A Thallium Mediated Route to \u3cem\u3eσ\u3c/em\u3e-Arylalkynyl Complexes of Bipyridyltricarbonylrhenium(I)

A simple, one-pot preparation of rhenium(I) σ-arylalkynyl complexes is reported using thallium(I) hexafluorophosphate as a halogen abstraction agent. This new route to rhenium σ-alkynyls enjoys higher yields compared to analogous preparations using silver salts by eliminating potential electrochemical degradation pathways

Using Sterics to Promote Reactivity in \u3cem\u3efac\u3c/em\u3e-Re(CO)\u3csub\u3e3\u3c/sub\u3e Complexes of Some ‘Non-Innocent’ NNN-Pincer Ligands

Two new redox active ligands based on di(2-(3-organopyrazolyl)-p-tolyl)amine have been prepared in order to investigate potential effects of steric bulk on the structures, electronic properties, or reactivity of tricarbonylrhenium(I) complexes. Replacing the hydrogens at the 3-pyrazolyl positions with alkyl groups causes significant distortion to the ligand framework due to potential interactions between these groups when bound to a fac-Re(CO)3 moiety. The distortions effectively increase the nucleophilic character of the central amino nitrogen and ligand-centered reactivity of the metal complexes

Manipulating Self-Assembly in Silver(I) Complexes of 1,3-Di-\u3cem\u3eN\u3c/em\u3e-pyrazolylorganyls

Three di-N-pyrazolylorganyls with different conformational flexibilities in the three-atom organyl spacers have been prepared, and the self-assembly properties with AgBF4 have been studied both in solution and in the solid state. All ligands give low-coordinate silver(I) centers that are capable of participating in multiple noncovalent interactions, but only the rigid 1,8-dipyrazolylnaphthalene ligand promotes very short Ag−Ag contacts

Chemical Switching Behaviour of Tricarbonylrhenium(I) Complexes of a New Redox Active ‘Pincer’ Ligand

The structures and optoelectronic properties of tricarbonylrhenium(I) complexes of di(2-pyrazolyl-p-tolyl)amine in its neutral and deprotonated (uninegative amido) form were investigated. Reactions of the complexes with Brønsted acids or bases result in distinctive changes of colour and electrochemical activity owing to the non-innocent nature of the ligand

Ligand-Promoted Solvent-Dependent Ionization and Conformational Equilibria of Re(CO)\u3csub\u3e3\u3c/sub\u3eBr[CH\u3csub\u3e2\u3c/sub\u3e(\u3cem\u3eS\u3c/em\u3e-tim)\u3csub\u3e2\u3c/sub\u3e] (tim = 1-methylthioimidazolyl). Crystal Structures of Re(CO)\u3csub\u3e3\u3c/sub\u3eBr[CH\u3csub\u3e2\u3c/sub\u3e(\u3cem\u3eS\u3c/em\u3e-tim)\u3csub\u3e2\u3c/sub\u3e] and {Re(CO)\u3csub\u3e3\u3c/sub\u3e(CH\u3csub\u3e3\u3c/sub\u3eCN)[CH\u3csub\u3e2\u3c/sub\u3e(S-tim)\u3csub\u3e2\u3c/sub\u3e]}(PF\u3csub\u3e6\u3c/sub\u3e)

The compounds Re(CO)3Br[CH2(S-tim)2] (1) and {Re(CO)3(CH3CN)[CH2(S-tim)2]}(PF6) (2), where tim is 1-methylthioimidazolyl, were prepared in high yields and characterized both in the solid state and in solution. The solid-state structures show that the ligand acts in a chelating binding mode where the eight-member chelate ring adopts twist-boat conformations in both compounds. A comparison of both solid-state IR data for CO stretching frequencies and the solution-phase voltammetric measurements for the Re1+/2+ couples between 1, 2, and related N,N-chelates of the rhenium tricarbonyl moiety indicate that the CH2(S-tim)2 ligand is a stronger donor than even the ubiquitous dipyridyl ligands. A combination of NMR spectroscopic studies and voltammetric studies revealed that compound 1 undergoes spontaneous ionization to form {Re(CO)3(CH3CN)[CH2(S-tim)2]+}(Br-) in acetonitrile. Ionization does not occur in solvents such as CH2Cl2 or acetone that are less polar and Lewis basic (less coordinating). The equilibrium constant at 293 K for the ionization of 1 in CH3CN is 4.3 × 10-3. The eight-member chelate rings in each 1 and 2 were found to be conformationally flexible in all solvents, and boat-chair conformers could be identified. Variable-temperature NMR spectroscopic studies were used to elucidate the various kinetic and thermodynamic parameters associated with the energetically accessible twist-boat to twist-boat and twist-boat to boat-chair interconversions

Single-Field Inflation After WMAP5

Single-field models of inflation are analysed in light of the WMAP five-year data. Assuming instantaneous reheating, we find that modular/new inflation models with small powers in the effective inflaton self-interaction are more strongly constrained than previously. The model with a cubic power lies outside the 2 sigma regime when the number of e-folds is less than 60. We also find that the predictions for the intermediate model of inflation do not overlap the 1 sigma region regardless of the power of the monomial potential. We analyse a number of ultra-violet, DBI braneworld scenarios involving both wrapped and multiple-brane configurations, where the inflaton kinetic energy is close to the maximum allowed by the warped geometry. In all cases, we find that the parameters of the warped throat are strongly constrained by observations.Comment: 10 pages, 5 figures, revtex4. Figures, table and text updated to match the version that has been accepted to Phys Rev

BORAZANs: Tunable Fluorophores Based on 2-(Pyrazolyl)aniline Chelates of Diphenylboron

The reaction between 2-pyrazolyl-4-X-anilines, H(pzAnX), (X = para-OMe (L1), Me (L2), H (L3), Cl (L4), CO2Et (L5), CF3 (L6), CN (L7)) and triphenylboron in boiling toluene affords the respective, highly emissive N,N‘-boron chelate complexes, BPh2(pzAnX) (X = para-OMe (1), Me (2), H (3), Cl (4), CO2Et (5), CF3 (6), CN (7)) in high yield. The structural, electrochemical, and photophysical properties of the new boron complexes can be fine-tuned by varying the electron-withdrawing or -donating power of the para-aniline substituent (delineated by the substituent\u27s Hammett parameter). Those complexes with electron-withdrawing para-aniline substituents such as CO2Et (5), CF3 (6), and CN (7) have more planar chelate rings, more ‘quinoidal\u27 disortion in the aniline rings, greater chemical stability, higher oxidation potentials, and more intense (φF = 0.81 for 7 in toluene), higher-energy (blue) fluorescent emission compared to those with electron-donating substituents. Thus, for 1 the oxidation potential is 0.53 V versus Ag/AgCl (compared to 1.12 V for 7), and the emission is tuned to the yellow-green but at an expense in terms of lower quantum yields (φF = 0.07 for 1 in toluene) and increased chemical reactivity. Density functional calculations (B3LYP/6-31G*) on PM3 energy-minimized structures of the ligands and boron complexes reproduced experimentally observed data and trends and provided further insight into the nature of the electronic transitions

Cosmic microwave background multipole alignments in slab topologies

Several analyses of the microwave sky maps from the Wilkinson Microwave Anisotropy Probe (WMAP) have drawn attention to alignments amongst the low-order multipoles. Amongst the various possible explanations, an effect of cosmic topology has been invoked by several authors. We focus on an alignment of the first four multipoles (\ell = 2 to 5) found by Land and Magueijo (2005), and investigate the distribution of their alignment statistic for a set of simulated cosmic microwave background maps for cosmologies with slab-like topology. We find that this topology does offer a modest increase in the probability of the observed value, but that even for the smallest topology considered the probability of the observed value remains below one percent.Comment: 6 pages RevTex with 6 figures included. Minor changes to match version accepted as Physical Review D Rapid Communicatio

Predictions of the causal entropic principle for environmental conditions of the universe

The causal entropic principle has been proposed as a superior alternative to the anthropic principle for understanding the magnitude of the cosmological constant. In this approach, the probability to create observers is assumed to be proportional to the entropy production \Delta S in a maximal causally connected region -- the causal diamond. We improve on the original treatment by better quantifying the entropy production due to stars, using an analytic model for the star formation history which accurately accounts for changes in cosmological parameters. We calculate the dependence of \Delta S on the density contrast Q=\delta\rho/\rho, and find that our universe is much closer to the most probable value of Q than in the usual anthropic approach and that probabilities are relatively weakly dependent on this amplitude. In addition, we make first estimates of the dependence of \Delta S on the baryon fraction and overall matter abundance. Finally, we also explore the possibility that decays of dark matter, suggested by various observed gamma ray excesses, might produce a comparable amount of entropy to stars.Comment: RevTeX4, 13pp, 10 figures; v2. clarified introduction, added ref

The Evolution of the Cosmic Microwave Background

We discuss the time dependence and future of the Cosmic Microwave Background (CMB) in the context of the standard cosmological model, in which we are now entering a state of endless accelerated expansion. The mean temperature will simply decrease until it reaches the effective temperature of the de Sitter vacuum, while the dipole will oscillate as the Sun orbits the Galaxy. However, the higher CMB multipoles have a richer phenomenology. The CMB anisotropy power spectrum will for the most part simply project to smaller scales, as the comoving distance to last scattering increases, and we derive a scaling relation that describes this behaviour. However, there will also be a dramatic increase in the integrated Sachs-Wolfe contribution at low multipoles. We also discuss the effects of tensor modes and optical depth due to Thomson scattering. We introduce a correlation function relating the sky maps at two times and the closely related power spectrum of the difference map. We compute the evolution both analytically and numerically, and present simulated future sky maps.Comment: 23 pages, 11 figures; references added; one figure dropped and minor changes to match published version. For high-resolution versions of figures and animations, see http://www.astro.ubc.ca/people/scott/future.htm