Libero J. Bartolotti

Density functional theory derived intermediates from the OH initiated atmospheric oxidation of toluene

Abstract A series of density functional based quantum mechanical calculations were carried out to identify potential intermediates produced by the OH addtion initiated atmospheric photo-oxidation of toluene. The potential for formation was assessed based on the relative stabilities of the assumed products. The calculations are consistent with OH addition occurring mainly at the ortho position, followed by addition of O2 at the meta position and formation of a bridged structure across the 1–3 position. In addition, the calculations suggest that carbonyl compounds containing epoxide structures may form during the oxidation.

The concept of pressure in density functional theory

Using density functional theory, a prescription is given for determining the internal scalar pressure at a point within an atom or molecule. From this expression for the pressure, a thermodynamic expression for the energy is obtained in terms of the chemical potential of the reference system, forces acting on the system, the internal pressure and an additional component X[ρ]; namely, Here μ0 is the chemical potential in the absence of fields, v is the potential due to nuclei, φ is the potential due to electrons, P is the scalar pressure, and X[ρ] is defined by the formula where T[ρ] and K[ρ] are the exact kinetic energy and exchange–correlation functionals. The functional X[ρ] vanishes as N approaches infinity, or in Thomas–Fermi or Thomas–Fermi–Dirac approximation, yet it is necessary to account for chemical binding.

Improvement in phosphorescence efficiency through tuning of coordination geometry of tridentate cyclometalated platinum(II) complexes.

A series of tridentate cyclometalated platinum(II) complexes (C(∧)N*N)PtL (L = Cl or acetylide) featuring a fused five-six-membered metallacycle were synthesized. The structure of the complexes was confirmed by X-ray crystallography. In contrast to the C(∧)N(∧)N platinum complexes with a fused five-five-membered metallacycle, the platinum coordination in C(∧)N*N complexes is much closer to a square planar geometry. The photophysical properties of the complexes were studied. The geometrical change from C(∧)N(∧)N to C(∧)N*N led to a substantial improvement in phosphorescence efficiency of the complexes with an acetylide ligand in solution at room temperature. For example, the quantum yield of (C(∧)N*N)PtCCPh was measured to be 56%, demonstrating a big jump from 4% reported for (C(∧)N(∧)N)PtCCPh.

Variation‐perturbation theory within a time‐dependent Kohn–Sham formalism: An application to the determination of multipole polarizabilities, spectral sums, and dispersion coefficients

The variation‐perturbation method within time‐dependent Kohn–Sham theory is used to calculate atomic multipole polarizabilities, spectra sums, and multipole–multipole two‐body dispersion coefficients. The first‐order corrections to Kohn–Sham amplitudes and phases were obtained from a direct variational approach and from the method of Cauchy moments. The multipole Cauchy moments were used to construct Pade approximants, which gave us upper and lower bounds to the two‐body dispersion coefficients. Four approximations to the exchange‐correlation energy were investigated in the present work and the gradient expansion for atoms proved to be most satisfactory.

The electron localization function description of aromaticity in five-membered rings

Abstract The electron localization function (ELF) has been calculated at the B3LYP/6-31+G(d,p)//MP2/6-31+G(d,p) level for a series of substituted five-membered cyclopentadienyl systems. While the behavior of the ELF data for the formally double CC bond is somewhat chaotic, that of the formally single C–C bond shows a strong and smooth correlation with resonance energies, E ( H ), calculated at the BLYP/6-311G(d,p)//BLYP/6-31G(d) level in the homomolecular homodesmotic approach. When appropriately scaled, the functional behavior of the C–C bond basin populations and pair numbers follow very closely that found empirically for the reduced vapor density of real liquid–vapor coexistence curves.

Highly luminescent tridentate N^C*N platinum(II) complexes featured in fused five-six-membered metallacycle and diminishing concentration quenching.

A series of cyclometalating ligands, N-phenyl-N-(3-(pyridin-2-yl)phenyl)pyridin-2-amine (L1), N-(3-(1H-pyrazol-1-yl)phenyl)-N-phenylpyridin-2-amine (L2), N-phenyl-N-(3-(quinolin-2-yl)phenyl)pyridin-2-amine (L3), N-phenyl-N-(3-(pyridin-2-yl)phenyl)quinolin-2-amine (L4), N-(3-(isoquinolin-1-yl)phenyl)-N-phenylpyridin-2-amine (L5), and N-phenyl-N-(3-(pyridin-2-yl)phenyl)isoquinolin-1-amine (L6), were synthesized, which reacted with K(2)PtCl(4) in glacial acetic acid to produce N^C*N-coordinated platinum(II) complexes featured in a fused five-six-membered metallacycle, 1-6, respectively. The structures of 1, 3, 4, and 6 were determined by single crystal X-ray crystallography. The square geometries of the complexes are improved when compared with those of the N^C^N-coordinated complexes as the bite angles for the platinum in N^C*N-coordinated complexes 1, 3, and 4 are increased. The Pt-C bonds (1.94-1.95 Å) are shorter than those of C^N^N-coordinated platinum complexes but longer than those found for N^C^N-coordinated platinum complexes. With the increase of the steric interaction, the distortion of the molecules from a planar coordination geometry becomes more and more severe from 1 to 3 to 4 and 6, and in 6, the N-phenyl ring has to stand up on the coordination sphere to minimize the steric interaction with the N-isoquinolyl ring. The photophysical properties of the complexes were studied, and their absorption and emission spectra were interpreted by relating to the structural features revealed by the X-ray crystal structures and the orbital characters predicted by DFT calculations. All complexes are emissive in fluid at room temperature, and the quantum yields (up to 0.65) are comparable to those of highly emissive N^C^N-coordinated platinum complexes. Self-quenching was not observed in the concentration range of 10(-6) to 10(-4) M. Large rigidochromic shifts for the emissions of 2, 4, and 6 upon cooling from room temperature to rigid glass (77 K) were observed. Two different triplet states that control the emissions were proposed to account for the photophysical properties of 6.

On the functional derivative of the kinetic energy density functional

The functional derivative of the kinetic energy Ts[ρ↑,ρ↓] of a noninteracting system of particles with density ρ=ρ↑+ρ↓ is evaluated in terms of the Kohn–Sham spin orbital densities ρiσ and Lagrange multipliers eiσ(σ=↑ or ↓). Of particular interest is the functional derivative of TΔ[ρ↑,ρ↓] =Ts[ρ↑,ρ↓]−Tw[ρ↑,ρ↓], where Tw[ρ↑,ρ↓] is the Weizsacker kinetic energy functional: δTΔ[ρ↑,ρ↓]/δρσ =(1/8ρσ){JNσi=1[(∇ρiσ ⋅  ∇ρiσ)/ρiσ −(∇ρσ ⋅ ∇ρσ)/ρσ]} −(1/ρσ)(JNσi=1 eiσρiσ −μσρσ). This quantity is used to analyze the approximate kinetic energy density functional proposed by Acharya et al.

Effect of additional hydrogen peroxide to H2O2⋯(H2O)n, n=1 and 2 complexes: Quantum chemical study

Hydrogen peroxide, H2O2, acts as a particularly strong reactant in aqueous environment. It has been demonstrated earlier that agglomerates with a single peroxide interacting with one and two water molecules manifest in several stable conformers within a narrow energy range. In the present study we seek structural changes brought out by adding an extra H2O2 to these systems at molecular level employing ab initio quantum chemical methods, viz., restricted Hartree-Fock and the second order Moller-Plesset perturbation theory. These clusters exhibit consistent trends in energy hierarchy at both the levels. Further, a many body interaction energy analysis quantifies the strength and cooperativity of hydrogen bonding in the (H2O2)2...(H2O)n, (n=1 and 2) clusters, bringing out structuring/destructuring effects attributed to attachment of water and hydrogen peroxide molecules.

The pair density description of aromaticity in some substituted cyclopentadienyl systems: a comparison of AIM and ELF bonding descriptors

Abstract Calculations at the B3LYP/6-31+G(d,p)//MP2(FC)/6-31+G(d,p) level of the atoms-in-molecules interbasin pair numbers were carried out for a number of substituted cyclopentadienyl five-membered rings and compared to the electron localization function (ELF) bond basin populations. A smooth correlation is found for the formally single C–C bond pair number with the corresponding homomolecular–homodesmotic resonance energy, as was previously been shown for the ELF bond basin numbers. The two measures of bonding are essentially equal for the non-polar C–C bond, but this is shown to be an exception rather than a rule, the situation being more complex when bonds are polar and/or lone pairs are nearby.

Ab initio investigations on neutral hydrogen peroxide clusters: (H2O2)n (n = 2-4)

Abstract Hydrogen-bonded neutral clusters of Hydrogen Peroxide, ( H 2 O 2 ) n , ( n=2–4 ), have been theoretically investigated employing various basis-sets at the second order Moller–Plesset (MP) perturbation theory. Electron correlation effects at third and fourth order of the MP perturbation theory are also considered at MP2 geometry. Detailed analysis of many body contributions to interaction energies of dimer, trimer and tetramer is also presented. While all these H-bonded conformers emerge as closed structures, the tetramer is the only configuration that exhibits a higher molecular symmetry and is nonpolar. The ab initio results presented here can assist towards experimental identification of these clusters.