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The unprecedented co-thermolysis of decaborane(14) (nido-B10 H14 ) and toluene results in a novel porous material (that we have named "activated borane") containing micropores between 1.0 and 1.5 nm in diameter and a specific surface area of 774 m2 g-1 (Ar, 87 K) that is thermally stable up to 1000 °C. Solid state 1 H, 11 B and 13 C MAS NMR, UV-vis and IR spectroscopies suggest an amorphous structure of borane clusters interconnected by toluene moieties in a ratio of about three toluene molecules for every borane cluster. In addition, the structure contains Lewis-acidic tri-coordinated boron sites giving it some unique properties. Activated borane displays high sorption capacity for pollutants such as sulfamethoxazole, tramadol, diclofenac and bisphenol A that exceed the capacity of commercially-available activated carbon. The consistency in properties for each batch made, and the ease of its synthesis, make activated borane a promising porous material worthy of broad attention.
- Klíčová slova
- activated borane, decaborane, gas adsorption, pollutant removal, porous polymer,
- Publikační typ
- časopisecké články MeSH
Mobilities of investigated boron cluster compounds in 3-(N-morpholino)propanesulfonic and phosphate buffers adjusted to pH 7 either with sodium hydroxide or with tris(hydroxymethyl)aminomethane depend on both buffer ions. The zone width and zone asymmetry, which are usually markedly higher than those of organic or common inorganic ions of comparable size, depend on the type of the borane cluster anion. Unusual shapes of zones of two investigated compounds have been found in tris phosphate buffer. Acetonitrile was superior to methanol as an organic additive to separation systems from the viewpoint of the zone symmetry and separation speed. Narrow trigonal zones, typical of organic ions non-interacting with the capillary wall, have been observed for some bridged sandwich cobalt complexes in run buffers with the addition of acetonitrile. The interaction of borane cluster anions with beta-cyclodextrin cavity is excessively strong in purely aqueous solutions. Methanol and acetonitrile, which generally weaken the interaction, sometimes affect the separation enantioselectivity of various compounds in different ways in addition to the weakening effect. Chiral discrimination was reached for all ten investigated anions, which belong to four different structural types of cluster boranes. Stability constants estimated for some analyte-beta-cyclodextrin complexes range between 100 and 1800 l/mol in acceptable separations. The relative difference of the constants was from 3 to 20%.
- MeSH
- borany chemie izolace a purifikace MeSH
- elektroforéza kapilární metody MeSH
- spektrofotometrie ultrafialová MeSH
- stereoizomerie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- borany MeSH
We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X+ 2 E←X 1 A1 transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE0K (NH3 BH3 , NH3 BH2 + )= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH3 -site. From the data, a 0 K bond dissociation energy for the B-H bond in the cation of 71.5±3 kJ mol-1 was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol-1 .
- Klíčová slova
- Jahn-Teller effect, ammonia borane, hydrogen storage, molecular orbitals, photoelectron spectroscopy,
- Publikační typ
- časopisecké články MeSH
Emission from electronically excited species forms the basis for an important class of light sources-lasers. So far, commercially available solution-processed blue-emitting laser materials are based on organic compounds or semiconductor nanocrystals that have significant limitations: either low solubility, low chemical- and/or photo-stability and/or uncompetitive prices. Here we report a novel and competitive alternative to these existing laser materials that is based on boron hydrides, inorganic cluster compounds with a rich and diverse chemistry. We demonstrate that solutions of the borane anti-B18H22 show, under pulsed excitation, blue laser emission at 406 nm with an efficiency (ratio of output/input energies) of 9.5%, and a photostability superior to many of the commercially available state-of-the-art blue laser dyes. This demonstration opens the doors for the development of a whole new class of laser materials based on a previously untapped resource for laser technology-the boranes.
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Single-cage boron cluster anions with at least 11 cluster atoms, free of bonded functional groups that strongly absorb UV light, and their cobalt complexes have been the investigated compounds. Their UV-absorption spectra have absolute maxima between 200 and 215 nm. Corresponding molar extinction coefficients that are of the order of 10(3)-10(4) L mol(-1) cm(-1) indicate medium detection sensitivity. Its reaching requires elimination of background electrolytes that weaken the UV-light beam in any way. Frequently used carboxylic acids and zwitterionic Good's buffers cannot be used as buffering compounds from this reason. Freshly prepared 1 mM solutions of boron cluster compounds in aqueous sodium chloride, chosen as indifferent electrolyte, which contain 20-30% (v/v) of methanol or acetonitrile, give zones free of tailing. After storing in the fridge, zones of the compounds became pronouncedly tailed even if their solutions remain clear and free of precipitation, turbidity or opalescence. The tailing usually disappeared if the acetonitrile or the methanol concentration in samples was 40-60% (v/v) depending on the dissolved compound hydrophobicity. Solutions of extremely hydrophobic compounds, stored in the fridge, require mild heating to 30-40 degrees C for half an hour for the avoiding of the tailing. Permanent slow decrease in effective mobilites of boron cluster anions was found if background electrolytes contained acetonitrile and beta-cyclodextrin. Analogous decrease was not observed with organic anions. Constant mobilities of boron cluster anions have been reached if acetonitrile was replaced with methanol. Analyte zones were more symmetrical in background electrolytes buffered with sodium borate of pH 9 than in background electrolytes buffered with sodium phosphate of pH 7.
Fluorinated arylborane-based Lewis acid catalysts have shown remarkable activity and serve as ideal examples of transition metal-free catalysts for diverse organic transformations. However, their homogeneous nature poses challenges in terms of recyclability and separation from reaction mixtures. This work presents an efficient technique for the heterogenization of boron Lewis acid catalysts by anchoring Piers' borane to allyl-functionalized iron oxide. This catalyst demonstrates excellent activity in the hydrosilylation of imines and the reductive amination of carbonyls using various silanes as reducing agents under mild reaction conditions. The catalyst exhibits broad tolerance towards a wide range of functional substrates. Furthermore, it exhibits good recyclability and can be easily separated from the products using an external magnetic field. This work represents a significant advance in the development of sustainable heterogenous metal-free catalysts for organic transformations.
- Klíčová slova
- Lewis acid, amine synthesis, heterogeneous borane, hydrosilylation, precious metal-free catalysis,
- Publikační typ
- časopisecké články MeSH
We present the first examples of alkylated derivatives of the macropolyhedral boron hydride, anti-B18H22, which is the gain medium in the first borane laser. This new series of ten highly stable and colorless organic-inorganic hybrid clusters are capable of the conversion of UVA irradiation to blue light with fluorescence quantum yields of unity. This study gives a comprehensive description of their synthesis, isolation, and structural characterization together with a delineation of their photophysical properties using a combined theoretical and experimental approach. Treatment of anti-B18H22 1 with RI (where R = Me or Et) in the presence of AlCl3 gives a series of alkylated derivatives, Rx-anti-B18H22-x (where x = 2 to 6), compounds 2-6, in which the 18-vertex octadecaborane cluster architectures are preserved and yet undergo a linear "polyhedral swelling", depending on the number of cluster alkyl substituents. The use of dichloromethane solvent in the synthetic procedure leads to dichlorination of the borane cluster and increased alkylation to give Me11-anti-B18H9Cl2 11, Me12-anti-B18H8Cl2 12, and Me13-anti-B18H7Cl2 13. All new alkyl derivatives are highly stable, extremely efficient (ΦF = 0.76-1.0) blue fluorophores (λems = 423-427 nm) and are soluble in a wide range of organic solvents and also a polystyrene matrix. The Et4-anti-B18H18 derivative 4b crystallizes from pentane solution in two phases with consequent multiabsorption and multiemission photophysical properties. An ultrafast transient UV-vis absorption spectroscopic study of compounds 4a and 4b reveals that an efficient excited-state absorption at the emission wavelength inhibits the laser performance of these otherwise remarkable luminescent molecules. All these new compounds add to the growing portfolio of octadecaborane-based luminescent species, and in an effort to broaden the perspective on their highly emissive photophysical properties, we highlight emerging patterns that successive substitutions have on the molecular size of the 18-vertex borane cluster structure and the distribution of the electron density within.
- Publikační typ
- časopisecké články MeSH
Borane cluster-based porous covalent networks, named activated borane (ActB), were prepared by cothermolysis of decaborane(14) (nido-B10H14) and selected hydrocarbons (toluene, ActB-Tol; cyclohexane, ActB-cyHx; and n-hexane, ActB-nHx) under anaerobic conditions. These amorphous solid powders exhibit different textural and Lewis acid (LA) properties that vary depending on the nature of the constituent organic linker. For ActB-Tol, its LA strength even approaches that of the commonly used molecular LA, B(C6F5)3. Most notably, ActBs can act as heterogeneous LA catalysts in hydrosilylation/deoxygenation reactions with various carbonyl substrates as well as in the gas-phase dehydration of ethanol. These studies reveal the potential of ActBs in catalytic applications, showing (a) the possibility for tuning catalytic reaction outcomes (selectivity) in hydrosilylation/deoxygenation reactions by changing the material's composition and (b) the very high activity toward ethanol dehydration that exceeds the commonly used γ-Al2O3 by achieving a stable conversion of ∼93% with a selectivity for ethylene production of ∼78% during a 17 h continuous period on stream at 240 °C.
- Publikační typ
- časopisecké články MeSH
New anti-octadecaborane(22) laser dyes have been recently introduced. However, their application in solid thin films is limited, despite being very desirable for electronics. Spectroscopic methods, photoluminescence (PL), and infrared reflection-absorption spectroscopy (IRRAS), are here used to reveal structural responses to a temperature change in thin polymer films made of π- and σ-conjugated and non-conjugated polymers and anti-octadecaborane(22) and its tetra-alkylatedderivatives. It has been observed that borane clusters are not firmly fixed within polymer matrices and that their ability for diffusion out of the polymer film is unprecedented, especially at higher temperatures. This ability is related to thermodynamic transitions of polymer macromolecular chains. PL and IRRAS spectra have revealed a clear correlation with β-transition and α-transition of polymers. The influence of structure and molecular weight of a polymer and the concentration and the substitution type of clusters on mobility of borane clusters within the polymer matrix is demonstrated. A solution is proposed that led to an improvement of the temperature stability of films by 45 °C. The well-known spectroscopic methods have proved to be powerful tools for a non-routine description of the temperature behavior of both borane clusters and polymer matrices.
- Klíčová slova
- borane cluster, infrared reflection–absorption spectroscopy, photoluminescence spectroscopy, thin film, transition temperature,
- MeSH
- barvicí látky MeSH
- borany * MeSH
- lasery MeSH
- polymery * chemie MeSH
- spektrofotometrie infračervená MeSH
- teplota MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- barvicí látky MeSH
- borany * MeSH
- polymery * MeSH
The noncovalent interactions of heteroboranes with aromatic systems have only recently been acknowledged as a source of stabilization in supramolecular complexes. The physical basis of these interactions has been studied in several model complexes using advanced computational methods. The highly accurate CCSD(T)/complete basis set (CBS) value of the interaction energy for the model diborane···benzene complex in a stacking geometry exhibiting a B(2)H···π hydrogen bond was calculated to be -4.0 kcal·mol(-1). The DFT-SAPT/CBS approach, which is shown to reproduce the CCSD(T)/CBS data reliably asserted that the major stabilizing component was dispersion, followed by electrostatics. Furthermore, the effect of the benzene heteroatom- and exosubstitutions was studied and found to be small. Next, when aromatic molecules were changed to cyclic aliphatic ones, van der Waals complexes stabilized by the dispersion term only were formed. As the last step, interactions of two larger icosahedral borane cages with benzene were explored. The complex of the monoanionic CB(11)H(12)(-) exhibited two minima: the first stacked above the plane of the benzene ring with a C-H···π hydrogen bond and the second planar, in which the carborane cage bound to benzene via five B-H···H-C dihydrogen bonds. The DFT-SAPT/CBS calculations revealed that both of these binding motifs were stabilized by dispersion followed by electrostatic terms, with the planar complex being 1.4 kcal·mol(-1) more stable than the stacked one. The dianionic B(12)H(12)(2-) interacted with benzene only in the planar geometry, similarly as smaller anions do. The large stabilization energy of 11.0 kcal·mol(-1) was composed of dominant attractive dispersion and slightly smaller electrostatic and induction terms. In summary, the borane/carborane···aromatic interaction is varied both in the complex geometries and in the stabilizing energy components. The detailed insight derived from high-level quantum chemical computations can help us understand such important processes as host-guest complexation or carborane···biomolecule interactions.
