Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1−5)

The density functional theory (DFT) and the complete active space self‐consistent‐field (CASSCF) method have been used for full geometry optimization of carbon chains C_2nH⁺ (n = 1–5) in their ground states and selected excited states, respectively. Calculations show that C_2nH⁺ (n = 1–5) have stable linear structures with the ground state of X³Π for C₂H⁺ or X³Σ^? for other species. The excited‐state properties of C_2nH⁺ have been investigated by the multiconfigurational second‐order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low‐lying states in C_2nH⁺ (n = 1–5). Present results indicate that the predicted vertical excitation and emission energies of C_2nH⁺ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Interaction of the Benzenium Ion with Inert Ligands: IR Spectra of C6H7+?Ln Cluster Cations (L=Ar,N2, CH4, H2O)

IR photodissociation spectra of mass‐selected clusters composed of protonated benzene (C₆H₇⁺) and several ligands L are analyzed in the range of the C? H stretch fundamentals. The investigated systems include C₆H₇⁺? Ar, C₆H₇⁺? (N₂)_n (n=1–4), C₆H₇⁺? (CH₄)_n (n=1–4), and C₆H₇⁺? H₂O. The complexes are produced in a supersonic plasma expansion using chemical ionization. The IR spectra display absorptions near 2800 and 3100 cm^?1, which are attributed to the aliphatic and aromatic C? H stretch vibrations, respectively, of the benzenium ion, that is, the σ complex of C₆H₇⁺. The C₆H₇⁺? (CH₄)_n clusters show additional C? H stretch bands of the CH₄ ligands. Both the frequencies and the relative intensities of the C₆H₇⁺ absorptions are nearly independent of the choice and number of ligands, suggesting that the benzenium ion in the detected C₆H₇⁺? L_n clusters is only weakly perturbed by the microsolvation process. Analysis of photofragmentation branching ratios yield estimated ligand binding energies of the order of 800 and 950 cm^?1 (≈9.5 and 11.5 kJ mol^?1) for N₂ and CH₄, respectively. The interpretation of the experimental data is supported by ab initio calculations for C₆H₇⁺? Ar and C₆H₇⁺? N₂ at the MP 2/6‐311 G(2df,2pd) level. Both the calculations and the spectra are consistent with weak intermolecular π bonds of Ar and N₂ to the C₆H₇⁺ ring. The astrophysical implications of the deduced IR spectrum of C₆H₇⁺ are briefly discussed.     

Two‐component molecular crystals from N‐heteroaromatics and nitro­benzoic acids

Five two‐component molecular crystals, benzimidazolium 3‐nitro­benzoate, C₇H₇N₂⁺·C₇H₄NO₄^?, (I), benzimidazolium 4‐nitro­benzoate, C₇H₇N₂⁺·C₇H₄NO₄^?, (II), 1H‐benzotriazole–3‐nitro­benzoic acid (1/1), C₆H₅N₃·C₇H₅NO₄, (III), imidazol­ium 3‐nitro­benzoate, C₃H₅N₂⁺·C₇H₄NO₄^?, (IV), and imid­azolium 4‐nitro­benzoate, C₃H₅N₂⁺·C₇H₄NO₄^?, (V), were prepared with the aim of making chiral crystals. Only (I) crystallizes in a chiral space group. The mol­ecules of (I) and (II) are linked by hydrogen bonds to form 2₁ spiral chains. In (III), (IV) and (V), macrocyclic structures are formed from two acid and two base components, by an alternate arrangement of the acid and base moieties.     

Assignment on the X,A, B,C, and D states of the C6H5Br+ cation based on high‐level calculations

Geometries, frequencies, and energies of the 1²B₁, 1²A₂, 1²B₂, 2²B₁, 2²B₂, and 1²A₁, of the C₆H₅Br⁺ ion were calculated by using CASSCF and CASPT2 methods in conjunction with an ANO‐RCC basis. The CASPT2//CASSCF adiabatic excitation energies and CASPT2 relative energies for the six states are in good agreement with experiment. The X, A, B, C, and D electronic states of the C₆H₅Br⁺ ion were assigned to be X²B₁, A²A₂, B²B₂, C²B₁, and D²B₂ based on the CASSCF and CASPT2 calculations. The assignment on the D state of the C₆H₅Br⁺ ion is different from the previously published works. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Heat of formation for the SH radical by photoionization mass spectrometry

Photoionization mass spectrometry has been used to measure the appearance energies for [C₂H₅]⁺ from ethanethiol, [C₃H₇]⁺ from 2-propanethiol and [C₃H₅]⁺ from 2-methylthiirane. From the known thermochemistry of these cations and their precursor molecules, a 298 K heat of formation of 138.6±0.4 kJ mol^?1 for the SH radical has been derived.     

Cationic Closo Carboranes—Promising Weakly Coordinating Ions

The unexplored carbon rich cationic closo carboranes, C₃B_n?3H_n⁺¹ (n=5, 6, 7, 10, 12) are investigated theoretically. The position isomers were calculated at the B3LYP/6‐31G* level, and the charge distribution in the cluster is estimated by NBO analysis. The criterion of ring‐cap orbital overlap compatibility along with the number of B? C, C? C, and B? B bonds help in explaining the stability order in each category. The most stable isomer is the one with maximum ring‐cap orbital overlap and largest number of B? C bonds. The order of relative stability among the trigonal bipyramid is 1c > 1b > 1a ′, where the stability is proportional to the number of CH caps over the small three‐membered ring. The C₃B₃H₆⁺ isomer with the one allyl C3 group ( 2b ) is more favorable than the one with a cyclopropenyl group ( 2a ). Among the C₃B₄H₇⁺ isomers the stability order is 3e > 3d > 3c > 3b > 3a , which mostly depends on the ring‐cap orbital overlap. In the bicapped square antiprism (4) where there is large number of isomers, the order follows the rule of ring cap compatibility and the number of B? C bonds. The order of 5e > 5d > 5c > 5b > 5a obtained from the calculations is in perfect agreement with the above sited rules. Equations (1) – (5) devised for estimating the stability of isomers of C₃B_n?3H_n⁺ indicate an increase in stability with cage size. The mono‐positive charge of the isomers is distributed throughout the cage, making them suitable candidates as weakly electrophillic cations. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1542–1551, 2001     

Gas‐Phase Synthesis of the Benzyl Radical (C6H5CH2)

Dicarbon (C₂), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas‐phase synthesis is presented of the benzyl radical (C₆H₅CH₂) by the crossed molecular beam reaction of dicarbon, C₂(X¹Σ_g⁺, a³Π_u), with 2‐methyl‐1,3‐butadiene (isoprene; C₅H₈; X¹A′) accessing the triplet and singlet C₇H₈ potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon–carbon double bond of the 2‐methyl‐1,3‐butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C₇H₇ radical species through atomic hydrogen elimination. The benzyl radical (C₆H₅CH₂), the thermodynamically most stable C₇H₇ isomer, is determined as the major product.     

Mass spectrometric evidence for collisionally induced removal of H2 from monoanions of 10B nido‐carborane derivatives investigated by electrospray ionization quadrupole linear ion trap and Fourier transform ion cyclotron resonance mass spectrometry

Some newly synthesized ¹⁰B nido‐carborane derivatives, i.e., 7,8‐dicarba‐nido‐undecaborane monoanions ([7‐Me‐8‐R‐C₂B₉H₁₀]^‐K⁺, R = H, butyl, hexyl, octyl and decyl), have been fully characterised and examined by electrospray ionization and Fourier transform ion cyclotron resonance mass spectrometry with liquid chromatographic separation (LC/ESI‐FTICR‐MS). These boron‐containing compounds exhibit abundant molecular ions ([M]^?) at m/z 140.22631 [CB₉H₁₄]^?, m/z 196.28883 [CB₉H₂₂]^?, m/z 224.32032 [CB₉H₂₆]^?, m/z 252.35133 [CB₉H₃₀]^? and m/z 280.38354 [CB₉H₃₄]^? at the normal tube lens voltage setting of ?90 V, which was an instrumental parameter value selected in the tuning operation. Additional [M–nH₂]^? (n = 1?4) ions were observed in the mass spectra when higher tube lens voltages were applied, i.e., ?140 V. High‐resolution FTICR‐MS data revealed the accurate masses of fragment ions, bearing either an even or an odd number of electrons. Collision‐induced dissociation of the [M–nH₂]^? ions (n = 0–4) in the quadrupole linear ion trap (LTQ) analyzer confirmed the loss of hydrogen molecules from the molecular ions. It is suggested that the loss of H₂ molecules from the alkyl chain is a consequence of the stabilization effect of the nido‐carborane charged polyhedral skeleton. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal Dehydrogenation of Base‐Stabilized B2H5+ Complexes and Its Role in CH Borylation

Thermally induced dehydrogenation of the H‐bridged cation L₂B₂H₅⁺ (L=Lewis base) is proposed to be the key step in the intramolecular C? H borylation of tertiary amine boranes activated with catalytic amounts of strong “hydridophiles”. Loss of H₂ from L₂B₂H₅⁺ generates the highly reactive cation L₂B₂H₃⁺, which in its sp²‐sp³ diborane(4) form then undergoes either an intramolecular C? H insertion with B? B bond cleavage, or captures BH₃ to produce L₂B₃H₆⁺. The effect of the counterion stability on the outcome of the reaction is illustrated by formation of LBH₂C₆F₅ complexes through disproportionation of L₂B₂H₅⁺ HB(C₆F₅)₃^?.     

Luminescence in near-thermal charge exchange. III. CH(+) and CD(+) A → X emission from He+ C2H2 and He+ + C2D2

A pulsed ICR cell fitted with synchronous photon counting equipment is used to investigate the emission produced between 185 and 500 nm by near-thermal charge exchange between He⁺ and C₂H₂ (C₂D₂). The emission bands observed are A ²Δ → X²π and (weakly) B²Σ^? → X²π in CH(CD) and A ¹π → X¹Σ in CH⁺(CD⁺). Wavelength measurements on the bandheads of the (0,0) and (0,1) bands of CD⁺ A → X are used to evaluate vibrational constants of CH⁺(CD⁺) X¹Σ⁺. The results are (in cm^?1): ω_e = 2869 ± 27 (2106 ± 20); ω_eχ_e = 65 ± 13 (35 ± 7). These constants are used to calculate Morse-potential Franck—Condon factors and vibrational branching ratios for CH⁺ and CD⁺ A → X emission. The spectral distributions and the (relatively low) absolute emission rates produced by He⁺/C₂H₂(C₂D₂) charge exchange are briefly discussed in the light of presently available information on the charge transfer reaction and on the excited states of C₂H_2?⁺     

Solid‐Liquid Equilibria in the Quinary Na+, K+//Cl−, SO2−4, B4O2−7‐H2O System at 298 K

The solid‐liquid equilibria in the quinary system Na⁺, K⁺//Cl^?, SO^2?₄, B₄O^2?₇‐H₂O at 298 K had been studied experimentally using the method of isothermal solution saturation. Solubilities and densities of the solution of the quinary system were measured experimentally. Based on the experimental data, the dry‐salt phase diagram and water content diagram of the quinary system were constructed, respectively. In the equilibrium diagram of the quinary system Na⁺, K⁺//Cl^?, SO^2?₄, B₄O^2?₇‐H₂O at 298 K, there are five invariant points F1, F2, F3, F4 and F5; eleven univariant curves E1F1, E2F2, E3F3, E4F5, E5F2, E6F4, E7F5, F1F4, F2F4 F1F3 and F3F5, and seven fields of crystallization saturated with Na₂B₄O₇ corresponding to Na₂SO₄, Na₂SO₄·10H₂O, Na₂SO₄·3K₂SO₄ (Gla), K₂SO₄, K₂B₄O₇·4H₂O, NaCl and KCl. The experimental results show that Na₂SO₄·3K₂SO₄ (Gla), K₂SO₄ and K₂B₄O₇·4H₂O have bigger crystallization fields than other salts in the quinary system Na⁺, K⁺//Cl^?, SO^2?₄, B₄O^2?₇‐H₂O at 298 K.     

Differences and similarities among hypoxanthinium nitrate hydrate structures

Crystals of hypoxanthinium (6‐oxo‐1H,7H‐purin‐9‐ium) nitrate hydrates were investigated by means of X‐ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C₅H₅N₄O⁺·NO₃^?·H₂O, Hx1 ) were collected at 20, 105 and 285 K. The room‐temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C 46 , 340–342] and the low‐temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P2₁/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H₃O⁺·C₅H₅N₄O⁺·2NO₃^?·2H₂O, Hx2 ) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H₃O⁺·H₂O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C₅H₅N₄O⁺·NO₃^?·H₂O, and oxonium nitrate monohydrate, H₃O⁺(H₂O)·NO₃^?.     

Synthesis of a Neutral Mixed‐Valence Diferrocenyl Carborane for Molecular Quantum‐Dot Cellular Automata Applications

The preparation of 7‐Fc⁺‐8‐Fc‐7,8‐nido‐[C₂B₉H₁₀]^? (Fc⁺FcC₂B₉^?) demonstrates the successful incorporation of a carborane cage as an internal counteranion bridging between ferrocene and ferrocenium units. This neutral mixed‐valence Fe^II/Fe^III complex overcomes the proximal electronic bias imposed by external counterions, a practical limitation in the use of molecular switches. A combination of UV/Vis‐NIR spectroscopic and TD‐DFT computational studies indicate that electron transfer within Fc⁺FcC₂B₉^? is achieved through a bridge‐mediated mechanism. This electronic framework therefore provides the possibility of an all‐neutral null state, a key requirement for the implementation of quantum‐dot cellular automata (QCA) molecular computing. The adhesion, ordering, and characterization of Fc⁺FcC₂B₉^? on Au(111) has been observed by scanning tunneling microscopy.     

Dysprosiacarboranes as Organometallic Single‐Molecule Magnets

The dicarbollide ion, nido‐C₂B₉H₁₁^2? is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C₂B₉H₁₁)₂Ln(THF)₂][Na(THF)₅] (Ln=Dy, 1Dy ) and [(THF)₃(μ‐H)₃Li]₂[{η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}Dy{η²:η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}₂Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central Dy^III ion. The effective energy barrier (U_eff) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido‐C₂B₉H₁₁^2? and nido‐[o‐xylylene‐C₂B₉H₉]^2?, which show a U_eff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C₂B₉H₁₁)₂]^? is predicted to have comparable properties with the linear [Dy(Cp^Me3)₂]⁺ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high‐performance single‐molecule magnets.     

The Versatile Coordination Modes of Monophosphine‐o‐Carborane in the Formation of Iridium and Rhodium Complexes: Synthesis,Reactivity, and Characterization

Monophosphine‐o‐carborane has four competitive coordination modes when it coordinates to metal centers. To explore the structural transitions driven by these competitive coordination modes, a series of monophosphine‐o‐carborane Ir,Rh complexes were synthesized and characterized. [Cp*M(Cl)₂{1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁}] (M=Ir ( 1 a ), Rh ( 1 b ); Cp*=η⁵‐C₅Me₅), [Cp*Ir(H){7‐(PPh₂)‐7,8‐C₂B₉H₁₁}] ( 2 a ), and [1‐(PPh₂)‐3‐(η⁵‐Cp*)‐3,1,2‐MC₂B₉H₁₀] (M=Ir ( 3 a ), Rh ( 3 b )) can be all prepared directly by the reaction of 1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁ with dimeric complexes [(Cp*MCl₂)₂] (M=Ir, Rh) under different conditions. Compound 3 b was treated with AgOTf (OTf=CF₃SO₃^?) to afford the tetranuclear metallacarborane [Ag₂(thf)₂(OTf)₂{1‐(PPh₂)‐3‐(η⁵‐Cp*)‐3,1,2‐RhC₂B₉H₁₀}₂] ( 4 b ). The arylphosphine group in 3 a and 3 b was functionalized by elemental sulfur (1 equiv) in the presence of Et₃N to afford [1‐{(S)PPh₂}‐3‐(η⁵‐Cp*)‐3,1,2‐MC₂B₉H₁₀] (M=Ir ( 5 a ), Rh ( 5 b )). Additionally, the 1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁ ligand was functionalized by elemental sulfur (2 equiv) and then treated with [(Cp*IrCl₂)₂], thus resulting in two 16‐electron complexes [Cp*Ir(7‐{(S)PPh₂}‐8‐S‐7,8‐C₂B₉H₉)] ( 6 a ) and [Cp*Ir(7‐{(S)PPh₂}‐8‐S‐9‐OCH₃‐7,8‐C₂B₉H₉)] ( 7 a ). Compound 6 a further reacted with nBuPPh₂, thereby leading to 18‐electron complex [Cp*Ir(nBuPPh₂)(7‐{(S)PPh₂}‐8‐S‐7,8‐C₂B₉H₁₀)] ( 8 a ). The influences of other factors on structural transitions or the formation of targeted compounds, including reaction temperature and solvent, were also explored.     

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.     

Analysis of ToF‐SIMS spectra of poly(2‐vinylpyridine) and poly(4‐vinylpyridine) with density functional theory calculations

The time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) positive and negative ion spectra of poly(2‐vinylpyridine) (P2VP) and poly(4‐vinylpyridine) (P4VP) were analyzed using density functional theory calculations. Most of the ions from these structural isomers shared the same accurate mass, but had different relative abundance. This could be attributed to the fact that from a thermodynamics perspective, the disparity in the molecular structures can affect the ion stability if we assume that they shared the same mechanistic pathway of formation with similar reaction kinetics. The molecular structures of these ions were assigned, and their stability was evaluated based on calculations using the Kohn‐Sham density functional theory with Becke's 3‐parameter Lee‐Yang‐Parr exchange‐correlation functional and a correlation‐consistent, polarized, valence, double‐zeta basis set for cations and the same basis set with a triple‐zeta for anions. The computational results agreed with the experimental observations that the nitrogen‐containing cations such as C₅H₄N⁺ (m/z = 78), C₈H₇N^+· (m/z = 117), C₈H₈N⁺ (m/z = 118), C₉H₈N⁺ (m/z = 130), C₁₃H₁₁N₂⁺ (m/z = 195), C₁₄H₁₃N₂⁺ (m/z = 209), C₁₅H₁₅N₂⁺ (m/z = 223), and C₂₁H₂₂N₃⁺ (m/z = 316) ions were more favorably formed in P2VP than in P4VP due to higher ion stability because the calculated total energies of these cations were more negative when the nitrogen was situated at the ortho position. Nevertheless, our assumption was invalid in the formation of positive ions such as C₆H₇N⁺˙ (m/z = 93) and C₈H₁₀N⁺ (m/z = 120). Their formation did not necessarily depend on the ion stability. Instead, the transition state chemistry and the matrix effect both played a role. In the negative ion spectra, we found that nitrogen‐containing anions such as C₅H₄N^? (m/z = 78), C₆H₆N^? (m/z = 92), C₇H₆N^? (m/z = 104), C₈H₆N^? (m/z = 116), C₉H₁₀N^? (m/z = 132), C₁₃H₁₁N₂^? (m/z = 195), and C₁₄H₁₃N₂^? (m/z = 209) ions were more favorably formed in P4VP, which is in line with our computational results without exception. We speculate that whether anions would form from P2VP and P4VP is more dependent on the stability of the ions.     

Synthesis and Spectroscopic Properties of Phthalocyanine–[60]Fullerene Conjugates Connected Directly by Means of a Four‐Membered Ring

New covalently C₆₀‐conjugated phthalocyanine (Pc) analogues in which the Pc and C₆₀ components are connected by means of a four‐membered ring have been synthesized by taking advantage of a [2+2] cycloaddition reaction of C₆₀ with benzyne units generated from either a phthalocyanine derivative ( 8 ) or its precursor ( 1 ). The reaction of 1 with PhI(OAc)₂ and trifluoromethanesulfonic acid (TfOH) followed by the [2+2] cycloaddition of C₆₀ in the presence of tetra‐n‐butylammonium fluoride (TBAF) yielded the C₆₀‐substituted Pc precursor ( 3 ). Mixed condensation of 3 and 4,5‐dibutylsulfonylphthalonitrile ( 4 ) in a thermally promoted template reaction using a nickel salt successfully gave the Pc–C₆₀ conjugate ( 5 ). Results of mass spectrometry and ¹H and ¹³C NMR spectroscopy clearly indicate the formation of the anticipated Pc–C₆₀ conjugate. Direct coupling of C₆₀ with the Pc analogue that contained eight peripheral trimethylsilyl (TMS) groups ( 8 ) also proceeded successfully, such that mono and bis C₆₀‐adducts were detected by their mass, although the isolation of each derivative was difficult. The absorption and magnetic circular dichroism (MCD) spectra of 5 and the reference compound ( 7 ) differ from each other in the Q‐band region, thereby suggesting that the presence of the C₆₀ moiety affects the electronic structure of the conjugate. The reduction and oxidation potentials of 5 and 7 obtained by cyclic voltammetry are comparative, except for the C₆₀‐centered reduction couple at ?1.53 V versus Fc⁺/Fc in o‐dichlorobenzene (o‐DCB). A one‐electron reduction of 5 and 7 in tetrahydrofuran (THF) by using the sodium mirror technique results in the loss of band intensity in the Q‐band region, whereas the characteristic marker bands for Pc‐ring‐centered reduction appear at around 430, 600, and 900 nm for both compounds. The final spectral shapes of 5 and 7 upon the reduction resemble each other, thus indicating that no significant molecular orbital (MO) interactions between the C₆₀ and Pc units are present for the reduced species of 5 . In contrast, the oxidized species of 5 and 7 generated by the addition of NOBF₄ in CH₂Cl₂ show significantly different absorption spectra from each other. Whereas the broad bands at approximately 400–550 nm of 7 ⁺ are indicative of the cationic π‐radical species of metallo‐Pcs and can be assigned to a transition from a low‐lying MO to the half‐filled MO, no corresponding bands were observed for 5 ⁺. These spectral characteristics have been tentatively assigned to the delocalized occupied frontier MOs for 5 ⁺. The experimental results are broadly supported by DFT calculations.     

Intramolecular easily polarizable hydrogen bonds with anilides of 1-piperidine carboxylic acids

IR spectra are plotted from anilides of 1-piperidine carboxylic acids C₅H₁₀N(CH₂)_n CONHC₆H₄R in CHCl₃ and CDCl₃ solutions. In the cases of n = 1 and n = 4, weak intramolecular (NH?N) hydrogen bonds are formed. An asymmetrical energy surface occurs and the proton is present at the N of the anilide group. In the cases of n = 2 and n = 3, intramolecular proton transfer hydrogen bonds of the types N_BH?N_P ? ^?N_B?H⁺N_p are formed. In contrast to the intramolecular OH? N ? O^?1 ? H⁺N bonds with 1-piperidine carboxylic acids, these bonds to not cause IR continua but two bands: one in the region 3250–3190 and one in the region 2500–2450 cm^?1. The fact that, instead of IR continua, bands are observed is explained by the following: (1) these hydrogen bonds are relatively long; (2) they show only a narrow distribution of bond length; (3) the electrical fields at these bonds are small, since they are strongly screened.     

Jahn–Teller Effect in Circulenes: X‐ray Diffraction Study of Coronene and Corannulene Radical Anions

Single‐crystal X‐ray diffraction studies of two polyaromatic radical anions crystallized as sodium salts, namely [Na(DME)₃]⁺[C₂₀H₁₀^?] ( 1 ) and [Na(DME)₃]⁺[C₂₄H₁₂^?] ( 2 ) are reported. This allowed the first structural evaluation of Jahn–Teller (JT) effects for monoreduced circulenes and a comparison between bowl‐shaped corannulene and planar coronene. The C_s and D_2h symmetrical distortions are found to fit the experimental data for C₂₀H₁₀^.? and C₂₄H₁₂^.?, respectively. The continuous symmetry measure (CSM) analysis was carried out to provide a quantitative measure of the JT distortions in 1 and 2 . In addition, the X‐ray crystallographic results were fully supported by DFT calculations.