Etude spectroscopique du role des liaisons PF et PO pontes dans les composes oxyfluores du phosphore V. Cas de P2O3F4 et de K2P2O5F2.

The compounds P₂O₃F₄ and K₂P₂O₅F₂ have been studied by vibrational spectroscopy. From the shifts of the symmetric vibration of the terminal PO bonds it appears that the molecular structure contracts as the number of PO (bridged) and/or PF bonds increases. The changes occur at the expense of PO terminal bonds. In these tetrahedral phosphorus (V) compounds the PO (bridged) and PF bonding have a similar role, and the same phenomenon occurs in sulfur VI oxide fluoride compounds.     

Hydrogen bonding: Part 18. The nature of the OHF hydrogen bond in choline fluoride

The infrared spectrum of the OHF hydrogen bond in choline fluoride is completely different from the spectra of the electrostatic O—H?X hydrogen bonds in the other choline halides; however, this spectrum cannot be accounted for in terms of a “very strong” covalent OHF bond such as those found in carboxylic acid—fluoride ion complexes or postulated for betaine hydrofluoride. The spectrum of choline fluoride is interpreted best in terms of an intermediate type of unsymmetrical hydrogen bond (r° O?F = ～ 256 pm) which shows strong intensity enhancement for the first overtone of the OHF bending vibration.     

Synthesis and characterization of hydrazinium(2+) tetrafluoroborate(III)

The reaction between hydrazinium(2+) fluoride and boron trifluoride in anhydrous hydrogen fluoride yielded slightly soluble hydrazinium(2+) tetrafluoroborate. It was characterized by chemical analysis, vibrational spectra and thermal analysis. An X-ray diffraction study showed that crystals of N₂H₆(BF₄)₂ are triclinic, space group P$\text{1}$ (No. 2). There are discrete N₂H²⁺₆ and BF^?₄ units in the crystals interlinked by hydrogen bonds of the type NH…F..     

Sur le diborure et le tétraborure de magnésium. Considérations cristallochimiques sur les tétraborures

MgB₂ and MgB₄ have been prepared at high temperature in sealed molybdenum vessels from mixtures of the elements. The utilization of an excess of metal in the vessel generates a pressure of magnesium vapor which inhibits thermal decomposition of the compounds during the synthesis. The structure of MgB₄ has been established from single crystal data collected on an automatic diffractometer. MgB₄ is orthorhombic, space group Pnam with a = 5.464; b = 7.472; c = 4.428Å and Z = 4. The structure of MgB₄, is based on chains of boron pentagonal pyramids in which the averaged BB bond is 1.787 Å. Interchain BB bonds of 1.730 Å are responsible for the three-dimensional boron framework. The Mg atoms, located in tunnels, form zigzag chains. The structure of MgB₄ is compared to those of ThB₄ and CrB₄; it is concluded that the size of the metal atom plays an important role in the nature of the boron framework which exists. In MgB₄, the fundamental unit of the boron skeleton is a pentagonal pyramid; a new feature, in boron-rich borides where this type of coordination polyhedron was previously found only in B₁₂ icosahedra.     

Bond length based bond orders for borane cluster compounds

The known molecular structures of several closo borane cluster compounds, together with established electron-counting rules, are used to derive a relationship between bond length and bond order for boronboron two-centre bonds. This relationship is useful in deducing the distribution of electronic charge, and the approach can be extended to other homonuclear clusters.     

Reactions of sulphuryl fluoride,sulphuryl chlorofluoride and sulphuryl chloride with amines

The reactions of sulphuryl fluoride, sulphuryl chlorofluoride and sulphuryl chloride with the amines tert-butylamine, benzylamine, piperidine, pyridine and quinoline have been investigated. The primary and secondary amines react with the elimination of hydrogen halides and formation of SN bonds whereas tertiary amines form 1:2 adducts.     

Bismuth–Boron Multiple Bonding in BiB2O− and Bi2B−

Despite its electron deficiency, boron is versatile in forming multiple bonds. Transition‐metal–boron double bonding is known, but boron–metal triple bonds have been elusive. Two bismuth boron cluster anions, BiB₂O⁻ and Bi₂B⁻, containing triple and double B−Bi bonds are presented. The BiB₂O⁻ and Bi₂B⁻ clusters are produced by laser vaporization of a mixed B/Bi target and characterized by photoelectron spectroscopy and ab initio calculations. Well‐resolved photoelectron spectra are obtained and interpreted with the help of ab initio calculations, which show that both species are linear. Chemical bonding analyses reveal that Bi forms triple and double bonds with boron in BiB₂O⁻ ([Bi≡B−B≡O]⁻) and Bi₂B⁻ ([Bi=B=Bi]⁻), respectively. The Bi−B double and triple bond strengths are calculated to be 3.21 and 4.70 eV, respectively. This is the first experimental observation of Bi−B double and triple bonds, opening the door to design main‐group metal–boron complexes with multiple bonding.     

Elongation of planar boron clusters by hydrogenation: boron analogues of polyenes

Dihydrogenated boron clusters, H(2)B(n)(-) (n = 7-12), were produced and characterized using photoelectron spectroscopy and computational chemistry to have ladderlike structures terminated by a hydrogen atom on each end. The two rows of boron atoms in the dihydrides are bonded by delocalized three-, four-, or five-center σ and π bonds. The π bonding patterns in these boron nanoladders bear similarities to those in conjugated alkenes: H(2)B(7)(-), H(2)B(8), and H(2)B(9)(-), each with two π bonds, are similar to butadiene, while H(2)B(10)(2-), H(2)B(11)(-), and H(2)B(12), each with three π bonds, are analogous to 1,3,5-hexatriene. The boron cluster dihydrides can thus be considered as polyene analogues, or "polyboroenes". Long polyboroenes with conjugated π bonds (analogous to polyacetylenes), which may form a new class of molecular wires, should exist.     

Formation and Reactivity of Electron‐Precise B−B Single and Multiple Bonds

Recent years have seen rapid advances in the chemistry of small molecules containing electron‐precise boron–boron bonds. This Review provides an overview of the latest methods for the controlled synthesis of B−B single and multiple bonds as well as the ever‐expanding range of reactivity displayed by B−B multiple bonds.     

The structure of a new isomer of dicarba-nido-undecaborane(13)

The intramolecular rearrangement involved in the electrophilic methylation of 7,8-B₉C₂H₁₁^2? leads after protonation to the methyl derivative of a new isomer of dicarba-nido-undecaborane(13). By an X-ray structure analysis the latter compound is shown to be 11-methyl-2,7-dicarba-nido-undecaborane(12). It has the structure of an icosahedron with one missing vertex, with the carbon atoms adjacent, one in the open face of the polyhedron and the other in its closed part. The methyl group is attached to the boron atom of the open face bonded to both carbon atoms. The open face has two BHB-bridges which are symmetric relative to its carbon atom. The main interatomic distances are: av. BB 1.794(8), av. BC 1.685(7), CC 1.606(6), BMe 1.551(8), av. BH (terminal) 1.08(3), av. BH (bridging) 1.26(4), av. CH 0.92(4) Å.     

Normal coordinate analysis of bilirubin vibrational spectra: Effects of intramolecular hydrogen bonding

Normal coordinate analyses are presented for half-bilirubin molecules. Calculations for the AB pyrromethenone include intramolecular hydrogen bonds, while those for the CD chromophore exclude intramolecular hydrogen bonds. Valence force-field parameters have been optimized to correlate closely with the IR and Raman spectra of the target molecules. The results of the calculations are compared with the spectra of bilirubin IXa and various model compounds in the solid state and solution.     

Quantum-chemical study of interaction of dipyrrolylmethenes with boron trifluoride and other lewis acids

The geometric parameters and energies of the products of donor-acceptor interaction of dipyrrolylmethenes with BF₃ and other inorganic Lewis acids were calculated by quantum-chemical methods. The bond nature and the energies of formation of the donor-acceptor complexes under consideration were analyzed. It was shown that the complexes with p-element fluorides are noticeably stabilized by hydrogen bonds involving the hydrogen atom of the NH group of dipyrrolylmethene and the nearest fluorine atom of a Lewis acid. Hydrogen bonding promotes further elimination of HF in the synthesis of boron fluoride complexes of dipyrrolylmethenes. The energy profile was calculated for the reaction of formation of the boron fluoride complex with dipyrrolylmethene through the intermediate donor-acceptor complex.     

Single,Double, Triple Bonds and Chains: The Formation of Electron‐Precise B?B Bonds

The construction of boron–boron bonds, despite the intense synthetic interest in diboranes and the high B? B bond enthalpy, is still difficult, uncontrollable, and unpredictable. Methods for the construction of B? B multiple bonds are rarer still. These problems have witnessed some progress in recent years; this Minireview attempts to provide a background to the history of B? B bond synthesis and summarize the recent results in the area.     

The condension reactions of bis(b-hydroxy)dicarba-closo-undecaborane(11)

The title compound, 4,7-(OH)₂-2,3-(CH₃)₂-2,3-C₂B₉H₇ (11), reacts cleanly with various glycols to yield exocyclic ring systems. The glycol fragment is fused to the carborane polyhedra through two boronoxygencarbon bonds. The use of ¹⁸O enriched ethylene glycol indicates the hydroxyl groups on the carborane polyhedra are displaced during the condension reaction. The reaction of optically active glycols with the title compound also indicates the hydroxyl groups on the glycol must adopt a cis conformation during the condensation reaction.     

Deformation of the valence electron distributions in the icosahedral boron structure of α-AlB12

X-ray difference electron densities in α-AlB₁₂ were examined. Broad peaks presumably characteristic of highly delocalized three-center bonds were observed at the centers of the triangular faces of the B₁₂ icosahedron. Another kind of prominent peak on the external BB bonds of the icosahedron indicated that the inter-icosahedral BB bonds are two-center bonds. An averaging over the icosahedral symmetry significantly reduced the random noises in the difference densities. Theoretical difference electron densities for a B₁₂H^?2₁₂ molecular ion, calculated by the $\text{CNDO}\text{2}$ molecular orbital method, were qualitatively in good agreement with the observed densities mentioned above. Residual peaks were observed on all the five edges of the open pentagonal face of the B₁₉ unit; they had broad tails extending toward the aluminum triplet sites. The observed difference densities around the “single” B(23) atom suggested that the atom belongs to the B₁₉ unit rather than being single.     

X-ray photoelectron study of the effect of the composition of the initial gas phase on changes in the electronic structure of hexagonal boron nitride films obtained by PECVD from borazine

Hexagonal boron nitride films are synthesized by plasma enhanced chemical vapor deposition (PECVD) from a gas mixture of borazine and ammonia or helium on Si(100) substrates. X-ray photoelectron spectroscopy is used to study changes in the electronic structure and chemical composition of the films depending on the composition of the initial gas mixture. It is found that the chemical composition of the samples depends on the gas used. The use of helium results in an excess of boron atoms on the film surface, the appearance of B–B bonds, and a decrease in the contribution of B–N bonds in the hexagonal structure. The preparation of h-BN films close to the stoichiometric composition by PECVD methods with the use of borazine is shown to be possible with the addition of ammonia. Based on the literature data, the binding energies in the B 1s XPS spectra are calculated for different boron environments in the hexagonal lattice.     

Insertion reactions of dimethylsilylene: relative reactivity towards oxygenz.sbnd;hydrogen,siliconhydrogen,and siliconz.sbnd;alkoxy bonds

Photochemically-generated dimethylsilylene is found in competition experiments to insert preferentially into oxygenhydrogen bonds of alcohols compared to either siliconhydrogen bonds of silanes or siliconoxygen bonds of alkoxysilanes. This selectivity for OH bonds compared to SiH bonds is quite high in tetrahydrofuran and in dilute hydrocarbon solutions. However, it decreases in more concentrated hydrocarbon solutions. These effects are discussed in terms of aggregation of alcohols, hydrogen bonding, and solvent-mediated dimethylsilylene reactivity.     

Vibrational study of strong CH · middot; X hydrogen bonds in solid complexes of boron decachlorocarboranes

Solid complexes of boron decachloro-o-carborane and boron decachloro-m-carborane (B₁₀Cl₁₀C₂H₂) with some oxygen and nitrogen bases have been investigated by infrared and Raman spectroscopy. Complexes containing CH · · O hydrogen bonds are characterized by a relative CH stretching frequency shift up to 12% and a halfwidth of the νCH band up to 220 cm^?1. CH · · N hydrogen bonds, with trimethylamine for example, are stronger with a relative shift of about 18% and $\text{ν}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of about 500 cm^?1. Triethylamine complexes, however, form a NH⁺ · · C^? proton transfer hydrogen bond while pyridine can give either CH · · N or C^? · · ⁺HN hydrogen-bonded adducts depending on the solvent and temperature. The CH · · N?c^? · · ⁺HN equilibrium appears to be shifted towards ion-pair formation at considerably smaller enthalpy values compared to the OH · · N?O^? · · ⁺HN system. CH and NH stretching frequencies are correlated with the acidity of the donor and the basicity of acceptor molecules.     

Infrared spectrum of the novel electron-deficient BH(4) radical in solid neon

Laser-ablated boron reacts with hydrogen on condensation in excess neon to give BH4 radical, BH4- anion, and B2H6 as the major products. Identifications are based on 10B and D substitution, DFT frequency calculations, and comparison to previous spectra. Infrared spectra of BH4 support the C2v structure deduced from previous ESR spectra and theoretical calculations with two normal B-H bonds and two long B-H bonds for this novel electron-deficient radical. NBO analysis suggests that the two long B-H bonds and the H- -H bond are one-electron bonds.     

Functionally substituted organotins: formation of organotin-containing phosphines

Additions of PH bonds to vinylstannes, of SnH bonds to alkynylphosphines, and of SnP bonds to allenes and alkynes are described.