Generation and reactivity of the fragment ion [B12I8S(CN)]- in the gas phase and on surfaces.

Gaseous fragment ions generated in mass spectrometers may be employed as "building blocks" for the synthesis of novel molecules on surfaces using ion soft-landing. A fundamental understanding of the reactivity of the fragment ions is required to control bond formation of deposited fragments in surface layers. The fragment ion [B12X11]- (X = halogen) is formed by collision-induced dissociation (CID) from the precursor [B12X12]2- dianion. [B12X11]- is highly reactive and ion soft-landing experiments have shown that this ion binds to the alkyl chains of organic molecules on surfaces. In this work we investigate whether specific modifications of the precursor ion affect the chemical properties of the fragment ions to such an extent that attachment to functional groups of organic molecules on surfaces occurs and binding of alkyl chains is prevented. Therefore, a halogen substituent was replaced by a thiocyanate substituent. CID of the precursor [B12I11(SCN)]2- ion preferentially yields the fragment ion [B12I8S(CN)]-, which shows significantly altered reactivity compared to the fragment ions of [B12I12]2-. [B12I8S(CN)]- has a previously unknown structural element, wherein a sulfur atom bridges three boron atoms. Gas-phase reactions with different neutral reactants (cyclohexane, dimethyl sulfide, and dimethyl amine) accompanied by theoretical studies indicate that [B12I8S(CN)]- binds with higher selectivity to functional groups of organic molecules than fragment ions of [B12I12]2- (e.g., [B12I11]- and [B12I9]-). These findings were further confirmed by ion soft-landing experiments, which showed that [B12I8S(CN)]- ions attacked ester groups of adipates and phthalates, whereas [B12I11]- ions only bound to alkyl chains of the same reagents.

Control of Intermediates and Products by Combining Droplet Reactions and Ion Soft-Landing.

Despite being recognized primarily as an analytical technique, mass spectrometry also has a large potential as a synthetic tool, enabling access to advanced synthetic routes by reactions in charged microdroplets or ionic thin layers. Such reactions are special and proceed primarily at surfaces of droplets and thin layers. Partial solvation of the reactants is usually considered to play an important role for reducing the activation barrier, but many mechanistic details still need to be clarified. In our study, we showcase the synergy between two sequentially applied "preparative mass spectrometry" methods: initiating accelerated reactions within microdroplets during electrospray ionization to generate gaseous ionic intermediates in high abundance, which are subsequently mass-selected and soft-landed to react with a provided reagent on a substrate. This allows the generation of products at a nanomolar scale, amenable to further characterization. In this proof-of-concept study, the contrasting reaction pathways between intrinsically neutral and pre-charged reagents, respectively, both in microdroplets and in layers generated by ion soft-landing are investigated. This provides new insights into the role of partially solvated reagents at microdroplet surfaces for increased reaction rates. Additionally, further insights into reactions of ions of the same polarity under various conditions is obtained.

Binding Properties of Small Electrophilic Anions [B6 X5 ]- and [B10 X9 ]- (X=Cl, Br, I): Activation of Small Molecules Based on π-Backbonding.

Superelectrophilic anions constitute a special class of molecular anions that show strong binding of weak nucleophiles despite their negative charge. In this study, the binding characteristics of smaller gaseous electrophilic anions of the types [B6 X5 ]- and [B10 X9 ]- (with X=Cl, Br, I) were computationally and experimentally investigated and compared to those of the larger analogues [B12 X11 ]- . The positive charge of vacant boron increases from [B6 X5 ]- via [B10 X9 ]- to [B12 X11 ]- , as evidenced by increasing attachment enthalpies towards typical σ-donor molecules (noble gases, H2 O). However, this behavior is reversed for σ-donor-π-acceptor molecules. [B6 Cl5 ]- binds most strongly to N2 and CO, even more strongly than to H2 O. Energy decomposition analysis confirms that the orbital interaction is responsible for this opposite trend. The extended transition state natural orbitals for chemical valence method shows that the π-backdonation order is [B6 X5 ]- >[B10 X9 ]- >[B12 X11 ]- . This predicted order explains the experimentally observed red shifts of the CO and N2 stretching fundamentals compared to those of the unbound molecules, as measured by infrared photodissociation spectroscopy. The strongest red shift is observed for [B6 Cl5 N2 ]- : 222 cm-1 . Therefore, strong activation of unreactive σ-donor-π-acceptor molecules (commonly observed for cationic transition metal complexes) is achieved with metal-free molecular anions.

Direct functionalization of C-H bonds by electrophilic anions.

Alkanes and [B12X12]2- (X = Cl, Br) are both stable compounds which are difficult to functionalize. Here we demonstrate the formation of a boron-carbon bond between these substances in a two-step process. Fragmentation of [B12X12]2- in the gas phase generates highly reactive [B12X11]- ions which spontaneously react with alkanes. The reaction mechanism was investigated using tandem mass spectrometry and gas-phase vibrational spectroscopy combined with electronic structure calculations. [B12X11]- reacts by an electrophilic substitution of a proton in an alkane resulting in a B-C bond formation. The product is a dianionic [B12X11CnH2n+1]2- species, to which H+ is electrostatically bound. High-flux ion soft landing was performed to codeposit [B12X11]- and complex organic molecules (phthalates) in thin layers on surfaces. Molecular structure analysis of the product films revealed that C-H functionalization by [B12X11]- occurred in the presence of other more reactive functional groups. This observation demonstrates the utility of highly reactive fragment ions for selective bond formation processes and may pave the way for the use of gas-phase ion chemistry for the generation of complex molecular structures in the condensed phase.

Chemical Synthesis with Gaseous Molecular Ions: Harvesting [B12 Br11 N2 ]- from a Mass Spectrometer.

Mass spectrometry frequently reveals the existence of transient gas phase ions that have not been synthesized in solution or in bulk. These elusive ions are, therefore, often considered to be primarily of analytical value in fundamental gas phase studies. Here, we provide proof-of-concept that the products of ion-molecule reactions in mass spectrometers may be collected on surfaces to generate condensed matter and thus serve as building blocks to synthesize new compounds. The highly reactive fragment anion [B12 Br11 ]- was generated in a mass spectrometer and converted to [B12 Br11 N2 ]- in the presence of molecular nitrogen followed by its mass-selection and soft-landing on surfaces. The molecular structure of [B12 Br11 N2 ]- , which has not been synthetically obtained before, was confirmed by conventional methods of molecular analysis, including nuclear magnetic resonance and infrared spectroscopy. The [B12 Br11 N2 ]- ion is stable on surfaces and in solution at room temperature, but thermal annealing induces elimination of N2 and provides access to the highly reactive intermediate [B12 Br11 ]- in the condensed phase, which can be further used as a reagent, for example, for electrophilic aromatic substitutions. Thus, isolation of [B12 Br11 N2 ]- expands the repertoire of the available diazo ions that can be employed as versatile intermediates in various chemical transformations.

Binding of saturated and unsaturated C6-hydrocarbons to the electrophilic anion [B12Br11]-: a systematic mechanistic study.

The highly reactive gaseous ion [B12Br11]- is a metal-free closed-shell anion which spontaneously forms covalent bonds with hydrocarbon molecules, including alkanes. Herein, we systematically investigate the reaction mechanism for binding of [B12Br11]- to the five hexane isomers yielding [B12Br11(C6H14)]-, as well as to cyclohexane and several hexene isomers (yielding [B12Br11(C6H12)]-) using collision-induced dissociation (CID), infrared photodissociation spectroscopy (IRPD) and computational methods. CID of the different [B12Br11(C6H14)]- ions results in distinct fragmentation patterns dependent on the structure of the hexane isomer. The observed fragmentation reactions provide insights into the addition mechanism of [B12Br11]- to hexane. Based on the observed CID patterns, we identified that either B-C bond formation through heterolytic C-C or C-H bond cleavages or B-H bond formation through heterolytic C-H cleavage occur dependent on the structure of the hexane isomer. Meanwhile, we observe identical CID spectra of adducts originating from isomers of C6H12. Spectroscopic investigations of adducts of 1-hexene and cyclohexane indicate the same product structure with an open C6 chain. Computational investigations evidenced that low lying transition states are present, which enable a ring opening reaction of cyclohexane when binding to [B12Br11]-.

Rational design of an argon-binding superelectrophilic anion.

Chemically binding to argon (Ar) at room temperature has remained the privilege of the most reactive electrophiles, all of which are cationic (or even dicationic) in nature. Herein, we report a concept for the rational design of anionic superelectrophiles that are composed of a strong electrophilic center firmly embedded in a negatively charged framework of exceptional stability. To validate our concept, we synthesized the percyano-dodecoborate [B12(CN)12]2-, the electronically most stable dianion ever investigated experimentally. It serves as a precursor for the generation of the monoanion [B12(CN)11]-, which indeed spontaneously binds Ar at 298 K. Our mass spectrometric and spectroscopic studies are accompanied by high-level computational investigations including a bonding analysis of the exceptional B-Ar bond. The detection and characterization of this highly reactive, structurally stable anionic superelectrophile starts another chapter in the metal-free activation of particularly inert compounds and elements.

Relevance of π-Backbonding for the Reactivity of Electrophilic Anions [B12 X11 ]- (X=F, Cl, Br, I, CN).

Electrophilic anions of type [B12 X11 ]- posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B12 X11 ]- with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N2 as σ-donor-π-acceptors. Temperature-dependent formation of [B12 X11 NG]- indicates the enthalpy order (X=CN)>(X=Cl)≈(X=Br)>(X=I)≈(X=F) almost independent of the NG in good agreement with calculated trends. The observed order is explained by an interplay of the electron deficiency of the vacant boron site in [B12 X11 ]- and steric effects. The binding of CO and N2 to [B12 X11 ]- is significantly stronger. The B3LYP 0 K attachment enthapies follow the order (X=F)>(X=CN)>(X=Cl)>(X=Br)>(X=I), in contrast to the NG series. The bonding motifs of [B12 X11 CO]- and [B12 X11 N2 ]- were characterized using cryogenic ion trap vibrational spectroscopy by focusing on the CO and N2 stretching frequencies ν C O and ν N 2 , respectively. Observed shifts of ν C O and ν N 2 are explained by an interplay between electrostatic effects (blue shift), due to the positive partial charge, and by π-backdonation (red shift). Energy decomposition analysis and analysis of natural orbitals for chemical valence support all conclusions based on the experimental results. This establishes a rational understanding of [B12 X11 ]- reactivety dependent on the substituent X and provides first systematic data on π-backdonation from delocalized σ-electron systems of closo-borate anions.

Role of low-energy electrons in the solubility switch of Zn-based oxocluster photoresist for extreme ultraviolet lithography.

The electron-induced chemistry of a resist material for extreme ultraviolet lithography (EUVL) consisting of Zn oxoclusters with methacrylate (MA) and trifluoroacetate (TFA) ligands (Zn(MA)(TFA)) has been studied. Electron energies of 80 eV and 20 eV mimic the effect of photoelectrons released by the absorption of EUV photons and low-energy secondary electrons (LESEs) produced by those photoelectrons. The chemical conversion of the resist is studied by mass spectrometry to monitor the volatile species that desorb during electron irradiation, combined with reflection absorption infrared spectra (RAIRS) measured before and after irradiation. The observed reactions are closely related to those initiated upon EUV absorption. Also, the conversion of the Zn(MA)(TFA) resist layer that is required in EUVL is achieved by a similar energy input upon electron irradiation. The dominant component of the desorbing gas is CO2, but CO detection also suggests Zn oxide formation during electron irradiation. In contrast, species deriving from the ligand side chains predominantly remain within the resist layer. RAIRS gives direct evidence that, during electron irradiation, C[double bond, length as m-dash]C bonds of the MA ligands are more rapidly consumed than the carboxylate groups. This supports that chain reactions occur and contribute to the solubility switch in the resist in EUVL. Remarkably, 20 eV electrons still evolve roughly 50% of the amount of the gas that is observed at 80 eV for the same electron dose. The present results thus provide complementary and new insight to the EUV-induced chemistry in the Zn(MA)(TFA) resist and point towards the important contribution of low-energy electrons therein.

Gaseous cyclodextrin-closo-dodecaborate complexes χCD·B12X122- (χ = α, ß, and γ; X = F, Cl, Br, and I): electronic structures and intramolecular interactions.

A fundamental understanding of cyclodextrin-closo-dodecaborate inclusion complexes is of great interest in supramolecular chemistry. Herein, we report a systematic investigation on the electronic structures and intramolecular interactions of perhalogenated closo-dodecaborate dianions B12X122- (X = F, Cl, Br and I) binding to α-, ß-, and γ-cyclodextrins (CDs) in the gas phase using combined negative ion photoelectron spectroscopy (NIPES) and density functional theory (DFT) calculations. The vertical detachment energy (VDE) of each complex and electronic stabilization of each dianion due to the CD binding (ΔVDE, relative to the corresponding isolated B12X122-) are determined from the experiments along α-, ß- and γ-CD in the form of VDE (ΔVDE): 4.00 (2.10), 4.33 (2.43), and 4.30 (2.40) eV in X = F; 4.09 (1.14), 4.64 (1.69), and 4.69 (1.74) eV in X = Cl; 4.11 (0.91), 4.58 (1.38), and 4.70 (1.50) eV in X = Br; and 3.54 (0.74), 3.88 (1.08), and 4.05 (1.25) eV in X = I, respectively. All complexes have significantly higher VDEs than the corresponding isolated dodecaborate dianions with ΔVDE spanning from 0.74 eV at (α, I) to 2.43 eV at (ß, F), sensitive to both host CD size and guest substituent X. DFT-optimized complex structures indicate that all B12X122- prefer binding to the wide openings of CDs with the insertion depth and binding motif strongly dependent on the CD size and halogen X. Dodecaborate anions with heavy halogens, i.e., X = Cl, Br, and I, are found outside of α-CD, while B12F122- is completely wrapped by γ-CD. Partial embedment of B12X122- into CDs is observed for the other complexes via multipronged B-XH-O/C interlocking patterns. The simulated spectra based on the density of states agree well with those of the experiments and the calculated VDEs well reproduce the experimental trends. Molecular orbital analyses suggest that the spectral features at low binding energies originated from electrons detached from the dodecaborate dianion, while those at higher binding energies are derived from electron detachment from CDs. Energy decomposition analyses reveal that the electrostatic interaction plays a dominating role in contributing to the host-guest interactions for the X = F series partially due to the formation of a O/C-HX-B hydrogen bonding network, and the dispersion forces gradually become important with the increase of halogen size.

Anion-Anion Chemistry with Mass-Selected Molecular Fragments on Surfaces.

While reactions between ions and neutral molecules in the gas phase have been studied extensively, reactions between molecular ions of same polarity remain relatively unexplored. Herein we show that reactions between fragment ions generated in the gas phase and molecular ions of the same polarity are possible by soft-landing of both reagents on surfaces. The reactive [B12 I11 ]1- anion was deposited on a surface layer built up by landing the generally unreactive [B12 I12 ]2- . Ex-situ analysis of the generated material shows that [B24 I23 ]3- was formed. A computational study shows that the product is metastable in the gas phase, but a charge-balanced environment of a grounded surface may stabilize the triply charged product, as suggested by model calculations. This opens new opportunities for the generation of highly charged clusters using unconventional building blocks from the gas phase.

Properties of gaseous closo-[B6X6]2- dianions (X = Cl, Br, I).

Electronic structure, collision-induced dissociation (CID) and bond properties of closo-[B6X6]2- (X = Cl-I) are investigated in direct comparison with their closo-[B12X12]2- analogues. Photoelectron spectroscopy (PES) and theoretical investigations reveal that [B6X6]2- dianions are electronically significantly less stable than the corresponding [B12X12]2- species. Although [B6Cl6]2- is slightly electronically unstable, [B6Br6]2- and [B6I6]2- are intrinsically stable dianions. Consistent with the trend in the electron detachment energy, loss of an electron (e- loss) is observed in CID of [B6X6]2- (X = Cl, Br) but not for [B6I6]2-. Halogenide loss (X- loss) is common for [B6X6]2- (X = Br, I) and [B12X12]2- (X = Cl, Br, I). Meanwhile, X˙ loss is only observed for [B12X12]2- (X = Br, I) species. The calculated reaction enthalpies of the three competing dissociation pathways (e-, X- and X˙ loss) indicated a strong influence of kinetic factors on the observed fragmentation patterns. The repulsive Coulomb barrier (RCB) determines the transition state for the e- and X- losses. A significantly lower RCB for X- loss than for e- loss was found in both experimental and theoretical investigations and can be rationalized by the recently introduced concept of electrophilic anions. The positive reaction enthalpies for X- losses are significantly lower for [B6X6]2- than for [B12X12]2-, while enthalpies for X˙ losses are higher. These observations are consistent with a difference in bond character of the B-X bonds in [B6X6]2- and [B12X12]2-. A complementary bonding analysis using QTAIM, NPA and ELI-D based methods suggests that B-X bonds in [B12X12]2- have a stronger covalent character than in [B6X6]2-, in which X has a stronger halide character.

Experimental and Theoretical Studies of a Spirostannole and Formation of a Pentaorganostannate.

A new spirostannole, 1,1',3,3'-tetrakis(5-methylthiophen-2-yl)-4,4',5,5',6,6',7,7'-octahydro-2,2'-spirobi[benzo[c]stannole] (4), is synthesised and the molecular structure is compared with the optimised geometry from DFT calculations. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are twice degenerated and show a small HOMO-LUMO energy gap of 3.2 eV. In addition, cyclic voltammetry measurements are conducted and three redox processes are observed. Absorption and emission spectra show maxima at λabs,max 436 nm and λem,max 533 nm, respectively. Spirostannole 4 is a strongly absorbing material, but an extremely weak emitter in solution at 295.15 K. However, when the solution is cooled from 280 to 80 K, the emission becomes visible. The reaction of spirostannole 4 with methyllithium is monitored by NMR spectroscopy at 238.15 K. The 119Sn{1H} NMR signal shifts from -36.0 (4) to -211.0 ppm, which is indicative of the formation of the lithium pentaorganostannate 5. The complex is thermally instable at 295.15 K, but insights into the molecular structure and electronic behaviour are obtained by DFT and TD-DFT calculations.

Tuning the Optoelectronic Properties of Stannoles by the Judicious Choice of the Organic Substituents.

Stannoles are organometallic rings in which the heteroatom is involved in a form of conjugation that is called σ*-π* conjugation. Only very little is known about how the substituents on the Sn atom or substituents on the stannole ring determine the optoelectronic properties of these heterocycles. In this work, this question has been studied experimentally and theoretically. Calculations of optimized equilibrium geometries, energy gaps between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), and of the absorption spectra of a wide range of compounds were performed. The computational data showed that the substituents on the Sn atom influence the optoelectronic properties to a lower extent than the substituents in the 2 and 5 positions of the ring. These substituents in the 2 and 5 positions of the stannole ring can also have a strong influence on the overall planarity of the structure, in which mesomeric effects can play a substantial role only if the structure is planar. Thus, only structures with a planar backbone are of interest in the context of tuning the optoelectronic properties. These were selected for the experimental studies. On the basis of this information, a series of six novel stannoles was synthesized by the formation of a zirconium intermediate and subsequent transmetalation to obtain the tin compound. The calculated electronic HOMO-LUMO energy gaps varied between 2.94 and 2.68 eV. The measured absorption maxima were located between 415 and 448 nm compared to theoretically calculated values ranging from 447 nm (2.77 eV) to 482 nm (2.57 eV). In addition to these optical measurements, cyclic voltammetry data could be obtained, which show two reversible oxidation processes for three of the six stannoles. With this study, it could be demonstrated how the judicious choice of the substituents can lead to large and predictable bathochromic shifts in the absorption spectra.

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12 Cl11 ].

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B12 Cl11 ]- spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of "superelectrophilic" dications. [B12 Cl11 Ng]- adducts, with Ng binding energies of 80 to 100 kJ mol-1 , contain B-Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B12 Cl11 ]- anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B12 Cl11 CO]- and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B12 Cl11 ]- results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C6 H5 ]+ . This introduces the new chemical concept of "dipole-discriminating electrophilic anions."

Towards Improved Humidity Sensing Nanomaterials via Combined Electron and NH3 Treatment of Carbon-Rich FEBID Deposits.

Focused Electron Beam Induced Deposition (FEBID) is a unique tool to produce nanoscale materials. The resulting deposits can be used, for instance, as humidity or strain sensors. The humidity sensing concept relies on the fact that FEBID using organometallic precursors often yields deposits which consist of metal nanoparticles embedded in a carbonaceous matrix. The electrical conductivity of such materials is altered in the presence of polar molecules such as water. Herein, we provide evidence that the interaction with water can be enhanced by incorporating nitrogen in the deposit through post-deposition electron irradiation in presence of ammonia (NH3). This opens the perspective to improve and tune the properties of humidity sensors fabricated by FEBID. As a proof-of-concept experiment, we have prepared carbonaceous deposits by electron irradiation of adsorbed layers of three different precursors, namely, the aliphatic hydrocarbon n-pentane, a simple alkene (2-methyl-2-butene), and the potential Ru FEBID precursor bis(ethylcyclopentadienyl)ruthenium(II). In a subsequent processing step, we incorporated C-N bonds in the deposit by electron irradiation of adsorbed NH3. To test the resulting material with respect to its potential humidity sensing capabilities, we condensed sub-monolayer quantities of water (H2O) on the deposit and evaluated their thermal desorption behavior. The results confirm that the desorption temperature of H2O decisively depends on the degree of N incorporation into the carbonaceous residue which, in turn, depends on the chemical nature of the precursor used for deposition of the carbonaceous layer. We thus anticipate that the sensitivity of a FEBID-based humidity sensor can be tuned by a precisely timed post-deposition electron and NH3 processing step.

Electron-Induced Decomposition of Different Silver(I) Complexes: Implications for the Design of Precursors for Focused Electron Beam Induced Deposition.

Focused electron beam induced deposition (FEBID) is a versatile tool to produce nanostructures through electron-induced decomposition of metal-containing precursor molecules. However, the metal content of the resulting materials is often low. Using different Ag(I) complexes, this study shows that the precursor performance depends critically on the molecular structure. This includes Ag(I) 2,2-dimethylbutanoate, which yields high Ag contents in FEBID, as well as similar aliphatic Ag(I) carboxylates, aromatic Ag(I) benzoate, and the acetylide Ag(I) 3,3-dimethylbutynyl. The compounds were sublimated on inert surfaces and their electron-induced decomposition was monitored by electron-stimulated desorption (ESD) experiments in ultrahigh vacuum and by reflection-absorption infrared spectroscopy (RAIRS). The results reveal that Ag(I) carboxylates with aliphatic side chains are particularly favourable for FEBID. Following electron impact ionization, they fragment by loss of volatile CO2. The remaining alkyl radical converts to a stable and equally volatile alkene. The lower decomposition efficiency of Ag(I) benzoate and Ag(I) 3,3-dimethylbutynyl is explained by calculated average local ionization energies (ALIE) which reveal that ionization from the unsaturated carbon units competes with ionization from the coordinate bond to Ag. This can stabilise the ionized complex with respect to fragmentation. This insight provides guidance with respect to the design of novel FEBID precursors.

π-Conjugated stannole copolymers synthesised by a tin-selective Stille cross-coupling reaction.

The synthesis of four well-defined conjugated polymers TStTT1-4 containing unusual heterocycle units in the main chain, namely stannole units as building blocks, is reported. The stannole-thiophenyl copolymers were generated by tin-selective Stille coupling reactions in nearly quantitative yields of 94% to 98%. NMR data show that the tin atoms in the rings remain unaffected. Weight-average molecular weights (M w) were high (4900-10 900 Da and 9600-21 900 Da); and molecular weight distributions (M w/M n) were between 1.9 and 2.3. The new materials are strongly absorbing and appear blue-black to purple-black. All iodothiophenyl-stannole monomers St1-4 and the resulting bisthiophenyl-stannole copolymers TStTT1-4 were investigated with respect to their optoelectronic properties. The absorption maxima of the polymers are strongly bathochromically shifted compared to their monomers by about 76 nm to 126 nm in chloroform. Density functional theory calculations support our experimental results of the single stannoles St1-4 showing small HOMO-LUMO energy gaps of 3.17-3.24 eV. The optical band gaps of the polymers are much more decreased and were determined to be only 1.61-1.79 eV. Furthermore, both the molecular structures of stannoles St2 and St3 from single crystal X-ray analyses and the results of the geometry optimisation by DFT confirm the high planarity of the molecules backbone leading to efficient conjugation within the molecule.

Isolated [B2(CN)6]2-: Small Yet Exceptionally Stable Nonmetal Dianion.

We report the observation of a small, yet remarkably stable, metal-free hexacyanodiborate dianion [B2(CN)6]2- in the gas phase. Negative ion photoelectron spectroscopy (NIPES) was employed to measure its spectra at multiple laser wavelengths, yielding a 1.9 eV electron binding energy (EBE) ─a remarkably high value of electronic stability and a ∼2.60 eV repulsive Coulomb barrier (RCB) for electron detachment. This rationalizes the observation of this dianion, although homolytic charge-separation dissociation into two [B(CN)3]•- is energetically favorable. Quantum chemical calculations demonstrate a D3d staggered conformation for both the dianion and radical monoanion, and the calculated EBE and RCB match the experimental values well. The simulated density of states spectrum reproduces all measured electronic transitions, while the simulated vibrational progressions for the ground state transition cover a much narrower EBE range compared to the experimental band, indicating appreciable auto-photodetachment via electronically excited dianion resonances.

New Perspectives in the Noble Gas Chemistry Opened by Electrophilic Anions.

Binding of noble gases (NGs) is commonly considered to be the realm of highly reactive electophiles with cationic or at least non-charged character. Herein, we summarize our latest results evidencing that the incorporation of a strongly electrophilic site within a rigid cage-like anionic structure offers several advantages that facilitate the binding of noble gases and stabilize the formed NG adducts. The anionic superelectrophiles investigated by us are based on the closo-dodecaborate dianion scaffold. The record holder [B12(CN)11]- binds spontaneously almost all members of the NG family, including the very inert argon at room temperature and neon at 50 K in the gas phase of mass spectrometers. In this perspective, we summarize the argumentation for the advantages of anionic electrophiles in binding of noble gases and explain them in detail using several examples. Then we discuss the next steps necessary to obtain a comprehensive understanding of the binding properties of electrophilic anions with NGs. Finally, we discuss the perspective to prepare bulk ionic materials containing NG derivatives of the anionic superelectophiles. In particular, we explore the role of counterions using computational methods and discuss the methodology, which may be used for the actual preparation of such salts.