1,404 research outputs found
Aurophilic interactions in polynuclear Au(I) complexes with phosphine ligands containing imidazole rings
Aurophilic interactions in polynuclear Au(I)
complexes with phosphine ligands containing
imidazole rings
Fiorella Bachechiaa*, Alfredo Burinib, Rossana Galassib
aIstituto di Strutturistica Chimica, C.N.R., Area della Ricerca di Roma,
C.P. 10, 00016 Monterotondo St. (Roma), Italy., bDipartimento di Scienze
Chimiche, Università di Camerino, 62032 Camerino, Italy. E-mail:
[email protected]
Keywords: gold complexes, aurophilicity, crystal
structures
The tertiary phosphines of the type (Bzim)3-nPhnP, where Bzim
is 1-benzyl-2-imidazolylphosphine and n varies from 0 to 2,
were synthesised as part of a program aimed to the study of
the coordination chemistry of phosphines containing imidazole
rings. The softer character of imidazole, with respect to other
heterocycles, turned out to be useful in the stabilization of
complexes with soft metals as those of Group 11 in low oxidation
states. These ligands can behave as monodentate or as P, N
bidentate forming dinuclear cationic complexes. With Au(I)
they were found to be able to favour the formation of intraand
intermolecular aurophilic interactions. TheAu(I) complexes
assume considerable interest when aurophilic bonds occur
between gold atoms, since their chemical and physical properties
change to particular characteristics with potential applications
in electronic, optical or sensor devices. In particular short
Au•••Au interactions are considered related to optoelectronic
properties as observed in a number of polynuclear gold
compounds. Here the structures of two Au(I) complexes are
reported. The binuclear complex [μ-(Bzim)Ph2PAu2(C6F5)2]
adopts a folded conformation with parallel, eclipsed C6F5
rings and a corresponding short AucccAu contact of 3.033(2)Ã….
The tetranuclear cluster complex {[μ-N,N’-(Bzim)3PAuCl]2
Au2}2+c AuCl2
- c AuCl4
- consists in a 12-membered macrocycle
with two gold atoms coordinated to two (Bzim)3P
molecules, in bridging mode, through the nitrogen atoms of the
imidazole rings and two gold atoms coordinated to the
phosphorus atoms of the (Bzim)3P ligands. Two chloride atoms
complete the Au bicoordination. Three strong aurophilic interactions,
Au(1)cccAu(4) [2.989(2)Ã…], Au(2)cccAu(3) [3.014(2)Ã…]
andAu(1)cccAu(2) [3.257(3)Ã…], occur.Aweak gold-gold contact,
Au(3)cccAu(4) [3.766(2)Ã…], is also present.
Understanding molecular interactions
23r
Gamma-ray Bursts, Classified Physically
From Galactic binary sources, to extragalactic magnetized neutron stars, to
long-duration GRBs without associated supernovae, the types of sources we now
believe capable of producing bursts of gamma-rays continues to grow apace. With
this emergent diversity comes the recognition that the traditional (and newly
formulated) high-energy observables used for identifying sub-classes does not
provide an adequate one-to-one mapping to progenitors. The popular
classification of some > 100 sec duration GRBs as ``short bursts'' is not only
an unpalatable retronym and syntactically oxymoronic but highlights the
difficultly of using what was once a purely phenomenological classification to
encode our understanding of the physics that gives rise to the events. Here we
propose a physically based classification scheme designed to coexist with the
phenomenological system already in place and argue for its utility and
necessity.Comment: 6 pages, 3 figures. Slightly expanded version of solicited paper to
be published in the Proceedings of ''Gamma Ray Bursts 2007,'' Santa Fe, New
Mexico, November 5-9. Edited by E. E. Fenimore, M. Galassi, D. Palme
The hidden X-ray breaks in afterglow light curves
Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a
perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift
era. Specifically, relatively few breaks, consistent with jet breaks, are
observed in the X-ray light curves of these bursts. If these breaks are truly
missing, it has serious consequences for the interpretation of GRB jet
collimation and energy requirements, and the use of GRBs as standard candles.
Here we address the issue of X-ray breaks which are possibly 'hidden' and
hence the light curves are misinterpreted as being single power-laws. We show
how a number of precedents, including GRB 990510 & GRB 060206, exist for such
hidden breaks and how, even with the well sampled light curves of the Swift
era, these breaks may be left misidentified. We do so by synthesising X-ray
light curves and finding general trends via Monte Carlo analysis. Furthermore,
in light of these simulations, we discuss how to best identify achromatic
breaks in afterglow light curves via multi-wavelength analysis.Comment: 4 pages, contributed talk, submitted to the proceedings of Gamma Ray
Bursts 2007, Santa Fe, New Mexico, November 5-9 200
GRBs and the thermalization process of electron-positron plasmas
We discuss the temporal evolution of the pair plasma created in Gamma-Ray
Burst sources. A particular attention is paid to the relaxation of the plasma
into thermal equilibrium. We also discuss the connection between the dynamics
of expansion and the spatial geometry of the plasma. The role of the baryonic
loading parameter is emphasized.Comment: 4 pages, 3 figures, in the Proceedings of the "Gamma Ray Bursts 2007"
meeting, November 5-9, 2007, Santa Fe, New Mexico, US
Dispersion analysis of the nucleon form factors including meson continua
Dispersion relations provide a powerful tool to analyse the electromagnetic
form factors of the nucleon for all momentum transfers. Constraints from
meson-nucleon scattering data, unitarity, and perturbative QCD can be included
in a straightforward way. In particular, we include the 2pi, rho-pi, and KKbar
continua as independent input in our analysis and provide an error band for our
results. Moreover, we discuss two different methods to include the asymptotic
constraints from perturbative QCD. We simultaneously analyze the world data for
all four form factors in both the space-like and time-like regions and
generally find good agreement with the data. We also extract the nucleon radii
and the omega-NN coupling constants. For the radii, we generally find good
agreement with other determinations with the exception of the electric charge
radius of the proton which comes out smaller. The omega-NN vector coupling
constant is determined relatively well by the fits, but for the tensor coupling
constant even the sign can not be determined.Comment: 24 pages, 9 figure
GRB 070714B - Discovery of the Highest Spectroscopically Confirmed Short Burst Redshift
Gemini Nod & Shuffle spectroscopy on the host of the short GRB 070714B shows
a single emission line at 7167 angstroms which, based on a grizJHK photometric
redshift, we conclude is the 3727 angstrom [O II] line. This places the host at
a redshift of z=.923 exceeding the previous record for the highest
spectroscopically confirmed short burst redshift of z=.546 held by GRB 051221.
This dramatically moves back the time at which we know short bursts were being
formed, and suggests that the present evidence for an old progenitor population
may be observationally biased.Comment: Conference procedings for Gamma Ray Bursts 2007 November 5-9, 2007
Santa Fe, New Mexico (4 pages, 2 figures
Optomechanical sideband cooling of a thin membrane within a cavity
We present an experimental study of dynamical back-action cooling of the
fundamental vibrational mode of a thin semitransparent membrane placed within a
high-finesse optical cavity. We study how the radiation pressure interaction
modifies the mechanical response of the vibrational mode, and the experimental
results are in agreement with a Langevin equation description of the coupled
dynamics. The experiments are carried out in the resolved sideband regime, and
we have observed cooling by a factor 350 We have also observed the mechanical
frequency shift associated with the quadratic term in the expansion of the
cavity mode frequency versus the effective membrane position, which is
typically negligible in other cavity optomechanical devices.Comment: 15 pages, 7 figure
The Construction of Sorkin Triangulations
Some time ago, Sorkin (1975) reported investigations of the time evolution
and initial value problems in Regge calculus, for one triangulation each of the
manifolds and . Here we display the simple, local characteristic
of those triangulations which underlies the structure found by Sorkin, and
emphasise its general applicability, and therefore the general validity of
Sorkin's conclusions. We also make some elementary observations on the
resulting structure of the time evolution and initial value problems in Regge
calculus, and add some comments and speculations.Comment: 5 pages (plus one figure not included, available from author on
request), Plain Tex, no local preprint number (Only change: omitted
"\magnification" command now replaced
Influence of static electric fields on an optical ion trap
We recently reported on a proof-of-principle experiment demonstrating optical
trapping of an ion in a single-beam dipole trap superimposed by a static
electric potential [Nat. Photonics 4, 772--775 (2010)]. Here, we first discuss
the experimental procedures focussing on the influence and consequences of the
static electric potential. These potentials can easily prevent successful
optical trapping, if their configuration is not chosen carefully. Afterwards,
we analyse the dipole trap experiments with different analytic models, in which
different approximations are applied. According to these models the
experimental results agree with recoil heating as the relevant heating effect.
In addition, a Monte-Carlo simulation has been developed to refine the
analysis. It reveals a large impact of the static electric potential on the
dipole trap experiments in general. While it supports the results of the
analytic models for the parameters used in the experiments, the analytic models
cease their validity for significantly different parameters. Finally, we
propose technical improvements for future realizations of experiments with
optically trapped ions.Comment: 16 pages, 16 figure
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