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Incorporating low-valent metals as nodes in metal-organic frameworks (MOFs) is orthogonal to the commonly accepted strategy to robust and porous structures. The electronic structures of low-valent metals are chemically unique and have driven the successes of organometallic chemistry. The translation of these properties into MOFs is largely impeded by the lack of generalizable synthetic approaches. Homoleptic metal carbonyls are bona fide zero-valent and volatile synthons, which, by partial chemical substitution may tether ditopic ligands into MOF architectures. We herein demonstrate the formation of CO2 adsorbing MOFs from the direct gas-phase substitution of CO by ditopic 4,4′-bipyridine at Mo and W centers. This approach allows facile gas phase coating of these MOFs onto substrates such as indium tin oxide. We envisage this strategy could be generalized to a multitude of mono- and polynuclear metal carbonyls, thereby paralleling the diversity of conventional MOFs.

The self-assembly of trivalent lanthanide ions with ditopic organic spacers results in the formation of complex tiling patterns that mimic the structural motifs of quasi-periodic 2D materials. The assembly of trans-{LnI2}+ nodes (Ln = Gd, Dy) with both closed-shell and anion radicals of 4,4'-bipyridine affords rare examples of Archimedean tessellations in a metal-organic framework. We furthermore demonstrate occurrence of sizable magnetic exchange interactions and slow relaxation of magnetization behaviour in a complex tessellation pattern. The implementation of Archimedean tessellations in lanthanide(III) coordination solids couriers a strategy to design elusive quasi-periodic metal-organic frameworks with inimitable magnetic properties

Five new polyketides were isolated from the rare filamentous fungus Aspergillus californicus IBT 16748 including calidiol A (1); three phthalide derivatives califuranones A1, A2, and B (2-4); and a pair of enantiomers (-)-calitetralintriol A (-5) and (+)-calitetralintriol A (+5) together with four known metabolites (6-9). The structures of the new products were established by extensive spectroscopic analyses including HRMS and 1D and 2D NMR. The absolute configurations of two diastereomers 2 and 3 and the enantiomers (-5) and (+5) were assigned by comparing their experimental and calculated ECD data, whereas the absolute configuration of 4 was proposed by analogy. Compound 1 showed moderate activity against methicillin-resistant Staphylococcus aureus.

We report the synthesis of pyrazine-pillared metal–organic frameworks (MOFs) generated through ligand substitution of the Group 6 metal hexacarbonyls. The obtained frameworks exhibit hexagonal pore channels with CO-plastered porewalls. This series constitutes the first crystallographically characterized examples of Cr(0), Mo(0), and W(0)-based MOFs and suggests the exploration of homoleptic metal carbonyls as starting materials to generate polymeric materials with low-valent metal nodes.

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.

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.

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.

We report the synthesis of pyrazine-pillared metal-organic frameworks (MOFs) generated through ligand substitution of the Group 6 metal hexacarbonyls. The obtained frameworks exhibit hexagonal pore channels with CO-plastered porewalls. This series constitutes the first crystallographically characterized examples of Cr(0), Mo(0), and W(0)-based MOFs and suggests the exploration of homoleptic metal carbonyls as starting materials to generate polymeric materials with low-valent metal nodes.

The quest for simple ligands to participate in concerted base metal-ligand multiple-electron redox events is driven by perspectives of replacing noble metals in catalysis and for discovering novel chemical reactivity. Yet the vast majority of simple ligand systems displays electrochemical potentials impractical for catalytic cycles substantiating the importance of new strategies towards aligned metal–ligand orbital energy levels. We herein demonstrate the possibility to establish and tame the elusive non-innocence of the ubiquitous acetylacetonate (acac), that is the most commonly employed anionic, chelating ligand towards elements across the entire Periodic Table. By employing the ligand field in the high-spin Cr(II) as a thermodynamic switch, we were able to chemically tailor the occurrence of metal–ligand redox events. The very mechanism can be understood as a destabilization of the dz2 orbital relative to the pi* LUMO of acac, which proffers a generalizable strategy to synthetically engineer non-innocence with seemingly redox-inactive ligands.

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 dz2 orbital relative to the π* LUMO of acac, which proffers a generalizable strategy to synthetically engineer redox-activity with seemingly redox-inactive ligands., Tailoring the chemical surroundings of chromium(ii) allows reversible electron-transfer to the ubiquitous, purportedly redox-inactive acetylacetonate.

β-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 Cr(II) spontaneously affords Cr(III) and a reduced beta-diketonate ligand radical, 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 β-diketonate coordination chemistry.

A systematic study of the rotation constants, vibration–rotation constants and quartic centrifugal distortion constants has been performed for furan, pyrrole, thiophene, both oxazoles and thiazoles, 1,2,4- and 1,2,5-oxa- and -thiadiazoles, 1,2,5-selenadiazole, and several 6-membered heterocycles (azines). The main study used cc-pVTZ basis sets. There is a very close correlation between the observed constants above and those calculated, especially using the cc-pVTZ + B3LYP procedures; some trends in these appear on substitution of HC by N in the azoles. This strong correlation between experimental values and this theoretical procedure is also apparent with vibrational differences in rotation constants, all over large numbers of measured values. However, a small number of calculated values do not correlate well with experiment; this may be a result of some of the experimental values being subject to resonance perturbations not included in the calculations. In general, a TZ2P basis set with B3LYP methodology, and cc-pVTZ results with MP2 methodology, lead to correlations of similar quality, but the latter require markedly more computing power. The present study draws attention to a tetrad in the IR spectrum of 1,2,5-oxadiazole, where further analysis is necessary.

The high-resolution infrared absorption spectrum of an equilibrium mixture of HCN and HCl in a static gas long-path absorption cell is recorded in the 2500 2900 cm(-1) spectral region at 205 K. The spectrum shows rovibrational structure which has the typical appearance of a parallel band of a linear molecule and is assigned to the intramolecular H-Cl stretching vibration band upsilon(2) of the linear HCN-(HCl)-Cl-35 heterodimer. The rovibrational analysis of the band yield a band origin upsilon(0) of 2779.0968(12) cm(-1) together with a value for the upper-state rotational constant B' of 0.067722(2) cm(-1). The observed red shift of 107 cm(-1) for the upsilon(2) band of HCN- (HCl)-Cl-35 relative to the H-Cl stretching vibration band of monomer (HCl)-Cl-35 is in excellent agreement with results from the MP2/ 6-311++G** level of theory. The value of the upper-state rotational constant shows that the intermolecular hydrogen bond shortens by 0.022 Angstrom upon intramolecular vibrational excitation of the upsilon(2) mode. (C) 2004 Elsevier B.V. All rights reserved. (Less)

The high-resolution far-infrared spectrum of the intermolecular HC1 libration band v(4)(1) of the OC-H(35)C1 heterodimer is recorded in the gas phase by means of Fourier transform IR spectroscopy in a static multipass absorption cell at 137 K using a synchrotron radiation source. This is the first direct observation of an intermolecular vibration band of the OC-HC1 dimer in the gas phase. The rotational structure of the band has the typical appearance of a perpendicular band of a linear polyatomic molecule. The structure is analyzed to yield the band origin nu(0) = 201.20464(27) cm(-1) together with values for the upper state rotational constant, the upper state quartic and sextic centrifugal distortion constants, and the l-type doubling constant. The determined values for the rotational constant and the centrifugal distortion constants are used to obtain a Morse potential for the stretching of the intermolecular distance. The results are compared to the results from quantum-chemical calculations. (Less)

The high-resolution infrared absorption spectrum for (HCN)2 in the spectral region 3100–3300 cm−1 is recorded in a static multipass cell at 240 K under equilibrium conditions. The spectrum shows extensive rovibrational structures which are due to the bound C–H stretching vibration band ν2 of (HCN)2 and several hot bands associated to ν2. We manage to assign 63 new rovibrational transitions [P(97) to R(98)] associated with the ν2 band leading to an extended analysis of the ν2 band. This enables the assignment of 60 rovibrational transitions associated with the hot band ν2 + ν91 − ν91 in (HCN)2 together with the first rovibrational analysis of this hot band. The determined positive value of the anharmonicity constant X2,9 of 0.2569(13) cm−1 indicates that the intermolecular low-frequency bending vibration ν91 increases in frequency upon simultaneous excitation of the ν2 mode. This result confirms that the HCN dimer is stiffer and more tightly bound upon vibrational excitation of the bound C–H stretching mode.

A total of six high-resolution FT-IR spectra for trans-glyoxal-d2, trans-glyoxal-d1 and trans-glyoxal-13C2 were recorded with a resolution ranging from 0.003 to 0.004 cm−1. By means of a simultaneous ground state combination difference analysis for each of these isotopologues using the Watson Hamiltonian in A-reduction and Ir-representation the ground state rotational constants are obtained. An empirical equilibrium structure is determined for trans-glyoxal using these experimental ground state rotational constants and vibration–rotation interaction constants calculated at the CCSD(T)/cc-pVTZ level of theory. The least-squares fit yields the following structural parameters for trans-glyoxal: re(C–C) = 1.51453(38) A, re(C–H) = 1.10071(26) A, re(CO) = 1.20450(27) A, αe(CCH) = 115.251(24)°, and αe(HCO) = 123.472(19)° in excellent agreement with theoretical predictions at the CCSD(T)/cc-pVQZ level of theory.

A combined microwave, infrared, and computational investigation of CHBrF(2) is reported. For the vibrational ground state, measurements in the millimeter- and sub-millimeter-wave regions for CH(79)BrF(2) and CH(81)BrF(2) provided rotational and centrifugal-distortion constants up to the sextic terms as well as the hyperfine parameters (quadrupole-coupling and spin-rotation interaction constants) of the bromine nucleus. The determination of the latter was made possible by recording of spectra at sub-Doppler resolution, achieved by means of the Lamb-dip technique, and supporting the spectra analysis by high-level quantum chemical calculations at the coupled-cluster level. In this context, the importance of relativistic effects, which are of the order of 6.5% and included in the present work using second-order direct perturbation theory, needs to be emphasized for accurate predictions of the bromine quadrupole-coupling constants. The infrared measurements focused on the ν(4) fundamental band of CH(79)BrF(2). Fourier transform investigations using a synchrotron radiation source provided the necessary resolution for the observation and analysis of the rotational structure. The spectroscopic parameters of the v(4) = 1 state were found to be close to those of the vibrational ground state, indicating that the ν(4) band is essentially unaffected by perturbations.

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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.

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. peerReviewed