Electronic stabilization of trigonal bipyramidal clusters: the role of the Sn(II) ions in [Pt5(CO)5{Cl2Sn(μ-OR)SnCl2}3]3- (R = H, Me, Et, iPr)

The new [Pt(5)(CO)(5){Cl(2)Sn(μ-OR)SnCl(2)}(3)](3-) (R = H, Me, Et, (i)Pr; 1-4) clusters contain trigonal bipyramidal (TBP) Pt(5)(CO)(5) cores, as certified by the X-ray structures of [Na(CH(3)CN)(5)][NBu(4)](2)[1]·2CH(3)CN and [PPh(4)](3)[4]·3CH(3)COCH(3). The TBP geometry, which is rare for group 10 metals, is supported by an unprecedented interpenetration with a nonbonded trigonal prism of tin atoms. By capping all the Pt(3) faces, the Sn(II) lone pairs account for both Sn-Pt and Pt-Pt bonding, as indicated by DFT and topological wave function studies. In the TBP interactions, the metals use their vacant s and p orbitals using the electrons provided by Sn atoms, hence mimicking the electronic picture of main group analogues, which obey the Wade's rule. Other metal TBP clusters with the same total electron count (TEC) of 72 are different because the skeletal bonding is largely contributed by d-d interactions (e.g., [Os(5)(CO)(14)(PR(3))(μ-H)(n)](n-2), n = 0, 1, 2). In 1-4, fully occupied d shells at the Pt(ax) atoms exert a residual nucleophilicity toward the adjacent main group Sn(II) ions permitting their hypervalency through unsual metal donation.     

Temperature effects upon aqueous micellar-assisted decarboxylation of 6-nitrobenzisoxazole-3-carboxylate and its 5-methyl derivative

An investigation of temperature effects upon first-order rate constants in the micellar pseudophase for decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) and its 5-methyl derivative (6-NBIC-5-Me) was carried out. Surfactants used were cationic cetyltrialkylammonium bromide with alkyl = methyl (CTABr), ethyl (CTEABr), n-propyl (CTPABr), and n-butyl (CTBABr). The investigation shows that micelles speed up reactions by decreasing enthalpies of activation. Increase in head group bulk further speeds reactions still by a small decrease in the enthalpies, for both substrates. Values of DeltaH# and DeltaS# for 6-NBIC in the various surfactants give linear isokinetic plot, with CTBABr as outlier.     

Grazing‐incidence X‐ray diffraction study of rubrene epitaxial thin films

The growth of organic semiconductors as thin films with good and controlled electrical performances is nowadays one of the main tasks in the field of organic semiconductor‐based electronic devices. In particular it is often required to grow highly crystalline and precisely oriented thin films. Here, thanks to grazing‐incidence X‐ray diffraction measurements carried out at the ELETTRA synchrotron facility, it is shown that rubrene thin films deposited by organic molecular beam epitaxy on the surface of tetracene single crystals have the structure of the known orthorhombic polymorph, with the (2 0 0) plane parallel to the substrate surface. Moreover, the exact epitaxial relationship between the film and the substrate crystalline structures is determined, demonstrating the presence of a unique in‐plane orientation of the overlayer.     

The Kolmogorov Operator Associated to a Burgers SPDE in Spaces of Continuous Functions

We are concerned with a viscous Burgers equation forced by a perturbation of white noise type. We study the corresponding transition semigroup in a space of continuous functions weighted by a proper potential, and we show that the infinitesimal generator is the closure (with respect to a suitable topology) of the Kolmogorov operator associated to the stochastic equation. In the last part of the paper we use this result to solve the corresponding Fokker-Planck equation.     

The resonance raman spectra of manganates (VII) with different counterions

As part of a study of the RR spectra of different manganates, the spectra of RbMnO₄, CsMnO₄, AgMnO₄, Sr(MnO₄)₂.3H₂O and La(MnO₄)₃.nH₂O were obtained and interpreted in comparison with those of other permanganates previously reported. The analysis of the corresponding X₁₁ anharmonicity constants and full-widths at half maxima of the members of the vν₁ progressions allowed a wider insight into the effects of the countercations on the vibrational properties of the MnO^?₄ ion.     

Investigation by solid-phase microextraction and gas chromatography/mass spectrometry of secondary metabolites in lichens deposited on stone monuments

Lichens are ubiquitous organisms formed by symbiotic associations of fungal hyphas and algae that also grow under often extreme environmental conditions. They produce secondary metabolites, the so-called lichen substances, whose structural characterization can give an important contribution to lichen taxonomy. Lichens are also widely employed as biomonitors of atmospheric pollution; being epiphyte organisms they tend, in fact, to accumulate exogenous compounds. Moreover, it could be questioned if the environmental stress alters their secondary metabolites production. Therefore, a new strategy for the analysis of the organic substances absorbed or metabolized by lichens has been developed. This method exploits the dry solid-phase microextraction (SPME) headspace technique coupled with gas chromatography/mass spectrometry (GC/MS). Lichens coating the stone surfaces of monuments, located in small towns between high mountains and far away from urban environments, have been investigated. In the field of cultural heritage, this study can contribute to the knowledge of the state of conservation of outdoor exposed historical monuments.     

Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as kinetic probe for piperazinium-based cationic micelles

A new class of cationic surfactants containing the heterocyclic piperazinium ring in their covalent structure was prepared; cetyldialkylpiperazinium halides, CRPX, with alkyl=Me (CMPX), Et (CEPX), n-Pr (CPPX), and with halide=Br and Cl. They were characterized by measures of critical micellar concentration, cmc, and ionization degree, alpha, and also by use of the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as a kinetic probe to investigate the properties of the microinterface they provide in aqueous solutions. The pseudophase kinetic treatment fails to fit the data at high [surfactant], which show anomalies with abrupt increase in k(obs), especially for CEPX and CPPX. Data can be fitted up to [surfactant] ca. 0.1 M, and 0.2 M in some cases. Compared with cetyltrialkylammonium halides, values of k'(M) indicate a water-richer microenvironment and less important interface property changes with increasing head group bulk. The reaction could be studied both in the presence and in the absence of NaOH; comparison shows that NaOH affects only the shape of the kinetic profile at low [surfactant], without affecting the microenvironment provided by mature micelles.     

Metal complexes of phytohormones. Part IV. Interactions of tetrakis-μ-acetato dirhodium(II) with 6-furfurilaminopurine, 6-benzylaminopurine, 6-furfurilaminopurine riboside and 6-benzylaminopurine riboside

Summary Interactions of tetrakis--acetato-dirhodium(II) with purine-derived ligands of biological interest such as the cytokinins 6-furfurilaminopurine (K), 6-benzylaminopurine (BAP), 6-furfurilaminopurine riboside (KR) and 6-benzylaminopurine riboside (BAPR) have been studied by means of magnetic susceptibility measurements at room temperature, i.r. and electronic spectroscopy and thermogravimetric analysis 11 metal:ligand adducts were obtained with all ligands; in addition 12 adducts were obtained with KR and BAPR. The most plausible structure for the 11 adducts is a polymeric bridging one, involving both axial positions of the Rh^II dimer and two N-sites of the purine moiety; for the 12 adducts only one N-site is involved.     

European and American options: The semi-Markov case

In this paper, we assume that the log return of the underlying asset follows a semi-Markov process, then from the knowledge of the kernel we derive an explicit expression for the value of the option and for the bare risk in the case of the European call (put) option and, by means of a recursive system, we derive the value and the bare risk in the case of the American option. The prices and risks we obtained depend explicitly on the waiting-time distributions of the asset and they are duration dependent. The link with models based on Markov Chains and Continuous Time Random Walks is debated.     

Erratum: Future pricing through homogeneous semi‐Markov processes

The original article to which this Erratum refers was published in Applied Stochastic Models in Business and Industry 2005; 21 (3):241–249