Search

The copper hydride nanocluster (NC) [Cu29Cl4H22(Ph2phen)12]Cl (2; Ph2phen = 4,7-diphenyl-1,10-phenanthroline) was isolated cleanly, and in good yields, by controlled growth from the smaller NC, [Cu25H22(PPh3)12]Cl (1), in the presence of Ph2phen and a chloride source at room temperature. Complex 2was fully characterized by single-crystal X-ray diffraction, XANES, and XPS, and represents a rare example of an N*= 2 superatom. Its formation from 1demonstrates that atomically precise copper clusters can be used as templates to generate larger NCs that retain the fundamental electronic and bonding properties of the original cluster. A time-resolved kinetic evaluation of the formation of 2reveals that the mechanism of cluster growth is initiated by rapid ligand exchange. The slower extrusion of CuCl monomer, its transport, and subsequent capture by intact clusters resemble elementary steps in the reactant-assisted Ostwald ripening of metal nanoparticles.

Spin crossover complexes are known to undergo bond length, volume, and enthalpy changes during spin transition. In an explosive spin crossover complex, these changes could affect the mechanical and initiation sensitivity of the explosive and lead to the development of a new class of sensitivity switchable materials. To explore this relationship, the well-known spin crossover compound [Fe(Htrz)3]n[ClO4]2n(1) was re-evaluated for its explosive properties, and its mechanical impact sensitivity was correlated to spin transition. A variable temperature impact test was developed and used to evaluate the impact sensitivity of 1in the low spin (LS, S = 0), thermally accessed high spin (HS, S = 2), and mixed LS and HS states. For comparison, the structurally similar Ni compound, [Ni(Htrz)3]n[ClO4]2n(2), which does not undergo a spin transition at accessible temperatures, was synthesized and characterized, and its explosive properties and variable temperature impact sensitivity measured. These results reveal a correlation between impact sensitivity and spin transition, where 1exhibits lower impact sensitivity in the LS state and increases in sensitivity upon transition to the HS state. Density functional theory was used to predict structural changes that occur upon spin transition that correlate to the change in sensitivity. This demonstrates, for the first time, an explosive spin crossover compound (ExSCO) that exhibits switchable impact sensitivity with a fully reversible internal switching mechanism.

Metal nitrides are strong refractory ceramic materials known for applications in the coatings, catalysis, and semiconductor industries. Lanthanide nitrides are difficult to prepare in high purity and often require high temperatures and sophisticated equipment. In this work, we present an approach to the synthesis of high-purity f-element nitrides through the use of simple lanthanide salts and the nitrogen-rich ligand 5,5′-bis(1H-tetrazolyl)amine (H2BTA) to form lanthanide complexes of 5,5′-bis(tetrazolato)amine (BTA2−). We have demonstrated that, when dehydrated, these types of complexes undergo a self-sustained combustion reaction under an inert atmosphere to yield nanostructured f-element nitride foams for lanthanum and cerium. The synthesis, characterization, and single-crystal X-ray crystallography of the BTA2−complexes of lanthanum, cerium, praseodymium, neodymium, and europium are also discussed.

High‐precision uranium‐thorium (U‐Th) dating of dead branching corals from Luhuitou reef, Sanya, northern South China Sea indicates that the reef framework grew episodically over the past 7,000 years. Episodes of coral reef growth (“switch‐on” phases) occurred in response to regional warming during the mid‐Holocene Climate Optimum, Medieval Warm Period, and Current Warm Period, when the East Asian summer monsoon was strong and the East Asian winter monsoon was weak. In contrast, episodes when reef growth dramatically slowed or ceased (“switch‐off” phases) occurred during comparatively cold periods (e.g., Dark Age Cold Period and Little Ice Age) and are linked to abrupt weakening of the East Asian summer monsoon and concurrent strengthening of the East Asian winter monsoon. In the context of global warming, the northern South China Sea may become an important refugium for coral reef growth of up to 2 °C above present, but only if local anthropogenic pressures are reduced. Understanding the response of coral reef growth to past warm periods allows better predictions of the response of coral reefs to future climate change and evaluations of the potential for the locality to act as climate change refugia for coral reefs in the 21st century. We identify abrupt coral reef recovery in the northern South China Sea (SCS) since the last century (especially post‐1960 CE), indicating that the Current Warm Period is an optimal episode for reef growth in the northern SCS. As our results suggest that expansive coral growth occurred in the mid‐Holocene when sea surface temperatures were up to 2 °C higher than present, the northern SCS may represent critical refugia for future reefs in the 21st century. U‐Th dating of corals reveals episodic reef growth in the northern South China Sea over the past 7,000 yearsEnhanced winter cooling associated with strengthened EAWM is the dominant stressor inhibiting reef growthReefs in the northern South China Sea are potential coral refugia in the context of global warming

We report a critical re-evaluation of the synthesis and characterization of Cu8(MPP)4. This product was reportedly formed by the reaction of Cu(NO3)2with 2-mercapto-5-n-propylpyrimidine (HMPP) and NaBH4, in ethanol, in the presence of [N(C8H17)4][Br]. In our hands, we found no experimental evidence to support the existence of Cu8(MPP)4in the reaction mixture. Instead, we demonstrate that the material isolated from this reaction is a complex mixture containing [N(C8H17)4]+, Br–, NO3–, and 2-mercapto-5-n-propyl-1,6-dihydropyrimidine (H2MPP*), along with the Cu(I) coordination polymer, [Cu(MPP)]n. To support our conclusions, we have independently synthesized H2MPP* and [Cu(MPP)]n, as well as the related Cu(I) coordination complexes, [Cu(HMPP*)]nand [Cu2(MPP*)]n. All new materials were characterized by NMR spectroscopy and mass spectrometry, while H2MPP*, [Cu(HMPP*)]n(n= 4), and [Cu(MPP)]n(n= 6) were also characterized by X-ray crystallography.

The group 11 hydride clusters [Ag6H4(dppm)4(OAc)2] (1) and [Cu3H(dppm)3(OAc)2] (2) (dppm = 1,1-bis(diphenylphosphino)methane) were synthesized in moderate yields from the reaction of M(OAc) (M = Ag, Cu) with Ph2SiH2, in the presence of dppm. Complex 1is the first structurally characterized homometallic polyhydrido silver cluster to be isolated. Both 1and 2catalyze the hydrosilylation of (α,β-unsaturated) ketones. Notably, this represents the first example of hydrosilylation with an authentic silver hydride complex.

A human transformed line of HeLa cells was treated with extracts prepared from Gymnocladus dioicus, Holodiscus discolor, Stephanandra tanakae, Ligustrum delavayanum, Ligustrum vulgare and Staphylea pinnata. The study evaluating the influence of the active extracts on HeLa cell division also reveals their acute, delayed and combined effect. A 35% degradation of HeLa cells was found after 72 h treatment with 62.5 µg/mL of the extract isolated from Stephanandra tanakae. A 100% lysis of HeLa cells was observed after 72 h treatment with a 125 µg/mL concentration of the extract prepared from Gymnocladus dioicus. The extracts from Ligustrum devayanum and Ligustrum vulgare were specifically effective only with HeLa cells. On the other hand, the extract prepared from Gymnocladus dioicus was effective on the bacteria and on the HeLa cells. Copyright © 2001 John Wiley & Sons, Ltd.

Phosphite, which often exists in growth solutions obtained directly from commercial P2O5, was found to have significant inhibiting effects on the growth of pyramidal face of KDP crystals. K(DxH1‐x)2PO4(referred to as DKDP) crystals with different deuterium fraction x were grown and the optical performances were investigated. The absorption coefficients at 1.05 μm decreases monotonically with the increase of x. The transmission threshold shift from 1.65μm at x=0 to 2.10 μm at x=0.96. The high temperature phase transition temperature and latent heat were measured using the method of differential scanning calorimetry (DSC). Thermal conditioning experiments were carried out at 180°C and 140°C for KDP and DKDP, respectively. After conditioning, a different degree of improvement was observed in the optical homogeneity of the samples, while the laser damage threshold and light absorption coefficient showed no significant change.

Summary The application of the multimoment integral method to the study of the base pressure behind a supersonic vehicle is examined. The primary purpose is to understand the exact nature of the Crocco-Lees critical point, which provides a uniqueness condition in the problem. The analysis is carried out mainly in Poincaré phase space, where the singularities of the differential equations are investigated. Two singular curves are found. The one which is physically meaningful for the near wake flow is located downstream of the rear stagnation point. This singular curve consists of saddle points which yield “wake” solutions, and focal points or saddle-foci. Only those saddle points which yield “wake” solutions correspond to Crocco-Lees critical points. Thus, the integration of the differential equations should be started from a saddle point both for the upstream and the downstream solutions. The current analysis then requires that one deal with only a one-parameter (freestream Mach number) family of solutions, rather than the two-parameter (freestream Mach number and Reynolds number based on thickness of the viscous shear layer at the rear stagnation point) family of solutions obtained in previous works. Finally, this paper clarifies anomalous details of previous numerical investigations carried out for the near wake by Webb, Golik, Vogenitz, and Lees.

A nonlinear theory for the calculation of the flow field of an oblique flat plate under blockage condition is given using the techniques of integral equations. Numerical results are obtained with the aid of a high-speed digital computer for the plate situated midchannel at values of the angle of attack from 10 to 90 deg and the channel width-chord ratio from 3 to 20. Although the theory is developed for arbitrary plate location, the midchannel case is of great interest due to the fact that most of the tests are performed at this position.

Reconstructing coral reef histories provides a window of understanding into reef response to changing environmental and climatic conditions over various temporal scales. Here we present the results of 117 U‐Th dates from emergent reef flat and slope cores and surface death assemblages, combined with previously published fossil microatoll data, to capture the entire sequence of reef growth at Mazie Bay, inshore Southern Great Barrier Reef (GBR). Coral U‐Th dates indicate that Mazie Bay reef initiated ~6,900 years before present (yr. BP) quickly filling accommodation space. While rates of vertical reef accretion (5.3 ± 1.0 mm year−1) were comparable to the GBR average during the mid‐Holocene (~5.0 mm year−1), reef flat progradation occurred at a rate 1.5‐ to 6‐fold previous GBR rates until 5,100 yr. BP (~70.4 cm year−1). Average progradation slowed to ~7.1 cm year−1in the subsequent ~4,000 years and reef slope cores indicate this reef had largely “turned‐off” by 400 yr. BP, with modern coral communities existing as a veneer over the largely senescent framework. Death assemblage dates highlight coral disturbance and recovery regimes in response to increased cyclone activity 1960–1985 AD and recent extreme sea surface temperature and flood events post 2000 AD. U‐Th dating of mid‐Holocene to modern coral deposits from Mazie Bay reef provides a unique insight into past reef development, response to recent disturbance regimes, and potential for future reef growth. In the case of Mazie Bay, our data suggest limited accommodation space and increased occurrence of sea surface temperature extremes will restrict future reef growth at this site. The 117 coral U‐Th dates from Mazie Bay reef provide an insight into reef dynamics at multiple temporal scalesMazie Bay reef initiated ~6,900 yr. BP and rapidly filled optimum available accommodation space, with reef growth slowing by 4,200 yr. BPU‐Th dating of death assemblages revealed quasi‐periodic cycles of disturbance and recovery over the past 60 years

The selected plant extracts exhibited antibacterial activity. The strongest effect was manifested by extracts prepared from Gymnocladus dioicus, Amelanchier ovalis, Exochorda racemosa, Holodiscus discolor, Philadelphus microphyllus, Philadelphus coronarius and Pelargonium tabulare. The percentage inhibition of bacterial growth was 0–41.8%. In addition it was found that extracts isolated from Amelanchier ovalis, Exochorda racemosa and Pelargonium tabulare were specifically effective only against the bacterial strains tested. Copyright © 2000 John Wiley & Sons, Ltd.