A zero-valent palladium cluster-organic framework.

Acquiring spatial control of nanoscopic metal clusters is central to their function as efficient multi-electron catalysts. However, dispersing metal clusters on surfaces or in porous hosts is accompanied by an intrinsic heterogeneity that hampers detailed understanding of the chemical structure and its relation to reactivities. Tethering pre-assembled molecular metal clusters into polymeric, crystalline 2D or 3D networks constitutes an unproven approach to realizing ordered arrays of chemically well-defined metal clusters. Herein, we report the facile synthesis of a {Pd3} cluster-based organometallic framework from a molecular triangulo-Pd3(CNXyl)6 (Xyl = xylyl; Pd3) cluster under chemically mild conditions. The formally zero-valent Pd3 cluster readily engages in a complete ligand exchange when exposed to a similar, ditopic isocyanide ligand, resulting in polymerization into a 2D coordination network (Pd3-MOF). The structure of Pd3-MOF could be unambiguously determined by continuous rotation 3D electron diffraction (3D-ED) experiments to a resolution of ~1.0 Å (>99% completeness), showcasing the applicability of 3D-ED to nanocrystalline, organometallic polymers. Pd3-MOF displays Pd03 cluster nodes, which possess significant thermal and aerobic stability, and activity towards hydrogenation catalysis. Importantly, the realization of Pd3-MOF paves the way for the exploitation of metal clusters as building blocks for rigidly interlocked metal nanoparticles at the molecular limit.

Fragmentation of Hydrophilic Guidewire Coatings During Neuroendovascular Therapy.

PURPOSE: Cerebral polymer coating embolism from intravascular devices may cause serious complications after endovascular therapy (EVT) for neurovascular diseases. Although polymer fragments are often created during endovascular procedures, exact mechanisms of their formation, especially if of small size, are largely unknown. METHODS: In this study eight microguidewires (Asahi Chikai 200 cm (Asahi Intecc, Aichi, Japan), Asahi Chikai Black (Asahi Intecc), Fathom™ (Boston Scientific, Marlborough, MA, USA), Hybrid (Balt Extrusion, Montmorency, France), Radifocus® Guide Wire GT (Terumo, Leuven, Belgium), Synchro2® (Stryker, Kalamazoo, MI, USA), Transend™ EX (Boston Scientific), and Traxcess™ (MicroVention®, Tustin, CA, USA)) frequently used during EVT were investigated ex vivo using their dedicated metal or plastic insertion tools to assess for coating delamination after backloading of the microguidewires. RESULTS: Backloading caused damage to the coating of all microguidewires especially when the main body of the guidewires was bent in front of the insertion tool. All studied microguidewires produced microscopic filamentous and/or band-like coating fragments. Few larger irregular fragments were observed, but also very small fragments measuring 1-3 µm in diameter were found. Spectroscopic measurements of polymer fragments and microguidewires identified various polymers. CONCLUSION: Backloading of polymer-coated microguidewires during EVT should be minimized if possible. More stable hydrophilic coatings on microguidewires and less traumatic insertion tools are desirable.

Polytetrafluoroethylene coating fragments during neuroendovascular therapy: An analysis of two damaged microguidewires.

Cerebral polymer coating embolism from intravascular devices represents a potentially serious complication to endovascular therapy (EVT). We report two cases of neuroendovascular treatment where filamentous polymer fragments were noted possibly due to damage of the surface coating during manipulation and backloading of microguidewires. As the exact origin of the debris was initially not known, microguidewires and fragments were examined with light microscopy, stereomicroscopy, scanning electron microscopy and attenuated-total-reflection Fourier transform infrared spectroscopy. Fragments consisted of polytetrafluoroethylene and silicone oil stemming from the proximal shaft of a standard microguidewire. To our knowledge, this is the first report of polytetrafluoroethylene coating fragments created during EVT. Future studies should assess the mechanism of polymer coating delamination and its potential consequences during EVT including inadvertent fragment migration into the cerebral circulation.

Spectroscopic Fingerprinting of Organic Material Extracted from Tight Chalk Core Samples of the North Sea.

The detailed chemical composition of crude oil in subsurface reservoirs provides important information about reservoir connectivity and can potentially play a very important role for the understanding of recovery processes. Relying on studying produced oil samples alone to understand the rock-fluid and fluid-fluid interactions is insufficient as the heavier polar components may be retained by tight reservoirs and not produced. These heavy and polar compounds that constitute the resin and asphaltene fractions of crude oil are typically present in low concentrations and yet are determining for the physical-chemical properties of the oil because of their polarity. In order to obtain a fingerprint analysis of oils including polar compounds from different wells, the oil content of drill cores has been extracted and analyzed. Infrared spectroscopy has been used to perform chemical fingerprinting of the oil extracted from drill cores sampled in different geographical locations of the Danish North Sea. Statistical analysis has been employed to identify the chemical differences within the sample set and explore the link between chemical composition and geographic location of the sample. A principal component analysis, based on spectral peak fitting in the 1800-1400 cm-1 range, has allowed for statistical grouping of the samples and identified the primary chemical feature characteristic of these groups. Statistically significant differences in the quantities of polar oxygen- and nitrogen-containing compounds were found between the oil wells. The results of this analysis have been used as guidelines and reference to establish an express statistical approach based on the full-range infrared spectra for a further expansion of the sample set. The chemical information presented in this work is discussed in relation to oil fingerprinting and geochemical analysis.

A Redox-Innocent Uranium(IV)-Quinoid Metal-Organic Framework.

Quinoid-based ligands constitute the most common class of redox-active ligands used to construct electrically conductive and magnetic metal-organic frameworks (MOFs). Whereas this chemistry is intensively explored for transition-metal and lanthanide ions, any related actinide compound has not received attention. In particular, the MOF chemistry of actinide ions in the lower oxidation states is underexplored. We herein report the synthesis, and structural and physical property characterization of a uranium(IV) quinoid-based MOF, [U(Cl2dhbq)2(H2O)2]·4H2O (1, Cl2dhbq2- = deprotonated 2,5-dichloro-3,6-dihydroxybenzoquinone). 1 is a rare example of a U(IV)-based coordination solid and the first material to incorporate bona fide reducible bridging ligands. Despite the anticipated thermodynamic driving force, no indications of valence tautomerism are evident from magnetometry, near-IR spectroscopy, and X-band electron paramagnetic resonance measurements. These initial results suggest that reduction potentials alone are insufficient as guidelines for the prediction of the occurrence of electron transfer in uranium-quinoid-based materials.

Ligand field-actuated redox-activity of acetylacetonate.

The quest for simple ligands that enable multi-electron metal-ligand redox chemistry is driven by a desire to replace noble metals in catalysis and to discover novel chemical reactivity. The vast majority of simple ligand systems display electrochemical potentials impractical for catalytic cycles, illustrating the importance of creating new strategies towards energetically aligned ligand frontier and transition metal d orbitals. We herein demonstrate the ability to chemically control the redox-activity of the ubiquitous acetylacetonate (acac) ligand. By employing the ligand field of high-spin Cr(ii) as a switch, we were able to chemically tailor the occurrence of metal-ligand redox events via simple coordination or decoordination of the labile auxiliary ligands. The mechanism of ligand field actuation can be viewed as a destabilization of the d z 2 orbital relative to the π* LUMO of acac, which proffers a generalizable strategy to synthetically engineer redox-activity with seemingly redox-inactive ligands.

Evidence for Non-Innocence of a ß-Diketonate Ligand.

ß-Diketonates, such as acetylacetonate, are amongst the most common bidentate ligands towards elements across the entire periodic table and are considered wholly redox-inactive in their complexes. Herein we show that complexation of 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac- ) to CrII spontaneously affords CrIII and a reduced ß-diketonate radical ligand scaffold, as evidenced by crystallographic analysis, magnetic measurements, optical spectroscopy, reactivity studies, and DFT calculations. The possibility of harnessing ß-diketonates as electron reservoirs opens up possibilities for new metal-ligand concerted reactivity in the ubiquitous ß-diketonate coordination chemistry.

A combined Raman- and infrared jet study of mixed methanol-water and ethanol-water clusters.

The vibrational dynamics of vacuum-isolated hydrogen-bonded complexes between water and the two simplest alcohols is characterized at low temperatures by Raman and FTIR spectroscopy. Conformational preferences during adaptive aggregation, relative donor/acceptor strengths, weak secondary hydrogen bonding, tunneling processes in acceptor lone pair switching, and thermodynamic anomalies are elucidated. The ground state tunneling splitting of the methanol-water dimer is predicted to be larger than 2.5 cm(-1). Two types of alcohol-water trimers are identified from the spectra. It is shown that methanol and ethanol are better hydrogen bond donors than water, but even more so better hydrogen bond acceptors. As a consequence, hydrogen bond induced red shifts of OH modes behave non-linearly as a function of composition and the resulting cluster excess quantities correspond nicely to bulk excess enthalpies at room temperature. The effects of weak C-H···O hydrogen bonds are quantified in the case of mixed ethanol-water dimers.

High-resolution FTIR, microwave, and ab initio investigations of CH2 79BrF: ground, v(5) = 1, and v(6) = 1, 2 state constants.

A spectroscopic study of CH279BrF in the infrared and microwave regions has been carried out. The rovibrational spectrum of the nu5 fundamental interacting with 2nu6 has been investigated by high-resolution FTIR spectroscopy. Owing to the weakness of the 2nu6 band, the v6 = 2 state constants have been derived from v6 = 1. For this reason, the rotational spectra of the ground and v6 = 1 states have been observed by means of microwave spectroscopy. Highly accurate ab initio computations have also been performed at the CCSD(T) level of theory in order to support the experimental investigation. As far as the nu5 band is concerned, the analysis of the rovibrational structure led to the identification of more than 3000 transitions, allowing the determination of a set of spectroscopic parameters up to sextic distortion terms and pointing out first-order c-type Coriolis interaction with the v6 = 2 state. With regard to the pure rotational spectra measurements, the assignment of several DeltaJ = 0, +1 transitions allowed the determination of the rotational, all the quartic, and most of the sextic centrifugal distortion constants, as well as the full bromine quadrupole coupling tensor for both the ground and v6 = 1 states.