Divide and Stack Up: Boron‐Based Sandwich Cluster as a Subnanoscale Propeller

Typical salts are composed of positive and negative ions that appear alternatively, whereas decorated layered materials normally have ions anchored on the polygonal sites. In this way, the ions are spatially fixed and the system is stabilized on electrostatic grounds. Here we report on a unique boron‐lithium cluster, B₇Li₄^?, which contains a disk‐like B₇ core, being sandwiched by a Li₃ ring and an isolated Li atom. All Li centers are stacked exactly on the B atoms from top or bottom, rather than being anchored on triangular B₃ sites. The cluster shows dynamic fluxionality, whose Li₃ ring rotates freely on the B₇ disk even at below room temperature (200 K), akin to a subnanoscale propeller. The rotation barrier is only 0.37 kcal mol^?1 at the single‐point CCSD(T) level. The sandwich shape facilitates intramolecular charge‐transfers, leading to a [Li₃]⁺[B₇]^3?[Li]⁺ salt complex. The [Li₃]⁺ layer has 2σ aromaticity, while [B₇]^3? core is robust with both π and σ sextets. Three‐fold π/σ aromaticity collectively stabilizes the system, as well as underlies its dynamic fluxionality. The interlayer bonding turns out to be strong, dominated by ionic interactions (of the order of 3–4 eV per Li₃/Li unit). The work demonstrates a propeller at the subnanoscale, which is dynamically fluxional despite strong covalent and ionic bonding.     

Cage‐Like B41+ and B422+: New Chiral Members of the Borospherene Family

The newly discovered borospherenes B₄₀^?/0 and B₃₉^? mark the onset of a new class of boron nanostructures. Based on extensive first‐principles calculations, we introduce herein two new chiral members to the borospherene family: the cage‐like C₁ B₄₁⁺ ( 1 ) and C₂ B₄₂²⁺ ( 2 ), both of which are the global minima of the systems with degenerate enantiomers. These chiral borospherene cations are composed of twelve interwoven boron double chains with six hexagonal and heptagonal faces and may be viewed as the cuborenes analogous to cubane (C₈H₈). Chemical bonding analyses show that there exists a three‐center two‐electron σ bond on each B₃ triangle and twelve multicenter two‐electron π bonds over the σ skeleton. Molecular dynamics simulations indicate that C₁ B₄₁⁺ ( 1 ) fluctuates above 300 K, whereas C₂ B₄₂²⁺ ( 2 ) remains dynamically stable. The infrared and Raman spectra of these borospherene cations are predicted to facilitate their experimental characterizations.     

IR Spectrum and Structure of Protonated Monosilanol: Dative Bonding between Water and the Silylium Ion

We report the spectroscopic characterization of protonated monosilanol (SiH₃OH₂⁺) isolated in the gas phase, thus providing the first experimental determination of the structure and bonding of a member of the elusive silanol family. The SiH₃OH₂⁺ ion is generated in a silane/water plasma expansion, and its structure is derived from the IR photodissociation (IRPD) spectrum of its Ar cluster measured in a tandem mass spectrometer. The chemical bonding in SiH₃OH₂⁺ is analyzed by density functional theory (DFT) calculations, providing detailed insight into the nature of the dative H₃Si⁺‐OH₂ bond. Comparison with protonated methanol illustrates the differences in bonding between carbon and silicon, which are mainly related to their different electronegativity and the different energy of the vacant valence p_z orbital of SiH₃⁺ and CH₃⁺.     

Tetrabutylammonium salt of the B24F224− anion. Two B12F112− icosahedra linked by a 2c–2e B?B bond and surrounded by a sheath of CH· · ·FB hydrogen bonds

The B₂₄F₂₂⁴⁻ anion, which was formed as a minor by‐product when the B₁₂H₁₂²⁻ anion was treated with F₂ in liquid HF, has been isolated as its N(n‐Bu)₄⁺ salt and characterized by ¹⁰B, ¹¹B, and ¹⁹F NMR spectroscopy, electrospray mass spectrometry, cyclic voltammetry, single‐crystal X‐ray diffraction, and calculations at the DFT level of theory. The B₂₄F₂₂⁴⁻ anion has idealized D₅ symmetry and consists of two B₁₂F₁₁²⁻ icosahedra linked by a 2c–2e boron–boron single bond with a B B distance of 1.725(4) Å. In the solid state, the anion interacts with eight N(n‐Bu)₄⁺ cations via a network of 34 CH···FB hydrogen bonds with H· · ·F distances that range from 2.26 to 2.55 Å. These hydrogen bonds were successfully modeled by DFT calculations, which showed that the hydrogen bonds probably have a measurable, albeit subtle, effect on the structure of the B₂₄F₂₂⁴⁻. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:181–187, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20220     

Formation of an Isolable Divinylborinium Ion through Twofold 1,2‐Carboboration between a Diarylborinium Ion and Diphenylacetylene

Borinium ions, that is, two‐coordinate boron cations, are the most electron‐deficient isolable boron compounds. As borinium ions have only four formal valence electrons on boron, they should show a strong tendency to accept electron pairs on the boron atom to fill its valence shell. Thus chemical reactions of borinium ions are expected to give products in which the coordination number of boron is increased from two to three or four. However, contrary to this expectation, we found that the dimesitylborinium ion (Mes₂B⁺) undergoes twofold 1,2‐carboboration reactions with two equivalents of diphenylacetylene to yield an unprecedented borinium ion ( 1 ⁺) with two substituted vinyl groups on the boron center. NMR spectroscopy and X‐ray diffraction analysis of 1 ⁺, together with electronic‐structure calculations, revealed that the positive charge is delocalized over the entire π‐conjugated system. The fact that the chemical transformation of a borinium ion gives rise to a different borinium ion without a change in the coordination number is remarkable and should provide new insight into the chemistry of the Group 13 elements.     

ChemInform Abstract: B+13: A Photodriven Molecular Wankel Engine.

Based on DFT and Born—Oppenheimer molecular dynamics calculations a model molecular Wankel motor, the dual‐ring structure B₁₃⁺, driven by circularly polarized IR radiation near 3 THz is proposed as a potential building block for nanomachines.     

Analysis of Why Boron Avoids sp2 Hybridization and Classical Structures in the BnHn+2 Series

We performed global minimum searches for the B_nH_n+2 (n=2‐5) series and found that classical structures composed of 2c–2e B? H and B? B bonds become progressively less stable along the series. Relative energies increase from 2.9 kcal mol^?1 in B₂H₄ to 62.3 kcal mol^?1 in B₅H₇. We believe this occurs because boron atoms in the studied molecules are trying to avoid sp² hybridization and trigonal structure at the boron atoms, as in that case one 2p‐AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p‐AOs and avoiding having one 2p‐AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron–hydride clusters as well as for pure boron clusters and boron compounds in general.     

Competing Insertion and External Binding Motifs in Hydrated Neurotransmitters: Infrared Spectra of Protonated Phenylethylamine Monohydrate

Hydration has a drastic impact on the structure and function of flexible biomolecules, such as aromatic ethylamino neurotransmitters. The structure of monohydrated protonated phenylethylamine (H⁺PEA?H₂O) is investigated by infrared photodissociation (IRPD) spectroscopy of cold cluster ions by using rare‐gas (Rg=Ne and Ar) tagging and dispersion‐corrected density functional theory calculations at the B3LYP‐D3/aug‐cc‐pVTZ level. Monohydration of this prototypical neurotransmitter gives an insight into the first step of the formation of its solvation shell, especially regarding the competition between intra‐ and intermolecular interactions. The spectra of Rg‐tagged H⁺PEA?H₂O reveal the presence of a stable insertion structure in which the water molecule is located between the positively charged ammonium group and the phenyl ring of H⁺PEA, acting both as a hydrogen bond acceptor (NH⁺???O) and donor (OH???π). Two other nearly equivalent isomers, in which water is externally H bonded to one of the free NH groups, are also identified. The balance between insertion and external hydration strongly depends on temperature.     

Tetraiododiborane(4) (B2I4) is a Polymer Based on sp3 Boron in the Solid State

Herein we present the first solid‐state structures of tetraiododiborane(4) (B₂I₄), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B₂F₄, B₂Cl₄, and B₂Br₄. Single‐crystal X‐ray diffraction, solid‐state NMR, and IR measurements indicate that B₂I₄ in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid‐state structures, and these are compared with the experimental spectra.     

Reinvestigation of the Structure of Protonated Lysine Dimer

To better understand inconsistencies between the predicted infrared (IR) spectra of previously suggested isomers of Lys₂H⁺ reported by Wu et al. (J. Am. Soc. Mass Spectrom. 22:1651–1659, 18) and the experimental IR photon dissociation (IRPD) spectrum obtained by Oh et al. (J. Am. Chem. Soc. 127:4076–4083, 4), the structure of Lys₂H⁺ was reinvestigated using IRPD spectroscopy in the extended region 2700–3700 cm^?1 and theoretical calculations. The new experimental IRPD spectrum is in good agreement with Oh’s spectrum in the corresponding wavelength range. Based on calculations at the MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) and MP2/6-31?+?G(d,p)//MP2/6-31?+?G(d,p) levels, a new salt-bridged isomer, ZW1, was found to be the most stable isomer; it is more energetically favored than the previously suggested charge-solvated isomer LL-CS01 by 10 or 26 kJ mol^?1. Although the calculated IR spectrum of ZW1 is in good agreement with the experimental one in the range 2700–3700 cm^?1, it is in poor agreement with the previous IRPD spectrum in the range 1000–1900 cm^?1. This investigation shows that the intermolecular interactions inside the dimer are more complex than previously supposed. It is possible that both salt-bridged and charge-solvated isomers of Lys₂H⁺ are stable in the gas phase, and the isomers generated during ionization are sensitive to the experimental conditions.

Unsymmetrical,Cyclic Diborenes and Thermal Rearrangement to a Borylborylene

Cyclic diboranes(4) based on a chelating monoanionic benzylphosphine linker were prepared through boron–silicon exchange between arylsilanes and B₂Br₄. Coordination of Lewis bases to the remaining sp² boron atom yielded unsymmetrical sp³‐sp³ diboranes, which were reduced with KC₈ to their corresponding trans‐diborenes. These compounds were studied with a combination of spectroscopic methods, X‐ray diffraction, and DFT calculations. PMe₃‐stabilized diborene 6 was found to undergo thermal rearrangement to gem‐diborene 8 . DFT calculations on 8 reveal a polar boron–boron bond, and indicate that the compound is best described as a borylborylene.     

Bridge‐Localized HOMO‐Binding Character of Divinylanthracene‐Bridged Dinuclear Ruthenium Carbonyl Complexes: Spectroscopic,Spectroelectrochemical, and Computational Studies

The electronic properties of four divinylanthracene‐bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe₃)₃}₂(μ? CH?CHArCH?CH)] (Ar=9,10‐anthracene ( 1 ), 1,5‐anthracene ( 2 ), 2,6‐anthracene ( 3 ), 1,8‐anthracene ( 4 )) obtained by molecular spectroscopic methods (IR, UV/Vis/near‐IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C?O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1 , except oxidized 1⁺ , the electronic absorption spectra of complexes 2⁺ , 3⁺ , and 4⁺ all display the characteristic near‐IR band envelopes that have been deconvoluted into three Gaussian sub‐bands. Two of the sub‐bands belong mainly to metal‐to‐ligand charge‐transfer (MLCT) transitions according to results from time‐dependent DFT calculations. EPR spectroscopy of chemically generated 1⁺ – 4⁺ proves largely ligand‐centered spin density, again in accordance with IR spectra and DFT calculations results.     

Using Ylide Functionalization to Stabilize Boron Cations

The metalated ylide YNa [Y=(Ph₃PCSO₂Tol)⁻] was employed as X,L‐donor ligand for the preparation of a series of boron cations. Treatment of the bis‐ylide functionalized borane Y₂BH with different trityl salts or B(C₆F₅)₃ for hydride abstraction readily results in the formation of the bis‐ylide functionalized boron cation [Y−B−Y]⁺ ( 2 ). The high donor capacity of the ylide ligands allowed the isolation of the cationic species and its characterization in solution as well as in solid state. DFT calculations demonstrate that the cation is efficiently stabilized through electrostatic effects as well as π‐donation from the ylide ligands, which results in its high stability. Despite the high stability of 2 [Y−B−Y]⁺ serves as viable source for the preparation of further borenium cations of type Y₂B⁺←LB by addition of Lewis bases such as amines and amides. Primary and secondary amines react to tris(amino)boranes via N−H activation across the B−C bond.     

IRPD spectroscopy and ensemble measurements: Effects of different data acquisition and analysis methods

Three different commonly used infrared photodissociation (IRPD) spectroscopy acquisition and analysis methods are described, and results from these methods are compared using the same dataset for an extensively hydrated metal cation, La³⁺(H₂O)₃₆. Using the first-order laser-induced photodissociation rate constant as an IRPD intensity has several advantages over photodissociation yield and depletion/appearance methods in that intensities can be more directly compared with calculated infrared absorption spectra, and the intensities can be readily corrected for changes in laser power or irradiation times used for optimum data acquisition at each frequency. Extending IRPD spectroscopy to large clusters can be complicated when blackbody infrared radiative dissociation competes strongly with laser-induced photodissociation. A new method to obtain IRPD spectra of single precursor ions or ensembles of precursor ions that is nearly equivalent to the photodissociation rate constant method for single precursor ions is demonstrated. The ensemble IRPD spectra represent the “average” structure of clusters of a given size range, and this method has the advantage that spectra with improved signal-to-noise ratios can be obtained with no increase in data acquisition time. Results using this new method for a precursor ensemble consisting of La³⁺(H₂O)_35–37 are compared with results for La³⁺(H₂O)₃₆.     

Synthesis,Crystal Structure,Vibrational Spectroscopy and Thermal Behavior of the First Alkali Metal Hydrated Hexaborate： K2[B6O9（OH）2]

New hydrated potassium hexaborate K2[B6O9（OH）2] has been synthesized under mild solvothermal conditions. The structure was determined by single-crystal X-ray diffraction and further characterized by FT-IR, Rarnan spectra and DTA-TG. It crystallizes in the monoclinic system with space group P21/n, a=0.9036（2） nm, b=0.66052（18） nm, c=1.5997（4） nm, β=91.862（4）°, V=0.9543（4） nm^3 and Z=4. Its crystal structure consists of K-O polyhedra and 1-D stepped polyborate chains constructed by new [B6O9（OH）2]2- fundamental building blocks. 1-D polyborate chains contain 3,8-membered boron rings. Adjacent chains are further linked via H-bonding interactions into 2-D layers. The K^＋ cations reside not only between the layers but also in the 8-membered boron rings of the chains, compensating the negative charges of the borate chains and holding the layers together into the 3-D structure through bonding with oxygen atoms of the chains.     

[Fc2B2(Br)(μ‐NPEt3)2]+Br– – ein Ferrocenyl‐substituierter Phosphaniminato‐Komplex des Bors

[Fc₂B₂(Br)(μ‐NPEt₃)₂]⁺Br^– – a Ferrocenyl‐substituted Phosphoraneiminato Complex of Boron [Fc₂B₂(Br)(μ‐NPEt₃)₂]⁺Br^– has been prepared from ferrocenylboron dibromide, [Fe(η⁵‐C₅H₅)(η⁵‐C₅H₄BBr₂)], and the silylated phosphoraneimine Me₃SiNPEt₃ in dichloromethane solution to give orange‐red single crystals which were characterized by IR, NMR and ⁵⁷Fe Mössbauer spectra, as well as by a crystal structure determination. [Fc₂B₂(Br)(μ‐NPEt₃)₂]⁺Br^– · 3 CH₂Cl₂ ( 1 · 3 CH₂Cl₂): Space group P2₁/n, Z = 4, lattice dimensions at –50 °C: a = 1370.6(3), b = 2320.9(5), c = 1454.4(2), β = 95.38(1)°, R₁ = 0.061. In the cation of 1 the ferrocenyl‐substituted boron atoms are connected by the nitrogen atoms of the [NPEt₃]^– groups to form a planar B₂N₂ four‐membered ring. One of the boron atoms having planar, the other tetrahedral coordination.     

The Boron conundrum: the case of cationic clusters B n + with n?=?2–20

We investigate the molecular and electronic structure and thermochemical properties of the cationic boron clusters B _n ⁺ with n?=?2–20, using both MO and DFT methods. Several functionals are used along with the MP2, G3, G3B3, G4, and CCSD(T)/CBS methods. The latter is the high accuracy reference. While the TPSS, TPSSh, PW91, PB86, and PBE functionals show results comparable to high-accuracy MO methods, both BLYP and B3LYP functionals are not accurate enough for three-dimensional (3D) structures. A negligible difference is observed between the B3LYP, MP2, and CCSD(T) geometries. A transition between 2D and 3D structures occurs for this series at the B₁₆ ⁺–B₁₉ ⁺ sizes. While smaller clusters B _n ⁺ with n?≤?15 are planar or quasi-planar, a structural competition takes place in the intermediate sizes of B _16–19 ⁺ . The B₂₀ ⁺ cation has a 3D tubular shape. The standard heats of formation are determined and used to evaluate the cluster stability. The average binding energy tends to increase with increasing size toward a limit. All closed-shell species B _n ⁺ has an aromatic character, but an enhanced stability is found for B₅ ⁺ and B₁₃ ⁺ whose aromaticity and electron delocalization are analyzed using the LOL technique.     

Structure and stability of B+13 clusters

The structures and energies of B⁺₁₃, observed experimentally to be an unusually abundant species among cationic boron clusters, have been studied systematically with B3LYP/6–31G* density functional theory. The most thermodynamically stable B⁺₁₂ and B⁺₁₃ clusters are confirmed to have planar or quasiplanar rather than globular structures. However, the computed dissociation energies of the 3-dimensional B⁺₁₃ clusters are much closer to the experimental values than those of the planar or quasiplanar structures. Hence, planar and 3-dimensional B⁺₁₃ may both exist. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 203–214, 1998     

High‐Resolution Photoelectron Imaging of IrB3−: Observation of a π‐Aromatic B3+ Ring Coordinated to a Transition Metal

In a high‐resolution photoelectron imaging and theoretical study of the IrB₃^? cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B₃ ring coordinated with the Ir atom. The isomer with the higher EA consists of a B₃ ring with a bridge‐bonded Ir atom (C_s , ²A′), and the second isomer features a tetrahedral structure (C_3v , ²A₁). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutral C_3v isomer involves significant covalent Ir?B bonding and weak ionic bonding with charge transfer from B₃ to Ir, and can be viewed as an Ir–(η³‐B₃⁺) complex. This study provides the first example of a boron‐to‐metal charge‐transfer complex and evidence of a π‐aromatic B₃⁺ ring coordinated to a transition metal.