Photolysis and oxidation of azidophenyl-substituted radicals: delocalization in heteroatom-based radicals

2-(4-Azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (14), 2-(4-azidophenyl)benzimidazole-1-oxide-3-oxyl (16), 2-(4-azidophenyl)-1,2,6-triphenylverdazyl (19), 2-(3-azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (21), and (3-azidophenyl)-N-tert-butyl-N-aminoxyl (25) were photolyzed in frozen solution to give S = 3/2 state ESR spectra of the corresponding nitrenophenyl radicals with the following zero-field splitting parameters: |D/hc| = 0.277 cm(-1), |E/hc| < or = 0.002 cm(-1) (7 from 14); |D/hc| = 0.256 cm(-1), |E/hc| < or = 0.002 cm(-1) (8 from 16); |D/hc| = 0.288 cm(-1), |E/hc| < or = 0.002 cm(-1) (9 from 19); |D/hc| = 0.352 cm(-1), |E/hc| = 0.006 cm(-1) (10 from 21); |D/hc| = 0.336 cm(-1), |E/hc| = 0.004 cm(-1) (11 from 25). UB3LYP/6-31G computations and ESR spectroscopic analyses suggest that these are nitreno radicals, even para-linked systems with possible quinonoidal resonance forms. Neat samples of azidophenyl radicals 14 and 21 showed bulk paramagnetic behavior, consistent with the lack of close contacts in their crystal structures. Efforts to make photolabile coordination complexes of 14 and 21 with paramagnetic transition metal ions were unsuccessful: Cu(ClO4)2 x 6H2O instead oxidized them to the corresponding diamagnetic nitrosonium perchlorate salts.     

An electron spin resonance study of azaallyl radicals

The ESR spectrum of the 2-aza-allyl radical, Me2CNCMe₂, has been recorded. A series of 1-aza-allyl radicals have been generated by reaction of 2-alkyl-4,4-dimethyloxazolines with t-butoxyl radicals and their ESR spectra studied. In this reaction 2-alkyl-4,4-dimethyloxazolin-5-yl radicals are also formed.     

Alkenylthioimidoyl radicals: competition between beta-scission and cyclization to dihydrothiophen-2-ylidene-amines

[reaction: see text] But-3-enylthioimidoyl radicals were shown by EPR spectroscopy and end product analysis to ring-close predominantly in the 5-exo mode with a rate constant of 2.4 x 10(4) s(-)(1) at 300 K to afford substituted dihydrothiophenylmethyl radicals. This ring closure was in competition with dissociation to but-3-enyl radicals and an isothiocyanate. The dissociation predominated at temperatures above ca. 300 K.     

Investigation of hydrothermal routes to mixed-metal cerium titanium oxides and metal oxidation state assignment using XANES

The reaction between TiF(3) or TiO(2) and Ce(3+) in sodium hydroxide solutions yields highly crystalline NaCeTi(2)O(6) at room temperature and under mild hydrothermal conditions (T < or = 240 degrees C). There is no evidence for the formation of ternary Ce-Ti-O materials by this method, and the use of bases other than NaOH always produces poorly crystalline materials. The material NaCeTi(2)O(6) has a distorted perovskite structure with sodium and cerium ions randomly occupying the A sites: Pnma, a = 5.4517(8) A, b = 7.7292(6) A, c =5.4573(3) A. XANES spectroscopy at the Ti K edge and Ce L(III) edge, with reference to crystalline model compounds, reveals that cerium is found solely as Ce(III) and titanium as Ti(IV) in NaCeTi(2)O(6). Isomorphous substitution of Ce(3+) by Nd(3+) or Ti(4+) by V(4+) is found to be very facile under hydrothermal conditions (at a temperature of 240 degrees C), by addition of appropriate amounts of metal salts to the hydrothermal reaction mixtures. The series NaCe(1-x)Nd(x)Ti2O6 (0 < or = x < or = 1) and NaCeTi(2-x)V(x)O6 (0 相似文献   

Improved morphed potentials for Ar-HBr including scaling to the experimentally determined dissociation energy

A lead salt diode infrared laser spectrometer has been employed to investigate the rotational predissociation in Ar-HBr for transitions up to J' = 79 in the v(1) HBr stretching vibration of the complex using a slit jet and static gas phase. Line-shape analysis and modeling of the predissociation lifetimes have been used to determine a ground-state dissociation energy D(0) of 130(1) cm(-1). In addition, potential energy surfaces based on ab initio calculations are scaled, shifted, and dilated to generate three-dimensional morphed potentials for Ar-HBr that reproduce the measured value of D(0) and that have predictive capabilities for spectroscopic data with nearly experimental uncertainty. Such calculations also provide a basis for making a comprehensive comparison of the different morphed potentials generated using the methodologies applied.     

Experimental observations of water-framework interactions in a hydrated microporous aluminum phosphate

Differential scanning calorimetry of the hydrated, microporous aluminum phosphate AlPO-14 shows two distinct water losses between room temperature and 120 degrees C, indicating the presence of two types of water in the solid. Multiple-quantum magic angle spinning (MQMAS) (27)Al NMR shows that, while in dehydrated AlPO-14 all aluminum is found in tetrahedral sites, on hydration a significant proportion of the aluminum increases its coordination number to 6. This accounts for the presence of tightly bound water. The first detailed incoherent inelastic neutron scattering (IINS) studies of such a system give a spectrum with distinct and sharp librational bands for bound water, significantly different than seen in ice Ih. Using these data, and by consideration of the crystal structure of dehydrated AlPO-14, we propose a model for the hydrated material in which the tightly bound water bridges pairs of Lewis acidic framework aluminums in a dense region of the structure, while loosely bound water resides in the pores of the solid. Further IINS measurements using a high-incident neutron energy provide data that are in agreement with our model. We can detect two O-H stretching modes for bound water in hydrated AlPO-14, consistent with the model of two types of water present in the material, with the loosely bound water connected to neighboring water molecules by intermolecular hydrogen bonds.