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We report the full characterization of a new organic nonlinear optical (NLO) crystal for intense THz generation: PNPA ((E)-4-((4-nitrobenzylidene)amino)-N-phenylaniline). We discuss crystal growth and structural characteristics. We present the wavelength dependence of THz generation, the thickness dependence of the THz spectrum for PNPA crystals, and measure the efficiency. PNPA enables intense THz generation that surpasses NLO crystals DAST and OH-1, which have been the standard in organic high-field THz generators for several years., 11 pages, 7 figures

We demonstrate a data mining approach to discover and develop new organic nonlinear optical crystals that produce intense pulses of terahertz radiation. We mine the Cambridge Structural Database for non-centrosymmetric materials and use this structural data in tandem with density functional theory calculations to predict new materials that efficiently generate terahertz radiation. This enables us to (in a relatively short time) discover, synthesize, and grow large, high-quality crystals of four promising materials and characterize them for intense terahertz generation. In a direct comparison to the current state-of-the-art organic terahertz generation crystals, these new materials excel. The discovery and characterization of these novel terahertz generators validates the approach of combining data mining with density functional theory calculations to predict properties of high-performance organic materials, potentially for a host of exciting applications., Comment: 16 pages, 5 figures

Due to their non-toxicity and their ability to be functionalized, magnetite (Fe3O4) nanoparticles (NPs) are good candidates for a variety of biomedical applications. To better implement their applications, it is crucial to well understand the basic structural and magnetic properties of the NPs in correlation with their synthesis method. Here, we show interesting properties of Fe3O4 NPs of various sizes ranging from 5 to 100 nm and the dependence of these properties on particle size and preparation method. One synthetic method based on heating Fe(acac)3 with oleic acid consistently gives 5 ± 1 nm NPs. A second method using the thermal decomposition of Fe(oleate)3 in oleic acid led to larger NPs, greater than 8 nm in size. Increasing the amount of oleic acid caused the average NP size to slightly increase from 8 to 10 nm. Increasing both the reaction temperature and the reaction time caused the NP size to drastically increase from 10 to 100 nm. Powder X-ray diffraction and electron-microscopy imaging show a pure single crystalline Fe3O4 phase for all NPs smaller than 50 nm and spherical in shape. When the NPs get larger than 50 nm, they notably tend to form faceted, FeO core–Fe3O4 shell structures. Magnetometry data collected in various field-cooling conditions show a pure superparamagnetic (SPM) behavior for all NPs smaller than 20 nm. The observed blocking temperature, $T_{B}$ , gradually increases with NP size from about 25–150 K. In addition, the Verwey transition is observed with the emergence of a strong narrow peak at 125 K in the magnetization curves when larger NPs are present. Our data confirm the vanishing of the Verwey transition in smaller NPs. Magnetization loops indicate that the saturating field drastically decreases with NP size. While larger NPs show some coercivity ( $H_{c}$ ) up to 30 mT at 400 K, NPs smaller than 20 nm show no coercivity ( $H_{c} = 0$ ), confirming their pure SPM behavior at high temperature. Upon cooling below $T_{B}$ , some of the SPM NPs gradually show some coercivity, with $H_{c}$ reaching 45 mT at 5 K for the 10 nm NPs, indicating emergent interparticle couplings in the blocked state.

Molecular organic crystals are strategically designed for nonlinear optical applications using push–pull chromophores as the core feature. In this approach, electron-donating and accepting groups are connected through a π-conjugated bridge to obtain planar molecules with high hyperpolarizability. However, the non-centrosymmetric packing that is required for nonlinear optical (NLO) applications is a critical challenge that must be addressed to design useful materials. In this article, we present the new organic cation 6MNEP that shows a large hyperpolarizability and can be crystallized in ideal non-centrosymmetric structures for NLO applications, when paired with T and 4NBS anions. The 6MNEP cation was obtained by extending the conjugation length of already existing chromophores. We compare the 6MNEP crystals with other crystals that also have cations with extended conjugation lengths, but result in centrosymmetric crystal structures. Using the effective hyperpolarizability, we found 6MNEP-T and 6MNEP-4NBS to have 1.6 to 2.5 times larger macroscopic nonlinearities than benchmark NLO organic crystals. Additionally, the significantly lower absorption wavelength compared with other state-of-the-art crystals make 6MNEP-T and 6MNEP-4NBS promising materials for NLO applications like intense terahertz generation.

We discover, develop, and test new organic nonlinear optical crystals that produce intense pulses of terahertz radiation through a combination of data mining from Cambridge Structural Database and density functional theory calculations.

We report the synthesis of a 2-phosphinoimidazole-derived bimetallic Rh(II) complex that enables intramolecular allene hydroamination to form 7- to 10-member rings in high yield. Monometallic Rh complexes, in contrast, fail to achieve any product formation. We demonstrate a broad substrate scope for formation of various

We report the synthesis of a bimetallic Rh(I) complex containing a bridging CO ligand that facilitates Rh–Rh bond formation. This bimetallic complex enables intramolecular allene hydroamination to form seven to ten-member rings in high yield. Monometallic Rh complexes, in contrast, fail to achieve any product formation. We demonstrate a broad substrate scope for formation of a variety of N-heterocycles in good to excellent yields. Macrocyclization reactions that form eleven to fifteen-membered heterocycles are also demonstrated. Mechanistic studies show that the reaction likely proceeds via catalyst protonation by trifluoroacetic acid, followed by reversible allene insertion and C–N bond-forming reductive elimination. The difference in product selectivity observed with our bimetallic catalyst vs monometallic Rh complexes may result from cooperativity between the two metals.

The synthesis of six chiral titanium-containing phosphinoamide ligands is discussed. These ligands assemble chiral heterobimetallic Pd–Ti complexes, enable enantioselective intramolecular allylic aminations with hindered amine nucleophiles and achieve selectivity up to 53% ee. Mechanistic studies demonstrate the reversibility of the enantio-determining C–N bond forming step, which leads to a gradual increase in the % ee of the reaction over time. These results represent a rare example of enantioselective heterobimetallic catalysis and suggest that these new ligands could find broad application in enantioselective transition metal catalysis.

To our knowledge, there is no precedent for the direct conversion of light alkanes to aminated products by CH activation. Previous molecular systems reported for alkane amination operate by radical...

Metal organic frameworks (MOFs) are a novel class of materials that consist of a lattice of metal centers linked by organic molecules. Previously, heat capacities and thermodynamic functions have been reported for a series of crystalline polymorphs of Zn(EtIm)2, a zeolitic imidazolate framework family of MOFs that have potential applications in CO2 sequestration. In those studies, an anomalous trend in the heat capacity and thermodynamic functions was observed that was not predicted. To further investigate these materials and their thermodynamic data, the low-temperature heat capacities of imidazole, 2-methylimidazole, and 2-ethylimidazole, organic linkers that are present in Zn(EtIm)2 and similar materials, were measured by a Quantum Design Physical Property Measurement System (PPMS) from 1.8–300 K. The data collected was fit to theoretical functions below 10 K, orthogonal polynomials from 5–60 K, and a sum of Debye and Einstein functions above 50 K. These functions were used to generate Cp,m°, Δ0TSm°, Δ0THm°, and Φm° values at smoothed temperatures from 0–300 K. This investigation revealed the presence of a second-order phase transition in 2-ethylimidazole that may yield insight into the anomalous heat capacity behavior present in Zn(EtIm)2.

A series of eight new ethyl (Z)-benzotriazolyl acrylates 6a–d and 7a–d have been synthesized by conventional heating and microwave irradiation from ethyl benzotriazolyl acetates 3 and 4 with the corresponding aromatic aldehydes. This work reports the synthetic approach and spectroscopic characterization (1H, 13C-NMR, HRMS) of all the synthesized compounds. X-ray diffraction analyses were performed for molecules 6a, 7a and 7d. Photophysical properties of compounds were evaluated. Finally, compound 6a was tested in a human cell line and showed low to no cytotoxicity at relevant concentrations. Initial testing demonstrates its potential use as a fluid-phase fluorescent marker for live cell imaging.

We report the synthesis of bimetallic Pd(I) and Pd(II) complexes scaffolded on bidentate 2-phosphinoimidazole ligands. These complexes display unique catalytic activity and enable the expeditious formation of 1,3-disubstituted naphthalenes via an unprecedented coupling of aryl iodides and methyl ketones in the presence of silver triflate. Excellent substrate scope for naphthalene formation is also demonstrated. Mechanistic studies suggest that the transformation proceeds via Pd-catalyzed arylation of a methyl ketone, followed by cyclization with a second equivalent of ketone. Importantly, this ketone arylation processes occurs under oxidizing conditions, suggesting involvement of higher oxidation state dimeric Pd catalysts. Based on experiments and DFT calculations, we propose a mechanism involving high oxidation state Pd(III) bimetallic catalysis. These new bimetallic complexes possess reactivity that is not seen with monometallic Pd catalysts and we confirm the importance of the palladium catalyst for both arylation and cyclization for naphthalene formation.

In this work, copper and tungsten were sputtered onto silicon wafers by direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering(HiPIMS). The resulting films were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy(SEM), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and X-ray diffraction (XRD). By EDX and XPS, all the sputtered films showed only the expected metal peaks. By XPS, the surfaces sputtered by DCMS were richer in oxygen than those produced by HiPIMS. By AFM, the surfaces were quite smooth. The root mean square (RMS) roughness values are as follows: 0.83 nm (W, HiPIMS), 1.10 nm (W,DCMS), 0.85 nm (Cu, HiPIMS), and 1.78 nm (Cu, DCMS). By SEM, the HiPIMS films exhibited smaller grain sizes, which was confirmed by XRD. The crystallite sizes estimated by XRD are as follows: 4 nm (W, body-centered cubic, HiPIMS), 13 nm (W,body-centered cubic, DCMS), 7 nm (W, cubic, HiPIMS), 14 nm (W, cubic, DCMS), 25nm (Cu, HiPIMS), and 35 nm (Cu, DCMS). By SE, the HiPIMS surfaces showed higher refractive indices, which suggested that they were denser and less oxidized than the DCMS surfaces. Refereed/Peer-reviewed

Deoxypodophyllotoxin is a secondary metabolite lignan possessing potent anticancer activity with potential as a precursor for known anticancer drugs, but its use is limited by scarcity from natural sources. We here report the total synthesis of racemic deoxypodophyllotoxin in seven steps using an intramolecular styryl Diels-Alder reaction strategy uniquely suited to assemble the deoxypodophyllotoxin core. Density functional theory was used to analyze concerted, polar, and singlet-open-shell diradical reaction pathways, which identified a low-energy concerted [4 + 2] Diels-Alder pathway followed by a faster di-t-butylhydroxytoluene assisted [1,3]-formal hydrogen shift.

Cross couplings between simple allylic alcohols and aryl and vinyl boronic acids are efficiently catalyzed by nickel(0) catalysts and bidentate N-heterocyclic carbene/phosphine ligands. The bidentate nature of the ligand is shown to extend catalyst lifetime and enable high yields of the corresponding cross coupling products. X-ray crystallography confirms the bidentate nature of the ligand scaffold. Multistep cross coupling-alkene/alkyne insertions reactions are also conducted and the bidentate nature of the substrate makes the pendant phosphine of the ligand unnecessary.

Optical rectification of nonlinear optical organic crystals has been widely employed to obtain terahertz (THz) frequencies with simple laser setups. Red organic crystals like DAST, DSTMS, and OH1 have generated intense THz pulses with peak electric fields up to a few megavolts per cm. Other newer organic crystals such as HMQ-TMS and EHPSI-4NBS have shown similar performance.Recently, the yellow organic crystals BNA and HMI-TMS have drawn attention due to improved phase matching conditions compared with red crystals in the technologically important 800 nm wavelength. This light is usually obtained with widely available Ti:Sapphire lasers and therefore, the development of materials that can efficiently generate THz with these sources is of high scientific interest. In this article, we introduce the THz generation capabilities of two yellow crystals, namely, MBST and MBSC. Electric fields of similar magnitude compared to the organic generator HMQ-TMS were obtained when MBST and MBSC crystals were pumped with 800-nm light. The THz absorption profile and crystal growth are also discussed to introduce new insights in how to improve the THz output of MBST and MBSC.

A series of eight new (E)-benzotriazolyl acrylonitrile derivatives were synthesized under reflux conditions via Knoevenagel condensation between acetonitrile analogs and a short series of aromatic aldehydes. X-ray diffraction analysis for one of the compounds was performed to determine the (E)-geometry of its double bond. The photoluminescent properties of all compounds in solution were also evaluated. These compounds exhibit strong blue, green and yellow emission under ultraviolet light excitation with fluorescence quantum yield in the 0.08–0.58% range. To determine the suitability of these compounds for use in cell-based analysis, cytotoxicity assays were performed on a representative molecule using a common mammalian cell line (HEK 293T cells) at different concentrations. The results showed limited toxicity (72 ± 16% viability) at the highest concentration tested (50 μM). Finally, confocal microscopy demonstrated that our compound was internalized into cells and localized to endosomes and/or lysosomes in a similar fashion to Dextran–Cascade Blue (DCB).

Polystyrene-supported ruthenium nanoparticles enable the selective hydrazine-mediated reduction of nitroarenes to hydroxylamine products in high yield and selectivity. Key to obtaining the hydroxylamine product in good yield was the use of organic solvents capable of solubilizing the polystyrene-supported nanoparticle catalyst. N -aryl and N -heteroaryl hydroxylamines are generated under exceptionally mild conditions and in the presence of a various easily reduced functional groups.

We present the structural and THz generation characteristics of the molecular salt crystal (E)-2-(4-(dimethylamino)styryl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium iodide (P-BI) using optical rectification with IR pump wavelengths. P-BI shows a peak-to-peak field ∼6 times greater than inorganic crystal GaP, and a broader THz spectrum. Data were obtained from 0–6 THz showing a significant dip in generation at 1.8 THz, similar to what has been observed with the THz generation crystal DAST at 1 THz. We characterized the power dependence of P-BI at different IR wavelengths, with optimal THz generation at the 1550-nm pump wavelength. To model THz generation as a function of P-BI crystal thickness, we measured the THz complex refractive index and the IR group index; modeling shows that imperfect phase matching leads to spectral narrowing centered at ∼2.5 THz as the crystal thickness is increased. P-BI could provide a useful alternative to inorganic THz generation crystals such a GaP.

Here, we report the most comprehensive characterization of nanodiamonds (NDs) yet undertaken. Five different samples from three different vendors were analyzed by a suite of analytical techniques, including X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), inductively coupled plasma mass spectrometry (ICP-MS), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), Brunauer-Emmett-Teller (BET) surface area measurements, and particle size distribution (PSD) measurements. XPS revealed the elemental compositions of the ND surfaces (83-87 at.% carbon and 12-14 at.% oxygen) with varying amounts of nitrogen (0.4-1.8 at.%), silicon (0.1-0.7 at.%), and tungsten (0.3 at.% only in samples from one vendor). ToF-SIMS and ICP showed metal impurities (Al, Fe, Ni, Cr, etc. with unexpectedly high amounts of W in one vendor's samples: ca. 900 ppm). Principal component analyses were performed on the ToF-SIMS and ICP data. DRIFT showed key functional groups (-OH, C=O, C-O, and C=C). BET showed surface areas of 50-214 m(2)/g. XRD and TEM revealed PSD (bimodal distribution and a wide PSD, 5-100 nm, for one vendor's samples). XRD also provided particle sizes (2.7-27 nm) and showed the presence of graphite. EELS gave the sp(2)/sp(3) contents of the materials (37-88% sp(3)). PSD measurements were performed via differential sedimentation of the particles (mean particle size ca. 17-50 nm). This comprehensive understanding should allow for improved construction of nanodiamond-based materials.

A series of novel chloro-complexes of Mn2+, Co2+, Ni2+ and Fe3+ with 2,4,6-tris-(2-pyridyl)-1,3,5-triazine (L1) and thiourea (L2) with the formulae, [Mn(L1)Cl2(EtOH)]L2 (1), [Co(L1)Cl2(H2O)]L2.1/2H2O (2), [Ni(L1)Cl2(H2O)]L2.1/2H2O (3) and [Fe(L1)Cl3]L2 (4) were investigated utilizing convenient methods. Conversely, similar reaction resulted in complex with structure [Mn(L1)(OAc)(H2O)Cl]·H2O (5) in presence of sodium acetate. Pentagonal-bipyramidal geometry around Mn2+ ion is suggested. The solid state ESR spectra of Mn2+, Co2+ and Ni2+ complexes parameters show g|| > g┴ > 2.0023 indicating that the ground state is dx2-y2. Electronic spectra of two Mn2+ and the other complexes and the values of magnetic moments suggest octahedral geometry for complexes while pentagonal-pyramidal for [Mn(L1)Cl2(EtOH)]L2. Biological activity of complexes was tested versus alpathogenic bacteria (E. Coli, S. Aureus and C. Albicans). Further, the cytotoxic activity was screened for in vitro against (HeLa), (MCF-7), (HePG2) and (HeP-2). The role of ionic radii of the metal ion on the biological activity was investigated.

High-density polyethylene (HDPE) has been extensively studied, both as a model for semi-crystalline polymers and because of its own industrial utility. During cold drawing, crystalline regions of HDPE are known to break up and align with the direction of tensile load. Structural changes due to deformation should also manifest at the surface of the polymer, but until now, a detailed molecular understanding of how the surface responds to mechanical deformation has been lacking. This work establishes a precedent for using vibrational sum-frequency generation (VSFG) spectroscopy to investigate changes in the molecular-level structure of the surface of HDPE after cold drawing. X-ray diffraction (XRD) was used to confirm that the observed surface behavior corresponds to the expected bulk response. Before tensile loading, the VSFG spectra indicate that there is significant variability in the surface structure and tilt of the methylene groups away from the surface normal. After deformation, the VSFG spectroscopic signatures are notably different. These changes suggest that hydrocarbon chains at the surface of visibly necked HDPE are aligned with the direction of loading, while the associated methylene groups are oriented with the local C2 v symmetry axis roughly parallel to the surface normal. Small amounts of unaltered material are also found at the surface of necked HDPE, with the relative amount of unaltered material decreasing as the amount of deformation increases. Aspects of the nonresonant SFG response in the transition zone between necked and undeformed polymer provide additional insight into the deformation process and may provide the first indication of mechanical deformation. Nonlinear surface spectroscopy can thus be used as a noninvasive and nondestructive tool to probe the stress history of a HPDE sample in situations where X-ray techniques are not available or not applicable. Vibrational sum-frequency generation thus has great potential as a platform for material state awareness (MSA) and should be considered as part of a broader suite of tools for such applications.

We have recently developed a “solvent-deficient” method of synthesizing high surface area γ-Al2O3 nanoparticles that show promise for catalyst support applications. Here, we investigate doping the alumina with La3+ to stabilize the γ phase to higher temperatures. The one-pot method for synthesizing La-doped γ-Al2O3 nanoparticles developed here has several advantages over conventional methods including requiring only 3 h instead of 3 days and wasting no lanthanum. TEM, X-ray PDF, and BET analyses as a function of calcination temperature show that the La stabilizes the γ phase by 100 °C. In order to begin understanding the mechanism of stabilization, the location of the La3+ atoms in our doped γ-Al2O3 nanoparticles is investigated via X-ray PDF and EXAFS analyses which indicate that the La dopant adsorbs as single, isolated atoms on the γ-Al2O3 surface. As calcination temperature increases, the immediate oxygen coordination shell of the La becomes increasingly like La2O3 though an extended La2O3 lattice is ...

Experiments and density functional calculations were used to quantify the impact of the Pd-Ti interaction in the cationic heterobimetallic Cl2Ti(N(t)BuPPh2)2Pd(η(3)-methallyl) catalyst 1 used for allylic aminations. The catalytic significance of the Pd-Ti interaction was evaluated computationally by examining the catalytic cycle for catalyst 1 with a conformation where the Pd-Ti interaction is intact versus one where the Pd-Ti interaction is severed. Studies were also performed on the relative reactivity of the cationic monometallic (CH2)2(N(t)BuPPh2)2Pd(η(3)-methallyl) catalyst 2 where the Ti from catalyst 1 was replaced by an ethylene group. These computational and experimental studies revealed that the Pd-Ti interaction lowers the activation barrier for turnover-limiting amine reductive addition and accelerates catalysis up to 10(5). The Pd-Ti distance in 1 is the result of the N(t)Bu groups enforcing a boat conformation that brings the two metals into close proximity, especially in the transition state. The turnover frequency of classic Pd π allyl complexes was compared to that of 1 to determine the impact of P-Pd-P coordination angle and ligand electronic properties on catalysis. These experiments identified that cationic (PPh3)2Pd(η(3)-CH2C(CH3)CH2) catalyst 3 performs similarly to 1 for allylic aminations with diethylamine. However, computations and experiment reveal that the apparent similarity in reactivity is due to very fast reaction kinetics. The higher reactivity of 1 versus 3 was confirmed in the reaction of methallyl chloride and 2,2,6,6-tetramethylpiperidine (TMP). Overall, experiments and calculations demonstrate that the Pd-Ti interaction induces and is responsible for significantly lower barriers and faster catalysis for allylic aminations.

We report a multi-instrument characterization of the carbon particles in carbon/polymer/nanodiamond core-shell materials used for high-performance liquid chromatography. These particles are prepared by the carbonization/pyrolysis of poly(divinylbenzene) (PDVB) microspheres. Scanning electron microscopy showed that the particles (4.9 µm initially) decreased in size after air oxidation (to 4.4 µm) and again after carbonization (down to 3.5 µm) but remained highly spherical. Brunauer–Emmett–Teller measurements showed low surface areas initially (as received: 1.6 m2/g, after air oxidation: 2.6 m2/g) but high values after carbonization (445 m2/g). Fourier transform infrared spectroscopy revealed the changes in the functional groups after air oxidation (C = O and C–O stretches appear), carbonization (carbon-oxygen containing moieties disappear), and acid treatment (reintroduction of carbon-oxygen containing moieties). X-ray photoelectron spectroscopy (XPS) and elemental analysis revealed the surface and bulk oxygen contents before and after treatments. By XPS, the atom percent oxygen for the as received, air oxidized, carbonized, and acid treated particles are 8.7, 16.6, 3.7, and 13.8, respectively, and by elemental analysis, the percent oxygen in the materials is 0.6, 8.1, 0.9, 16.9, respectively. A principal components analysis of time-of-flight secondary ion mass spectrometry data identified ions that were enhanced in the different materials, where almost 90% of the variation in the analyzed peak areas was captured by two principle components. X-ray diffraction and Raman spectroscopy suggested that the carbonized PDVB was disordered. Thermogravimetric analysis showed significant differences between the differently treated PDVB microspheres. This work applies directly to a commercial product and the process for preparing it. Copyright © 2015 John Wiley & Sons, Ltd.

Several conflicting reports have suggested that heat capacities and the thermodynamic properties of materials change as their particle size decreases into the nanoscale. To further investigate this, we have measured the constant pressure heat capacities of three 7 nm TiO2 anatase samples containing varying amounts of surface-adsorbed water using a combination of adiabatic and semi-adiabatic calorimetric methods. These samples have a high degree of chemical, phase, and size purity determined by rigorous characterization. Molar heat capacities were measured from T = (0.5 to 320) K, and data were fit to a sum of theoretical functions in the low temperature (T T > 75 K), and a combination of Debye and Einstein functions in the high temperature range (T > 35 K). These fits were used to generate C p ,m ° , Δ 0 T S m ° , Δ 0 T H m ° , and φ m ° values at smoothed temperatures between (0.5 and 300) K for all hydrated samples. Standard molar entropies at T = 298.15 K were calculated to be 73.868, 66.072, and 63.845 J · K−1 · mol−1 all with a standard uncertainty of 0.002· Δ 0 T S m ° for samples TiO2 · 0.677H2O, TiO2 · 0.532H2O, and TiO2 · 0.379H2O, respectively. These and other thermodynamic values were then corrected for water content to yield bare nano-TiO2 thermodynamic properties at T = 298.15 K, and we show that the resultant thermodynamic properties of anhydrous TiO2 anatase nanoparticles equal those of bulk TiO2 anatase within experimental uncertainty. Thus we show quantitatively that the difference in thermodynamic properties between bulk and nano-TiO2 must be attributed to surface adsorbed water.

Several conflicting reports have suggested that the thermodynamic properties of materials change with respect to particle size. To investigate this, we have measured the constant pressure heat capacities of three 7 nm TiO2 rutile samples containing varying amounts of surface-adsorbed water using a combination of adiabatic and semi-adiabatic calorimetric methods. These samples have a high degree of chemical, phase, and size purity determined by rigorous characterization. Molar heat capacities were measured from T = (0.5 to 320) K, and data were fitted to a sum of theoretical functions in the low temperature (T T/K > 75), and a combination of Debye and Einstein functions in the high temperature range (T > 35 K). These fits were used to generate Cp , m ∘ , Δ 0 T S m ∘ , Δ 0 T H m ∘ , and φ m ∘ values at selected temperatures between (0.5 and 300) K for all samples. Standard molar entropies at T = 298.15 K were calculated to be (62.066, 59.422, and 58.035) J · K−1 · mol−1 all with a standard uncertainty of 0.002· Δ 0 T S m ∘ for samples TiO2·0.361H2O, TiO2·0.296H2O, and TiO2·0.244H2O, respectively. These and other thermodynamic values were then corrected for water content to yield bare nano-TiO2 thermodynamic properties at T = 298.15 K, and we show that the resultant thermodynamic properties of anhydrous TiO2 rutile nanoparticles equal those of bulk TiO2 rutile within experimental uncertainty. Thus we show quantitatively that the difference in thermodynamic properties between bulk and nano-TiO2 must be attributed to surface adsorbed water.

We report an efficient, general methodology for producing high-surface area metal oxide nanomaterials for a vast range of metal oxides, including at least one metal oxide nanomaterial from nearly every transition metal and semi-metal group in the periodic table (groups 3–4 and 6–15) as well as several from the lanthanide group (see Table 1). The method requires only 2–3 simple steps; a hydrated metal salt (usually a nitrate or chloride salt) is ground with bicarbonate (usually NH4HCO3) for 10–30 minutes to form a precursor that is then either untreated or rinsed before being calcined at relatively low temperatures (220–550 °C) for 1–3 hours. The method is thus similar to surfactant-free aqueous methods such as co-precipitation but is unique in that no solvents are added. The resulting “solvent-deficient” environment has interesting and unique consequences, including increased crystallinity of the products over other aqueous methods and a mesoporous nature in the inevitable agglomerates. The products are chemically pure and phase pure with crystallites generally 3–30 nm in average size that aggregate into high surface area, mesoporous agglomerates 50–300 nm in size that would be useful for catalyst and gas sensing applications. The versatility of products and efficiency of the method lend its unique potential for improving the industrial viability of a broad family of useful metal oxide nanomaterials. In this paper, we outline the methodology of the solvent-deficient method using our understanding of its mechanism, and we describe the range and quality of nanomaterials it has produced thus far.

Conventional magnetic tape is the most widely used medium for archival data storage. However, data stored on it need to be migrated every ca. 5 years. Recently, optical discs that store information for hundreds, or even more than 1000 years, have been introduced to the market. We recently proposed that technology in these optical discs be used to make an optical tape that would show greater permanence than its magnetic counterpart. Here we provide a detailed optical characterization of a sputtered thin film of bismuth, tellurium, and selenium (BTS) that is a proposed data storage layer for these devices. The methodology described herein should be useful in the future development of related materials. Spectroscopic ellipsometry (SE) data are obtained using interference enhancement, and the modeling of this data is guided by results from atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray reflectivity (XRR). By AFM, ca. 40 nm BTS films show ca. 10 nm roughness. SEM images also suggest considerable roughness in the films and indicate that they are composed of 13.1 ± 5.9 nm grains. XRD confirms that the films are crystalline and predicts a grain size of 17 ± 2 nm. XRD results are consistent with the composition of the films — a mildly oxidized BTS material. Three models of increasing complexity are investigated to explain the SE data. The first model consists of a smooth, homogeneous BTS film. The second model adds a roughness layer to the previous model. The third model also has two layers. The bottom layer is modeled as a mixture of BTS and void using a Bruggeman effective medium approximation. The upper layer is similarly modeled, but with a gradient. The first model was unable to adequately model the SE data. The second model was an improvement — lower MSE (4.4) and good agreement with step height measurements. The third model was even better — very low MSE (2.6) and good agreement with AFM results. The third SE model predicted ca. 90% void at the film surface. XRR modeling of the film agreed well with the predictions from SE. The uniquenesses of the SE models were confirmed.

Porous metal oxide nanoparticles is a new class of material of great scientific and technological importance with a wide range of applications. In this article, we briefly review the synthetic methods and thermodynamic properties of such materials. We compare and summarize common synthetic routes of such materials including solid-state, solution- phase (co-precipitation, sol-gel, microemulsion, solvothermal/hydrothermal, non-aqueous), and vapor-phase methods. As for the thermodynamics of porous metal oxide nanoparticles, we review experimental determinations, mainly by calorime- try, on surface and interfaces energetics. The interplay among particle size, surface area, morphology, surface stabilizer, phase stability, and redox potentials is discussed.

A series of air-stable nickel complexes of the form L2Ni(aryl) X (L = monodentate phosphine, X = Cl, Br) and LNi(aryl)X (L = bis-phosphine) have been synthesized and are presented as a library of precatalysts suitable for a wide variety of nickel-catalyzed transformations. These complexes are easily synthesized from low-cost NiCl2·6H2O or NiBr2·3H2O and the desired ligand followed by addition of 1 equiv of Grignard reagent. A selection of these complexes were characterized by single-crystal X-ray diffraction, and an analysis of their structural features is provided. A case study of their use as precatalysts for the nickel-catalyzed carbonyl-ene reaction is presented, showing superior reactivity in comparison to reactions using Ni(cod)2. Furthermore, as the precatalysts are all stable to air, no glovebox or inert-atmosphere techniques are required to make use of these complexes for nickel-catalyzed reactions.

One-pot solvothermal synthesis of a robust tetranuclear sodium hexakis(glycolato)tris(methanolato)aluminate complex Na3[Al4(OCH3)3(OCH2CH2O)6] via a modified yet rigorous base-catalyzed transesterification mechanism is presented here. Single crystal X-ray diffraction (SCXRD) studies indicate that this unique Al complex contains three pentacoordinate Al3+ ions, each bound to two bidentate ethylene glycolate chelators and one monodentate methanolate ligand. The remaining fourth Al3+ ion is octahedrally coordinated to one oxygen atom from each of the six surrounding glycolate chelators, effectively stitching the three pentacoordinate Al moieties together into a novel tetranuclear Al complex. This aluminate complex is periodically self-assembled into well-ordered layers normal to the [110] axis with the intra-/inter-layer bonding involving extensive ionic bonds from the three charge-counterbalancing Na+ cations rather than the more typical hydrogen bonding interactions as a result of fewer free hydroxyl groups present in its structure. It can also serve as a valuable precursor toward the facile synthesis of high-surface-area alumina powders using a very efficient rapid pyrolysis technique.

We have found that coordination of B(C6F5)3 to an oxo ligand in tungsten oxo alkylidene bis(aryloxide) complexes, where the aryloxide is O-2,6-(mesityl)2C6H3 (HMTO) or 2,6-diadamantyl-4-methylphenoxide (dAdPO), accelerates the formation of metallacyclobutane complexes from alkylidenes as well as the rearrangement of metallacyclobutane complexes. In contrast, a tungstacyclopentane complex, W(O)(C4H8)(OHMT)2, is relatively stable toward rearrangement in the presence of B(C6F5)3. A careful balance of steric factors allows a single isomer of W(O)(trans-4,4-dimethylpent-2-ene)(dAdPO)2 to be formed from W(O)(CH-t-Bu)(dAdPO)2 in the presence of both ethylene and B(C6F5)3.

Ring-opening metathesis polymerization of a series of 3-substituted cyclooctenes (3-MeCOE, 3-HexCOE, and 3-PhCOE) initiated by various Mo and W MAP complexes leads to cis,HT-poly(3-RCOE) polymers. The apparent rate of polymerization of 3-HexCOE by W(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1c; Pyr = pyrrolide; OHMT = O-2,6-Mesityl2C6H3) is greater than the rate of polymerization by Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1b), but both gave the same cis,HT polymer structures. Formation of HT-poly(3-RCOE) employing 1c takes place via propagating species in which the R group (methyl, hexyl, or phenyl) is on C2 of the propagating alkylidene chain, a type of intermediate that has been modeled through the preparation of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT). The rate of ROMP is exceedingly sensitive to steric factors: e.g., W(N-t-Bu)(CH-t-Bu)(Me2Pyr)(OHMT), the dimethylpyrrolide analogue of 1c, essentially did not polymerize 3-HexCOE at 22 °C. When a sample of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) and 3-methyl-1-pentene in CDCl3 is cooled to −2...

Reactions between Mo(NAr)(CHR)(Me2Pyr)-(OTPP) (Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph4C6H) and CH2=CHX where X = B(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo(NAr)(CHX)-(Me2Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh2). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo=CHX species.

The bisDFTO alkylidene complexes of molybdenum Mo(NR)(CHCMe2Ph)(DFTO)2 (R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3, C6F5, 1-adamantyl; DFTO = 2,6-(C6F5)2C6H3O) and monoaryloxide monopyrrolide (MAP) complexes Mo(NR)(CHCMe2Ph)(Me2Pyr)(OAr) (Me2Pyr = 2,5-dimethylpyrrolide; R = C6F5, OAr = DFTO, 2,6-dimesitylphenoxide (HMTO); R = 2,6-Me2C6H3, OAr = DFTO) have been prepared in good yields. Addition of dicarbomethoxynorbornadiene (DCMNBD) to bisDFTO complexes yielded polymers that have a cis,isotactic structure. Polymerization of DCMNBD by Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(HMTO) gives a polymer that contains the expected cis,syndiotactic structure, but polymerization of DCMNBD by Mo(NR)(CHCMe2Ph)(Me2Pyr)(DFTO) (R = C6F5, 2,6-Me2C6H3) generates a polymer that has a cis,isotactic structure, the first observation of a cis,isotactic polymer prepared employing a MAP initiator. Norbornene is polymerized to give what is proposed to be highly tactic cis-polyNBE. Addition of ethylene to Mo(NC6F5)(CHCMe2Ph)(DFTO)2 leads to formation of Mo...

Ferrihydrite is a fine-grained and variable, in terms of structure and water content, iron oxyhydroxide found in many geologic environments, in living organisms, and in environmental pollution. The thermodynamic study of ferrihydrite is important for understanding geochemical transformations involving iron as well as in the study of iron in chemical synthesis and biological systems. In this study, the heat capacity of a synthetic two-line ferrihydrite, which showed typically broad X-ray diffraction peaks due to small particle size and/or disorder but had a rather low excess water content, FeOOH·0.027H2O, was measured over the temperature range of (2 to 300) K. Using these data, the standard molar entropy, S m o , of this two-line ferrihydrite was calculated to be (71.7 ± 0.2) J · K−1 · mol−1, while that of the stoichiometric (no excess water) material, FeOOH was estimated to be (69.8 ± 0.2) J · K−1 · mol−1. These measured entropies are in moderate agreement with, though slightly higher, than those estimated much more indirectly by Majzlan et al. (2004) [15] The heat capacity data below T = 12 K were fit to theoretical models to study the underlying contributions to the heat capacity. The fit required an anisotropic ferrimagnetic spin wave component, which agrees with studies that characterize two-line ferrihydrite as a ferrimagnet. The fit also required a linear term, which most likely stems from defects in the ferrihydrite particles. Using enthalpy of formation from the elements −(542.3 ± 0.8 kJ · mol−1 for FeOOH·0.027H2O or −(534.6 ± 1.0) kJ · mol−1 for FeOOH obtained from acid solution calorimetry of the same sample, the standard Gibbs energy of formation from the elements for this ferrihydrite sample was calculated to be −(473.0 ± 1.0) kJ · mol−1 for FeOOH·0.027H2O and −(465.3 ± 1.0) kJ · mol−1 for FeOOH.

The specific heats of highly hydrated 7 nm nanoparticles and lightly hydrated 200 nm particles of rutile and anatase show a small, broad maximum below 5 K. The excess heat capacity can be modeled w...