CO-induced formation of an interpenetrating bicuboctahedral Au2Pd18 kernel in nanosized Au2Pd28(CO)26(PEt3)10: formal replacement of an interior (μ12-Pd)2 fragment in the corresponding known isostructural homopalladium Pd30(CO)26(PEt3)10 with nonisovalent (μ12-Au)2 and resulting experimental/theoretical implications

Initially isolated from Pd(10)(CO)(12)(PEt(3))(6) (5) and Au(SMe(2))Cl precursors in a two-step carbon monoxide (CO)-involved procedure, the nanosized interpenetrating bicuboctahedral gold (Au)-palladium (Pd) Au(2)Pd(28)(CO)(26)(PEt(3))(10) (1) was then directly obtained in 25-30% yield from the CO-induced reaction of the CO-stable Au-centered cuboctahedral Au(2)Pd(21)(CO)(20)(PEt(3))(10) (3) with the structurally analogous CO-unstable Pd(23)(CO)(20)(PEt(3))(10) (4). Our hypothesis that this latter synthesis is initiated by the reaction of 3 with coordinatively unsaturated homopalladium species resulting from CO-induced fragmentation of 4 was subsequently substantiated by the alternatively designed synthesis of 1 (～25% yield) from the CO-induced reaction of 3 with the structurally dissimilar CO-unstable Pd(38)(CO)(28)(PEt(3))(12) (6). The composition of 1, unambiguously established from a 100 K CCD X-ray diffractometry study, is in accordance with single-crystal X-ray Au-Pd field-emission microanalysis. The pseudo-C(2h) 30-atom Au(2)Pd(28) geometry of 1 may be formally derived via substitution of the interior (μ(12)-Pd)(2) moiety in the interpenetrating bicuboctahedral Pd(20) kernel of the known isostructural Pd(30)(CO)(26)(PEt(3))(10) (2) with the corresponding interior (μ(12)-Au)(2) moiety, in which the otherwise entire metal-core geometry and CO/PR(3)-ligated environment are essentially not altered. Of major significance is that this interior nonisovalent Pd-by-Au replacement in 2 produces CO-stable 1, whereas nanosized CO/PR(3)-ligated homopalladium Pd(n) clusters with n > 10 are generally unstable under CO. Because the two adjacent encapsulated Au atoms of 2.811(1) ? separation are not present on the metal surface, isolation of 1 under CO is ascribed to an electronic property. The virtually ideal geometrical site-occupancy fit between 1 and 2 provides definite crystallographic evidence for extensive delocalization in 1 of the two valence Au 6s electrons over the entire cluster (instead of a "localized" covalent Au-Au electron-pair interaction). Gradient-corrected (pseudo-scalar-relativistic) density functional theory (DFT) calculations were performed on the isostructural Au(2)Pd(28)(CO)(26)(PH(3))(10) (1-H) and Pd(30)(CO)(26)(PH(3))(10) (2-H) model clusters along with hypothetical [Au(2)Pd(28)(1-H)](2+) and [Pd(30)(2-H)](2-) analogues (with phosphine ethyl substituents replaced by hydrogen ones). Natural population analysis of these four model clusters revealed similar highly positively charged metal surfaces of 28 Pd atoms relative to the two negatively charged interior metal atoms, which reflect a partially oxidized metal surface due to dominant CO back-bonding. The surprising observation that each less electronegative interior Pd atom in 2-H is more negatively charged by 0.30e than each interior Au atom in 1-H points to a more cationic Au in 1 than interior Pd in 2; this unexpected (opposite) charge difference is consistent with delocalization of each Au 6s valence electron toward a Au(+) configuration. This premise is in agreement with the calculated Wiberg bond index (WBI) value of 0.055 for the Au-Au bond order in 1-H versus the WBI single-bond value of 1.01 obtained from analogous DFT calculations for the bare, neutral Au(2) dimer, which has a much shorter spectroscopically determined gas-phase distance of 2.472 ? (that corresponds to a "localized" electron-pair interaction). Isolation of 1 under CO is of prime importance in nanoscience/nanotechnology in establishing relative stabilizations toward CO in well-defined CO/PEt(3)-ligated nonisovalent Pd(2)-by-Au(2)-substituted Au(2)Pd(n-2) clusters [namely, n = 30 (1) and 23 (3)]. These important stereochemical implications have a direct relevance to the recent report of the higher tolerance to CO poisoning of highly active Au-Pd nanoparticle catalysts used for the complete conversion of formic acid into high-purity hydrogen (and CO(2)) for chemical hydrogen storage.     

Optimization of Composition,Synthesis, and Study of Broadband Multilayer Mirrors for the EUV Spectral Range

Technical Physics - Broadband Mo/Si and Mo/Be multilayer stack-type mirrors for wavelength intervals of 11.1–13.8, 17–21, and 28–33 nm have been developed and fabricated. Uniform...     

Near-infrared luminescence of RbPb2Cl5:Bi crystals

A wideband near-IR (NIR) luminescence centered at 1080 nm was found in a RbPb(2)Cl(5):Bi single crystal grown by the Bridgman technique. Absorption, luminescence, and excitation of luminescence spectra were investigated at room and cryogenic temperatures. The luminescence was proposed to be due to the (3)P(1)-->(3)P(0) transition in Bi(+) ion.     

Side‐chain functionalized liquid crystalline polymers and blends, 2. Phase behavior of comb‐shaped liquid crystalline ionomers containing ions of alkaline metals

An effective way to synthesize liquid crystalline ionomers by an exchange reaction between the acid groups of functionalized LC polymers and a metal acetate was examined. A number of LC ionomers containing ions of the alkaline metals Na and Rb (1.2–18.3 mol‐%) were obtained. The introduction of small amounts (1.2–5 mol‐%) of metal ions into a functionalized LC polymer matrix leads to significant changes in the phase state of copolymers – the nematic phase is replaced by a SmA phase; an increase of the content of alkaline metal ions causes linear growth of clearing temperatures. The influence of the nature of the metal ions on the phase behavior of LC ionomers was determined. To describe the peculiarities of the LC ionomers' phase behavior a model based on the assumption that an ion multiplet is formed was proposed. Here, the rigidity of the functionalized LC copolymer chains used as a matrix for the preparation of LC ionomers was taken into consideration.     

Electronic and infrared absorption spectra of linear and cyclic C6+ in a neon matrix

Electronic and infrared absorption spectra of mass-selected C6+, generated by dissociative electron impact ionization of C6Cl6 and C6Br6, have been recorded in 6 K neon matrices. Linear and cyclic forms of C6+ have been observed. The 2Pig<--Chi2Piu electronic transition of linear C6+ has its origin band at 646 nm whereas for the (2) 2B2<--Chi2A1 system of the cyclic isomer it lies at 570 nm. An infrared active fundamental mode in the ground electronic state of C6+ is observed at 2092 and 1972 cm(-1) for the linear and cyclic isomer, respectively.     

Nanosized Pd37(CO)28{P(p-Tolyl)3}12 containing geometrically unprecedented central 23-atom interpenetrating tri-icosahedral palladium kernel of double icosahedral units: its postulated metal-core evolution and resulting stereochemical implications

Pd37(CO)28{P(p-Tolyl)3}12 (1) was obtained in approximately 50% yield by the short-time thermolysis of Pd10(CO)12{P(p-Tolyl)3}6 in THF solution followed by crystallization via layering with hexane under N2. The low-temperature (100 K) CCD X-ray diffraction study of 1 revealed an unusual non-spheroidal Pd37-atom polyhedron, which may be readily envisioned to originate via the initial formation of a heretofore non-isolated central Pd23 kernel composed of three interpenetrating trigonal-planar double icosahedra (DI) that are oriented along the three bonding edges of its interior Pd3 triangle. This central Pd23 kernel is augmented by face condensations with two additional phosphorus-free and 12 tri(p-C6H4Me)phosphine-ligated Pd atoms, which lower the pseudo-symmetry of the resulting 37-atom metal core from D(3h) to C2. The 12 P atoms and 28 bridging CO connectivities preserve the pseudo-C2 symmetry. The central Pd23 kernel in 1 provides the only crystallographic example of the 23-atom member of the double icosahedral family of "twinned" interpenetrating icosahedra (II), which includes the 19-atom two II (1 DI), the 23-atom three II (3 DI), the 26-atom four II (6 DI), and the 29-atom five II (9 DI). The n-atoms of these DI models coincide exactly with prominent atom-peak maxima of 19, 23, 26, and 29, respectively, in the mass spectrum of charged argon clusters formed in a low-temperature free-jet expansion. The only previous crystallographically proven 26- and 29-atom DI members are the central pseudo-T(d) tetrahedral Pd26 kernel (4 II, 6 DI) in the PMe3-ligated Pd29Ni3(CO)22(PMe3)13 (2) and the central pseudo-D(3h) trigonal-bipyramidal Pd29 kernel (5 II, 9 DI) in the PMe3-ligated Pd35(CO)23(PMe3)15 (3). Two highly important major stereochemical implications are noted: (1) The formation of geometrically identical idealized architectures for these three II palladium kernels with corresponding DI models constructed for the charged argon clusters provides compelling evidence that the nature of delocalized Pd-Pd bonding in these II (and presumably other nanosized) Pd clusters, in which each zerovalent Pd atom individually has a closed-subshell 4d (10) ground state, may likewise (as in argon clusters) be viewed primarily in terms of (considerably stronger) attractive dispersion interactions. (2) The existence of the 23-atom II Pd23 kernel in 1 provides an essential heretofore "missing" geometrical link as an intermediate in the same sequential growth pathway to give the 26- and 29-atom II Pd(n) kernels found in 2 and 3, respectively. Accommodation of the 12 bulky P(p-Tolyl)3 ligands around the entire 37-atom palladium core necessitates an extended metal surface that originates from the pseudo-2D trigonal-planar Pd23 kernel found in 1. The much smaller PMe3 ligands in 2 and 3 would sterically allow further sequential transformations of an initially formed 23-atom II intermediate palladium kernel into the 26-atom spheroidal II palladium kernel in 2 or further into the 29-atom semi-spheroidal II palladium kernel in 3, but with smaller total metal-atom nuclearities of 32 and 35, respectively.     

Near-infrared fluorophores containing benzo[c]heterocycle subunits

The syntheses and spectroscopic properties of eight new push-pull-type near-infrared fluorophores that contain either isobenzofuran or isothianaphthene subunits are presented. The isobenzofuran dyes demonstrate significantly red-shifted absorption compared with their isothianaphthene counterparts, which is attributed to isobenzofuran's more potent pro-quinoidal character.     

Radial limits of inner functions and Bloch spaces

Let be an inner function in the unit ball , . Assume that

where and is the radial derivative. Then, for all , the set has a non-zero real Hausdorff -content, and it has a non-zero complex Hausdorff -content.

     

Self-assembled monolayer initiated electropolymerization: a route to thin-film materials with enhanced photovoltaic performance

Continuing progress in the field of organic polymer photovoltaic (PV) devices requires the development of new materials with better charge-transport efficiency. To improve this parameter, we have investigated surface-attached bilayer polymer PV thin films prepared starting from a covalently attached monolayer of an electroactive initiator using sequential electropolymerization of dithiophene and its derivatives. These systems were found to show significantly increased photocurrent generation quantum yields as compared to systems made through conventional approaches. In addition, the described PV thin films possess remarkable mechanical, air, and photostability. These properties likely arise from the more uniform and better ordered bulk layer morphologies as well as tighter covalently bonded contacts at the interfacial junctions, contributing to improved charge transport. While more studies on the fundamental reasons behind the discovered phenomenon are currently underway, this information can be readily applied to build more efficient organic polymer photovoltaics.