Search results for "Bridging"

Vibrational properties of the surface-nonbridging oxygen in silica nanoparticles

2008

By studying the site-selective luminescence spectra of oxidized silica nanoparticles we identify the electronic and the vibrational lines associated with the surface nonbridging oxygen, $\ensuremath{\equiv}{\text{Si-O}}^{\ifmmode\bullet\else\textbullet\fi{}}$. This defect emits a zero-phonon line inhomogeneously distributed around 2.0 eV with full width at half maximum of 0.04 eV, weakly coupled with the local ${\text{Si-O}}^{\ifmmode\bullet\else\textbullet\fi{}}$ stretching mode whose frequency is measured to be $920\text{ }{\text{cm}}^{\ensuremath{-}1}$. These findings are different from those of the well-characterized defect in the bulk silica thus evidencing structural peculiarities of …

Time Resolved Photoluminescence Associated with Non Bridging Oxygen Hole Centers in Irradiated Silica

2007

Interconversion between non-bridging oxygen hole center and peroxy radical in F2-laser-irradiated SiO2 glass

2004

Formation processes of the peroxy radical (POR) were examined in high-purity SiO 2 glass exposed to F 2 -laser light which creates mobile atomic oxygen (O 0 ) by photolyzing the interstitial oxygen molecules (O 2 ). It was proved that under these conditions POR is formed by a reaction of the non-bridging oxygen hole center (NBOHC, an oxygen dangling bond) with O 0 , not by a reaction between the E' center (a silicon dangling bond) and O 2 . Subsequent exposure to KrF laser light photolyzes POR and recoveres NBOHC by dissociating the O-O bond in POR. These findings corroborate the important role of O° in defect processes in SiO 2 glass.

Ethnographic Knowledge in Urban Planning:Bridging the Gap between the Theories of Knowledge-Based and Communicative Planning

2021

Publisher Copyright: © 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. ‘Knowledge-based’ approaches have recently made a breakthrough in urban planning. How to develop balance in knowledge-based planning between abstract and scientific knowledge, on the one hand, and ‘local knowledge’ on the other hand has been long debated. To this debate, we add a form of knowledge with potential for sustainable urban planning, i.e. ethnographic knowledge that could transmit an understanding of urban dwellers’ daily practices and values to planning organisations. Theoretical literature is the foundation of our argument, which we illustrate with a case study involvin…

Spin Density Maps in the Triplet Ground State of [Cu2(t-Bupy)4(N3)2](ClO4)2 (t-Bupy = p-tert-butylpyridine):  A Polarized Neutron Diffraction Study

1998

This paper is devoted to the determination of the spin distribution in the spin triplet ground state of [Cu-2(t-Bupy)(4)(N-3)(2)](ClO4)(2), With t-Bupy = p-tert-butylpyridine. The crystal structure, previously solved at room temperature from X-ray diffraction, has been redetermined at 18 K from unpolarized neutron diffraction. The structure consists of binuclear cations in which Cu2+ ions are doubly bridged by azido groups in the 1,1-fashion, and noncoordinated perchlorate anions. The experimental spin distribution has been determined from polarized neutron diffraction (PND) at 1.6 K under 50 kOe. The spin populations have been found to be strongly positive on the Cu2+ ions, weakly positive…

Solvent-dependent SCO Behavior of Dinuclear Iron(II) Complexes with a 1,3,4-Thiadiazole Bridging Ligand

2016

Two dinuclear iron(II) complexes [Fe2(μ-L)2]X4*4DMF (X = BF4(-) (1·4DMF) and ClO4(-) (2·4DMF)) with a 1,3,4-thiadiazole bridging ligand have been synthesized and show a very distinct solvent-depending SCO behavior. The complexes represent new solvatomorphs of the first dinuclear iron(II) complexes with the ligand L (2,5-bis[(2-pyridylmethyl)amino]methyl-1,3,4-thiadiazole). The incorporated lattice DMF molecules directly affect the spin state of these complexes. This behavior reveals a structural insight into the role of the solvent molecules on the spin transition.

Solid‐State Anion–Guest Encapsulation by Metallosupramolecular Capsules Made from Two Tetranuclear Copper(II) Complexes

2007

A new cationic tetranuclear copper(II) complex self-assembles from one 1,3-phenylenebis(oxamato) (mpba) bridging ligand and four CuII ions partially blocked with N,N,N′,N′-tetramethylethylenediamine (tmen) terminal ligands. In the solid state, two of these tetracopper(II) oxamato complexes of bowl-like shape and helical conformation then serve as a building block for the generation of either hetero- (MP) or homochiral (MM/PP) dimeric capsules depending on the nature of the encapsulated anion guest, perchlorate or hexafluorophosphate. The overall magnetic behaviour of these metallosupramolecular capsules does not depend on the nature of the encapsulated anion guest, but it is consistent with…

Synthesis, X‐ray Studies and Magnetic Properties of Dinuclear Ni II and Cu II Complexes Bridged by the Azo‐2,2′‐bipyridine Ligand

2003

Two new paramagnetic transition metal complexes that contain the bridging ligand azo-2,2-bipyridine (abpy) have been prepared and characterized by X-ray crystallography and magnetic susceptibility measurements. The compound [Ni2(µ-abpy)(CH3CN)2(NO3)4]·2CH3CN (1·2CH3CN) crystallizes in the triclinic space group P1 ¯ with a = 8.290(5) A u , b = 8.343(5) A u , c = 11.180(5) A u , α = 105.36(3)°, β = 94.39(3)°, γ = 107.56(3)°, V = 700.5(7) A u 3 and Z = 1. The related salt [Cu2(µ

Intramolecular versus intermolecular exchange pathways in the binuclear complex [Cu2(H2tea)2(4,4′-bipy)](ClO4)2·3H2O (H3tea=triethanolamine and 4,4′-…

2001

Abstract The binuclear copper(II) complex of formula [Cu2(H2tea)2(4,4′-bipy)](ClO4)2·3H2O (1) (H3tea=triethanolamine and 4,4′-bipy=4,4′-bipyridine) has been isolated and characterized by X-ray diffraction. Its structure consists of dinuclear [Cu2(H2tea)2(4,4′-bipy)]2+ cations, uncoordinated perchlorate anions and crystallization water molecules. Each copper atom exhibits a trigonal-bipyramidal environment with the three triethanolamine-oxygen atoms building the equatorial plane, and the triethanolamine-nitrogen and one of the 4,4′-bipy nitrogen atoms defining the three-fold axis. The 4,4′-bipy molecule acts as a bismonodentate bridging ligand, the copper–copper separation across it being 11…

Long-distance magnetic coupling in dinuclear copper(II) complexes with oligo-para-phenylenediamine bridging ligands

2010

Abstract Two novel dinuclear copper(II) complexes of formulae [Cu2(tren)2(bpda)](ClO4)4 (2) and [Cu2(tren)2(tpda)](ClO4)4 (3) containing the tripodal tris(2-aminoethyl)amine (tren) terminal ligand and the 4,4′-biphenylenediamine (bpda) and 4,4″-p-terphenylenediamine (tpda) bridging ligands have been synthesized and structurally, spectroscopically, and magnetically characterized. Their experimentally available electronic spectroscopic and magnetic properties have been reasonably reproduced by DFT and TDDFT calculations. Single crystal X-ray diffraction analysis of 2 shows the presence of dicopper(II) cations where the bpda bridging ligand adopts a bismonodentate coordination mode toward two …