Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains

New Co(II) members of the family of multifunctional materials of general formula [DAMS](4)[M(2)Co(C(2)O(4))(6)]·2DAMBA·2H(2)O (M(III) = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II), Mn(II), and Ni(II). This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the Rh(III) derivative demonstrate that high spin octacoordinated Co(II) centers behave very similarly to the hexacoordinated Co(II) ones, being dominated by a large orbital contribution. The Cr(III) derivative is characterized by ferromagnetic Cr(III)-Co(II) interactions. Most relevantly, the Fe(III) compound is characterized by a moderate antiferromagnetic interaction between Fe(III) and Co(II), resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ(0) = 8.6 × 10(-11) s and ΔE = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.     

N 1s photoelectron angular distributions from fixed-in-space NO2 molecules: stereodynamics and symmetry considerations

Angular distributions of N 1s photoelectrons from fixed-in-space NO(2) molecules have been measured over the energy region of shape resonance and above. A multiple-coincidence velocity-map imaging technique for observation of molecular frame photoelectron angular distributions (MF-PADs) has been extended to nonlinear molecular targets. Density functional theory calculations have also been conducted to elucidate the photoionization dynamics and shape resonance in the N 1s photoionization of NO(2). Results show that the N 1s MF-PADs exhibit strong shape variation as a function of both photoelectron kinetic energy and symmetries of final states, whereas asymmetry parameters of laboratory frame PADs show a local minimum around the shape resonance region and increase monotonically as the photon energy increases. Over the shape resonance, the spatial shape of the photoelectron wave function with b(2)-symmetry closely resembles that of 5b(2)(?) unoccupied molecular orbital of NO(2), although the MF-PAD pattern for b(2)-symmetry does not correspond directly to the 5b(2)(?) orbital shape. At higher kinetic energy of 90 eV, MF-PADs become less structured, but still show a significant dependence on the symmetry of final states.     

Existence conditions for non-safe loads in masonry-like bodies

We study the existence of minimizers for a class of noncoercive functionals, representing the strain energy of masonry-like bodies subject to loads that are not “safe” with respect to certain existence conditions estblished in the literature. Some more general sufficient conditions for existence are proved, and two simple noncoercive examples are discussed making use of these conditions.     

Free radical chemistry of disinfection-byproducts. 1. Kinetics of hydrated electron and hydroxyl radical reactions with halonitromethanes in water

Halonitromethanes are disinfection-byproducts formed during ozonation and chlorine/chloramine treatment of waters that contain bromide ion and natural organic matter. In this study, the chemical kinetics of the free-radical-induced degradations of a series of halonitromethanes were determined. Absolute rate constants for hydroxyl radical, *OH, and hydrated electron, e(aq)-, reaction with both chlorinated and brominated halonitromethanes were measured using the techniques of electron pulse radiolysis and transient absorption spectroscopy. The bimolecular rate constants obtained, k (M(-1) s(-1)), for e(aq)-/*OH, respectively, were the following: chloronitromethane (3.01 +/- 0.40) x 10(10)/(1.94 +/- 0.32) x 10(8); dichloronitromethane (3.21 +/- 0.17) x 10(10)/(5.12 +/- 0.77) x 10(8); bromonitromethane (3.13 +/- 0.06) x 10(10)/(8.36 +/- 0.57) x 10(7); dibromonitromethane (3.07 +/- 0.40) x 10(10)/(4.75 +/- 0.98) x 10(8); tribromonitromethane (2.29 +/- 0.39) x 10(10)/(3.25 +/- 0.67) x 10(8); bromochloronitromethane (2.93 +/- 0.47) x 10(10)/(4.2 +/- 1.1) x 10(8); bromodichloronitromethane (2.68 +/- 0.13) x 10(10)/(1.02 +/- 0.15) x 10(8); and dibromochloronitromethane (2.95 +/- 0.43) x 10(10) / (1.80 +/- 0.31) x 10(8) at room temperature and pH approximately 7. Comparison data were also obtained for hydroxyl radical reaction with bromoform (1.50 +/- 0.05) x 10(8), bromodichloromethane (7.11 +/- 0.26) x 10(7), and chlorodibromomethane (8.31 +/- 0.25) x 10(7) M(-1) s(-1), respectively. These rate constants are compared to recently obtained data for trichloronitromethane and bromonitromethane, as well as to other established literature data for analogous compounds.     

A practical synthetic route to functionalized THBCs and oxygenated analogues via intramolecular Friedel-Crafts reactions

A practical catalytic approach to the synthesis of 4-substituted 1,2,3,4-tetrahydro-beta-carbolines (THBCs, 1) and 1,2,3,9-tetrahydropyrano[3,4-b]indoles (2) via InBr3-catalyzed intramolecular Friedel-Crafts (F-C) cyclization is described. The use of cross-metathesis reaction represents a direct route to the cyclization precursors and the use of InBr3 (5 mol%) allowed polycyclic indole compounds to be isolated in high yields under mild reaction conditions (rt, DCM, minutes). Finally, efforts toward the development of a stereocontrolled version of the present cyclization are presented, highlighting [salenAlCl] and bimetallic [(salenAlCl)2-InBr3] system as promising chiral Lewis acids (ee up to 60%).     

Chelating versus bridging bonding modes of N-substituted bis(diphenylphosphanyl)amine ligands in Pt complexes and Co2Pt clusters

N-substituted dppa ligands Ph2P-NR-PPh2 [R = -CH2CH2SCH2C6H5 (1), -CH2CH2S(CH2)5CH3 (2), -(CH2)9CH3 (3), -C6H5 (4)] were used for the synthesis of cis-[PtCl2{Ph2PN(R)PPh2}] complexes [R = -CH2CH2SCH2C6H5 (5), -CH2CH2S(CH2)5CH3 (6), -(CH2)9CH3 (7), -C6H5 (8)] and heterotrinuclear clusters of formula [PtCo2(CO)7{Ph2PN(R)PPh2}] [R = -CH2CH2SCH2C6H5 (9), -CH2CH2S(CH2)5CH3 (10), -(CH2)9CH3 (11), -C6H5 (12)]. The presence of relatively bulky substituents on N resulted in a higher chelating power of the ligands. The thermodynamic study of the equilibrium between the chelate and the bridged forms of clusters 9-11 showed that the bridged form is favoured by enthalpic factors whereas entropic factors favour chelation. The structures of 5 and 9 were determined by single crystal X-ray diffraction.     

Near-infrared spectroscopy investigation of the water confined in tricalcium silicate pastes

Near-infrared (NIR) spectroscopy has been employed to investigate the evolution of the vibrational spectrum of water entrapped in a tricalcium silicate paste. The overall free water, which decreases as a function of time due to the formation of the hydrated phases (portlandite, Ca(OH)(2), and hydrated calcium silicate, C-S-H) during the hydration reaction, is quantified by the decrease in the area of the NIR band at about 5000 cm(-1). The coexistence of two types of water in the hydrated phases (a "surface-interacting water" (type I) and a "bulklike water" (type II)) during the hydration is obtained by the analysis of the band at about 7000 cm(-1). The deconvolution of this band allows the quantification of the two water types. As the reaction advances, part of the "bulklike water" is converted to "surface-interacting water" in direct agreement with the C-S-H surface development. Finally, the Ca(OH)(2) formation can be concurrently monitored by NIR through the increase of a very sharp peak at 7083 cm(-1). Near-infrared spectroscopy allows determination in a very simple way of the most important features of the tricalcium silicate setting process.     

Third-order multireference perturbation theory: the n-electron valence state perturbation-theory approach

A formulation of the n-electron valence state perturbation theory (NEVPT) at the third order of perturbation is presented. The present implementation concerns the so-called strongly contracted variant of NEVPT, where only a subspace of the first-order interacting space is taken into account. The resulting strongly contracted NEVPT3 approach is discussed in three test cases: (a) the energy difference between the 3B1 and 1A1 states of the methylene molecule, (b) the potential-energy curve of the N2 molecule ground state, and (c) the chromium dimer (Cr2) ground-state potential-energy profile. Particular attention is devoted to the last case where large basis sets comprising also h orbitals are adopted and where remarkable differences between the second- and third-order results show up.     

A new massively parallel version of CRYSTAL for large systems on high performance computing architectures

Fully ab initio treatment of complex solid systems needs computational software which is able to efficiently take advantage of the growing power of high performance computing (HPC) architectures. Recent improvements in CRYSTAL, a periodic ab initio code that uses a Gaussian basis set, allows treatment of very large unit cells for crystalline systems on HPC architectures with high parallel efficiency in terms of running time and memory requirements. The latter is a crucial point, due to the trend toward architectures relying on a very high number of cores with associated relatively low memory availability. An exhaustive performance analysis shows that density functional calculations, based on a hybrid functional, of low‐symmetry systems containing up to 100,000 atomic orbitals and 8000 atoms are feasible on the most advanced HPC architectures available to European researchers today, using thousands of processors. © 2012 Wiley Periodicals, Inc.