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Molecular rings of N carbon atoms (cyclo[N]carbons, or CN) are excellent benchmarking systems for testing quantum chemical theoretical methods and valuable precursors to other carbon-rich materials. Odd-N cyclocarbons, which have been elusive to date, are predicted to be even less stable than even-N cyclocarbons. We report the on-surface synthesis of cyclo[13]carbon, C13, by manipulation of decachlorofluorene with a scanning probemicroscope tip. We elucidated the properties of C13 by experiment and theoretical modeling. C13 adopts an open-shell configuration with a triplet ground state and a kinked geometry, which shows different extents of distortion and carbene localization depending on themolecular environment. Moreover, we prepared and characterized the C13 dimer, cyclo[26]carbon, demonstrating the potential of cyclocarbons and their precursors as building blocks for carbon allotropes. [ABSTRACT FROM AUTHOR]

Solution-state nitroso monomer-azodioxide equilibria and conformational freedom of several aromatic dinitroso derivatives, differing in the spacer group between the aromatic rings, were studied by one- and two-dimensional variable temperature 1H NMR spectroscopy and by quantum chemical calculations. The proton signals of nitroso monomer-azodioxide mixtures revealed by low-temperature NMR were assigned and validated using B3LYP-D3/6-311+G(2d,p)/SMD level of theory. In almost all cases, a preference towards the formation of only one azodioxy isomer of aromatic dinitroso compounds was found, which was assigned to Z-dimer according to computational data. Nevertheless, the computed small energy difference between the Z- and E-isomer could not account for the extreme preference for Z-dimer formation, indicating an influence of entropic or solvent effects. The formation of shorter oligomers in solution was excluded based on integrated 1H NMR signal intensities. The experimental results indicated an average dimerization Gibbs energy of about − 5 kJ/mol at 223 K and were found to be in very good correlation with dimerization energies obtained by solution-phase optimization. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy has been used to determine the barriers of rotation of surface-mounted fullerenes (2.3 ± 0.1 and 4.3 ± 0.1 kcal mol−1). In order to achieve this, a C60 derivative equipped with an anchoring group designed to form a surface inclusion with the hexagonal form of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) has been synthesized. Solid-state NMR analysis revealed that approximately 50% of the surface-mounted molecules have a chemical environment different from the others suggesting two distinct insertion modes. These observations correlate with results of DFT calculations. [ABSTRACT FROM AUTHOR]

We assembled photoresponsive mono‐ and bilayer systems with well‐defined properties from rod‐shaped molecules equipped with different photoswitches. Using properly chosen chromophores (diarylethene‐based switch and unidirectional light‐driven molecular motor), we then selectively targeted layers made of the same types of photoswitches using appropriate monochromatic light. UV‐vis analysis confirmed smooth and unrestricted photoisomerization. To achieve this, we synthesized a new class of triptycene‐based molecular pedestals adept at forming sturdy Langmuir‐Blodgett films on a water‐air interface. The films were smoothly transferred to gold and quartz surfaces. Repeated deposition afforded bilayer systems: one layer containing diarylethene‐based photoswitches and the other a unidirectional light‐driven molecular motor. Structural analysis of both mono‐ and bilayer systems revealed the molecules to be tilted with carboxylic functions pointing to the surface. At least two different polymorphs differing in monolayer thickness and tilt angle (~40° and ~60°) were identified on the gold surface. [ABSTRACT FROM AUTHOR]

In this study, the structure of the polycrystalline poly(l,4-phenyleneazine N,N-dioxide) was investigated by Scanning Electron Microscopy and related with the previously calculated molecular structure. Kinetics of polymerization of 1,4-dinitrosobenzene, prepared by both cryogenic UV photolysis and in vacuo deposition were measured by time-resolved FT-IR spectroscopy. Acquired data was analyzed by curve fitting with the standard Avrami-Erofeev and two-step consecutive reactions models. Activation parameters were calculated from Arrhenius and Eyring-Polanyi equations, for both models. The results obtained by using the two models, along with the goodness-of-fit parameters, were compared. It was shown that both bulk-based and reaction-based models can be used to adequately describe solid-state chemical reaction kinetics. Furthermore, a two-step consecutive reactions model is a suitable alternative to the most commonly used Avrami- Erofeev model. [ABSTRACT FROM AUTHOR]

π‐Conjugated nanoribbons attract interest because of their unusual electronic structures and charge‐transport behavior. Here, we report the synthesis of a series of fully edge‐fused porphyrin‐anthracene oligomeric ribbons (dimer and trimer), together with a computational study of the corresponding infinite polymer. The porphyrin dimer and trimer were synthesized in high yield, via oxidative cyclodehydrogenation of singly linked precursors, using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). The crystal structure of the dimer shows that the central π‐system is flat, with a slight S‐shaped wave distortion at each porphyrin terminal. The extended π‐conjugation causes a dramatic red‐shift in the absorption spectra: the absorption maxima of the fused dimer and trimer appear at 1188 nm and 1642 nm, respectively (for the nickel complexes dissolved in toluene). The coordinated metal in the dimer was changed from Ni to Mg, using p‐tolylmagnesium bromide, providing access to free‐base and Zn complexes. These results open a versatile avenue to longer π‐conjugated nanoribbons with integrated metalloporphyrin units. [ABSTRACT FROM AUTHOR]

π‐Conjugated nanoribbons attract interest because of their unusual electronic structures and charge‐transport behavior. Here, we report the synthesis of a series of fully edge‐fused porphyrin‐anthracene oligomeric ribbons (dimer and trimer), together with a computational study of the corresponding infinite polymer. The porphyrin dimer and trimer were synthesized in high yield, via oxidative cyclodehydrogenation of singly linked precursors, using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). The crystal structure of the dimer shows that the central π‐system is flat, with a slight S‐shaped wave distortion at each porphyrin terminal. The extended π‐conjugation causes a dramatic red‐shift in the absorption spectra: the absorption maxima of the fused dimer and trimer appear at 1188 nm and 1642 nm, respectively (for the nickel complexes dissolved in toluene). The coordinated metal in the dimer was changed from Ni to Mg, using p‐tolylmagnesium bromide, providing access to free‐base and Zn complexes. These results open a versatile avenue to longer π‐conjugated nanoribbons with integrated metalloporphyrin units. [ABSTRACT FROM AUTHOR]

The reactions of N-benzyliminodiacetic acid (BnidaH2) and its para-substituted derivatives, namely N-(p-chlorobenzyl) iminodiacetic acid (p-ClBnidaH2), N-(p-nitrobenzyl)iminodiacetic acid (p-NO2BnidaH2), and N-(p-methoxybenzyl) iminodiacetic acid (p-MeOBnidaH2) with sodium tetrachloropalladate(II) were performed in aqueous solutions. Three new complexes [Pd(p-ClBnidaH)2]·2H2O (2), [Pd(p-NO2BnidaH)2]·2H2O (3), and [Pd(p-MeOBnidaH)2] (4) were prepared and characterized by infrared spectroscopy and thermogravimetric and differential thermal analyses. The molecular geometry and infrared spectra of these three complexes, together with the previously synthesized [Pd(BnidaH)2]·2H2O (1a) and [Pd(BnidaH)2] (1b) were also modelled using density functional theory calculations at the BP86/6-311+G(d,p) level of theory with SDD pseudopotentials. [ABSTRACT FROM AUTHOR]

The structure of oligomers constructed from 1,4-dinitrosobenzene was studied computationally by DFT methods for shorter oligomers, and by the FMO approach for longer ones. It was demonstrated that the oligomers have helical structure. Formation of 1,4-dinitrosobenzene azodioxides from the corresponding nitroso monomers in solid state was examined by studying the kinetics of their oligomerization under cryogenic conditions. Dissociation of azodioxide bonds to nitroso groups was induced either by UV irradiation at cryogenic temperatures or by sublimation followed by cryogenic deposition. While warming the monomers prepared by UV photodissociation to 150 K gave E- polymers, oligomerization or polymerization of monomers prepared by cryogenic vapor deposition was less pronounced, giving Z- forms. Above 150 K, Z- dimers or short oligomers isomerized, probably by the dissociation-dimerization mechanism, to more stable E- forms. Fast formation of azodioxide bonds and the high stability of corresponding polymers can be ascribed to the strong topochemical effect in the solid state. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to find an adequate level of theory for the computational investigation of the reduction mechanisms of aromatic nitro- and nitroso compounds. To this end, five standard reduction potentials of nitro- and nitrosobenzene in three different solvents and four pKa values of species involved in the mechanism were compared with the values calculated at different DFT and CBS-X levels of theory. Out of fourteen tested functionals, five showed good linear correlation between calculated and experimental ΔrG° values. However, at all explored levels of theory, the calculated ΔrG° values systematically deviate from the experimental ones, indicating the necessity of better description of solvation effects for charged species, possibly via a cluster-continuum approach. [ABSTRACT FROM AUTHOR]

We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2− dianion to form the [closo-1-CB11H12]− anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70–90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]− to [closo-1-CB11H12]−, and CCl2 and CBr2, which require more. [ABSTRACT FROM AUTHOR]

The reactions of N-alkyliminodiacetamide derivatives, namely N-ethyliminodiacetamide (CHCHN(CHCONH); Etimda) and N-isopropyliminodiacetamide (CH)CHN(CHCONH); i-Primda), with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Three new palladium(II) complexes, [Pd(Etimda)]∙2HO ( 1), [Pd( i-Primda)]∙2HO ( 2) and [PdCl( i-Primda)] ( 3), were obtained and characterized by X-ray structural analysis, infrared spectroscopy and thermal analysis (TGA). The square planar coordination environments around the palladium(II) ions in complexes 1 and 2 consist of two N,N′-bidentate N-alkyliminodiacetamidato ligands, with imino N atoms in trans-position. The complex 3 also exhibits a square planar coordination environment around Pd(II), but with two chloride ions and one neutral N-isopropyliminodiacetamide ligand bound in an N,O′-bidentate coordination mode. The described coordination modes, as well as the presence of deprotonated amide groups in ligands in 1 and 2, are found for the first time in palladium(II) complexes with iminodiacetamide type ligands. The molecular geometries and infrared spectra of these three complexes were also modelled using DFT calculations, at the BP86-D3/def2-TZVPP/PCM level of theory. The RMSD values suggest a good agreement of the calculated and experimental geometries. A QTAIM analysis suggests a qualitative correlation between bond lengths and energy densities, also supported by an NBO analysis. The dimer interaction energy between complex units was estimated at about −15 kcal/mol for all complexes. [ABSTRACT FROM AUTHOR]

Crystal and molecular structure of poly(1,4-phenyleneazine- N , N -dioxide) (PDNB, 1), obtained from polymerization of 1,4-dinitrosobenzene, is investigated by X-ray powder diffraction (XRPD) and DFT calculations. Starting with the determined crystal structure, we have calculated the electronic structure of the polymer, which reveals that 1 is potentially a wide-bandgap (WBG) semiconductor with a band gap of 2.3 eV. Its calculated electronic spectrum with the absorbance at 400 nm is in good agreement with the experimental data. A highly organized crystal structure with linear chains of polymer indicates possible anisotropic electronic properties that could be useful in molecular photoelectronics (e.g OLEDs). Photolysis of 1 at cryogenic temperatures yields dinitrosobenzene monomers, which re-polymerize at higher temperatures. After this reversible photo-thermal cycle, the starting polymorph of 1 is recovered. Thermal analysis (TG/DSC/DTA) and in situ XRPD measurements show the high thermal stability of 1 until around 150 °C. Image 1 • The crystal structure is determined via X-ray powder diffraction. • The ON-OFF polymerization mechanism is studied at low temperature. • Reversible polymerization always gives the same polymorphic form. • Calculation of electronic properties reveals wide-bandgap semiconductivity. • Thermal analyses and in situ studies show stability up to circa 150 °C. [ABSTRACT FROM AUTHOR]

A family of seven symmetrical molecular rods, which are sharing 4-ethynylpyridyl terminal groups and differ in the structure of the linker have been investigated. Although structurally related they show unique electrochemical behavior, which clearly correlates with their conformational flexibility. Two flexible compounds are reduced by two electrons. Their reduction yields intensive charge transfer UV-vis absorption bands and is accompanied by characteristic EPR spectra. In contrast, all conformationally rigid structures are reduced by four electrons and do not yield neither charge transfer bands nor distinct EPR signals. Simple irreversible voltammetry of all derivatives is similar to the reduction of 4-ethynylpyridine at -2.1 V. The experimental observations were supported by the extensive DFT calculations. Electrochemical techniques proved to be valuable in distinction between molecular rigidity and flexibility. [Display omitted] [ABSTRACT FROM AUTHOR]