Metal complexes of 2-(2′-or 8′-quinolyl)benzimidazoles and benzothiazoles

Summary The copper(II), cobalt(II) and nickel(II) chloride and bromide complexes with the ligands 2-(2-quinolyl)-benzimidazole (qbi), 2-(4-methyl-2-quinolyl)benzimidazole (mqbi), 2-(4-methyl-8-quinolyl)benzothiazole (m'q'bt) have been prepared and characterized by analytical methods, magnetic measurements as well as by electronic absorption, e.s.r. and far i.r. spectra. Complexes of various stoichiometries have been isolated, namely MLX₂ (all cobalt complexes with exception of the bromide qbi complex; the chloride and bromide nickel m'q'bt and mq'bt complexes), ML₂X₂ (M=Co,L=qbi and X=Br; M=Ni, L=mqbi, X=Cl or Br, M=Ni, L=qbi, X=Cl) and ML₃X₂(M=Ni, L=qbi or mqbi, X=Br). The cobalt ion has a distorted tetrahedral N₂X₂ coordination in all the CoLX₂ complexes, whereas Co(qbi)₂Br₂ is six-coordinate. The following conclusions may be drawn for the nickel complexes: in those with the 11 metal-to-ligand molar ratio the metal ion is four-or five-coordinate; in those with the 12 and 13 ratios the metal ion is hexa-coordinate, being essentially bound to four nitrogen atoms with halogens, oxygens from water or methanol or nitrogen atoms (from the third ligand) occupying the axial positions.     

Stepwise electron-induced demolition of the Ni-I σ-bond in complexes with tetradentate tripodal ligands: A theoretical rationalization of structural and electrochemical results

The X-ray structural analysis of the compound [(pp₃)Nil]BPh₄ (complex d), pp₃ = P(CH₂CH₂PPh₂)₃, is presented. The complex cation has an almost regular trigonal bipyramidal geometry (TBP) with distances Ni-I and Ni-P_ax of 2.546(2) and 2.142(3) Å, respectively. This structure completes a series of strictly related nickel complexes, namely [(np₃)Nil]I, complex a; (np₃)Nil, complex b; (np₃)Ni, complex c; [(pp₃)NiHClO₄), complex e; [np₃ = N(CH₂CH₂PPh₂)₃] The complexes are redox derivatives [Ni(II), Ni(I), Ni(O)] that can be isolated via chemistry and/or electrochemistry. In the solid state complexes c and e have a trigonal pyramidal (TP) structure, whereas, electrochemical measurements suggest that in solution the TBP structure with a very elongated Ni-I bond can also have a finite lifetime. EHMO calculations offer a satisfying interpretation of the main structural trends in complexes a e, in particular, those relative to axial bond stretching, and clarify the different roles of phosphine vs. the amine axial donor. Moreover, the correlation is discussed between the electrode potentials and the nature of the Ni-I ^* MO that accepts or releases the electrons exceeding thed ⁸ configuration of Ni(II).     

2h-1p Cl calculations of ionization potentials of small molecules: Corrections to the koopmans theorem

2h-1p Cl calculations of ionization potentials have been performed on N₂, F₂, HNO, HOF, trans-N₂H₂, cis-N₂H₂, H₂NN, O₃, F₂O and C₂N₂, both with ground state and relaxed orbitals. Several inversions present at the KT level are recovered and a good qualitative agreement with experimental values and results of accurate calculations is achieved. Interaction with the 2h-1p configurations is found to be responsible for the major correlation effects.     

Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers

We report the synthesis and characterization of nanosized zinc oxide particles and their application on cotton and wool fabrics for UV shielding. The nanoparticles were produced in different conditions of temperature (90 or 150 °C) and reacting medium (water or 1,2-ethanediol). A high temperature was necessary to obtain small monodispersed particles. Fourier transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray powder diffractometry (XRD) were used to characterize the nanoparticles composition, their shape, size and crystallinity. The specific surface area of the dry powders was also determined. ZnO nanoparticles were then applied to cotton and wool samples to impart sunscreen activity to the treated textiles. The effectiveness of the treatment was assessed through UV–Vis spectrophotometry and the calculation of the ultraviolet protection factor (UPF). Physical tests (tensile strength and elongation) were performed on the fabrics before and after the treatment with ZnO nanoparticles.     

Comment on “The structure of monolayer SiO2 on Mo(1 1 2): A 2-D [Si-O-Si] network or isolated [SiO4] units?”

In a recent paper by Chen and Goodman [M. Chen, D.W. Goodman, Surf. Sci. 600 (2006) L255] the structure of SiO₂ films epitaxially grown on Mo(1 1 2) has been revisited. This structure has been the subject of several experimental and theoretical studies but it is still controversial, with some authors claiming that it is formed by isolated [SiO₄] units and others in favor of a two-dimensional [Si-O-Si] network. With this Comment we want do underline some aspects of the discussion, in particular related to the theoretical work performed so far on this subject, which in our opinion have not been properly represented in Ref. [M. Chen, D.W. Goodman, Surf. Sci. 600 (2006) L255].     

Elastic theory of surface deformation in C60 adsorption

In molecular physisorption, beyond attractive and repulsive forces, a third contribution arises from the elastic deformation of the surface. In this paper the dimple appearing on a gold surface upon physisorption of a C₆₀ molecule is studied and its effect on the adsorption energy is evaluated.The depth and shape of the dimple are studied on the basis of the theory of elasticity. The equilibrium equation is solved in the presence of the body forces originating from a suitable Au-C₆₀ interaction potential and the solution for the deformation field is obtained by means of a two-step procedure. In the first step a curl-free deformation field is obtained, which takes the effects of the body forces into account, but generates mismatch of the boundary conditions. In the second step the solution of the equilibrium problem in the absence of body force is generated, which compensates the previous boundary condition violation. Thanks to linearity, the final solution is obtained as the sum of the results of the two steps. An (approximate) iterative scheme is applied for taking the surface deformation into account in imposing that no forces act on the Au surface.When the distance z₀ of the centre of the C₆₀ cage from the surface is rather large, the dimple is represented by a bulging surface, but, as the C₆₀ approaches the Au surface, the surface recedes and a well formed dimple appears. The corresponding depth at the mechanical equilibrium position (z₀ = 4.8 Å) turns out to be 36.3 pm.     

The influence of thermal annealing on oxygen uptake and combustion rates of a bituminous coal char

The effect of thermal annealing on the combustion reactivity of a bituminous coal char has been investigated with a focus on the role of the formation of surface oxides by oxygen chemisorption. The combined use of thermogravimetric analysis and of analysis of the off-gas during isothermal combustion of char samples enabled the determination of the rate and extent of oxygen uptake along burn-off. Combustion was carried out at temperatures between 350 and 510 °C. Char samples were prepared by controlled isothermal heat treatment of coal for different times (in the range between 1 s and 30 min) at different temperatures (in the range 900–2000 °C). Results indicate that oxygen uptake is extensive along burn off of chars prepared under mild heat treatment conditions. The maximum oxygen uptake is barely affected by the combustion temperature within the range of combustion conditions investigated. The severity of heat treatment has a pronounced effect on char combustion rate as well as on the extent and rate at which surface oxides are built up by oxygen chemisorption. Chars prepared under severe heat treatment conditions show negligible oxygen uptake and strongly reduced combustion rates. Altogether it appears that a close correlation can be established between the extent and the accessibility of active sites on the carbon surface and the combustion rate. Despite the investigation has been carried out at temperatures well below those of practical interest, results provide useful insight into the relationship existing between thermal annealing, formation of surface oxide and combustion reactivity which is relevant to the proper formulation of detailed kinetic models of char combustion.     

On a dynamical system related to fluid mechanics

We introduce a dynamical system strictly related to fluid mechanics and similar to the classical N point vortex system. In the first part we analyze the qualitative behavior of the time evolution and in particular we show the properties of collapse and chaoticity. In the second part of the paper we investigate the relation of the dynamical system with a system of N concentrated large enough smoke rings in an incompressible and inviscid fluid, with axial symmetry and without swirl. We prove the rigorous connection between the two models at time zero for any N. The extension of the same result to any time is obtained only for a smoke ring alone, while for the general case it is just a matter of conjecture. Received June 1998; Revised November 1998     

A global condition for periodic Duffing-like equations

We study Duffing-like equations of the type ,with periodic. We prove that if the stable and unstable manifolds to the origin do not coincide, then the system exhibits positive topological entropy.

     

NHCs as Neutral Donors towards Polyphosphorus Complexes

The first adducts of NHCs (=N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η⁵-P₅)] ( 1 ) (Cp*=pentamethyl-cyclopentadienyl) with IMe (=1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp′′Ta(CO)₂(η⁴-P₄)] (Cp′′=1,3-di-tert-butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo-P₃-containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.