Search

The synthesis, structure and reactions of (acylimino)triaryl-lambda(super 5)-bismuthanes and a comparative study of the structure and reactivity of a series of (acylimino)pnictoranes is given. The unique reactivities of (acylimino)triaryl-lambda(super 5)-bismuthanes demonstrate their potential utility in organic synthesis.

Initial cleavage of a ring CC bond to form a trans .CHsub2SiHsub2Chsub2Chsub2. diradical is the most likely route from silacyclobutane to ethylene + silene, according to multiconfigurational self-consistent field wave functions and second order perturbation theory. The trans diradical is predicted to be a minimum on the MCSCF ground state potential energy surface. The addition of dynamic correlation leads to the disappearance of the transition state.

The synthesis, structures, optical and redox properties, and reactivity of phosphaporphyrins prepared via acid-promoted dehydrative condensation is presented. The incorporation of a phosphorus atom into the core is found to be a highly promising way to modify the fundamental properties of the porphyrin 18[pi] system which could also be used as reliable tool to stabilize uncommon 22[pi] and 20[pi] systems through the chemical modifications at the core phosphorus atom.

The experiments have disclosed that isophlorin-metal complexes are accessible by redox-coupled complexation of P,S,[N.sub.2]-hybrid porphyrin. The results have shown that core-modification with phosphorus might be promising method to develop coordination chemistry of 4n[pi] porphyrinoids.

Frozen-core four-component multiconfigurational quasidegenerate perturbation theory was used to study the electronic structure of the molecules La[F.sup.+] and LaF. The findings provide insight into excitation energies of La[F.sup.+] based on electronic correlations between the outermost valence electrons and ionic core electrons.

The activation mechanism of NH3 in the selective catalytic reduction of NO by NH3 on a V2O7H4 cluster is investigated. A complete active space self-consistent field method is used for this purpose.

The excited states (Q and B bands) of free-base porphyrins (FBP), Mg-porphyrin and Zn-porphyrin and their derivatives were investigated. The results of multireference Moller-Plesset perturbation studies with complete active space self-consistent field reference that the weakness of the Q band of FBP is due to pseudoparity-forbidden status that came from the pairing properties of alternant hydrocarbons. It was shown that breaking the pairing properties results in the strengthening of the Q band intensity, which can be accomplished by the substitution of C atoms with N atoms in the meso position.

The role of water in host-ligand binding was investigated using a combination of molecular dynamics simulation and three-dimensional reference interaction site model theory. Three different hosts were selected (CB6, CB7, and CB8). Six organic molecules were used as representative ligands: dimethyl sulfoxide (DMSO), N , N -dimethylformamide (DMF), acetone, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), cyclopentanone (CPN), and pyrrole. From the binding free energy and its components, we divided the ligands into two groups: those with relatively small molecular size (DMSO, DMF, acetone, and pyrrole) and those with relatively large molecular size (DBO and CPN). We established that the solvent water in the CB6 cavity can be completely displaced by small ligands, resulting in a greater binding affinity compared with larger CBs, except in the case of the small pyrrole ligand, due to outstanding intrinsic properties such as the relatively high hydrophobicity and low dipole moment. In the case of the large ligands, the solvent water can be displaced by DBO and CPN in both CB6 and CB7; there were similar tendencies in their binding affinities, with the greatest affinity in the CB7 complexes. However, the tendencies of the binding affinity components are completely different due to the difference between the complex structure and the solvation structure when a ligand binds with a CB structure. The binding affinities suggest that the size fit between the ligand and CB cannot guarantee the greatest binding affinity gain because the binding structure and intrinsic properties of CB and ligand equally play a crucial role.

The effect of molecular orientational correlations on the solvation free energy (SFE) of one-dimensional and three-dimensional reference interaction site models (1D- and 3D-RISM) is investigated. The repulsive bridge correction (RBC) and the partial wave (PW) expansion are representative approaches for accounting for the orientational correlation partially lacking in original 1D- and 3D-RISM. The SFEs of 1D- and 3D-RISM for a set of small organic molecules are compared with the simulation results. Accordingly, the SFE expressions, based on RBC and PW, provide more accurate results than those of the uncorrected HNC or KH SFE expressions, which indicates that accounting for molecular orientational dependencies significantly contributes to the improvement of the SFE. The SFE component analysis indicates that the nonpolar component mainly contributes to the correction. The dependence of the error in the RISM SFE on the number of solute sites is examined. In addition, we discuss the differences between 1D- and 3D-RISM through the effect of these corrections.

The molecular and solvation structures of the hydrated Cu 2+ ions and their excitation spectra were investigated using the Kohn-Sham density functional theory (DFT) and the three-dimensional reference interaction site model (3D-RISM) self-consistent field method. Five stable geometrical structures were found to exist in aqueous solution: the distorted octahedral [Cu(H 2 O) 6 ] 2+ in C i and D 2 h symmetries, the square pyramidal and trigonal bipyramidal [Cu(H 2 O) 5 ] 2+ , and the square planar [Cu(H 2 O) 4 ] 2+ . The distorted octahedral structure in the C i symmetry is preferred in [Cu(H 2 O) 6 ] 2+ , and the square pyramidal and trigonal bipyramidal [Cu(H 2 O) 5 ] 2+ show almost the same stability. Among these geometries, the six-coordinate complex [Cu(H 2 O) 6 ] 2+ in the C i symmetry had the lowest Helmholtz energy. [Cu(H 2 O) 6 ] 2+ had a distorted octahedral structure, that is, two long axial bonds and four short equatorial bonds. The spatial and radial distribution function analyses for [Cu(H 2 O) 5 ] 2+ and [Cu(H 2 O) 4 ] 2+ showed that [Cu(H 2 O) 5 ] 2+ and [Cu(H 2 O) 4 ] 2+ had one and two solvent water molecules that constituted a distorted octahedron with ligand water distribution. The coordination numbers (CNs) derived from the distribution functions were 5.2-5.4 for [Cu(H 2 O) 5 ] 2+ and 5.3 for [Cu(H 2 O) 4 ] 2+ . These results indicated that the Cu 2+ ion in an aqueous solution had 5-6 coordination water molecules in the first hydration shell and some structures with different CNs may interchange in the solution. The excitation energies and electronic configurations of low-lying d-d excited states were calculated using the time-dependent DFT with the electric field generated by 3D-RISM. The orbital energies and electronic configurations were in a similar picture to those of the classical crystal field theory because of the highly symmetrical features of all structures. In [Cu(H 2 O) 6 ] 2+ , the degeneracies of orbitals were resolved, whereas in [Cu(H 2 O) 5 ] 2+ and [Cu(H 2 O) 4 ] 2+ , weak and strong quasi-degeneracies remained. As a result, only the four-coordinate complex generated third and fourth excited states, whereas in other complexes, there were no obvious characters of degeneracies. The resulting excitation energies were in good agreement with the absorption spectra.

Two diazaporphyrin (DAP)-porphyrin hetero dimers, in β-meso and β-β configurations, were prepared to study their photoinduced intramolecular electron transfer properties. The two meso nitrogen atoms in the porphyrin ring of DAP change its redox potential, making DAP more easily reduced, compared to its porphyrin counterpart. A charge-transfer from porphyrin to DAP in both hetero dimers was verified by versatile optical spectroscopic methods. The steady-state fluorescence spectra indicated an efficient intramolecular exciplex formation for both dimers. For the β-meso dimer, ultrafast time-resolved spectroscopic methods revealed the subpicosecond formation of two types of primary short-living (1-18 ps) intramolecular exciplexes, which relaxed in toluene to form a long-living final exciplex (1.4 ns) followed by a longer-living charge transfer complex (>5 ns). However, in benzonitrile, the lifetime of the final exciplex was longer (660 ps) as was that of the charge transfer complex (180 ps). The β-β analogue formed similar short-living exciplexes in both solvents, but the final exciplex and the charge transfer state had significantly shorter lifetimes. The electrochemical redox potential measurements and density functional theory calculations supported the proposed mechanism.

The three-dimensional reference interaction-site model self-consistent-field (3D-RISM-SCF) method was applied to the electronic structure of hexahydrated chromium trication [Cr(H2O)6](3+) in aqueous solution. The 3D distribution around [Cr(H2O)6](3+) showed 12 maximum density points arising from hydrogen bonds, as well as eight local maximum points at the hollow sites, in the second hydration shell. The 3D distribution function also indicated 20 local maximum sites in the third hydration shell. The low-lying excited states of vertical transitions were computed using time-dependent density functional theory (TD-DFT), including the electric field from the solvent. The electronic configurations and excitation energies calculated using DFT and 3D-RISM-SCF were very similar, although the orbital energies involved in the transition were rather different. The two lowest excited states (1(4)T and 2(4)T) were roughly assigned to the d-d transitions, and the third and fourth excited states (3(4)T and 4(4)T) were assigned to ligand-to-metal charge-transfer transitions. The computed excited energies were in good agreement with the experimental values.

A new, efficient parallel algorithm for four-component relativistic generalized multiconfigurational quasidegenerate perturbation theory (GMC-QDPT) introducing Kramers symmetry is implemented. Because it utilizes the independence of the terms in the matrix element computations, this algorithm both speeds up the calculation and reduces the computational resources required for each node. In addition, the amount of memory for two-electron integrals is reduced to three-eigths by Kramers restriction. The algorithm is applied to the d-d excitation energies of the platinum halide complexes, [PtCl4](2-), [PtBr4](2-), and [PtCl6](2-) and to the 6p-7s and 6p-7p excitation energies of the radon atom. It is shown to provide high parallelization efficiency and accurate excitation energies that agree well with experimental data.

The 18pi-sigma3- and 22pi-sigma4-phosphaporphyrins were successfully prepared by an acid-promoted condensation between a phosphatripyrrane and a 2,5-bis[hydroxy(phenyl)methyl]pyrrole, and their structures, aromaticity, and optical and electrochemical properties were disclosed. Notably, a sigma4-phosphaporphyrinogen and the 18pi-sigma3-phosphaporphyrin undergo oxidative pi-extension at the peripherally fused carbocycle to afford the 22pi-sigma4-phosphaporphyrin.

A phosphorus-containing hybrid porphyrin was successfully prepared via the BF3-promoted dehydrative condensation between sigma4-phosphatripyrrane and 2,5-bis[hydroxy(phenyl)methyl]thiophene. The NMR and UV-vis absorption spectra, electrochemical measurements, and DFT calculations revealed that the sigma3-P,N2,S-hybrid porphyrin exhibits high aromaticity as an 18pi-electron system in terms of both geometric and magnetic criteria. [structure: see text]