Dynamic processes in silyl palladium complexes: evidence for intermediate Si-H and Si-Si sigma-complexes

The silyl palladium complexes (dcpe)PdH(SiHtBu2) and (dcpe)Pd(SiHMe2)2 display NMR spectra that vary with temperature. The dynamic NMR behavior is consistent with long-lived sigma-complexes as intermediates. In the case of (dcpe)PdH(SiHtBu2), the intermediate is believed to be a symmetric complex with doubly bridged hydrogen atoms between the silicon and palladium. Dynamic interchange of the two silicon atoms in (dcpe)Pd(SiHMe2)2 is consistent with an intermediate Si-Si sigma-complex.     

Flow equivalence of sofic shifts

We classify certain sofic shifts (the irreducible Point Extension Type, or PET, sofic shifts) up to flow equivalence, using invariants of the canonical Fischer cover. There are two main ingredients.

1. (1)
   An extension theorem, for extending flow equivalences of subshifts to flow equivalent irreducible shifts of finite type which contain them.
    
2. (2)
   The classification of certain constant to one maps from SFTs via algebraic invariants of associated G-SFTs.
    

     

Binding of carboxylic acids by fluorescent pyridyl ureas

Fluorescent pyrid-2-yl ureas were prepared by treating halogenated 2-aminopyridines with hexyl isocyanate, followed by Sonogashira coupling with arylacetylenes. The sensors emit light of ～360 nm with quantum yields of 0.05-0.1 in acetonitrile solution. Addition of strong organic acids (pK(a) < 13 in CH(3)CN) shifts the fluorescence band to lower energy, and clean isoemissive behavior is observed. Fluorescence response curves (i.e., F/F(0) vs [acid](total)) are hyperbolic in shape for CCl(3)COOH and CF(3)COOH, with association constants on the order of 10(3) M(-1) for both acids. (1)H NMR titrations and DFT analyses indicate that trihaloacetic acids bind in ionized form to the receptors. Pyridine protonation disrupts an intramolecular H-bond, thereby unfolding an array of ureido NH donors for recognition of the corresponding carboxylates. Methanesulfonic acid protonates the sensors, but no evidence for conjugate base binding at the urea moiety is found by NMR. An isosteric control compound that lacks an integrated pyridine does not undergo significant fluorescence changes upon acidification.     

CdSe infiltrated TiO2 based omnidirectional photonic crystals for visible light control

Control of light emission by engineering the electromagnetic vacuum is important in photonics for fundamental understanding as well as in applications. Omnidirectional photonic crystals such as logpile photonic crystals provide a very interesting system to study such phenomena. Here, we describe the first steps towards achieving systematic and reproducible control of light using titanium dioxide (TiO₂) logpile photonic crystals (PC) with incorporated cadmium chalcogenide (CdSe) quantum dots (QDs) (λ  600 nm) to potentially modify QD photoluminescence (PL). We present a technique for coating a monolayer of the QDs on the PC rods based on 3-mercaptopropyltrimethoxysilanol linkage and measured the resulting PL response. Comparison of the PL spectra to a finite difference time domain model shows the need for further localization of QDs and fabrication of additional PC unit cells to observe PL modification.     

Synthesis of and structure–property relationships in zinc complexes of bis‐metaphenylene semiquinone biradical species

The design of novel, functionalized bis‐metaphenylene semiquinone (SQ) ligands and their corresponding metal complexes which combine conformational flexibility and electron‐withdrawing, electron‐donating, and conjugating substituents enable investigation of multiple structure–property relationships. Along these lines, we report the synthesis of three new bis(Zn^II(SQ)Tp^Cum,Me) complexes containing the bis‐metaphenylene coupling fragment. Using electron paramagnetic resonance spectroscopy, ab initio computations and superconducting quantum interference device magnetometry, we show how spin‐density is affected by the bis‐metaphenylene system substituents. Copyright © 2011 John Wiley & Sons, Ltd.     

Factoring Factor Maps

A noninjective bounded-to-one factor map from an irreducibleshift of finite type onto a sofic system can be factored asa composition of other such maps in only finitely many ways(up to isomorphism). This generalizes to factor maps from systemswith canonical coordinates to finitely presented dynamical systems.     

Magnetic penetration depths of (BiPb)-2212 and (TlPb)-1212 — Universal correlations revisited

A systematic study of the dependence of the critical temperature on the superconducting carrier density, as measured by ⁺SR, was carried out for a variety of cuprate oxides. We have shown that substitution of Pb for Bi and La for Sr result in well pinned vortex lattices in Bi₂Sr₂CaCu₂O_x, and studied (BiPb)-2212 from the underdoped to the slightly overdoped regime. We also found that Tl-1212 samples, which have optimal maximumT _c=108 K, trace a separate line with parameters comparable to overdoped Tl-2223 at the maximum. These data, together with data on Y-124/247, Tl-2201 and other cuprates result in an larger set of universal correlations between T_c and(0) n _s /m ^* for the high temperature superconductors.     

N2′-acetyl-6-diacetoxymethylpterin

Treatment of folic acid with bromine in 48% hydrobromic acid gives the hydrobromide salt of 6-formylpterin ( 1 ), and acetylation of 1 with recovered acetic anhydride leads to N^2′-acetyl-6-diacetoxymethylpterin ( 3 ).     

The polarization phenomena of spherical molecules

The calculation of the polarizabilities of spherical molecules is discussed in the light of the average excitation energy approximation to perturbation theory. It is shown that whilst information about the energy in external fields can always be obtained from polarization phenomena, some information about the unperturbed wave function also can be obtained from magnetic susceptibility and Cotton–Mouton effect measurements. In the case of argon such information was found to agree with the results of self-consistent-field calculations. Predictions of the Cotton–Mouton constants of krypton and xenon are made.     

Hydrolysis of tin(II) neo-pentoxide: syntheses, characterization, and X-ray structures of [Sn(ONep)(2)](infinity), Sn(5)(mu(3)-O)(2)(mu-ONep)(6), and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) where ONep = OCH(2)CMe(3)

The reaction of [Sn(NMe(2))(2)](2) (1) with 4 equiv of HOCH(2)CMe(3) (HONep) leads to the isolation of [Sn(ONep)(2)](infinity) (2). Each Sn atom is four coordinated with mu-ONep ligands bridging the metal centers; however, if the free electrons of the Sn(II) metal center are considered, each Sn center adopts a distorted trigonal bipyramidal (TBP) geometry. Through (119)Sn NMR experiments, the polymeric compound 2 was found to be disrupted into smaller oligomers in solution. Titration of 2 with H(2)O led to the identification of two unique hydrolysis products characterized by single-crystal X-ray diffraction as Sn(5)(mu(3)-O)(2)(mu-ONep)(6) (3) and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) (4). Compound 3 consists of an asymmetrical molecule that has five Sn atoms arranged in a square-based pyramidal geometry linked by four basal mu-ONep ligands, two facial mu(3)-O, and two facial mu-ONep ligands. Compound 4 was solved in a novel octahedral arrangement of six Sn cations with an asymmetric arrangement of mu(3)-O and mu-ONep ligands that yields two square base pyramidal and four pyramidal coordinated Sn cations. These compounds were further identified by multinuclear ((1)H, (13)C, (17)O, and (119)Sn) solid-state MAS and high resolution, solution NMR experiments. Because of the complexity of the compounds and the accessibility of the various nuclei, 2D NMR experiments were also undertaken to elucidate the solution behavior of these compounds. On the basis of these studies, it was determined that while the central core of the solid-state structures of 3 and 4 is retained, dynamic ligand exchange leads to more symmetrical molecules in solution. Novel products 3 and 4 lend structural insight into the stepwise hydrolysis of Sn(II) alkoxides.