Orbital Coefficients Research Articles

Substituent effects in the intramolecular photoredox reactions of benzophenones in aqueous solution

A number of α-hydroxy-3-benzylbenzophenones 7–11 have been synthesized for the purpose of studying the effect of a phenyl substituent on the intramolecular photoredox reaction of 3-(hydroxymethyl)benzophenone (5) discovered in our laboratory. This latter compound was found to undergo a unimolecular (formal) intramolecular redox reaction upon photolysis in aqueous acid that results in clean reduction of the benzophenone ketone (to secondary alcohol) and oxidation of the alcohol to aldehyde. Three of the phenyl-substituted compounds with simple phenyl (7), p-methylphenyl (8), and p-methoxyphenyl (9) were found to undergo the acid-catalyzed intramolecular photoredox reaction with the observation that 9 also undergoes a residual photoredox reaction that is not acid-mediated and may involve initial photoinduced electron transfer, which is supported by LFP data. The m-methoxyphenyl (10) compound did not undergo the reaction. The trend in observed relative reactivity may be partially rationalized by examining changes in molecular orbital coefficients observed in the calculated HOMOs and LUMOs. The photoredox reaction has also been applied twice in succession in a single compound 11, demonstrating that the photoredox reaction may be useful for sequential photoredox reactions in a multifunctional compound.Key words: intramolecular photoredox, acid catalysis, meta effect, benzophenone photochemistry.

Unravelling the Origin of Intermolecular Interactions Using Absolutely Localized Molecular Orbitals

An energy decomposition analysis (EDA) method is proposed to isolate physically relevant components of the total intermolecular interaction energies such as the contribution from interacting frozen monomer densities, the energy lowering due to polarization of the densities, and the further energy lowering due to charge-transfer effects. This method is conceptually similar to existing EDA methods such as Morokuma analysis but includes several important new features. The first is a fully self-consistent treatment of the energy lowering due to polarization, which is evaluated by a self-consistent field calculation in which the molecular orbital coefficients are constrained to be block-diagonal (absolutely localized) in the interacting molecules to prohibit charge transfer. The second new feature is the ability to separate forward and back-donation in the charge-transfer energy term using a perturbative approximation starting from the optimized block-diagonal reference. The newly proposed EDA method is used to understand the fundamental aspects of intermolecular interactions such as the degree of covalency in the hydrogen bonding in water and the contributions of forward and back-donation in synergic bonding in metal complexes. Additionally, it is demonstrated that this method can be used to identify the factors controlling the interaction of the molecular hydrogen with open metal centers in potential hydrogen storage materials and the interaction of methane with rhenium complexes.

Lagrangian approach to molecular vibrational Raman intensities using time-dependent hybrid density functional theory

The authors propose a new route to vibrational Raman intensities based on analytical derivatives of a fully variational polarizability Lagrangian. The Lagrangian is constructed to recover the negative frequency-dependent polarizability of time-dependent Hartree-Fock or adiabatic (hybrid) density functional theory at its stationary point. By virtue of the variational principle, first-order polarizability derivatives can be computed without using derivative molecular orbital coefficients. As a result, the intensities of all Raman-active modes within the double harmonic approximation are obtained at approximately the same cost as the frequency-dependent polarizability itself. This corresponds to a reduction of the scaling of computational expense by one power of the system size compared to a force constant calculation and to previous implementations. Since the Raman intensity calculation is independent of the harmonic force constant calculation more, computationally demanding density functionals or basis sets may be used to compute the polarizability gradient without much affecting the total time required to compute a Raman spectrum. As illustrated for fullerene C60, the present approach considerably extends the domain of molecular vibrational Raman calculations at the (hybrid) density functional level. The accuracy of absolute and relative Raman intensities of benzene obtained using the PBE0 hybrid functional is assessed by comparison with experiment.

Synthesis, characterization, crystal structure and DFT studies on 1-acetyl-3-(2,4-dichloro-5-fluoro-phenyl)-5-phenyl-pyrazoline

The title compound, 1-acetyl-3-(2,4-dichloro-5-fluoro-phenyl)-5-phenyl-pyrazoline, has been synthesized and characterized by elemental analysis, IR, UV–vis and X-ray single crystal diffraction. Density functional (DFT) calculations have been carried out for the title compound by using B3LYP method at 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. Predicted vibrational frequencies have been assigned and compared with experimental IR spectra and they are supported each other. The theoretical electronic absorption spectra have been calculated by using TD-DFT method. Molecular orbital coefficients analyses suggest that the above electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated, revealing the correlations between C p , m 0 , S m 0 , H m 0 and temperatures.

An EPR and optical absorption study of VO 2+ ions in di-ammonium hydrogen citrate [(NH 4) 2C 6H 6O 7] single crystals

Single crystal and powder EPR studies of VO 2+ doped di-ammonium hydrogen citrate [(NH 4) 2C 6H 6O 7] are carried out at room temperature. The angular variation of the EPR spectra show three different VO 2+ complexes that are located in different chemical environment, and each environment contains two magnetically inequivalent VO 2+ sites in distinct orientations occupying substitutional positions in the lattice. Crystalline field around the VO 2+ ion is nearly axial. The optical absorption spectrum shows two bands centred at 16,949 and 12,345 cm −1. Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.

PSI3: An open‐source Ab Initio electronic structure package

PSI3 is a program system and development platform for ab initio molecular electronic structure computations. The package includes mature programming interfaces for parsing user input, accessing commonly used data such as basis-set information or molecular orbital coefficients, and retrieving and storing binary data (with no software limitations on file sizes or file-system-sizes), especially multi-index quantities such as electron repulsion integrals. This platform is useful for the rapid implementation of both standard quantum chemical methods, as well as the development of new models. Features that have already been implemented include Hartree-Fock, multiconfigurational self-consistent-field, second-order Møller-Plesset perturbation theory, coupled cluster, and configuration interaction wave functions. Distinctive capabilities include the ability to employ Gaussian basis functions with arbitrary angular momentum levels; linear R12 second-order perturbation theory; coupled cluster frequency-dependent response properties, including dipole polarizabilities and optical rotation; and diagonal Born-Oppenheimer corrections with correlated wave functions. This article describes the programming infrastructure and main features of the package. PSI3 is available free of charge through the open-source, GNU General Public License.

Synthesis, structure, spectroscopic and electrochemical properties of (2-amino-4-methylpyrimidine)-(pyridine-2,6-dicarboxylato)copper(II) monohydrate

The (2-amino-4-methylpyrimidine)-(pyridine-2,6-dicarboxylato)copper(II) monohydrate complex was synthesized and characterized by spectroscopic (IR, UV/Vis, EPR), thermal (TG/DTA) and electrochemical methods. X-ray structural analysis of the title complex revealed that the copper ion can be considered to have two coordination spheres. In the first coordination sphere the copper ion forms distorted square-planar geometry with trans-N 2O 2 donor set, and also the metal ion is weakly bonded to the amino-nitrogen in the layer over and to the carboxylic oxygen in the layer underneath in the second coordination sphere. The second coordination environment on the copper ion is attributed to pseudo octahedron. The powder EPR spectra of Cu(II) complex at room and liquid nitrogen temperature were recorded. The calculated g and A parameters have indicated that the paramagnetic centre is axially symmetric. The molecular orbital bond coefficients of the Cu(II) ion in d 9 state is also calculated by using EPR and optical absorption parameters. The cyclic voltammogram of the title complex investigated in DMSO (dimethylsulfoxide) solution exhibits only metal centered electroactivity in the potential range −1.25 to 1.5 V versus Ag/AgCl reference electrode.

Investigations on the superhyperfine parameters for Cr3+ in the fluorides

The superhyperfine parameters A′ and B′ for Cr3+ ions in K2NaGaF6, K2NaCrF6, KMgF3 and CsCdF3 are theoretically studied from the cluster approach. In the present treatments, the orbital admixture coefficients and the unpaired spin densities in 2s, \( 2{\text{p}}_{\sigma } \) and \( 2{\text{p}}_{\pi } \)2 fluorine orbitals are obtained in a uniform way. The experimental A′ and B′ are reasonably explained, and the unpaired spin densities for the 2s, 2pσ and 2pπ orbitals of the ligand F− are also compared with those in the previous works.

EPR, optical, infrared and Raman studies of VO 2+ ions in polyvinylalcohol films

Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been carried out on vanadyl ions doped in polyvinylalcohol (PVA) films. The spin-Hamiltonian parameters ( g and A) and the molecular orbital coefficients ( β 2 * 2 and k) have been evaluated. The values of spin-Hamiltonian parameters confirm that the vanadyl ions are present in PVA films as VO 2+ molecular ions in an octahedral site with a tetragonal compression (C 4v). The temperature variation EPR studies reveal that the variation of number of spins with temperature is in accordance with Boltzmann law. It is interesting to observe that the variation of susceptibility with temperature obeys Curie–Weiss law. The FT-IR and FT-Raman spectrum exhibits few bands, which are attributed to O–H, C–H, C C and C–O groups of stretching and bending vibrations. The optical absorption spectrum exhibits two bands, which are assigned to 2B 2 g → 2B 1 g and 2B 2 g → 2E g transitions in the decreasing order of energy.

Regioselectivity in the 1,3-Dipolar Cycloaddition Reactions of Nitrile Oxides and Organic Azides with Bromocarbazole-1,4-diones

The effect exerted by the presence of a bromine atom in 2 or 3 position of a carbazole-1,4-dione on the regiocontrol of 1,3-dipolar cycloaddition reactions with nitrile oxides and organic azides was investigated. Comparison with the results obtained with 2,3-unsubstituted-carbazole-l,4-dione shows that bromine substituents on para-carbazolequinones effectively orient the 1,3-dipolar cycloadditions. The regiochemistry observed may be explained by the orienting effect of the bromine atom independently of the values of the orbital coefficients.

Synthesis, structure, spectroscopic and electrochemical properties of bis(histamine-saccharinate) copper(II) complex

Crystal structure of [Cu(hsm) 2(sac) 2] (hsm is histamine and sac is saccharinate) complex has been determined by X-ray diffraction analyses and its magnetic environment has been identified by electron paramagnetic resonance (EPR) technique. The title complex crystallizes in the monoclinic system, space group P 21/ c with a = 7.4282(4), b = 22.5034(16), c = 8.3300(5) Å, β = 106.227(4)°, V = 1336.98(14) Å 3, and Z = 2. The structure consist of discrete [Cu(hsm) 2(sac) 2] molecules in which the copper ion is centrosymmetrically coordinated by two histamine ligands forming an equatorial plane [Cu–N hsm = 2.024(2) and Cu–N hsm = 2.0338(18) Å]. Two N atoms from the saccharinate ligands coordinate on the elongated axial positions with Cu–N sac being 2.609(5) Å. The complex is also characterized by spectroscopic (IR, UV/Vis) and thermal (TG, and TDA) methods. The cyclic voltammogram of the title complex investigated in DMSO (dimethylsulfoxide) solution exhibits only metal centred electroactivity in the potential range – 1.25–1.5 V versus Ag/AgCl reference electrode. The molecular orbital bond coefficients of Cu(II) ion in d 9 state is also calculated by using EPR and optical absorption parameters.

Molecular structural identification of Cu(II) ion in Diaquamalonatozinc(II): Anisotropic behavior with low hyperfine coupling constant

Single crystal EPR studies on Cu(II) doped Diaquamalonatozinc(II) are carried out at room temperature to identify the local structure of the host ion. Angular variation of copper hyperfine lines in the three orthogonal planes shows the presence of a single site in an interstitial position and the location has been identified. The spin-Hamiltonian parameters calculated from the spectra are: g 11 = 2.077, g 22 = 2.087, g 33 = 2.442; A 11 = 1.83, A 22 = 2.88; A 33 = 14.74 mT. A slightly lower parallel value noticed for copper nucleus has been explained by considering a small admixture of ground state with the excited state. The optical, infra-red and EPR data have been collaborated to obtain various admixture and molecular orbital coefficients.

Effect of transannular interaction on the redox-potentials in a series of bicyclic quinones

BackgroundBetter understanding of the transannular influence of a substituent on the redox-potentials of bicyclo[2.2.2]octane-derived quinones will help in the design of new compounds with controlled biological activity. However, attempts to directly relate the reduction potentials of substituted triptycene-quinones to the electronic effects of substituents are often unsuccessful.ResultsFirst and second redox-potentials of a series of bicyclic quinones are compared to computed energies of their LUMO, LUMO+1, and energies of reduction. Transannular influence of substituent on the redox-potentials is rationalized in terms of MO theory. Acetoxy-substituents in the 5,8-positions of the triptycene-quinone system selectively destabilize the product of the two-electron reduction.ConclusionWe have shown that first redox-potentials of substituted bicyclic quinones correlate with their calculated LUMO energies and the energies of reduction. The second redox-potentials correlate with calculated LUMO+1 energies. As opposed to the LUMO orbitals, the LUMO+1 orbital coefficients are weighted significantly on the non-quinone part of the bicyclic system. This accounts for: (1) significantly larger substituent effect on the second redox-potentials, than on the first redox-potentials; (2) lack of stability of the product of two electron reduction of 5,8-diacetoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4-dione 5.

LOCALLY PROJECTED MOLECULAR ORBITAL THEORY FOR MOLECULAR INTERACTION WITH A HIGH-SPIN OPEN-SHELL MOLECULE

Locally projected molecular orbital method for molecular interactions is extended to a cluster consisting of a high-spin open-shell molecule and many closed-shell molecules. While deriving the equations, the Hartee–Fock–Roothaan equation without the orthonormal condition is obtained. The stationary conditions for molecular orbitals are expressed in a form of a generalized Brillouin condition. To obtain the molecular orbital coefficient matrix, which satisfies the stationary condition, a single Fock operator form is presented. For the locally projected molecular orbitals for the open-shell cluster, the working matrix representaion is given.

Synthesis, crystal structure, Cu 2+ doped EPR and voltammetric studies of bis[ N-(2-hydroxyethyl)ethylenediamine]zinc(II) squarate monohydrate

Crystal structure of [Zn(hydet-en) 2]·C 4O 4·H 2O (ZHES) (hydet-en is N-(2-hydroxyethyl)ethylenediamine) complex has been synthesized and characterized by analytical, spectroscopic (IR, UV/Vis) and voltammetric techniques. After doping Cu 2+ ion, its magnetic environment has been identified by electron paramagnetic resonance (EPR) technique. The title complex crystalizes in monoclinic system with space group P2 1/c and with Z=4. Each hydet-en ligand acts as a tridentate ligand through the two N atoms and the hydroxyl O atom, resulting in a six coordinate Zn(II) ion. The EPR spectra were recorded in three perpendicular planes of Cu 2+ doped ZHES single crystal. The calculated g and A values indicated that the paramagnetic center is rhombic symmetry with the Cu 2+ ion having distorted octahedral environment. The molecular orbital bond coefficients of the Cu(II) ion in d 9 state is also calculated by using EPR and optical absorption parameters. The dianion SQ 2− is oxidized reversibly in two consecutive steps to the corresponding radical monoanion and neutral form.

Fast noniterative orbital localization for large molecules

We use Cholesky decomposition of the density matrix in atomic orbital basis to define a new set of occupied molecular orbital coefficients. Analysis of the resulting orbitals ("Cholesky molecular orbitals") demonstrates their localized character inherited from the sparsity of the density matrix. Comparison with the results of traditional iterative localization schemes shows minor differences with respect to a number of suitable measures of locality, particularly the scaling with system size of orbital pair domains used in local correlation methods. The Cholesky procedure for generating orthonormal localized orbitals is noniterative and may be made linear scaling. Although our present implementation scales cubically, the algorithm is significantly faster than any of the conventional localization schemes. In addition, since this approach does not require starting orbitals, it will be useful in local correlation treatments on top of diagonalization-free Hartree-Fock optimization algorithms.

Density functional perturbational orbital theory of spin polarization in electronic systems. I. Formalism

A perturbational approach is presented for the general analysis of spin-polarization effect on electronic structures and energies within spin-density functional formalism. Explicit expressions for the changes in Kohn-Sham [Phys. Rev. 140, 1133 (1965)] orbital energies and coefficients as well as for the change in total electronic energy are derived upon using the local spin density and self-interaction-corrected exchange-correlation functionals. The application of the method for atoms provides analytical expressions for the exchange splitting energy and spin-polarization energy. The atomic exchange parameters are obtained from the expressions for the elements with Z=1-92 and they match well with Stoner exchange parameters for 3d metal elements.

Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing CuO – An EPR and optical study

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of 0.5mol% CuO doped xLi2O–(30−x)Na2O–69.5B2O3 (5⩽x⩽25) mixed alkali glasses have been investigated. The EPR spectra of all the investigated samples exhibit resonance signals characteristic of Cu2+ ions in octahedral sites with tetragonal distortion. It is found that the spin-Hamiltonian parameters do not vary much with x. It is interesting to observe that the number of Cu2+ ions participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. It is observed that the temperature dependence of paramagnetic susceptibility (χ) obeys Curie–Weiss law. The paramagnetic Curie temperature (θp) is negative for the investigated sample, which suggests that the copper ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. A broad band corresponding to the transition 2B1g→2B2g in the optical absorption spectrum shows a blue shift with x. By correlating the EPR and optical absorption data, the molecular orbital coefficients α2 and β12 have been evaluated. It is interesting to observe that the optical band gap (Eopt) and Urbach energies (ΔE) exhibit the mixed alkali effect. The theoretical values of optical basicity (Λth) have also been evaluated.

Design, synthesis, SAR, and biological evaluation of new 4-(phenylamino)thieno[2,3- b]pyridine derivatives

In this work, we performed the design, synthesis, and the structure–activity relationship studies of 13 new derivatives of thieno[2,3- b]pyridine. These derivatives were prepared in high yields (96–70%) and their structures were elucidated by IR, 1H, 13C NMR, and MS. The biological results showed some derivatives as antiparasitic agents against Giardia lamblia. Computational analysis of HOMO and LUMO energy, HOMO orbital coefficient distribution, electrostatic potential map, dipole moment, and density HOMO was performed to gain insight into the SAR aspects. This study pointed the p-methoxy substituted derivative as a leading compound for the development of new microbicidal medicines based on thieno[2,3- b]pyridine analogs.

Trypanocidal agents with low cytotoxicity to mammalian cell line: A comparison of the theoretical and biological features of lapachone derivatives

Starting from α- and β-lapachones, in this work we compared the biological and theoretical profile of several oxyran derivatives of lapachone as potential trypanocidal agents. Our biological results showed that the oxyrans tested act as trypanocidal agents against Trypanosoma cruzi with minimal cytotoxicity in the VERO cell line compared to naphthoquinones. The oxyran derivative of α-lapachone ( 7a) showed to be one of the most potent compounds. In our molecular modeling study, we analyzed the C-ring moiety and the redox center of β-lapachone molecule as the moieties responsible for the trypanocidal and cytotoxic effects on mammalian cell line. The computational methods used to delineate the structural requirements for the trypanocidal profile pointed out that the transposition of the C-ring moiety of β-lapachone, combined with its oxyran ring, introduced important molecular requirements for trypanocidal activity in the HOMO energy, HOMO orbital coefficient, LUMO density, electrostatic potential map, dipole moment vector, and calculated log P (c log P) parameter. This study could lead to the development of new antichagasic medicines based on α-lapachone analogs.