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The geometry of the neutral Au18 gold cluster was probed by a combination of quantum chemical calculations and far-infrared multiple photon dissociation (FIR-MPD) spectroscopy of a Kr messenger complex.

The Au17 gold cluster was experimentally produced in the gas phase and characterized by its vibrational spectrum recorded using far-IR multiple photon dissociation (FIR-MPD) of Au17Kr. DFT and coupled-cluster theory PNO-LCCSD(T)-F12 computations reveal that, at odds with most previous reports, Au17 prefers two star-like forms derived from a pentaprism added by two extra Au atoms on both top and bottom surfaces of the pentaprism, along with five other Au atoms each attached on a lateral face. A good agreement between calculated and FIR-MPD spectra indicates a predominant presence of these star-like isomers. Stabilization of a star form arises from strong orbital interactions of an Au12 core with a five-Au-atom string.

A convenient method to access the above perchlorates has been developed, based on the cyclocondensation of 3-aminofurazans with 1,3-diketones in the presence of HClO

Quantum chemical computations were used to reinvestigate the geometries, spectroscopic, and energetic properties of the gold clusters Au27q in three charge states (q = 1, 0, -1). Density functional theory (DFT) and the domain-based local pair natural orbital modification of the coupled-cluster theory DLPNO-CCSD(T) calculations revealed that, at variance with earlier reports in the literature, while the anion Au27- tends to exist in a tube-like form, both the lowest-energy Au27 and Au27+ isomers exhibit a pyramidal shape. However, several isomers were found to lie very close in energy, thus rendering a structural transition and their coexistence easy to occur. More specifically, the equilibrium geometry of the neutral Au27 is a core-shell pyramid-like structure with one gold atom located inside. We also identified a novel ground state for the anion Au27- and located for the first time the global minimum of the cation Au27+ . The vertical detachment energies of the neutral and anionic states were also computed and used to assign the available experimental photoelectron spectra. Although many Au27 isomers were predicted to be energetically quasi-degenerate, the corresponding distinctive vibrational signatures can be used as fingerprints for the identification of cluster geometrical features.

A reliable kinetic description of the thermal stability of energetic materials (EM) is very important for safety and storage-related problems. Among other pertinent issues, autocatalysis very often complicates the decomposition kinetics of EM. In the present study, the kinetics and decomposition mechanism of a promising energetic compound, 5-amino-3,4-dinitro-1

The standard state enthalpy of formation and the enthalpy of sublimation are essential thermochemical parameters determining the performance and application prospects of energetic materials (EM). Direct experimental measurements of these properties are complicated by low volatility and high heat release in bomb calorimetry experiments. As a result, the uncertainties in the reported enthalpies of formation for a number of even well-known CHNO-containing compounds might amount up to tens kJ mol-1, while for some novel high-nitrogen molecules they reach even hundreds of kJ mol-1. The present study reports a facile approach to determining the solid-state formation enthalpies comprised of complementary high-level quantum chemical calculations of the gas-phase thermochemistry and advanced thermal analysis techniques yielding sublimation enthalpies. The thermogravimetric procedure for the measurement of sublimation enthalpy was modified by using low external pressures (down to 0.2 Pa). This allows for observing sublimation/vaporization instead of thermal decomposition of the compounds studied. Extensive benchmarking on nonenergetic and energetic compounds reveals the average and maximal absolute errors of the sublimation enthalpies of 3.3 and 11.0 kJ mol-1, respectively. The comparison of the results with those obtained from the widely used Trouton-Williams empirical equation shows that the latter underestimates the sublimation enthalpy up to 140 kJ mol-1. Therefore, we performed a reparametrization of the latter equation with simple chemical descriptors that reduces the mean error down to 30 kJ mol-1. Highly accurate multi-level procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach were used to calculate theoretically the gas-phase formation enthalpies. In several cases, the DLPNO-CCSD(T) enthalpies of isodesmic reactions were also employed to obtain the gas-phase thermochemistry for medium-sized important EMs. Combining the obtained thermochemical properties, we determined the solid-state enthalpies of formation for nearly 60 species containing various important explosophoric groups, from common nitroaromatics, nitroethers, and nitramines to novel nitrogen-rich heterocyclic species (e.g., the derivatives of pyrazole, tetrazole, furoxan, etc.). The large-scale benchmarking against the available experimental solid-state enthalpies of formation yielded the maximal inaccuracy of the proposed method of 25 kJ mol-1.

A series of energetic nitrogen-rich salts comprised of a 5-(trinitromethyl)tetrazolate anion and high-nitrogen cations was synthesized by simple and efficient chemical routes from readily available commercial reagents. These energetic materials were fully characterized by IR and multinuclear NMR (1H, 13C, 14N) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Additionally, the structure of an energetic salt containing the 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazolium cation was confirmed by single-crystal X-ray diffraction. The synthesized compounds exhibit decent experimental densities (1.648–1.845 g cm−3) and positive enthalpies of formation (up to 725.5 kJ mol−1) and, as a result, superior detonation performance (detonation velocities 8.2–9.2 km s−1 and detonation pressures 28.5–37.8 GPa), which is comparable to or even exceeding those of commonly used booster explosive PETN. On the other hand, high mechanical sensitivity of several novel 5-(trinitromethyl)tetrazolate salts along with their high combined nitrogen-oxygen content (>81%) and excellent detonation performance render them environmentally friendly alternatives to lead-based primary explosives.

Cyanuric triazide reacts with several transition metal precursors, extruding one equivalent of N2 and reducing the putative diazidotriazeneylnitrene species by two electrons, which rearranges to N-(1′H-[1,5′-bitetrazol]-5-yl)methanediiminate (biTzI2−) dianionic ligand, which ligates the metal and dimerizes, and is isolated from pyridine as [M(biTzI)]2Py6 (M = Mn, Fe, Zn, Cu, Ni). Reagent scope, product analysis, and quantum chemical calculations were combined to elucidate the mechanism of formation as a two-electron reduction preceding ligand rearrangement., Cyanuric triazide reacts with transition metal precursors, extruding N2 and reducing the ligand by two electrons, which breaks an aromatic ring and rearranges to a bitetrazolylmethanediiminate (biTzI2−) ligand, forming two new aromatic rings.

In the present work, we studied in detail the thermochemistry, thermal stability, mechanical sensitivity, and detonation performance for 20 nitro-, cyano-, and methyl derivatives of 1,2,5-oxadiazole-2-oxide (furoxan), along with their bis-derivatives. For all species studied, we also determined the reliable values of the gas-phase formation enthalpies using highly accurate multilevel procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach and isodesmic reactions with the domain-based local pair natural orbital (DLPNO) modifications of the coupled-cluster techniques. Apart from this, we proposed reliable benchmark values of the formation enthalpies of furoxan and a number of its (azo)bis-derivatives. Additionally, we reported the previously unknown crystal structure of 3-cyano-4-nitrofuroxan. Among the monocyclic compounds, 3-nitro-4-cyclopropyl and dicyano derivatives of furoxan outperformed trinitrotoluene, a benchmark melt-cast explosive, exhibited decent thermal stability (decomposition temperature &gt, 200 &deg, C) and insensitivity to mechanical stimuli while having notable volatility and low melting points. In turn, 4,4&prime, azobis-dicarbamoyl furoxan is proposed as a substitute of pentaerythritol tetranitrate, a benchmark brisant high explosive. Finally, the application prospects of 3,3&prime, azobis-dinitro furoxan, one of the most powerful energetic materials synthesized up to date, are limited due to the tremendously high mechanical sensitivity of this compound. Overall, the investigated derivatives of furoxan comprise multipurpose green energetic materials, including primary, secondary, melt-cast, low-sensitive explosives, and an energetic liquid.

Highly accurate theoretical values of formation enthalpies and bond energies are crucial for reliable predictions of performance and detonation-related phenomena of energetic materials (EM). However, high-level ab initio calculations even for medium-sized important EMs still remain a demanding challenge. In the present work, we studied in detail the gas-phase thermochemistry of novel high-energy polynitro derivatives of 5/6/5 structural frameworks comprised of fused 1,2,3,4,-tetrazine and two 1,2,4-triazole or pyrazole rings. To this end, we proposed and benchmarked a "bottom-up" approach. First, highly accurate multilevel procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach were utilized for smaller species. In turn, for medium-sized species (up to 24 non-H atoms), these values were complemented with the enthalpies of isodesmic reactions calculated using the recently proposed domain-based local pair natural orbital (DLPNO) modifications of coupled cluster techniques. The benchmarks on a number of atomization energies and enthalpies of isodesmic reactions reveal that the DLPNO-CCSD(T)/aVQZ approach does not deteriorate the quality of the W1-F12 and W2-F12 procedures and exhibits overall accuracy close to "chemical" (∼1 kcal mol-1). We obtained a set of accurate and mutually consistent gas-phase formation enthalpies for 12 energetic heterocyclic species. Among them, the gas-phase formation enthalpy of 1,2,9,10-tetranitrodipyrazolo[1,5-d:5',1'-f][1,2,3,4]tetrazine, a novel promising EM, turned out to be ΔfHgas0 = 214.5 kcal mol-1, which is ∼12 kcal mol-1 higher than the best theoretical estimates available in the literature. The formation enthalpy of another novel EM, a fused tricyclic 1,2,3,4-tetrazine with two nitro-1,2,4-triazole moieties, was predicted to be ΔfHgas0 = 213.5 kcal mol-1, which is also ∼4 kcal mol-1 higher than the reported value. Apart from this, we considered the thermodynamics of radical reactions (viz., C-NO2 bond scission) and the thermochemistry of the corresponding radicals. The difference between DLPNO-CCSD(T)/aVQZ and CCSD(T)-F12/VTZ-F12 benchmark values did not exceed 1 kcal mol-1. In a more general sense, the use of DLPNO-CCSD(T) in conjunction with the bottom-up approach is promising for quantitative thermochemical calculations of energetic materials composed of species up to several dozens of CHNO atoms.

The UV-photodissociation at 266 nm of a widely used TiO2 precursor, titanium tetraisopropoxide (Ti(OiPr)4, TTIP), was studied under molecular-beam conditions. Using the MS-TOF technique, atomic titanium and titanium(II) oxide (TiO) were detected among the most abundant photofragments. Experimental results were rationalized with the aid of quantum chemical calculations (DLPNO–CCSD(T) and DFT). Contrary to the existing data in the literature, the new four-centered acetone-elimination reaction was found to be the primary decomposition process of TTIP. According to computational results, the effective activation barrier of this channel was ∼49 kcal/mol, which was ∼13 kcal/mol lower than that of the competing propylene elimination. The former process, followed by the dissociative loss of an H atom, was a dominating channel of TTIP unimolecular decay. The sequential loss of isopropoxy moieties via these two-step processes was supposed to produce the experimentally observed titanium atoms. In turn, the combinati...

Thermal decomposition and combustion of a series of novel promising nitro and amino substituted energetic pyrazolyltetrazoles were studied using a number of complementary experimental (thermogravimetry, differential scanning calorimetry, manometry, microthermocouple measurements in a combustion wave, and HPLC) and theoretical (quantum chemical calculations) techniques. According to the DSC and manometry data, the N-(pyrazolyl)tetrazoles turned out to be less thermally stable than the C-(pyrazolyl)tetrazole: the activation energies of their melt-phase decomposition are 117–127 and 140 kJ mol−1, respectively. The kinetics of decomposition in the solid phase is more complicated due to a strong influence of the effect of sub-melting and possible azido-tetrazole isomerization. The reliable CCSD(T)-F12 quantum chemical calculations provided mechanistic insight into the thermolysis of the compounds studied. All species decompose via the ring-opening reaction yielding a transient azide intermediate followed by the N2 elimination. The effective activation barriers of the latter reactions are in reasonable agreement with the melt-phase experiments for N-pyrazolyltetrazoles. On the basis of the HPLC detected products, we also outlined the reactions leading to the stable decomposition products observed. All compounds studied showed a self-sustained fast-burning character. Their typical burning rates are 70−80 mm s−1 at 10 MPa, which is as much as two times higher than the burning rate of a powerful explosive CL-20 under the same conditions. Using the pressure dependence of the surface temperature, we also determined the vapor pressures of (nitropyrazolyl)tetrazoles studied. The boiling points of the latter species are higher than the boiling point of hexogen. The melt-phase kinetic parameters also agree well with the condensed-phase-controlled burning rate model. The low activation energies of the leading combustion reactions are responsible for low pressure exponents of these compounds varying in the range of 0.5 – 0.75.

Highly accurate theoretical values of bond energies and activation barriers of primary decomposition reactions are crucial for reliable predictions of thermal decomposition and detonation-related phenomena of energetic materials (EM). However, due to the prohibitive computational cost, high-level ab initio calculations had been impractical for a large number of important EMs, including, e.g., hexanitrohexaazaisowurtzitane (CL-20). In the present work, we obtained accurate bond dissociation energies and the activation barriers for primary decomposition reactions for a series of novel promising caged polynitroamino and polynitro EMs, viz., CL-20, TEX, octanitrocubane (ONC), and hexanitro derivatives of adamantane, using the recently proposed domain-localized pair natural orbitals (DLPNO) modifications of coupled cluster techniques. DLPNO-CCSD(T) allows for routine quadruple-ζ basis set quality coupled cluster calculations for the species comprised of ∼30 non-H atoms. The benchmarks on a number of simpler congeners of CL-20 and ONC revealed that the DLPNO approach does not deteriorate the quality of the quadruple-ζ coupled cluster procedure. With the aid of this technique, the full set of gas-phase primary decomposition reactions for all 9 conformers of CL-20 was considered. For all species studied, C-NO

The thermal stability of energetic materials, being of the utmost importance for safety issues, is often considered in terms of kinetics, e.g., the Arrhenius parameters of the decomposition rate constant. The latter, in turn, are commonly determined using conventional thermoanalytical procedures with the use of simple Kissinger or Ozawa methods for kinetic data processing. However, thermal decomposition of energetic materials typically occurs via numerous exo- and endothermal processes including fast parallel reactions, phase transitions, autocatalysis, etc. This leads to numerous drawbacks of simple approaches. In this paper, we proposed a new methodology for characterization of the thermochemistry and thermal stability of melt-cast energetic materials, which is comprised of a complementary set of experimental and theoretical techniques in conjunction with a suitable kinetic model. With the aid of the proposed methodology, we studied in detail a novel green oxidizer, tetranitroacetimidic acid (TNAA). The experimental mass loss kinetics in the melt was perfectly fitted with a model comprised of zero-order reaction (sublimation or evaporation) and first-order thermal decomposition of TNAA with the effective Arrhenius parameters Ea = 41.0 ± 0.2 kcal mol-1 and log(A/s-1) = 20.2 ± 0.1. We rationalized the experimental findings on the basis of highly accurate CCSD(T)-F12 quantum chemical calculations. Computations predict that thermolysis of TNAA involves an intricate interplay of multiple decomposition channels of the three tautomers, which are equilibrated via either monomolecular reactions or concerted double hydrogen atom transfer in the H-bonded dimers; the calculated Arrhenius parameters of the effective rate constant coincide well with experiment. Most importantly, calculations provide detailed mechanistic evidence missing in the thermoanalytical experiment and explain formation of the experimentally observed primary products N2O and NO2. Along with the kinetics and mechanism of decomposition, the proposed approach yields accurate thermochemistry and phase change data of TNAA.

Differential scanning calorimetry at an elevated external pressure (Pressure DSC) allows for shifting the vaporization of a sample to higher temperatures, thus often facilitating the direct observation of its thermal decomposition. In the present work, the thermolysis of a promising energetic material 3,5-dinitropyrazole was studied under pressures up to 10 MPa. The thermokinetic analysis of the datasets acquired at 2 and 5 MPa exhibited a pronounced kinetic compensation, thus allowing to build the joint formal kinetic model. The final kinetic scheme is comprised of the two parallel reactions, viz., the first-order process (Ea = 198 kJ mol-1) along with a first-order autocatalysis (Ea = 127 kJ mol-1). The experiment was complemented with the highly accurate CCSD(T)-F12 quantum chemical calculations. Theory revealed an unusual primary decomposition channel, viz., a sigmatropic [ 1 , 5 ]H-shift followed by the pyrazole ring opening yielding a molecular nitrogen and a nitro radical as simple primary products. Apart from this, the comparative thermogravimetry at a normal pressure yielded the vapor pressure of 3,5-dinitropyrazole along with the internally consistent set of phase change enthalpies. In general, the pressure DSC is a facile technique to study the true decomposition kinetics of the compounds that vaporize/sublime in conventional DSC experiments.

Thermochemistry, kinetics, and mechanism of thermal decomposition of 1,5-diaminotetrazole (DAT), a widely used "building block" of nitrogen-rich energetic compounds, were studied theoretically at a high and reliable level of theory (viz., using the explicitly correlated CCSD(T)-F12/aug-cc-pVTZ procedure). Quantum chemical calculations provided detailed insight into the thermolysis mechanism of DAT missing in the existing literature. Moreover, several contradictory assumptions on the mechanism and key intermediates of thermolysis were resolved. The unimolecular primary decomposition reactions of the seven isomers of DAT were studied in the gas phase and in the melt using a simplified model of the latter. The two-step reaction of N2 elimination from the diamino tautomer was found to be the primary decomposition process of DAT in the gas phase and melt. The effective Arrhenius parameters of this process were calculated to be E a = 43.4 kcal mol-1 and log( A/s-1) = 15.2 in a good agreement with the experimental values. Contrary to the existing literature data, all other decomposition channels of DAT isomers turned out to be kinetically unimportant. Apart from this, a new primary decomposition channel yielding N2, cyanamide, and 1,1-diazene was found for some H-bonded dimers of DAT. We also determined a reliable and mutually consistent set of thermochemical values for DAT (Δ f H solid0 = 74.5 ± 1.5 kcal·mol-1) by combining theoretically calculated (W1 multilevel procedure along with an isodesmic reaction) gas phase enthalpy of formation (Δ f H gas0 = 100.7 ± 1.0 kcal·mol-1) and experimentally measured sublimation enthalpy (Δ sub H0 = 26.2 ± 0.5 kcal·mol-1).

The UV-photodissociation at 266 nm of a widely used TiO

Molecular arrangement in the thin films of gallium(III) phthalocyanine chloride (PcGaCl) and its μ-(oxo)dimer (μ-(oxo)bis[phthalocyaninato] gallium(III), (PcGa)2O) has been studied using complementary spectroscopic techniques: viz., X-ray photoelectron and optical (polarized Raman and UV-vis) spectroscopies, as well as atomic force microscopy. The former films grown by physical vapor deposition on ITO substrates transformed into the films of the latter μ-(oxo)dimer upon thermal annealing at 300 °C under controlled environmental conditions. The polarized Raman spectroscopy revealed that both films are well organized, and the mean tilt angle between the molecular planes and the substrate surface increases from 53 ± 5° (PcGaCl) to 85 ± 5° ((PcGa)2O). All intense bands in the experimental Raman spectra of PcGaCl and (PcGa)2O were assigned using density functional theory calculations. The theoretically predicted wavenumbers are in a good agreement with the experimental values.

The pH-dependent kinetics of C-ON bond homolysis reactions of the four alkoxyamines (viz., the derivatives of 2-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-2-(pyridin-4-yl)-2,5-dihydro-1H-imidazol-1-oxyl and 2-(2-carboxyethyl)-5,5-diethyl-2,4-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl) in water solution have been scrutinized using DFT calculations (M06-2X/6-311++G(2df,p) level of theory with the PCM model). On the basis of computations, the experimental results obtained before (J. Org. Chem. 2011, 76, 5558) have been rationalized. The concentration dependence of all possible protonated forms of the four alkoxyamines was obtained from pH measurements. The contributions of particular protonated forms into the overall rate constants of thermolysis were estimated using the DFT calculated Gibbs free energies Δ(r)⁰G of C-ON bond homolysis reactions. The computations revealed that the observed rate constants of thermolysis of the two species at several pH values are dominated by decomposition reactions of two or even three protonated forms. The observed trends in reactivity of the alkoxyamines were mainly attributed to destabilization of the radical products of C-ON bond scission reactions. A linear correlation between the sum of radical stabilization energies (RSEs) of products of thermolysis and the calculated Gibbs free energies of reactions was found for various protonated forms of the species studied. Apart from this, the linear correlation exists between the relative RSE and nitrogen hyperfine constants aN of various protonated forms of the nitroxide radical products.

The molecular arrangement in the thin films of chloroaluminium hexadecafluorophthalocyanine (AlClPcF 16 ) grown by physical vapor deposition has been studied using atomic force microscopy and optical spectroscopy techniques. It was shown that AlClPcF 16 films, 20 nm thick, prepared on the quartz substrate at 60 °C are well organized and characterized by a predominantly co-facial parallel arrangement of molecules vertical to the surface. According to the polarized Raman spectroscopy measurements, the mean tilt angle between the AlClPcF 16 species and the substrate surface was found to be 75 ± 5°. All intense bands in the experimental Infrared and Raman spectra of AlClPcF 16 were assigned using density functional theory calculations. The theoretically predicted geometry and wavenumbers are in a good agreement with the experimental values. Apart from this, the temperature dependence of vapor pressure and sublimation enthalpy of AlClPcF 16 were determined by the Knudsen effusion method.

The molecular arrangement and phase transitions in the vanadyl hexadecafluorophthalocyanine (VOPcF16) thin films grown by physical vapor deposition have been studied using in situ X-ray diffraction...

The reactions of O((1)D) atoms with VF(5) at room temperature have been studied by time-resolved laser magnetic resonance at the buffer gas (SF(6)) pressure of 6 Torr. The O((1)D) atoms were produced by the photodissociation of ozone using an excimer laser (KrF, 248 nm). By monitoring the kinetics of FO radical formation, the bimolecular rate constant of O((1)D) consumption in collisions with VF(5) has been determined to be k(VF(5)) = (7.5 ± 2.2) × 10(-11) cm(3) s(-1). The branching ratio for the channel producing FO radicals (k(8a)) has been found to be k(8a)/k(VF(5)) = 0.11 ± 0.02. Quantum chemical calculations at the CCSD(T)/CBS level of theory give evidence that the reactions of O((1)D) with VF(5) proceed via the VF(4)OF intermediate. The enthalpy of the reaction leading to this intermediate formation was calculated to be -245.8 kJ/mol. In qualitative agreement with the experimental results, the reaction channel O((1)D) + VF(5) → FO + VF(4) (8a) turned out to be 72.9 kJ/mol energetically more favorable than the channel O((1)D) + VF(5) → F + OVF(4) (8b). The dissociation enthalpy of the OVF(4) radical was calculated to be very low (18.1 kJ/mol); hence, the decay of OVF(4) to F + OVF(3) should proceed very fast. The molecular channel O((1)D) + VF(5) → F(2) + VF(3)O, though being most favorable thermodynamically, is kinetically unimportant.

The IR- and Raman spectra of two palladium β-diketonates, viz., palladium(II) hexafluoroacetylacetonate, Pd(hfac) 2 , and palladium(II) dipivaloylmethanate, Pd(dpm) 2 , were studied experimentally and theoretically. Density functional theory calculations were employed for detailed assignment of all important bands in the vibrational spectra of Pd(hfac) 2 and Pd(dpm) 2 . The theoretically predicted geometry and wavenumbers are in a good agreement with the experimental values. The comparison of Raman spectra of palladium β-diketonates in crystalline and gas phases allowed to separate the intramolecular and crystalline lattice normal modes.

A comparative study of the sensor response toward gaseous ammonia of hexadecafluorinated 3d-metal phthalocyanine (MPcF16, M Cu(II), Co(II), Zn(II), Ni(II)) thin films was performed using complementary experimental (viz., surface plasmon resonance, SPR, and IR absorption spectroscopy) along with theoretical (density functional theory calculations, DFT) techniques. SPR measurements revealed changes of both thickness and optical parameters (refraction indices and extinction coefficients) of the MPcF16 films caused by adsorption of NH3. The MPcF16 species studied exhibited the following order of sensor response: ZnPcF16 > CoPcF16 ≥ CuPcF16 > NiPcF16. A good correlation was found between the DFT calculated (B3LYP/6-311++G(2df,p)) binding energies, experimentally measured shift of the selected IR bands, and the optical sensor response. Apart from this, we performed a detailed assignment of all intense bands in the vibrational spectra (IR and Raman) of fluorinated 3d-metal phthalocyanines studied.

Peripherally and nonperipherally tetrakisoctylthio- and tetrakisoctyloxy-substituted lead(II) phthalocyanines (PbPcs) were synthesized and characterized using elemental analysis, nuclear magnetic resonance, ultra violet-visible (UV-Vis), infrared (IR), and mass spectroscopies. The mesogenic properties of PbPcs were studied by differential scanning calorimetry, polarized optical microscopy, and x-ray diffraction. The effects of the substitution position and nature of linkage heteroatom on the liquid-crystalline properties and the orientation of the molecules were also studied. Visible absorption spectroscopy yielded an evidence of a thermally induced molecular reorganization in the films. Reflection-absorption IR spectroscopy was used to study the preferential orientation of molecules relative to the substrate surface. The intense bands in the IR spectra of the PbPcs were assigned with the aid of quantum chemical (density functional theory) computations.

Two novel mesomorphic octakis and tetrakis (alkylthio)-substituted phthalocyanines of Pb(II) were synthesized and characterized using NMR, UV–Vis, FT-IR and mass-spectrometry. The mesogenic properties of these new materials forming columnar-hexagonal mesophases were studied by differential scanning calorimetry, optical microscopy and X-ray diffraction. Visible absorption spectroscopy provided evidence of thermally induced molecular reorganization in films. IR spectroscopy and density functional theory calculations were used to study the preferential orientation of molecules relative to the substrate surface. The intense IR bands in the spectra of the lead phthalocyanines were assigned with the aid of quantum chemical computations. The observed increase in the intensity of the out-of-plane modes in the IR spectra correlate with an average preferential edge-on orientation of the molecules on the substrate surface in the film. The current-voltage characteristics of films before and after thermal treatment were also measured. The results confirmed the film ordering proposed on the basis of the IR and DFT studies.

The mutual interconversion and decomposition reactions of four tetrazole isomers (1H-TZ, 2H-TZ, 5H-TZ, and an N-heterocyclic carbene 14H) have been studied theoretically using the W1 high-level procedure. Computations allowed resolution of the existing discrepancies in the mechanism and key intermediates of TZ thermolysis. The tautomeric equilibria between 1H-TZ, 2H-TZ, and 14H turned out to play a very important role in the mechanism of thermal decomposition. Although the barriers of monomolecular tautomeric transformations were found to be high (∼50-70 kcal/mol), the concerted double H atom transfer reactions in the H-bonded complexes of TZ tautomers have profoundly lower barriers (∼18-28 kcal/mol). These reactions lead to fast interconversion between 1H-TZ, 2H-TZ, and 14H. The carbene 14H has never been considered before; however, it was predicted to be a key intermediate in the mechanism of thermal decomposition of TZ. For all species considered, the unimolecular reactions of N(2) elimination were predicted to dominate over the elimination of hydrazoic acid. In agreement with existing experimental data, the effective activation energy of thermolysis was calculated to be 36.2 kcal/mol.

The electric field influence on the molecular orientation and the surface morphology of the chloroaluminum(III) phthalocyanine (AlClPc) films has been studied using polarization dependent Raman spectroscopy and atomic force microscopy. The experimental studies were supported by DFT quantum chemical computations of the AlClPc vibrational spectra and 15N isotopic shifts. The electric field of 1.4 kV mm−1 applied parallel to the substrate plane during the physical vapour deposition modified the film structure noticeable. The AlClPc molecules were aligned nearly perpendicular to the substrate surface (the mean tilt angle increased to ∼80° from ∼20° in the films grown without the electric field). The AFM images of the AlClPc films grown in the absence of electric field revealed a predominant amount of crystallites of polyhedron shape, whereas in the case of the applied electric field the surface was more ordered and consisted of the crystallites of a smoother shape.

The far-infrared and Raman spectra of binuclear molecules [Me2AuX]2 (X = Cl, Br, I) and [Me2Au(OOCR)]2 (R = Me, CF3, But, Ph) in the 600–70 cm−1 region are reported. The experimentally measured vibrational frequencies of [Me2AuX]2 are in a good agreement with density functional theory predictions. The Au…Au vibrational interactions predicted to be in the 270–60 cm−1 region of [Me2AuX]2 far-IR and Raman spectra have been observed. The Raman-active Au…Au vibrations of the [Me2Au(OOCR)]2 molecules were found to be in the same region as those of [Me2AuX]2. The Au–X stretching modes were observed between 100 and 250 cm−1 in accordance with the DFT predictions. Their frequencies in the IR spectra of [Me2AuX]2 increase in the sequence I

The primary reactions of the thermal decomposition of hydrazinium nitroformate (HNF) as well as ammonium nitroformate (ANF) were investigated theoretically using the G3 multilevel procedure. Calculations were performed for the reactions in the gas phase and in the melt using a simplified model of the latter. The influence of the melt on the reaction barriers was taken into account by calculation of the solvation free energies using a PCM model. In contrast with many other energetic salts, the ionic salt structures of the HNF and ANF were found to be minima on the PES. However, the most energetically favorable structures of the HNF and ANF in the gas phase are H-bonded complexes. In the melt, on the contrary, the ionic structure is lowest in free energy because of solvation effects. In both the gas phase and melt, the HNF decomposes preferably to nitroform and hydrazine. This fact agrees well with the experimentally observed absence of HNF among the gas-phase decomposition products. Thermolysis of HNF occurs mainly through the intermediacy of nitroform; computations do not support the suggestion that the aci-nitroform is an important intermediate of HNF thermolysis. The primary dissociation reactions of ANF resemble those of the HNF.

The thermal decomposition of 5-aminotetrazole was studied theoretically using the G3 multilevel procedure and DFT B3LYP technique. The unimolecular primary decomposition reactions of the three most stable isomers of 5-ATZ were studied in the gas phase and in the melt using a simplified model of the latter. The influence of the melt on the elementary reaction barrier was taken into account by the calculation of the solvation free energies using the PCM model. In contrast to all previous publications, we considered the bimolecular reactions of 5-ATZ and demonstrated that they are very important especially in the condensed phase. It was found that the imino form undergoes fast isomerization to the amino form in the H-bonded dimers and does not participate in the 5-ATZ thermolysis. On the contrary, amino and, probably, the 2H isomer are the main isomers of 5-ATZ in the melt and gas phase. The N(2) elimination reaction was found to be the dominant unimolecular channel of the amino and 2H isomer decomposition in both the gas phase and melt. The significant lowering of the activation barriers of decomposition reactions in H-bonded dimers was found. In agreement with the existing experimental data, HN(3) elimination dominates for some of the considered complexes. It was concluded that the initial stages of thermolysis of 5-ATZ cannot be satisfactory described by the simple unimolecular reactions proposed in the literature.

The enthalpy of formation in the standard state for the promising novel energetic material [1,2,5]oxadiazolo[3,4-e][1,2,3,4]-tetrazine-4,6-di-N-dioxide (furazano-1,2,3,4-tetrazine-1,3-dioxide) was calculated using a theoretically calculated value of the heat of formation in the gas phase and am experimentally measured value of the heat (enthalpy) of sublimation. The theoretical calculations were performed using the G2, G3, and CBS-QB3 high-accuracy multilevel quantum chemical techniques.

The hybrid method B3LYP/6-311G* of density functional theory is used to optimize the geometries of nitroform and some intermediates of its decomposition (CH(NO 2 ) 2 , CH(NO 2 ) 2 ONO, CH(NO 2 ), and HC(O)NO) and to locate the transition states of the dissociation and isomerization reactions involving these species. The heat of formation of nitroform and of the intermediates of its decomposition and the Gibbs energies of activation of the reactions examined are calculated using the modern ab initio multilevel procedures G2M(CC5) and G2. The high-pressure limits of the rate constants of these reactions in the temperature range 300-2000 K are calculated using transition state theory or its variational analogue.

The primary thermolysis reactions of a promising insensitive explosive 1,1-diamino-2,2-dinitroethylene (DADNE, FOX-7) have been studied in the gas phase at a high level of theory (CCSD(T)-F12/aVTZ). Our calculations revealed that none of the conventional reactions (C-NO2 bond fission, nitro-nitrite and nitro-aci-nitro rearrangements) dominate thermolysis of FOX-7. On the contrary, two new decomposition pathways specific for this particular species that commenced with enamino-imino isomerization and intramolecular cyclization were found instead to be more feasible energetically. The activation barriers of these primary isomerization reactions were calculated to be 48.4 and 28.8 kcal/mol, while the activation energies of the overall decomposition pathways are predicted to be ∼49 and ∼56 kcal/mol, respectively. The new pathways can also be relevant for a wide series of unsaturated hydrocarbons substituted with both nitro- and amino-groups (e.g., triaminotrinitrobenzene, TATB).

In a recent paper Fayet et al. scrutinized primary decomposition reactions for various derivatives of 1,1,1-trinitrobutane (TNB) and nitroaromatics using DFT computations. The authors compared the calculated Gibbs free energy of activation (DG298) for various competing reaction channels and inferred that the C–NO2 bond fission dominates the gas-phase thermolysis of all species studied. For clarity, we will consider the reactions of TNB at room temperature. In contrast to isomerisation channels (reactions R2 and R3 in the manuscript), the C–NO2 bond rupture (R1) is a barrierless process, and in such case the variational transition state theory (TST) is typically used to locate the transition state (TS). In the framework of TST, either canonical or variational, the rate constant of a unimolecular reaction reads as

Different uni- and bimolecular reactions of hydroxymethylene, an important intermediate in the photochemistry of formaldehyde, as well as its halogenated derivatives (XCOH, X = H, F, Cl, Br), have been considered using high-level CCSD(T)/CBS quantum chemical methods. The Wentzel-Kramers-Brillouin (WKB) and Eckart approximations were applied to estimate the tunneling rate constant of isomerization of trans-HCOH to H(2)CO, and the WKB procedure was found to perform better in this case. In agreement with recent calculations and experimental observations [Schreiner et al., Nature 2008, 453, 906], the half-life of HCOH at the low temperature limit in the absence of bimolecular processes was found to be very long (approximately 2.1 h). The corresponding half-life at room temperature was also noticeable (approximately 35 min). Bimolecular reactions of trans-hydroxymethylene with parent formaldehyde yield primarily more thermodynamically favorable glycolaldehyde via the specific mechanism involving 5-center transition state. The most preferable reaction of cis-hydroxymethylene with formaldehyde yields carbon monoxide and methanol. Due to very low activation barriers, both processes occur with nearly a collision rate. If the concentration of HCOH (and its halogenated analogues XCOH as well) is high enough, the bimolecular reactions of this species with itself become important, and H(2)CO (or X(H)CO) is then formed with a collision rate. The singlet-triplet energy separation of trans-HCOH is confirmed to be approximately -25 kcal/mol.

The IR- and Raman spectra of copper phthalocyanine (CuPc), as well as the isotopic wavenumber shifts upon N-15 substitution in CuPc, were investigated experimentally and theoretically. The symmetry of molecular vibrations was determined using polarized Raman spectra of an oriented CuPc single crystal. Density functional theory (DFT) calculations were used for the detailed assignment of different bands in the vibrational spectra of CuPc. Theoretically predicted geometry, wavenumbers and isotopic shifts are in a very good agreement with the experimental values. A comparison of experimentally obtained isotopic shifts with theoretical predictions allowed us to reveal some characteristic features of normal vibrations of CuPc molecule. Copyright (C) 2009 John Wiley & Sons, Ltd.

The gas phase enthalpies of formation of mono-, di-, tri-, tetranitromethane and nitroethane, as well as of their nitrite and aci-form isomers were calculated using different multilevel (G2, G3, G2M(CC5)) and density functional theory (DFT)-based (B3LYP, MPW1B95 and MPWB1K) techniques. The enthalpies of the C-N bond dissociation and isomerization of these nitroalkanes were also calculated. The calculated values of the formation and reaction enthalpies were compared with the experimental data when these data were available. It was found that only the G3 procedure gave accurate (within 1 kcal/mol) results for the formation enthalpy of nitroalkanes, their isomers, and radical products. The G3 procedure and two new hybrid meta DFT methods proposed by Truhlar's group (Zhao, Y.; Truhlar, D. J. Phys. Chem. A 2004, 108, 6908) showed good results for the reaction enthalpies of the nitromethane isomerization and the C-N bond dissociation. Our calculation results were used to analyze thermodynamics of the dissociation and isomerization reactions of the poly nitro-substituted methanes.