significant effect on the competition between the primary sequence products, [b2]+ and [y1 + 2H]+, suppressing the [b2]+ cross section by raising its threshold energy, while enhancing that of [y1 + 2H]+ by lowering its threshold energy.

Higher-Energy Hexafluoroisopropanol···Water Isomer and Its Large Amplitude Motions: Rotational Spectra and DFT Calculations.

Rotational spectra of the 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)···water complex were measured using a chirped pulse Fourier-transform microwave spectrometer. The spectral analyses, aided by density functional theory calculations, reveal two HFIP···water isomers: one previously reported, trans HFIP (HFIPt)···water (Phys. Chem. Chem. Phys. 2015, 119, 5650-5657), and a new isomer, gauche HFIP (HFIPg)···water. To confirm the identity of the new isomer, rotational spectra of seven of its deuterated species were also measured and analyzed. Both the experimental and theoretical pieces of evidence indicate that the intermolecular interaction with water preferentially stabilizes the HFIPg monomer configuration over the global minimum configuration, HFIPt. The relative energy difference between these monomeric forms is 4.1 kJ mol-1 and decreases to 2.5 kJ mol-1 in the respective monohydrates at the B3LYP-D3(BJ)/def2-QZVP level of theory. Both rigid and relaxed potential energy surface scans were carried out to gain insights into the large-amplitude water motions in HFIPg···water. The nonobservation of a water tunneling splitting in HFIPt···water has been explained to be a result of a barrier-less (after zero-point-energy correction) pathway for the water motion, whereas in HFIPg···water, a relatively large water tunneling barrier was identified as the cause of barely resolved water tunneling splittings. Noncovalent interaction and quantum theory of atoms and molecule analyses were used to evaluate the changes in HFIPg···water when going from the minimum to the transition state in terms of attractive interactions such as the OH···H and OH···F contacts. The effect of fluorination is discussed by comparing the vastly different binding topologies of isopropanol···water and HFIP···water.

Theoretical study on pentiptycene molecular brake: photoinduced isomerization and photoinduced electron transfer.

The isomerization of the double bond plays an important role in the braking and de-braking of the light-controlled molecular brake. Therefore, the pentiptycene-type (Pp-type) light-controlled molecular brake system ((E)- and (Z)-4'-pentiptycyl vinyl-[1,1'-biphenyl]-4-carbonitrile) containing the C = C double bond was theoretically studied. Combining the 6-31G(d) basis set, the ωB97XD functional with dispersion correction was applied to implement the (E)-configuration and (Z)-configuration initial optimization. Next, using the 6-311G(d,p) basis set, the relaxed potential energy surface scans of the rotation angle were operated, and then the optimization calculations of the transition states at the extremum high points. Analyzing the stagnation points and the rotational transition states on the potential energy profiles, the rotation mechanism and basic energy parameters of the molecular brake were obtained. Then, the DFT computations at ground states and the TD-DFT computations of vertical excitation energy were put into practice at the accuracy of the def-TZVP basis set for the two configurations, and using the natural transition orbital (NTO) analyses combining the excitation energies and absorption spectra, the electronic transition characteristics and electron transfer properties of light-controlled molecular brake were studied. Afterwards, in order to investigate the photoinduced isomerization reaction, the C = C double bond was scanned on the relaxed potential energy surface, and the intermediates of the isomerization reaction were searched and analyzed; thus, the braking mechanism of the light-controlled molecular brake was proposed.

2‐Hydroxy‐5‐nitropyridine and 5‐nitro‐2‐pyridone: Tautomerism, infrared, Raman, and NMR spectral interpretations, normal coordinate analysis, and DFT calculations

AbstractRaman (3700–50 cm−1) and infrared (IR) (4000–230 cm−1) spectra of 2‐hydroxy‐5‐nitropyridine (HNP; C5H4N2O3) have been recorded in the solid phase in addition to 1H, 13C, and 15N nuclear magnetic resonance (NMR) spectra of the sample in dimethyl sulfoxide‐d6 (DMSO‐d6). Initially, keto and enol tautomeric forms were proposed owing to proton transfer from the hydroxyl group to pyridine nitrogen atom. Quantum mechanical calculations based on density functional theory (DFT; B3LYP, ωB97XD, and mPW1PW91) were carried out using 6‐31G(d) and 6‐311++G(d,p) basis sets favoring keto‐NPO, 5‐nitro‐2‐pyridone, tautomer by ~0.857–1.345 kcal/mol with minor enol‐HNP in the gas phase. Moreover, 1H, 13C, and 15N NMR chemical shifts were predicted using gauge‐invariant atomic orbital‐DFT calculation at 6‐311++G(d,p) basis set using integral equation formalism of the polarization continuum solvation model including solvent effects. The calculated chemical shifts and spin–spin coupling constants (JHH) for keto tautomer better resemble those experimentally observed rather than the enol form. The observed IR/Raman bands were assigned quantitatively to their normal modes based on the calculated vibrational frequencies, force constants in internal coordinates, normal coordinate analysis, and potential energy distributions. Finally, the nitro and hydroxyl barriers to internal rotations were predicted via a relaxed potential energy surface scan using B3LYP/6‐311++G(d,p) calculations. The results are reported herein and compared with similar molecules whenever appropriate.

Theoretical research of covalent and controllable molecular brake based on 9-triptycene

In order to understand the mechanism of molecular brake more clearly, the brake system (3-(9-triptycyl)-6,6′-dimethoxy-2,2′-bipyridine) was studied in computational methods using the density functional theory (DFT). The M06-2X functional is used to obtain various parameters of the molecules. The relaxed potential energy surface scans were performed to obtain the minimum energy profiles (MEPs). The ground state and transition state during rotation are accurately found, and then a lot of thermodynamic data are obtained and analyzed. For the purpose of proving the occurrence of rotation motion, the transition state theory (TST) was used to investigate the kinetic properties. The Boltzmann statistics was used to analyze the conformer populations, which can also explain some thermodynamic properties of molecular brake. Based on these results, the braking mechanism was pointed out: The rotation of triptycene (Tp) rotor was suppress by a chemical method, to terminate the motion completely, the temperature was lowered appropriately. The molecular dynamics (MD) simulations of the ground states and transition states were also carried out to further verify the rationality of the mechanism. Comparing with the experimental results, the conclusions were figured out.

Intermolecular Interactions Involving Heavy Alkenes H2Si=TH2 (T = C, Si, Ge, Sn, Pb) with H2O and HCl: Tetrel Bond and Hydrogen Bond.

The intermolecular interactions between the heavy alkenes H2Si=TH2 (T = C, Si, Ge, Sn, Pb) and H2O or HCl have been explored at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level. The various hydrogen bond (HB) and tetrel bond (TB) complexes can be located on the basis of molecular electrostatic potential maps of the isolated monomers. The competition between TB and HB interactions has been investigated through the relaxed potential energy surface scan. The results indicate that the HB complexes become more and more unstable relative to the TB complexes with the increase of the T atomic number, and cannot even retain as a minimum in some cases, for H2Si=TH2···H2O systems. In contrast, the HB complexes are generally more stable than TB complexes, and the TB complexes exhibit rather weak binding strength, for H2Si=TH2···HCl systems. The majority of the TB complexes formed between H2Si=TH2 and H2O possesses very strong binding strength with covalent characteristics. The noncovalent TB complexes can be divided into two types on the basis of the orbital interactions: π-hole complexes, with binding angles ranging from 91 to 111°, and hybrid σ/π-hole complexes, with binding angles ranging from 130 to 165°. The interplay between different molecular interactions has been explored, and an interesting result is that the covalent TB interaction is significantly abated and becomes noncovalent because of the competitive effect.

Synthesis, Conformational Analysis, Infrared, Raman and UV-Visible Spectra of Novel Schiff Bases compiled with DFT Calculations.

Two novel Schiff bases named, 2-((2-Hydroxybenzylidene)amino)-4,5,6,7- tetrahydrobenzo[b] thiophene-3-carbonitrile (BESB1) and 2-((Furan-2-ylmethylene)amino)-4,5,6, 7-tetrahydro-benzo[b]thiophene-3-carbonitrile (BESB2) were synthesized. The structures were characterized based on CHN elemental analysis, mid-infrared (400- 4000 cm-1), Raman (100-4000 cm-1), 1H NMR, mass and UV-Vis spectroscopic measurements. In addition, quantum mechanical calculations using DFT-B3LYP method at 6-31G(d) basis set were carried out for both Schiff bases. Initially, we have carried out complete geometry optimizations followed by frequency calculations for the proposed conformational isomers; BESB1 (A-E) and BESB2 (F-J) based on the orientations of both CN and OH groups against the azomethine lonepair (NLP) in addition to the 3D assumption. The computational outcomes favor conformer A for BESB1 in which the C≡N and OH moieties are cis towards the NLP while conformer G is preferred for BESB2 (the C≡N/furan-O are cis/trans towards the NLP) which was found consistent with the results of relaxed potential energy surface scan. Aided by normal coordinate analysis of the Cartesian coordinate displacements, we have suggested reliable vibrational assignments for all observed IR and Raman bands. Moreover, the electronic absorption spectra for the favored conformers were predicted in DMSO solution using TD-B3LYP/6-31G(d) calculations. Similarly, the 1H NMR chemical shifts were also estimated using GIAO approach implementing PCM including solvent effects (DMSO-d6). Proper interpretations of the observed electronic transition, chemical shifts, IR and Raman bands were presented in this study.

Characterization of 2 trifluormethyl 4 nitroaniline by Spectroscopic and Quantum Mechanical Methods

Bu çalışmada, 2-triflorometil-4-nitroanilin bileşiğinin yapısal, titreşimsel ve elektronik özellikleri deneysel ve hesaplamalı yöntemler kullanılarak elde edilmiştir. Tek kristal X-ışını kırınım çalışmalarından elde edilen moleküler yapı ile optimize edilen moleküler yapı karşılaştırıldı ve bağ uzunlukları için RMS değeri 0.07 Å olarak hesaplandı. NH2 ve CF3 grupları arasındaki etkileşimi incelemek için üç-boyutlu serbest potansiyel enerji yüzeyi taraması yapıldı. DFT/B3LYP/6-311++G(d,p) yöntemi ile yapılan teorik hesaplamaların yardımıyla deneysel FT-IR, 1H ve 13C NMR, UV spektrumları analiz edildi. Doğrusal olmayan optik özellikleri ve sınır moleküler orbitalleri sonraki çalışmalar için verildi.

Thiadiazole-2-Thiol-5-Thione and 2,5-Dimercapto-1,3,4-Thiadiazol Tautomerism, Conformational Stability, Vibrational Assignments, Inhibitor Efficiency and Quantum Chemical Calculations

Abstract Raman (3700–100 cm−1) and infrared (4000–400 cm−1) spectra of 2,5-Dimercapto-1,3,4-thiadiazol (DMTD) were recorded in the solid phase. Six structures (1–6) were initially proposed for DMTD as a result of thiol-thione tautomerism and internal rotation(s) of thiol group(s) around the C–S bond. Quantum chemical calculations were carried out for an isolated molecule (1–6) using density functional theory (B3LYP) and ab initio MP2(full) methods utilizing 6-31G(d) and 6-311++G(d,p) basis sets which favor thiol-thione tautomerism (structure 4). Relaxed potential energy surface scans of structure 4 revealed an additional conformer (the thiol group is out-of-plane, structure 7) using the aforementioned methods at 6-311++G(d,p) basis set. For additional verification, plane-wave solid state calculations were carried out at PW91 and PBEsol came out in favor of conformer 7. This is in agreement with the computed/observed SH in-plane bending of S-7 (959/941 cm−1) rather than the one estimated at (880 cm−1) for S-4. Moreover, the observed split IR/Raman bands were found consistent with solid state calculated frequencies of S-7 assuming two molecules per unit cell bonded via H-bonding intermolecular interactions. Aided by vibrational frequency calculations, normal coordinate analysis, force constants and potential energy distributions (PEDs), a complete vibrational assignment for the observed IR and Raman bands is proposed herein. Furthermore, we have estimated the frontier molecular orbitals and atomic charges to account for the corrosion inhibition efficiency of DMTD along with its binding sites to the metal surface. Our results are discussed herein and compared to similar molecules whenever appropriate.

Thermodynamics and Reaction Mechanisms for Decomposition of a Simple Protonated Tripeptide, H+GAG: a Guided Ion Beam and Computational Study.

We present a thorough characterization of fragmentations observed in threshold collision-induced dissociation (TCID) experiments of protonated glycylalanylglycine (H+GAG) with Xe using a guided ion beam tandem mass spectrometer. Kinetic energy dependent cross sections for nine ionic products were observed and analyzed to provide 0K barriers for the six primary products: [b2]+, [y1 + 2H]+, [b3]+, CO loss, [y2 + 2H]+, and [a1]+; and three secondary products: [a2]+, [a3]+, and CH3CHNH2+, after accounting for multiple ion-molecule collisions, internal energy of reactant ions, unimolecular decay rates, competition between channels, and sequential dissociations. Relaxed potential energy surface scans performed at the B3LYP-GD3BJ/6-311+G(d,p) level of theory are used to identify transition states (TSs) and intermediates of the six primary and one secondary products (where the other two secondary products have mechanisms previously established). Geometry optimizations and single-point energy calculations were performed at several levels of theory. These theoretical energies are compared with experimental threshold energies and are found to give reasonably good agreement, with B3LYP-GD3BJ and M06-2X levels of theory performing better than other levels. The results obtained here are also compared with previous results for decomposition of H+GGG. The primary difference observed is a lowering of the threshold for the [b2]+ product ion and a concomitant suppression of the directly competing [y1 + 2H]+ product, the result of specific methylation of the [b2]+ product ion.

Hydration of l-glycylvaline and l-glycylvalylglycine zwitterions: Structural and vibrational studies using DFT method

Solvent effects on the structural and vibrational features of l-glycylvaline (L-GV) and l-glycylvalylglycine (L-GVG) in zwitterionic forms have been performed by means of DFT method. Relaxed potential energy surface scans (RPES) performed at B3LYP/6–31++G(d) level were used to map the reaction coordinate surfaces and to identify the geometries corresponding to the minima energy. Explicit solvation model, where L-GV and L-GVG are respectively surrounded by 9 and 11 water molecules interacting with H-donor and H-acceptor sites, as well as the different hybrid solvation models of solvation (explicit/COSMO, explicit/PCM and explicit/CPCM) allowed to analyze the hydration effects. Those number of water molecules are sufficient to fully hydrate carboxyl(CtOO-), amine (NtH3+) and amide (NH, C=O) groups. Harmonic vibrational modes calculated after geometry optimization on each solvated complex are performed at B3LYP/6–31++g(d) and PBE0/6–31++g(d) methods and a post-processing treatment enable us to assign the vibrational modes of LGV and L-GVG. The frequencies of the assigned modes obtained using B3LYP in explicit/COSMO are in good agreement with available IR and Raman values than those found in both explicit/PCM and explicit/CPCM which proved to be very close.

Synthesis of 3,4-Biaryl-2,5-Dichlorothiophene through Suzuki Cross-Coupling and Theoretical Exploration of Their Potential Applications as Nonlinear Optical Materials

We report herein the efficient one-pot synthesis of 3,4-biaryl-2,5-dichlorothiophene derivatives (2a–2i) via a palladium-catalyzed Suzuki cross-coupling reaction. A series of thiophene derivatives were synthesized, starting from 3,4-dibromo-2,5-dichlorothiophene (1) and various arylboronic acids using Pd(PPh3)4 and K3PO4 with moderate to good yields. For further insights about the structure and property relationship, density functional theory (DFT) calculations were performed. A relaxed potential energy surface (PES) scan was performed to locate the minimum energy structure. A frontier molecular orbitals analysis was performed to explain the reactivity of all synthesized derivatives. As the synthesized derivatives had extended conjugations, therefore the first hyperpolarizability (βo) was calculated to investigate their potential as non-linear optical (NLO) materials and significant βo values were found for the 2b and 2g derivatives.

Samarium cation (Sm+) reactions with H2, D2, and HD: SmH+ bond energy and mechanistic insights from guided ion beam and theoretical studies.

Guided ion beam tandem mass spectrometry is used to study the reaction of the lanthanide samarium cation (Sm+) with H2 and its isotopologues (HD and D2) as a function of collision energy. Modeling the resulting energy dependent product ion cross sections from these endothermic reactions yields 2.03 ± 0.06 eV (two standard deviations) for the 0 K bond dissociation energy of SmH+. Quantum chemical calculations are performed to determine stabilities of the ground and low-energy states of SmH+ for comparison with the experimentally measured thermochemistry. The calculations generally overestimate the SmH+ bond energy, but a better agreement between experiment and theory is achieved after correcting for spin-orbit energy contributions, with coupled-cluster with single, double and perturbative triple excitations/complete basis set [CCSD(T)/CBS] results reproducing the experiment well. In the HD reaction, the SmH+ product is observed to be favored over the SmD+ by about a factor of three, indicating that the reaction proceeds via a direct mechanism with short-lived intermediates. This is consistent with quantum chemical calculations of relaxed potential energy surface scans of SmH2 +, which show that there is no strongly bound dihydride intermediate. The reactivity and hydride bond energy of Sm+, which has a valence electron configuration typical of most lanthanides, are compared with previous results for the lanthanide cations La+, Gd+, and Lu+, which exhibit configurations more closely related to the group 3 metal cations, Sc+ and Y+. Periodic trends across the lanthanide series and insights into the role of the electronic configurations on hydride bond strength and reactivity with H2 are discussed.

Order and disorder in (E)-[1-(biphenyl-4-yl)ethylidene]hydrazine: a structural, spectroscopic and theoretical study.

An unexpected global disorder (co-existing rotational disorder and glide disorder) has been observed during an X-ray investigation of the crystal structure of (E)-[1-(biphenyl-4-yl)ethylidene]hydrazine, C14H14N2, at room temperature. When the temperature decreases to 273 K, the disorder disappears, but the quality of the data set is low. The diffraction data were collected again at 110 K. Differential scanning calorimetry (DSC) analysis and polarizing-microscopy experiments, as well as a fourth set of single-crystal data collected at 283 K, proved that the order-disorder transformation occurs continuously. The analyses of these crystal structures and full-range relaxed potential energy surface scans showed that this kind of global disorder is not very difficult to achieve inside the crystal. Experimental and theoretical studies via UV-Vis and fluorescence spectra impart an understanding on the prediction methods of optical properties, which are essential for the rational design of biphenyl-based materials with pre-defined properties.

2,2′‐Azobispyridine in Phosphorus Coordination Chemistry: A New Approach to 1,2,4,3‐Triazaphosphole Derivatives

Oxidative addition of 2,2′‐azobispyridine (abpy) to PCl3 in CH2Cl2 or THF gave the 1:1 addition product, containing phosphorus in high oxidation state (+5) and a reduced form of the ligand. 2,2′‐Hydrazobispyridine (hbpy) was prepared by reduction of abpy with hydrazine‐hydrate in 63 % yield. Interaction of hbpy with PCl3 in the presence of triethylamine gave (abpy)2–PCl (2) in 25 % preparative yield. A similar reaction of hbby with (Et2N)2PCl afforded (abpy)2–PNEt2 (4) in 89 % yield. Compound 4 after work‐up with PCl3 or PBr3 gave 2 and (abpy)2–PBr (6) respectively in high yields. Diethylamino‐derivative 4 formed (κ2‐N,N) adduct with SiCl4 7 (coordination by Py and azo‐functions), while the chloro‐derivative 2 did not. Reaction of 2 with PCl5 is accompanied with liberation of PCl3 and formation of spirocyclic ate complex [(abpy)2–2P]+PCl6–. All structurally characterized compounds demonstrated short distances between pyridyl nitrogen and the phosphorus atom. However, the QTAIM analysis did not reveal the presence of appropriate bond critical points (3, –1) for the intramolecular noncovalent interactions N···P in 2, 4, and 6. We theoretically estimated values of the rotation barriers for the pyridyl and Et2N moieties in 4 using the relaxed potential energy surface scan at the B3LYP/6‐31G(d) level of theory. The values of rotation barriers are very close to each other, viz. 13.2 (pyridyl) and 13.0 (Et2N) kcal/mol.

Quantum Chemistry Study on the Extraction of Trivalent Lanthanide Series by Cyanex301: Insights from Formation of Inner- and Outer-Sphere Complexes.

The extraction of lanthanide series by Cyanex301, i.e., bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301), has been modeled by density functional theory calculation, taking into account the formation of both inner- and outer-sphere complexes. The inner-sphere complex Ln(C301)3 and the outer-sphere complex Ln(H2O)9(C301)3 are optimized, followed by the analysis of interaction energy, bond length, Laplacian bond orders, and Mulliken populations. The covalency degree increases in Ln–S and Ln–O bonds in the inner- and outer-sphere complexes, respectively, as the lanthanide series is traversed. Mulliken population analysis indicates the important role of the 5d-orbital participation in bonding in the formation of inner- and outer-sphere complexes. Two thermodynamic cycles regarding the formation of inner- and outer-sphere complexes are established to calculate the extraction Gibbs free energies (ΔGextr), and relaxed potential energy surface scan is utilized to model the kinetic complexation of C301 anion with hydrated metal ions. Light lanthanides can form both inner- and outer-sphere complexes, whereas heavy lanthanides only form outer-sphere complexes in biphasic extraction. After adopting the data of forming inner-sphere complex for light Ln(III) and that of forming outer-sphere complexes for heavy Ln(III), the trend of the calculated −ΔGextr agrees very well with that of the experimental distribution ratios on crossing the Ln(III) series. Results from this work help to theoretically understand the extraction behavior of Cyanex301 with respect to different Ln(III).

Synthesis, crystal structure and computational studies of a new Schiff base compound: (E)-4-bromo-2-eth-oxy-6-{[(2-meth-oxy-phen-yl)imino]meth-yl}phenol.

The title compound, C16H16BrNO3, which shows enol-imine tautomerism, crystallizes in the monoclinic P21/c space group. All non-H atoms of the mol-ecule are nearly coplanar, with a maximum deviation of 0.274 (3) Å. In the crystal, mol-ecules are held together by weak C-H⋯O, π-π and C-H⋯π inter-actions. The E/Z isomerism and enol/keto tautomerism energy barriers of the compound have been calculated by relaxed potential energy surface scan calculations with DFT methods. To observe the changes in the aromatic ring, HOMA aromaticity indexes were calculated during the scan process. Total energy and HOMA change curves were obtained to visualize results of the scan calculations.