Ab initio study of the mechanism of the reaction ClO + O --> Cl + O2

Ab initio investigation on the reaction mechanism of ClO + O --> Cl + O2 reaction has been performed using correlation consistent triple zeta basis set. The geometry and frequency of the reactants, products, minimum energy geometries and transition states are obtained using MP2 method and energetics are obtained at the QCISD(T)//MP2 level of theory. Primarily, a possible reaction mechanism is obtained on the basis on IRC calculations using MP2 level of theory. To obtain true picture of the reaction path, we performed IRC calculations using CASSCF method with a minimal basis set 6-31G**. Some new equilibrium geometries and transition states have been identified at the CASSCF level. Energetics are also obtained at the QCISD(T)//CASSCF method. Possible reaction paths have been discussed, which are new in literature. Heat of reaction is found to be consistent with the experimental data. Bond dissociation energies to various dissociation paths are also reported.

Calculation and interpretation of classical turning surfaces in solids

Classical turning surfaces of Kohn–Sham potentials separate classically allowed regions (CARs) from classically forbidden regions (CFRs). They are useful for understanding many chemical properties of molecules but need not exist in solids, where the density never decays to zero. At equilibrium geometries, we find that CFRs are absent in perfect metals, rare in covalent semiconductors at equilibrium, but common in ionic and molecular crystals. In all materials, CFRs appear or grow as the internuclear distances are uniformly expanded. They can also appear at a monovacancy in a metal. Calculations with several approximate density functionals and codes confirm these behaviors. A classical picture of conduction suggests that CARs should be connected in metals, and disconnected in wide-gap insulators, and is confirmed in the limits of extreme compression and expansion. Surprisingly, many semiconductors have no CFR at equilibrium, a key finding for density functional construction. Nonetheless, a strong correlation with insulating behavior can still be inferred. Moreover, equilibrium bond lengths for all cases can be estimated from the bond type and the sum of the classical turning radii of the free atoms or ions.

Equilibrium Geometries, Adiabatic Excitation Energies and Intrinsic C=C/C–H Bond Strengths of Ethylene in Lowest Singlet Excited States Described by TDDFT

Seventeen singlet excited states of ethylene have been calculated via time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the geometries of 11 excited states were optimized successfully. The local vibrational mode theory was employed to examine the intrinsic C=C/C–H bond strengths and their change upon excitation. The natural transition orbital (NTO) analysis was used to further analyze the C=C/C–H bond strength change in excited states versus the ground state. For the first time, three excited states including πy′ → 3s, πy′ → 3py and πy′ → 3pz were identified with stronger C=C ethylene double bonds than in the ground state.

Quantifying and understanding errors in molecular geometries

Electronic structure calculations are ubiquitous in most branches of chemistry, but all have errors in both energies and equilibrium geometries. Quantifying errors in possibly dozens of bond angles and bond lengths is a Herculean task. A single natural measure of geometric error is introduced, the geometry energy offset (GEO). GEO links many disparate aspects of geometry errors: a new ranking of different methods, quantitative insight into errors in specific geometric parameters, and insight into trends with different methods. GEO can also reduce the cost of high-level geometry optimizations and shows when geometric errors distort the overall error of a method. Results, including some surprises, are given for both covalent and weak interactions.

A theoretical study of structure, bonding and property of platinum(II)-8-hydroxyquinolines complexes with carbene and heavier homologues

In this work, a theoretical study for platinum(II)-8-hydroxyquinoline-tetrylene complexes [{PtCl–C9H6NO}–NHEPh] (Pt–EPh) is carried out for the first time by using the density functional theory (DFT). Quantum chemical calculations with DFT and charge methods at the BP86 level with basic sets SVP and TZVPP have been perfomed to get insight into the structures and property of Pt–EPh. The optimization of equilibrium geometries of the ligands EPh in Pt–EPh, bonded in the distorted end-on way to the Pt fragment is studied, in which the bending angle slightly decreases from carbene Pt–CPh to germylene Pt–GePh. Quantum chemical parameters such as EHOMO, ELUMO, the energy gap (ELUMO – EHOMO), electronegativity, global hardness, and global softness in the neutral molecules have been calculated and discussed. Bond dissociation energies decrease from the slighter to the heavier homologues. The hybridization of atoms E has large p characters, while the hybridization of atom Pt has a greater d character. Thus, the Pt–E bond possesses not only NHEPh→{PtCl–C9H6NO} strong -donation but also a significant contribution of π-donation NHEPh→{PtCl–C9H6NO}, and a weak π-backdonation metal-ligand NHEPh←{PtCl-C9H6NO} in complexes Pt-EPh is also considered.

A theoretical study of structure, bonding and property of platinum(II)-8-hydroxyquinolines complexes with carbene and heavier homologues

<p>In this work, a theoretical study for platinum(II)-8-hydroxyquinolines-tetrylene complexes [{PtCl-C₉H₆NO}-NHE_Ph] (<strong>Pt-EPh</strong>)<strong> </strong>are investigated for the first time using density functional theory (DFT). Quantum chemical calculations using DFT and charge methods at the BP86 level with basic sets SVP, TZVPP have been carried out to get insight into the structures and property for <strong>Pt-EPh</strong>. The optimization of equilibrium geometries of the ligands<strong> EPh</strong> in <strong>Pt-EPh</strong> are bonded in distorted end-on way to <strong>Pt</strong> fragment with the bending angle, a, slightly decreases from carbene <strong>Pt-CPh</strong> to germylene <strong>Pt-GePh</strong>. Quantum chemical parameters such as <em>E</em>_HOMO, <em>E</em>_LUMO, the energy gap (<em>E</em>_LUMO– <em>E</em>_HOMO), electronegativity (χ), global hardness (η), and global softness (<em>S</em>) in the neutral molecules have been calculated and discussed. Bond dissociation energies (BDEs), D_e(kcal.mol^-1), decrease from the slighter to the heavier homologues. The hybridization of atoms E have large p characters while the hybridization of atom Pt has greater d character which lead to the Pt-E bond possesses not only NHE_Ph→{ PtCl-C₉H₆NO} strong σ-donation but also a significant contribution π-donation NHE_Ph→{PtCl-C₉H₆NO} and a weak π-backdonation metal-ligand NHE_Ph←{PtCl-C₉H₆NO} in complexes <strong>Pt-Eph </strong>was also considered.</p>

Complex formation in a liquid-liquid extraction-chromogenic system for vanadium(IV)

The azo dye 4-(2-thiazolylazo)orcinol (TAO) and the cationic ion-pair reagent 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) were examined as constituents of a water-chloroform extraction-chromogenic system for vanadium(IV). The effects of TAO concentration, TTC concentration, pH and extraction time were examined. Under the optimum conditions the extracted complex has a composition of 1:2:1 (V:TAO:TTC). The absorption maximum, molar absorptivity and constant of extraction were determined to be λmax=544 nm, ε544=1.75×104 dm3 mol–1 cm–1 and Log Kex=4.1. The ground state equilibrium geometries of the possible monoanionic VIV-TAO 1:2 species were optimized by the HF method using 3-21G* basis functions. Their theoretical time dependent electronic spectra were simulated and compared with the experimental spectrum. The best fit was obtained for the structure in which one of the TAO ligands is tridentate, but the other is monodentate (bound to VIV through the oxygen which is in the ortho-position to the azo group) and forms a hydrogen bond N–H...O=V through its protonated heterocyclic nitrogen. Based on this unusual structure, which can explain some peculiarities of the complex formation between VIV and commonly used azo dyes, the ground state equilibrium geometry of the whole ternary 1:2:1 complex was computed at the HF and BLYP levels.