Martin Breza

Photocatalytic hydroxylation of benzoic acid in aqueous titanium dioxide suspension

The photocatalytic hydroxylation of benzoic acid in aqueous TiO2 suspension is suggested as evidence for the generation of hydroxyl radicals in the H2O(l)—TiO2(s) system. The hydroxylation reaction was studied by UV spectroscopy and high performance liquid chromatography (HPLC). The experimental results are discussed in terms of the formal kinetic analysis and the aromatic carbon charges calculated by the INDO method.

The spectroscopic and structural properties of copper(II) complexes of the novel tridentate (ONO) pyridine N-oxide ligand Hpoxap

Abstract A tridentate ligand (Hpoxap=2-(o-hydroxyphenyliminomethyl)pyridine N-oxide) has been synthesised by the Schiff condensation of 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol. A series of copper(II) complexes with this ONO-donor ligand has been prepared and their spectroscopic properties (electron, vibration, ESR) were studied. The structures for two complexes have been determined by X-ray analysis. The structure of [Cu(poxap)(OAc)] consists of isolated neutral molecules in which the copper(II) atom is situated in a slightly distorted square-planar surrounding. The structure of [Cu(poxap)(H2O)(NO3)] consists of neutral molecules which are interconnected by hydrogen bonds giving rise to a ladder structure of copper(II) ions with two different Cu⋯Cu distances of 5.27 and 7.41 A. The copper atoms are in a slightly distorted square-pyramidal environment with the tridentate ligand poxap− and the water molecule in the basal plane; the apical position being occupied by an oxygen atom of the nitrate anion. Magnetic susceptibility studies were undertaken and these confirm predominantly a dimeric character of the complex.

The electronic structure of planar phosphazene rings

Abstract Using a standard ab initio method, the electronic structure and optimal geometries of cyclo-(NPX 2 ) n ( n =2, 3, 4 and X=H, F, Cl) have been investigated using the DZP basis set. The out-of-plane π bonds as well as the in-plane π′ bonds in phosphazenes are dominated by p orbitals, although the bonding interaction between p orbitals on N atoms and d orbitals on P atoms is symmetrically forbidden in rings of D nh symmetry with odd n only. In-plane π′ and σ bonds in cyclic planar phosphazenes can be distinguished using Mulliken population analysis of cylindrical atomic orbitals. The d functions on P atoms do not correspond to their d orbitals and can be explained as polarization functions only.

On the dependence of optical properties on conformational changes in oligothiophenes I. Electron absorption spectra

Abstract The geometries of 2,2′-bithiophene, 2,2′:5′,2″-terthiophene and 2,2:5′,2″:5″,2′‴-quaterthiophene molecules were optimized by using semiempirical AM1 method for fixed equidistant dihedral angles between neighboring thiophene rings. Corresponding electron spectra are calculated by semiempirical AM1 and ZINDO/S methods. The vibronic interaction between the low lying monoexcited electronic states is symmetry forbidden for any torsion coordinate in all planar oligothiophenes and similar compounds because these electron states are constructed from π molecular orbitals. Mutual orientation of torsion angles is not important for electronic structure of oligothiophenes. The dependence of maximal wavelength λ max on the torsion angle is of similar shape as its squared sine function. Using this dependence the torsional angles for some alkylated oligothiophenes in solution are estimated.

Syntheses, Electronic Structures, and EPR/UV−Vis−NIR Spectroelectrochemistry of Nickel(II), Copper(II), and Zinc(II) Complexes with a Tetradentate Ligand Based on S-Methylisothiosemicarbazide

Template condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde S-methylisothiosemicarbazone with pentane-2,4-dione and triethyl orthoformate at elevated temperatures resulted in metal complexes of the type M(II)L, where M = Ni and Cu and H(2)L = a novel tetradentate ligand. These complexes are relevant to the active site of the copper enzymes galactose oxidase and glyoxal oxidase. Demetalation of Ni(II)L with gaseous hydrogen chloride in chloroform afforded the metal-free ligand H(2)L. Then by the reaction of H(2)L with Zn(CH(3)COO)(2)·2H(2)O in a 1:1 molar ratio in 1:2 chloroform/methanol, the complex Zn(II)L(CH(3)OH) was prepared. The three metal complexes and the prepared ligand were characterized by spectroscopic methods (IR, UV-vis, and NMR spectroscopy), X-ray crystallography, and DFT calculations. Electrochemically generated one-electron oxidized metal complexes [NiL](+), [CuL](+), and [ZnL(CH(3)OH)](+) and the metal-free ligand cation radical [H(2)L](+•) were studied by EPR/UV-vis-NIR and DFT calculations. These studies demonstrated the interaction between the metal ion and the phenoxyl radical.

Electronic structure of the nickel(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylprolinamide and glycine

The experimental charge density of the Ni(II) complex of the Schiff base of (S)-N-(2-benzoylphenyl)-1-benzylprolinamide and glycine was derived from high-resolution single-crystal X-ray diffraction data (lambda = 0.5604 A) at low temperature (100 K) with synchrotron radiation at the beamline F1 using a CCD area detector. The central Ni atom is pseudo-square-planar coordinated by three N atoms [1.9414 (3), 1.8559 (3) and 1.8533 (3) A] and by one O atom [1.8620 (4) A]. The N(1) atom is 0.359 A above the plane defined by the atoms Ni(1), N(2) and N(3). The d-orbital population analysis reveals an oxidation state for the Ni atom of +2 with the configuration d(8) and a hole mainly in the d(x(2)-y(2)) orbital, located in the plane of the four ligating atoms. The prochiral reaction centre was examined by topological analysis.

Optical properties of furanic and thiophenic ethane-1,2-diones: A combined experimental and theoretical study

Abstract The syntheses, spectral measurements and the AM1 geometries of di-furan-2-yl-ethane-1,2-dione, di-thiophen-2-yl-ethane-1,2-dione, bis-[2,2′]-bithiophen-2,5-yl-ethane-1,2-dione and bis-[2,2′; 5′,2″]-terthiophen-2,5-yl-ethane-1,2-dione are presented. The electron absorption spectra for stable conformers are obtained by ZINDO/S method and they reasonably well agree with the experimental data. The increasing chain length influences the electronic polarizability and hyperpolarizabilities as demonstrated by the finite field method in AM1 approach.

Non-linear optical properties of new bridged bis-thienyls: I. Pyrazine-based bridges: theory, synthesis and spectra

Abstract The conformational analysis of 2,3-bis(2′-thienyl)pyrazine (A), 2,3-dicyano-5,6-bis(2′-thienyl)pyrazine (B), 2,3-difluoro-5,6-bis(2′-thienyl)pyrazine (C), 2,3-bis(2′-thienyl)furo[3,4-b]pyrazine (D), 2,3-bis(2′-thienyl)pyrrolo[3,4-b]pyrazine (E), 2,3-bis(2′-thienyl)thieno[3,4-b]pyrazine (F), 2,3-bis(2′-thienyl)quinoxaline (G), 2,3-bis(2′-thienyl)pyrido[3,4-b]pyrazine (H) and 2,3-bis(2′-thienyl)pyrido[2,3-b]pyrazine (I) is elaborated using semiempirical Austin Model 1 (AM1) method. The electron absorption spectra for stable conformers are calculated by ZINDO/S method. The influence of the bridge variations on the electronic polarisability and second hyperpolarisability is investigated using the time-dependent Hartree–Fock method in AM1 approach. The synthesis and spectral measurements of the most promising B, F, G and I compounds are presented. Our results indicate that the G and I ones seem to be suitable candidates for the subsequent preparation of the electro-optical materials.

Vibronic interactions in the stereochemistry of metal complexes

A survey of the theoretical foundations of vibronic interactions in molecular systems, with special attention to metal complexes, is given. A detailed analysis of the conditions leading to the adiabatic potential surface in various degrees of generality represents the central idea of the article. Use of the partitioning method enables consideration of the Jahn-Teller effect, the Renner-Teller effect and the pseudo Jahn-Teller effect on an equal footing. Analytic forms of the adiabatic potential surfaces are rederived for the most important cases by including the totally symmetric vibrational mode up to the second order of vibronic expansion. A complete third-order formula for the adiabatic potential surface of Eg − (a1g + eg) vibronic coupling is presented. The consequences for structural features of molecular systems are discussed and exemplified by various metal complexes. Recent progress in molecular-orbital calculations of vibronic constants is reviewed.

Structure and electronic properties of bithiophenes. I. Torsional dependence

The dependence of energy, dipole moment and the static electronic polarisability of 2,2′-bithiophene, 2,3′-bithiophene and 3,3′-bithiophene on the inter-ring plane angle is investigated using ab initio/MP2 treatment. The calculated data are fitted by Fourier expansion up to the fourfold term and the trends of its parameters are discussed. Similar trends of the leading twofold and/or onefold terms of the studied torsional dependencies of different quantities indicate their implicit relationships. The tendency of individual bithiophene isomers to planarity (2,2′-<2,3′-<3,3′-bithiophene) may be explained by these terms.