UV photodissociation of N-methylpyrrole: The role of πσ states in non-hydride heteroaromatic systems

The photophysics of jet-cooled N-methylpyrrole molecules following excitation to their first excited singlet state (the ¹A₂ state, arising from a 3s/σ^*←π electron promotion) has been investigated by resonance enhanced multiphoton ionisation spectroscopy, by measurements of wavelength resolved ‘action’ spectra for forming CH₃ photoproducts, and by velocity map imaging studies of these CH₃ products (in their v = 0 and v₂ = 1 vibrational levels). CH₃ products are observed at all excitation wavelengths within the NMP absorption band. Direct dissociation on the ¹A₂ potential energy surface (PES) yields ‘fast’ CH₃ fragments, with an average total kinetic energy release (TKER) of 6500 cm⁻¹, but this product channel is only observed in a narrow wavelength range near the absorption band origin. All of the measured CH₃ images also show a broad component, peaking at lower TKER (1700 cm⁻¹); this component extends beneath the ‘fast’ feature in images recorded at wavelengths near the origin, and accounts for all of the CH₃ products observed at shorter photolysis wavelengths. These products are attributed to decay of highly vibrationally excited ground state molecules formed by radiationless transfer from the ¹A₂ state. Similarities and differences with the results of previous studies of the H + pyrrolyl products arising in the UV photodissociation of pyrrole are discussed in terms of the likely nuclear motions on the relevant ground and excited PESs (along R_N–CH3/R_N–H), and the possible couplings between these surfaces. The present study confirms that the proposed model of ¹πσ^* state induced bond fission in heteroaromatic molecules [A.L. Sobolewski, W. Domcke, Chem. Phys. 259 (2000) 181] is also applicable to non-hydride substituted heteroaromatics, but that mass effects can have an important influence on the subsequent nuclear dynamics.     

Synthesis and crystal and molecular structure of CdPhen( iso -C4H9OCS2)2 and CdPhen( n -C4H9OCS2)2 mixed-ligand complexes

Mixed-ligand complexes CdPhen(i-BuOCS₂)₂ (I) and CdPhen(n-BuOCS₂)₂ (II) have been synthesized. Their structures were solved using X-ray diffraction data (X8 APEX diffractometer, MoK _α radiation, 1641 and 2497 F _hkl , R = 0.0359 and 0.0389). Crystals I are orthorhombic with unit cell parameters a = 6.5883(3) Å, b = 19.7123(10) Å, c = 20.1936(11) Å, V = 2622.6(2) ų; Z = 4, space group Pbcn; crystals II are monoclinic, a = 6.5845(2) Å, b = 19.1522(6) Å, c = 20.7091(7) Å, β = 97.106(1), V = 2591.5(1) ų, Z = 4, space group C2/c. The structures consist of discrete mononuclear molecules in which the coordination polyhedron of the Cd atom is a distorted N₂S₄ octahedron. Molecular packing and interactions in the structures are discussed. Original Russian Text Copyright ? 2007 by R. F. Klevtsova, T. G. Leonova, L. A. Glinskaya, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 2, pp. 274–281, March–April, 2007.     

The cobaloximes trans-bis(dimethylglyoxime)(R) Co = n-C14H29 or n-C15H31. Surprising ambiphilic nature observed in the molecular packing of the longest n-alkyl organometallic compound to be structurally characterized

The cobaloximes, trans-bis(dimethylglyozxime)(pyridine)(R)cobalt(III) where R = (n-tetradecyl or (n-pentadecyl) have been synthesized and fully characterized. The crystal structure of the n-tetradecyl compound has been determined and found to be analogous to that of common ambiphilic molecules.     

Crystal and molecular structures of Ni[(iso-C4H9)2PS2]2 and Pd[(iso-C4H9)2PS2]2 chelates

Crystal structures of chelate compounds Ni[(iso-C₄H₉)₂PS₂]₂ (I) and Pd[(iso-C₄H₉)₂PS₂]₂ (II) have been determined by X-ray diffraction: diffractometer X8-APEX, MoK _α∔ -radiation, 1048 F _hkl , R = 0.0544 for I and CAD-4 diffractometer, MoK _α∔ -radiation, 1283 F _hkl , R = 0.0347 for II. The crystals are rhombic: a = 12.921(5) Å, b = 17.094(5) Å, c = 22.971(5) Å; V = 5074(3) ų, Z = 8, calc = 1.250 g/cm³, space group Pbca for I and a = 13.312(3) Å, b = 16.130(7) Å, c = 23.171(5) Å; V = 4975(3) ų, Z = 8, ρ_calc = 1. 208 g/cm³, space group Pbca for II. The structures of I and II are formed by discrete mononuclear molecules. Coordination cores MS₄ (M = Ni, Pd) approach planar square configurations. Original Russian Text Copyright ? 2005 by L. A. Glinskaya, T. G. Leonova, T. E. Kokina, R. F. Klevtsova, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 4, pp. 715–720, July–August, 2005.     

Reduction reactions of the metallocene complex (η-C5H4CMe2C9H7)2ZrCl2

The preparation and characterization of the substituted bis(cyclopentadienyl) zirconium dichloride complexes (η⁵-C₅H₄CMe₂C₉H₇)₂ZrCl₂ (1a, b) is reported. The isomer mixture of 1a, b was treated with different reducing agents such as sodium and n-butyllithium under various reaction conditions. In these reactions CC and CH activation and cleavage reactions were observed. In combination with methylaluminoxane (MAO) 1a, b and 3 showed low activities as homogeneous ethylene polymerization catalysts and no activities towards propylene. Compounds 2 and 3 were characterized by NMR spectroscopy and X-ray crystallography.     

Lubrication of the mixed system of Triton X-100/n-C10H21OH/H2O lamellar liquid crystal and ZnS nanoparticles

ZnS nanoparticles could be synthesized, when two kinds of Triton X-100/n-C₁₀H₂₁OH/H₂O lamellar liquid crystal were mixed, in which Zn(CH₃COO)₂ and Na₂S were dissolved in the solvent layer, respectively. The size of ZnS nanoparticles was about 10 nm and limited by the thickness of the solvent layer of the lamellar liquid crystal. The lubrication properties of the mixed system of Triton X-100/n-C₁₀H₂₁OH/H₂O lamellar liquid crystal and ZnS nanoparticles were determined. The results showed that the presence of ZnS nanoparticles could improve the anti-wear ability of the Triton X-100/n-C₁₀H₂₁OH/H₂O lamellar liquid crystal and decrease its friction coefficient.     

Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation

The photodissociation dynamics of ClONO₂ at 235 nm has been reinvestigated using velocity map ion imaging. We report branching ratios for the Cl + NO₃ and ClO + NO₂ channels to be 0.49:0.51 with anisotropy parameters of β = 0.5 ± 0.1 and β = −0.1 ± 0.3 for the Cl and ClO production channels, respectively. Photodissociation at 248 nm and 262 nm results in similar branching ratios and dynamics as observed at 235 nm. Measured O(³P₂) images arising from ClONO₂ dissociation at 226 nm suggest that oxygen atoms result from the spontaneous dissociation of metastable NO₃. The quantum yield of O atoms arising from the spontaneous dissociation of NO₃ varies from 0.09 at 262 to 0.38 at 235 nm based on the derived internal energy distributions of the NO₃ fragments. We also describe a Monte-Carlo forward-convolution fitting of imaging data which permits detailed analysis of both spontaneous secondary dissociation and secondary photodissociation.     

Normal alkylbenzenes of the composition C12H18-C23H40 in oils from the Nepa-Botuoba oil-and-gas-bearing region and possible mechanism of n -pentadecylbenzene formation

Specific features of the distribution of high-molecular-weight normal alkylbenzenes in crude oils from the Nepa-Botuoba anteclise were studied by chromatography-mass spectrometry. The possible biochemical precursors and mechanisms of formation of normal alkylbenzenes with an odd number of carbon atoms in the molecule were determined. Original Russian Text ? I.K. Ivanova, O.N. Chalaya, V.A. Kashirtsev, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10, pp. 1730–1734.     

Uncompensated magnetization in the layered molecular antiferromagnet {N(n-C5H11)4[MnFe(ox)3]}∞

Studies on the magnetic properties of the molecular antiferromagnetic material {N(n-C₅H₁₁)₄[Mn^IIFe^III(ox)₃]}_∞, carried out by various physical techniques (AC/DC magnetic susceptibility, magnetization, heat capacity measurements and Mössbauer spectroscopy) at low temperatures, have been presented. Different experimental observations complement each other and provide a clue for the observation of an uncompensated magnetization below the Néel temperature and short-range correlations persisting high above T_N. It is understood that the honeycomb layered structure of the compound contains non-equivalent magnetic sub-lattices, (Mn^II–ox–Fe^III_A–...) and (Mn^II–ox–Fe^III_B–...), where different responses of the Fe^III_A and Fe^III_B spin sites towards an external magnetic field might be responsible for the observation of the uncompensated magnetization in this compound at T < T_N. The present magnetic system is an S = 5/2 2-D Heisenberg antiferromagnet system with the intralayer exchange parameter J/k_B = −3.29 K. A very weak interlayer exchange interaction was anticipated from the spin wave modeling of the magnetic heat capacity for T < 0.5T_N. The positive sign of the coupling between the layers has been concluded from the Mössbauer spectrum in the applied magnetic field. Frustration in the magnetic interactions gives rise to the uncompensated magnetic moment in this compound at low temperatures.     

Pair-correlated speed distributions for the OH+CH4/CD4 reactions: Further remarks on their classical trajectory calculations in a quantum spirit

Ten years ago, Liu and co-workers measured pair-correlated speed distributions for OH+CH₄/CD₄ reactions by means of velocity map imaging (VMI) techniques at a collision energy of ∼10 kcal/mol [B. Zhang, W. Shiu, J. J. Lin and K. Liu, J. Chem. Phys 122, 131102 (2005); B. Zhang, W. Shiu and K. Liu, J. Phys. Chem. A 109, 8989 (2005)]. Recently, two of us could semi-quantitatively reproduce these measurements by performing full-dimensional quasi-classical trajectory calculations in a quantum spirit on an ab-initio potential energy surface of their own [J. Espinosa-Garcia and J. C. Corchado, Theor. Chem. Acc. (2015) 134: 6; J. Phys. Chem. B 120, 1446 (2016)]. The goal of the present work is to show that these results can be significantly improved by adding a few more constraints in order to better comply with the restrictions imposed by VMI. Overall, the level of agreement between theory and experiment is remarkable owing to the large dimensionality of the reactions under scrutiny. This is an encouraging result considering the computational challenges of quantum scattering calculations for such large processes.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

Synthesis and characterization of three new fluorovanadate complexes: N(C2H5)4[VOF4], N(CH3)4[VOF3Cl], N(C4H9)4[VOF3Br] and theoretical calculations of VOF4, VOF3Cl and VOF3Br ions

The reaction of VOF₃ with (C₂H₅)₄NF, (CH₃)₄NCl and (C₄H₉)₄NBr salts in anhydrous CH₃CN produced new complexes with the anion general formula [VOF₃X]⁻ in that (X = F⁻, Cl⁻, Br⁻). These were characterized by elemental analysis, IR, UV/Visible and ¹⁹F NMR spectroscopy. The optimized geometries and frequencies of the stationary point are calculated at the B3LYP/6-311G level of theory. Theoretical results showed that the VX (X = F, Cl, Br) bond length values for the [VOF₃X]⁻ in compounds 1-3 are 1.8247, 2.4031 and 2.5595 Å, respectively. Also, the VF₅ bond length values in [VOF₃X]⁻ are 1.824, 1.812 and 1.802 Å, respectively. These results reveal that the bond order for VX bonds decrease from compounds 1 to 3, while for VF₅ bonds, the bond orders increase. It can be concluded that the decrease of VX bonds lengths and the increase of VF₅ bond lengths in compounds 1-3 result from the increase of the hyperconjugation from compounds 1 to 3. Harmonic vibrational frequencies and infrared intensities for VOF₄⁻, VOF₃Cl⁻ and VOF₃Br⁻ are studied by means of theoretical and experimental methods. The calculated frequencies are in reasonable agreement with the experiment values. These data can be used in models of phosphoryl transfer enzymes because vanadate can often bind to phosphoryl transfer enzymes to form a trigonal-bipyramidal structure at the active site.     

The preparation of [closo-1-CB9H8-1-COOH-10-(4-C3H7C5H9S)] as intermediate to polar liquid crystals

The preparation of iodo acid [closo-1-CB₉H₈-1-COOH-10-I]⁻ (1) is optimized and scaled from 1 to 40 g of B₁₀H₁₄. The improved preparation of the [arachno-6-CB₉H₁₃-6-COOH]⁻ (5) uses four times smaller volume and can be run conveniently in up to 40 g scale in a 3-L vessel. The optimized oxidation of 5 to [closo-2-CB₉H₉-2-COOH]⁻ (4) requires less oxidant, 12 times smaller volume, and significantly shorter reaction time. The overall yields of the iodo acid 1 as the [NMe₄]⁺ salt are typically 8-10% (10-12 g) for 40 g of B₁₀H₁₄. The iodo acid 1 was transformed to amino acid 8, then to dinitrogen acid 10, and finally to sulfonium acid 2[3] in overall yield of about 13%. The search for a more efficient phosphine ligand for the Pd-catalyzed amination process was not fruitful. Three routes to the sulfonium acid 2[n] were investigated, and the best yield of about 47% was obtained for Cs₂CO₃-assisted cycloalkylation. Liquid crystalline ester of acid 2[3] and 4-butoxyphenol was prepared and investigated.     

Photodissociation study of ethyl bromide in the ultraviolet range by the ion-velocity imaging technique.

The photodissociation of ethyl bromide has been studied in the wavelength range of 231-267 nm by means of the ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton ionization (REMPI) scheme. The velocity distributions for the Br ((2)P(1/2)) (denoted Br*) and Br ((2)P(3/2)) (denoted Br) fragments are determined, and each can be well-fitted by a narrow single-peaked Gaussian curve, which suggests that the bromine fragments are generated as a result of direct dissociation via repulsive potential-energy surfaces (PES). The recoil anisotropy results show that beta(Br) and beta(Br*) decrease with the wavelength, and the angular distributions of Br* suggest a typical parallel transition. The product relative quantum yields at two different wavelengths are Phi(234nm)(Br*)=0.17 and Phi(267nm)(Br*)=0.31. The relative fractions of each potential surface for the bromine fragments' production at 234 and 267 nm reveal the existence of a curve crossing between the (3)Q(0) and (1)Q(1) potential surfaces, and the probability of curve crossing decreases with the laser wavelength. The symmetry reduction of C(2)H(5)Br from C(3v) to C(s) invokes a nonadiabatic coupling between the (3)Q(0) and (1)Q(1) states, and with higher energy photons, the probability that crossing will take place increases.     

Calorimetric study of the adducts CdBr2·nL (n = 1 and 2; L = ethyleneurea and propyleneurea)

A calorimetric study was performed for adducts of general formula CdBr₂·nL (n=1 and 2; L=ethyleneurea (eu) and propyleneurea (pu)). The standard molar reaction enthalpy in condensed phase: CdBr₂(c)+nL(c)=CdBr₂·nL(c); Δ_rH_m^θ, were obtained by reaction–solution calorimetry, to give the following values for mono- and bis-adducts: −19.54 and −34.59; −7.77 and −19.05 kJ mol⁻¹ for eu and pu adducts, respectively. Decomposition (Δ_DH_m^θ) and lattice (Δ_MH_m^θ) enthalpies, as well as the mean cadmium---oxygen bond dissociation enthalpy, DCd---O, were calculated for all adducts.     

Synthesis and Characterization of N3P3(O2C12H8)2(OC6H4Si(CH3)3)(OC6H4Br) and Its Conversion to Nanostructured Si Material

A new silicated cyclotriphosphazene N₃P₃(O₂C₁₂H₈)₂(OC₆H₄Si(CH₃)₃)(OC₆H₄Br) 1 has been synthesized and characterized. The solid state pyrolysis of 1 in air gives a nanostructured SiP₂O₇ 3D network. The morphology of the network strongly depends on the temperature of the pyrolysis. Spinal-like columns and ring-shaped SiP₂O₇ are formed at 800 °C, while, at 600 °C, fused grains of about 300 nm were observed. Based on air TG and DSC thermal studies, we propose the mechanism of formation for the nanostructured network.