Stable Lewis Base Adducts of Tetrahalodiboranes: Synthetic Methods and Structural Diversity

A series of 22 new bis(phosphine), bis(carbene), and bis(isonitrile) tetrahalodiborane adducts has been synthesized, either by direct adduct formation with highly sensitive B₂X₄ precursors (X=Cl, Br, I) or by ligand exchange at stable B₂X₄(SMe₂)₂ precursors (X=Cl, Br) with labile dimethylsulfide ligands. The isolated compounds have been fully characterized using NMR spectroscopy, elemental analysis, and, for 20 of these compounds, single-crystal X-ray diffraction, revealing an unexpected variation in the bonding motifs. In addition to the classical B₂X₄L₂ diborane(4) bis-adducts, certain more sterically demanding carbene ligands induce a halide displacement which led to the first halide-bridged monocationic diboron species, [B₂X₃L₂]A (A=BCl₄, Br, I). Furthermore, low-temperature 1:1 reactions of B₂Cl₄ with sterically demanding N-heterocyclic carbenes led to the formation of kinetically unstable mono-adducts, one of which was structurally characterized. A comparison of the NMR spectra and structural data of new and literature-known bis-adducts shows several trends pertaining to the nature of the halides and the stereoelectronic properties of the Lewis bases employed.     

Calculated vibrational transition probabilities of OH(X2Π)

The theoretically derived dipole moment function of OH(X²Π) obtained by Stevens Das, Wahl, Neumann, and Krauss is used to calculate the absolute intensities of the vibrational-rotational transitions of the OH Meinel bands. The calculations take full account of the spin uncoupling and vibration-rotation coupling which markedly influence the radiative transition probabilities. The effect of lambda-doubling on the vibrational transitions is analyzed and generally found to be negligible. Results are tabulated for Δv = v′ – v″ ranging from the fundamental transitions Δv = 1 to the Δv = 5 overtone, for v′ = 1–9 and J′ = 0.5 – 15.5. A comparison is made with available data, and various features of the OH spectrum are examined that are of aeronomical and experimental interest. Thermally averaged emission rates are presented for Δv = 1–5, and the validity of the rotational temperatures commonly derived from experimental intensity distributions is questioned.     

Polymeric Nanogels with Tailorable Degradation Behavior

The aim of this study is to design a polymeric nanogel system with tailorable degradation behavior. To this end, hydroxyethyl methacrylate‐oligoglycolates‐derivatized poly(hydroxypropyl methacrylamide) (pHPMAm‐Gly‐HEMA) and hydroxyethyl methacrylamide‐oligoglycolates‐derivatized poly(hydroxyethyl methacrylamide) (pHEMAm‐Gly‐HEMAm) are synthesized and characterized. pHEMAm‐Gly‐HEMAm shows faster hydrolysis rates of both carbonate and glycolate esters than the same ester groups of pHPMAm‐Gly‐HEMA. pHEMAm‐Gly‐HEMAm nanogels have tailorable degradation kinetics from 24 h to more than 4 d by varying their crosslink densities. It is shown that the release of a loaded macromolecular model drug is controlled by degradation of nanogels. The nanogels show similar cytocompatibility as PLGA nanoparticles and are therefore considered to be attractive systems for drug delivery.

     

Ionic Liquids with More than One Metal: Optical and Electrochemical Properties versus d-Block Metal Combinations

Thirteen N-butylpyridinium salts, including three monometallic [C₄Py]₂[MCl₄], nine bimetallic [C₄Py]₂[M_1−x^aM_x^bCl₄] and one trimetallic compound [C₄Py]₂[M_1−y-z^aM_y^bM_z^cCl₄] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 °C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10⁻⁴ and 10⁻⁸ S cm⁻¹. Some Cu-based ILs reach conductivities of 10⁻² S cm⁻¹, which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47×10⁻¹ S cm⁻¹ at 70 °C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.     

Exclusive π Encapsulation of Light Alkali Metal Cations by a Neutral Molecule

Cation–π interactions are one of the most important classes of noncovalent bonding, and are seen throughout biology, chemistry, and materials science. However, in almost every documented case, these interactions play only a supporting role to much stronger covalent or dative bonds, thus making examples of exclusive cation–π bonding exceedingly rare. In this study, a neutral diboryne molecule is found to encapsulate the light alkali metal cations Li⁺ and Na⁺ in the absence of a net charge, covalent bonds, or lone‐pair donor groups. The resulting encapsulation complexes are, to our knowledge, the first structurally authenticated species in which a neutral molecule binds the light alkali metals exclusively through cation–π interactions.