Density functional calculation of the electronegativity and other related properties of atoms and ions of the principal groups of the periodic table

The relation between the electronegativityχ of an atom or an ion (χ=??E(Z,N)/?N) and its finite difference (Mulliken like) counterpart has been studied for the elements of the groups IA to VIIA of the Periodic Table, using an approximate Density Functional Theory. Only the valence electrons are taken into account and the effect of the ionic core is simulated by a simple empty core pseudopotential. The first derivative ?χ/6N of the electronegativity has also been computed. The interest inχ and?χ/?N is illustrated by a simple model for the transfer of electronic charge in a molecule. Molecular electronegativities are then computed.     

Determination of arsenic in petroleum refinery streams by electrothermal atomic absorption spectrometry after multivariate optimization based on Doehlert design

This paper reports the development of a methodology for the determination of arsenic in petroleum refinery aqueous streams containing large amounts of unknown volatile organic compounds, employing electrothermal atomic absorption spectrometry with polarized Zeeman-effect background correction. In order to make the procedure applicable, the influence of chemical modification and the drying step was examined. Also, pyrolysis and atomization temperatures and the amount of nitric acid added to the sample were optimized using a multivariate approach based on Doehlert matrix. Obtained results indicate that, in this kind of sample, arsenic must be determined by standard addition procedure with a careful control of the drying step temperature and ramp pattern. In order to evaluate the accuracy of the procedure, a test was performed in six spiked samples of petroleum refinery aqueous streams and the relative errors verified in the analysis of such samples (added As between 12.5 and 190 μg l⁻¹) ranged from −7.2 to +16.7%. The detection limit and the relative standard deviation were also calculated and the values are 68 pg and 7.5% (at 12.5 μg l⁻¹ level), respectively.     

Glueball spectroscopy in strongly coupled lattice gauge theories

We study the mass spectrum up to –7 (1–) log of pure three-dimensional lattice gauge theories with action (g _P) for real irreducible and small . Besides the lowest excitationm ₀–4log, we find two nearly degenerate excited statesm ₁,m ₂ withm _i–6log (i=1, 2) and (m ₁–m ₂) at leastO().Work partially supported by CNPq (Brasil)     

The particle structure ofv-dimensional Ising models at low temperatures

In this work we study thev-dimensional Ising model at low temperatures and establish the existence of an upper gap in the energy-momentum spectrum of the two-point function forv3. Forv=2, it is known that this gap is absent.Supported in part by Conselho Nacional de Pesquisas (CNPq-Brazil), Universidade Federal de Minas Gerais (Brazil) and the National Science Foundation under Grant PHY76-17191     

Synthesis of some 2-(heteroarylamino)benzimidazoles and their cyclization with phosgene

2-(Benzimidazol-2-ylamino)pyridine (4a) , 2-(benzimidazol-2-ylamino)pyrazine (4b) , and 2-(benzimidazol-2-ylamino)thiazole (4c) underwent a ring-closure reaction on treatment with phosgene affording 6H-pyrimido-[1′,2′:5,4][1,3,5]triazino[1,2-a]benzimidazol-6-one (1a) , 6H-pyrazino[1′,2′:5,4][1,3,5]triazino[1,2-a]benzimidazol-6-one (1b) , and 5H-thiazolo[2′,3′:4,5][1,3,5]triazino[1,2-a]benzimidazol-5-one (1c) respectively. The structure of these hitherto unknown heterocyclic systems was confirmed by their ir and mass spectra.     

Photophysics of aromatic molecules with low-lying pi sigma* states: excitation-energy dependence of fluorescence in jet-cooled aromatic nitriles

Excitation-energy dependence of fluorescence intensity and fluorescence lifetime has been measured for 4-dimethylaminobenzonitrile (DMABN), 4-aminobenzonitrile (ABN), 4-diisopropylaminobenzonitrile (DIABN), and 1-naphthonitrile (NN) in a supersonic free jet. In all cases, the fluorescence yield decreases rather dramatically, whereas the fluorescence lifetime decreases only moderately for S1 (pi pi*, L(b)) excess vibrational energy exceeding about 1000 cm(-1). This is confirmed by comparison of the normalized fluorescence excitation spectrum with the absorption spectrum of the compound in the vapor phase. The result indicates that the strong decrease in the relative fluorescence yield at higher energies is due mostly to a decrease in the radiative decay rate of the emitting state. Comparison of the experimental results with the TDDFT potential energy curves for excited states strongly suggests that the decrease in the radiative decay rate of the aminobenzonitriles at higher energies is due to the crossing of the pi pi* singlet state by the lower-lying pi sigma*(C[triple bond]N) singlet state of very small radiative decay rate. The threshold energy for the fluorescence "break-off" is in good agreement with the computed energy barrier for the pi pi*/pi sigma* crossing. For NN, on the other hand, the observed decrease is in fluorescence yield at higher excitation energies can best be attributed to the crossing of the pi pi* singlet state by the pi sigma* triplet state.     

Carboxylate-bridged copper(II)-lanthanide(III) complexes [(Cu(3)Ln(2)(oda)(6)(H(2)O)(6)).12H(2)O](n)(Ln = Dy,Ho, Er,Y; oda = oxydiacetate)

The hydrothermal reaction of Ln(2)O(3) (Ln = Dy and Ho), Cu(OAc)(2).2H(2)O, and oxydiacetic acid in the approximate mole ratio of 1:3:8 resulted in the formation of two new members of the isostructural series of polymers formulated as [(Cu(3)Ln(2)(oda)(6)(H(2)O)(6)).12H(2)O](n), crystallizing in the hexagonal crystal system, space group P6/mcc (No. 192). Temperature-dependent magnetic susceptibilities and EPR spectra are reported for the heterometallic compounds Cu-Dy 1, Cu-Ho 2, Cu-Er 3, and Cu-Y 4. The results are discussed in terms of the structure of the compounds, the electronic properties of the lanthanide ions, and the exchange interactions between the magnetic ions.     

Bis(1,10‐phenanthroline)(thio­sulfato)­manganese(II) methanol solvate and catena‐poly­[[di­aqua(2,9‐di­methyl‐1,10‐phenanthroline)­manganese(II)]‐μ‐thio­sulfato]

The structure of bis(1,10‐phenanthroline‐κ²N,N′)(thio­sulfato‐κ²O:S)­manganese(II) methanol solvate, [Mn(S₂O₃)(C₁₂H₈N₂)₂]·CH₃OH, is made up of Mn²⁺ centers coordinated to two bidentate phenanthroline (phen) groups and an S,O‐chelating thio­sulfate anion, forming monomeric entities. The structure of catena‐poly­[[di­aqua(2,9‐di­methyl‐1,10‐phen­anthro­line‐κ²N,N′)­manganese(II)]‐μ‐thio­sulfato‐κ²O:S], [Mn(S₂O₃)(C₁₄H₁₂N₂)(H₂O)₂]_n, is polymeric, consisting of Mn(dmph)(H₂O)₂ units (dmph is 2,9‐di­methyl‐1,10‐phenanthroline) linked by thio­sulfate anions acting in an S,O‐chelating manner.     

Two nickel complexes stabilized by nitrate counter‐ions

Two new nickel nitrates, di­aqua­bis(3,4,7,8‐tetra­methyl‐1,10‐phenanthroline‐κ²N,N′)­nickel(II) dinitrate methanol solvate, [Ni(C₁₆H₁₆N₂)₂(H₂O)₂](NO₃)₂·CH₄O, (I), and tri­aqua­[2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine‐κ³N¹,N²,N⁶]nickel(II) di­ni­trate trihydrate, [Ni(C₁₈H₁₂N₆)(H₂O)₃](NO₃)₂·3H₂O, (II), are reported. In both structures, the cation is octahedrally coordinated, to two bidentate 3,4,7,8‐tetra­methyl‐1,10‐phenanthroline (tmp) and two water mol­ecules in (I), and to one tridentate 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tpt) and three water mol­ecules in (II). Both structures are stabilized by extensive hydrogen‐bonding interactions.