Heptabismuthate [Bi7I24]3–: a main group element anderson-type structure and its relationships with the polyoxometalates

We describe the unique structural and electronic arrangement in the heptanuclear polyiodobismuthate [Bi(7)I(24)](3-) which displays striking similarities with the Anderson-type structures found in polyoxometalates. This main group element anion is part of the complex [Bi(OAc)(2)(thf)(4)](3)[Bi(7)I(24)] (1) which has been characterized by X-ray crystallography. We investigated the structure, stability, and bonding of [Bi(7)I(24)](3-) using relativistic dispersion-corrected density functional theory in combination with a quantitative energy decomposition and electron localization function analysis in order to better understand the main features of this isopolyanion. A comparative analysis of the properties of [Bi(7)I(24)](3-) and previously reported high-nuclearity [Bi(n)X(3n+m)](m-) anions, in the gas phase and in solution, has been performed, in the latter case to track the macroscopic solvent effects. [Bi(7)I(24)](3-) is the largest building block in the class of trianionic iodobismuthates and the sole heptanuclear framework in the family of iodobismuthates.     

B-norsteroids from Hymenoscyphus pseudoalbidus

Two viridin-related B-norsteroids, B-norviridiol lactone (1) and B-norviridin enol (2), both possessing distinct unprecedented carbon skeletons, were isolated from a liquid culture of the ash dieback-causing fungus Hymenoscyphus pseudoalbidus. Compound 2 was found to degrade to a third B-norsteroidal compound, 1β-hydroxy-2α-hydro-asterogynin A (3), which was later detected in the original culture. The proposed structure of 1 is, regarding connectivity, identical to the original erroneous structure for TAEMC161, which was later reassigned as viridiol. Compound 2 showed an unprecedented 1H-13C HMBC correlation through an intramolecular hydrogen bond. The five-membered B-ring of compounds 1-3 was proposed to be formed by a benzilic acid rearrangement. The known compound asterogynin A was found to be formed from 3 by a β-elimination of water. All compounds were characterized by NMR spectroscopy, LC-HRMS and polarimetry.     

Electrochemical cleavage of sulfonamides: an efficient and tunable strategy to prevent β-fragmentation and epimerization

The electrochemical reduction of sensitive sulfonamides is described. The addition of a benzoyl group on the nitrogen atom facilitates the reductive cleavage of sulfonamides preventing β-fragmentation and epimerization. This strategy was successfully applied to the cyclopropylamine and to α-amino stannanes.     

One-pot Crabbé homologation-radical cascade cyclisation with memory of chirality

The tandem Crabbé homologation-radical rearrangement of terminal enediynes leads, in a one-pot procedure, to the enantioselective synthesis of six- and seven-membered ring α-aminoesters bearing a quaternary stereocenter based on the phenomenon of memory of chirality.     

Rigid orthogonal bis-TEMPO biradicals with improved solubility for dynamic nuclear polarization

The synthesis and characterization of oxidized bis-thioketal-trispiro dinitroxide biradicals that orient the nitroxides in a rigid, approximately orthogonal geometry are reported. The biradicals show better performance as polarizing agents in dynamic nuclear polarization (DNP) NMR experiments as compared to biradicals lacking the constrained geometry. In addition, the biradicals display improved solubility in aqueous media due to the presence of polar sulfoxides. The results suggest that the orientation of the radicals is not dramatically affected by the oxidation state of the sulfur atoms in the biradical, and we conclude that a biradical polarizing agent containing a mixture of oxidation states can be used for improved solubility without a loss in performance.     

Restricted photochemistry in the molecular solid state: structural changes on photoexcitation of Cu(I) phenanthroline metal-to-ligand charge transfer (MLCT) complexes by time-resolved diffraction

The excited-state structure of [Cu(I)[(1,10-phenanthroline-N,N') bis(triphenylphosphine)] cations in their crystalline [BF(4)] salt has been determined at both 180 and 90 K by single-pulse time-resolved synchrotron experiments with the modified polychromatic Laue method. The two independent molecules in the crystal show distortions on MLCT excitation that differ in magnitude and direction, a difference attributed to a pronounced difference in the molecular environment of the two complexes. As the excited states differ, the decay of the emission is biexponential with two strongly different lifetimes, the longer lifetime, assigned to the more restricted molecule, becoming more prevalent as the temperature increases. Standard deviations in the current Laue study are very much lower than those achieved in a previous monochromatic study of a Cu(I) 2,9-dimethylphenanthroline substituted complex ( J. Am. Chem. Soc. 2009 , 131 , 6566 ), but the magnitudes of the shifts on excitation are similar, indicating that lattice restrictions dominate over the steric effect of the methyl substitution. Above all, the study illustrates emphatically that molecules in solids have physical properties different from those of isolated molecules and that their properties depend on the specific molecular environment. This conclusion is relevant for the understanding of the properties of molecular solid-state devices, which are increasingly used in current technology.     

A water soluble Cu(I)-NHC for CuAAC ligation of unprotected peptides under open air conditions

A reducing agent-free version of CuAAC able to operate under open air conditions is reported. A readily-synthesizable, hydrophilic and highly stable Cu(I)-NHC allows the clean ligations of unprotected peptides comprising sensitive side chains, at millimolar concentrations.     

Nature and structure of aluminum surface sites grafted on silica from a combination of high-field aluminum-27 solid-state NMR spectroscopy and first-principles calculations

The determination of the nature and structure of surface sites after chemical modification of large surface area oxides such as silica is a key point for many applications and challenging from a spectroscopic point of view. This has been, for instance, a long-standing problem for silica reacted with alkylaluminum compounds, a system typically studied as a model for a supported methylaluminoxane and aluminum cocatalyst. While (27)Al solid-state NMR spectroscopy would be a method of choice, it has been difficult to apply this technique because of large quadrupolar broadenings. Here, from a combined use of the highest stable field NMR instruments (17.6, 20.0, and 23.5 T) and ultrafast magic angle spinning (>60 kHz), high-quality spectra were obtained, allowing isotropic chemical shifts, quadrupolar couplings, and asymmetric parameters to be extracted. Combined with first-principles calculations, these NMR signatures were then assigned to actual structures of surface aluminum sites. For silica (here SBA-15) reacted with triethylaluminum, the surface sites are in fact mainly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands. Tetrahedral sites, resulting from the incorporation of Al inside the silica matrix, are also seen as minor species. No evidence for putative tri-coordinated Al atoms has been found.     

Fragmentation cross sections of protonated water clusters

We have measured fragmentation cross sections of protonated water cluster cations (H(2)O)(n=30-50)H(+) by collision with water molecules. The clusters have well-defined sizes and internal energies. The collision energy has been varied from 0.5 to 300 eV. We also performed the same measurements on deuterated water clusters (D(2)O)(n=5-45)D(+) colliding with deuterated water molecules. The main fragmentation channel is shown to be a sequential thermal evaporation of single molecules following an initial transfer of relative kinetic energy into internal energy of the cluster. Unexpectedly, that initial transfer is very low on average, of the order of 1% of collision energy. We evaluate that for direct collisions (i.e., within the hard sphere radius), the probability for observing no fragmentation at all is more than 35%, independently of cluster size and collision energy, over our range of study. Such an effect is well known at higher energies, where it is attributed to electronic effects, but has been reported only in a theoretical study of the collision of helium atoms with sodium clusters in that energy range, where only vibrational excitation occurs.     

A canted antiferromagnetic ordered phase of cyanido-bridged Mn(III)(2)Re(IV) single-chain magnets

A new cyanido-bridged Re(IV)-Mn(III) heterometallic 1D system, [Mn(III)(5-Me-saltmen)](2)[Re(IV)Cl(4)(CN)(2)]·3CH(3)CN (), was designed and structurally characterized. Interchain interactions stabilize a canted antiferromagnetic ordered state below 6.2 K that does not prevent slow relaxation of the magnetization reminiscent of the single-chain magnet properties of the individual chains.