Diethyl Ether Solution Research Articles

Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters.

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

Removal and Reoccurrence of LLZTO Surface Contaminants under Glovebox Conditions.

The reactivity of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolytes to form lithio-phobic species such as Li2CO3 on their surface when exposed to trace amounts of H2O and CO2 limits the progress of LLZTO-based solid-state batteries. Various treatments, such as annealing LLZTO within a glovebox or acid etching, aim at removing the surface contaminants, but a comprehensive understanding of the evolving LLZTO surface chemistry during and after these treatments is lacking. Here, glovebox-like H2O and CO2 conditions were recreated in a near ambient pressure X-ray photoelectron spectroscopy chamber to analyze the LLZTO surface under realistic conditions. We find that annealing LLZTO at 600 °C in this atmosphere effectively removes the surface contaminants, but a significant level of contamination reappears upon cooling down. In contrast, HCl(aq) acid etching demonstrates superior Li2CO3 removal and stable surface chemistry post treatment. To avoid air exposure during the acid treatment, an anhydrous HCl solution in diethyl ether was used directly within the glovebox. This novel acid etching strategy delivers the lowest lithium/LLZTO interfacial resistance and the highest critical current density.

White Phosphorus Reduction and Oligomerization by a Potassium Diamidoalumanyl

AbstractReactions of the potassium alumanyl derivative, [K{Al(SiNDipp)}]2(SiNDipp={CH2SiMe2NDipp}2), with white phosphorus result in two electron reduction to provide controlled access to species containing the (P4)2−dianion. Two examples have been crystallographically characterized, a monomeric derivative in which the potassium cation is encapsulated by 18‐crown‐6 (18‐cr‐6) and a 1‐dimensional polymeric species isolated from diethyl ether solution. Although reactions performed at more elevated temperatures and in the presence of additional equivalents of P4resulted in similar outcomes, these conditions also result in P4oligomerization, albeit by as yet unidentified mechanisms. The structures of [{(SiNDipp)AlK(THF)2}2(P6)] and [{(SiNDipp)AlK(toluene)2}2(P16)] have, thus, also been crystallographically characterized and interrogated computationally by quantum chemical (DFT, QTAIM) methods.

Excited states of chlorophyll a and b in solution by time-dependent density functional theory.

The ground state and excited state electronic properties of chlorophyll (Chl) a and Chl b in diethyl ether, acetone, and ethanol solutions are investigated using quantum mechanical and molecular mechanical calculations with density functional theory (DFT) and time-dependent DFT (TDDFT). Although the DFT/TDDFT methods are widely used, the electronic structures of molecules, especially large molecules, calculated with these methods are known to be strongly dependent on the functionals and the parameters used in the functionals. Here, we optimize the range-separated parameter, μ, of the CAM-B3LYP functional of Chl a and Chl b to reproduce the experimental excitation energy differences of these Chl molecules in solution. The optimal values of μ for Chl a and Chl b are smaller than the default value of μ and that for bacteriochlorophyll a, indicating the change in the electronic distribution, i.e., an increase in electron delocalization, within the molecule. We find that the electronic distribution of Chl b with an extra formyl group is different from that of Chl a. We also find that the polarity of the solution and hydrogen bond cause the decrease in the excitation energies and the increase in the widths of excitation energy distributions of Chl a and Chl b. The present results are expected to be useful for understanding the electronic properties of each pigment molecule in a local heterogeneous environment, which will play an important role in the excitation energy transfer in light-harvesting complex II.

Improved Methods for the Synthesis of KB3H8, NH3B3H7, and N-Alkyl Analogues of NH3B3H7

Improved methods for the synthesis of KB3H8, NH3B3H7, and N-alkyl analogues of NH3B3H7 have been developed based on previous works. KB3H8 was synthesized by the reaction of metallic potassium (K) with borane dimethyl sulfide ((CH3)2S·BH3) with high yield and atom-economy. In the preparation of NH3B3H7 and its N-alkyl analogues, KB3H8 served as a starting material and was converted to THF·B3H7 first through reactions with HCl diethyl ether solution or oxidation agent CoCl2. Then, the formed THF·B3H7 in situ reacted with the corresponding ammonia or amines to form the amine borane final products. This work paves an alternative way for preparing organic-inorganic hybrid materials containing B, N, and C atoms.

BF3·OEt2 Mediated Ethylation of Phenols: A New Protection Group Strategy

An efficient ethylation reaction of phenols was accomplished by using boron triflouride diethyletherate solution as alkyl source at elevated temperatures. The reaction furnished a repertoire of aryl ethyl ethers in decent yields and tolerated a range of functional groups. The method is robust and therefore provides a convenient procedure to protect phenols expeditiously.

Ultra-sensitive detection of Cr2O72− in farmland achieved by an electrosynthesized fluorescent poly(Fmoc-succinimide)

Hexavalent chromium (Cr(VI)) pollution is related to human health, and the detection of its concentration has a decisive effect on pollution treatment. In this work, we designed a Cr2O72− sensor P(Fmoc-Osu) and applied it in farmland. In the boron trifluoride diethyl etherate solution, the monomer Fmoc-Osu was electropolymerized and obtained its conjugated polymer P(Fmoc-Osu). The introduction of succinimide and carbonic ester group in side chain enabled it to show high selectivity to Cr2O72− in comparison to anions and twenty amino acids. Furthermore, by taking advantage of the signal amplification effect of a conjugated polymer, P(Fmoc-Osu) could analyze Cr2O72− in trace amounts and the limit of detection was 8.3 fM. For agricultural application, we employed it in farmland water, soil, Chinese cabbage, carrot and the results showed a satisfactory result. All these results showed that P(Fmoc-Osu) is an efficient tool to detect Cr2O72− in practical application.

Electron-Vibrational Spectra and Dynamics of the Lutein Molecule.

The carotenoid molecules such as lutein play an important role in the absorption of light and the following transfer of energy during photosynthesis. However, the study of these processes by the experimental methods only is quite difficult because some of the transitions between the electronic states of carotenoids are optically forbidden and the effect of vibrational states change also must be taken into account. In the present work, electronic-vibrational states of the lutein molecule in the LHCII complex of higher plants and in the diethyl ether solution were described using the ab initio methods. For lutein of LHCII, the electronic energy transfer processes were modeled. The role of the "hot" S1 states of lutein was shown to be of great importance.

Preparation and electrochemical performance of TEMPO-modified polyterthiophene electrode obtained by electropolymerization

A novel monomer of terthiophene with a side chain TEMPO, 4-(2,5-di(thiophen-2-yl)thiophen-3-yl)acetyl-oxy-2,2,6,6-tetramethylpiperidin-1-yloxy (TT-TEMPO) was successfully synthesized. Its corresponding polymer PTT-TEMPO was prepared via electrochemical polymerization on Pt electrode in boron trifluoride diethyl etherate solution. PTT-TEMPO film showed a uniform network structure. Compared with bare Pt electrode, PTT-TEMPO electrode exhibited high electrocatalytic performance for oxidation of benzyl alcohol in the presence of 2,6-lutidine under similar conditions. Benzyl alcohol was selectively oxidized to benzaldehyde based on in situ FTIR analysis.

Silver catalyzed proto- and sila-Nakamura-type α-vinylation of silyl enol ethers with dichloroacetylene. Divergent formation of stereochemically pure tri- and tetrasubstituted olefins

The silver-catalyzed reaction of silyl enol ethers with dichloroacetylene (DCA) is described. When DCA was used as a solution in diethyl ether, we found that the silyl group was transferred to the vinyl group, resulting in stereochemically pure tetrasubstituted olefins. However, when DCA was used as a solution in the more polar acetonitrile, protonation was the major pathway, and trisubstituted olefins were the dominant products.

Structural and SQMFF study of potent insecticide 4′,4′-DDT combining the FT-IR and FT-Raman spectra with DFT calculations

The experimental FT-IR and FT-Raman spectra in the solid state have been employed to vibrationally characterize the potent insecticide dichlorodiphenyltrichloroethane (4′,4′-DDT). The complete vibrational assignments of 4′,4′-DDT in gas phase and in acetone and diethyl-ether were performed combining hybrid B3LYP/6-31G* and B3LYP/6–311++G** calculations with the internal coordinates, the scaled quantum mechanical force field (SQMFF) methodology and the experimental spectra. Here, the molecular structures of 4′,4′-DDT were theoretically determined in gas phase and in acetone and diethyl-ether solutions by using those two methods. The self-consistent reaction field (SCRF) method and the integral equation formalism variant polarised continuum model (IEFPCM) model were employed to study the properties in solution while the solvation energies were predicted by using the solvation model. The B3LYP/6–311++G** calculations show higher solvation energy in the solvent with lower permittivity, diethyl-ether. A clear and direct correlation was found with both basis sets between solvation energy and dipole moment for those two solvents. NBO studies clearly show that dichlorodiphenyl groups confer to 4,4′-DDT higher stability than the trichloroethyl group due to the fact that the lone pairs of Cl21 and Cl22 atoms present the n→π* transitions while the AIM study shows the participation of trichloroethyl group in halogen bonds clearly justifying the stability of 4′,4′-DDT in the three media and with both basis sets. The MK and NPA charges evidence different behaviors in both media and with both basis sets. The frontier orbitals show that the reactivity of 4,4′-DDT strongly depends on the basis set while it is more reactive than dieldrin, hexachlorobenzene and saxitoxin but 3,3′,4,4′-tetrachloroazobenzene, 3,3′,4,4′ tetrachloroazoxybenzene, CN− and CO species present higher reactivity than 4,4′-DDT. The number of Cl atoms could justify the differences observed in the nucleophilicity indexes of 4,4′-DDT, dieldrin, hexachlorobenzene, 3,3′,4,4′-tetrachloroazobenzene and 3,3′,4,4′ tetrachloroazoxybenzene.

Crystal structures and spectroscopic characterization of MBr2(CNXyl)n (M = Fe and Co, n = 4; M = Ni, n = 2; Xyl = 2,6-dimethylphenyl), and of formally zero-valent iron as a cocrystal of Fe(CNXyl)5 and Fe2(CNXyl)9.

Structures and spectroscopic characterization of the divalent complexes cis-dibromidotetrakis(2,6-dimethylphenyl isocyanide)iron(II) dichloromethane 0.771-solvate, [FeBr2(C9H9N)4]·0.771CH2Cl2 or cis-FeBr2(CNXyl)4·0.771CH2Cl2 (Xyl = 2,6-dimethylphenyl), trans-dibromidotetrakis(2,6-dimethylphenyl isocyanide)iron(II), [FeBr2(C9H9N)4] or trans-FeBr2(CNXyl)4, trans-dibromidotetrakis(2,6-dimethylphenyl isocyanide)cobalt(II), [CoBr2(C9H9N)4] or trans-CoBr2(CNXyl)4, and trans-dibromidobis(2,6-dimethylphenyl isocyanide)nickel(II), [NiBr2(C9H9N)2] or trans-NiBr2(CNXyl)2, are presented. Additionally, crystals grown from a cold diethyl ether solution of zero-valent Fe(CNXyl)5 produced a structure containing a cocrystallization of mononuclear Fe(CNXyl)5 and the previously unknown dinuclear [Fe(CNXyl)3]2(μ2-CNXyl)3, namely pentakis(2,6-dimethylphenyl isocyanide)iron(0) tris(μ2-2,6-dimethylphenyl isocyanide)bis[tris(2,6-dimethylphenyl isocyanide)iron(0)], [Fe(C9H9N)5][Fe2(C9H9N)9]. The (M)C-N-C(Xyl) angles of the isocyanide ligand are nearly linear for the metals in the +2 oxidation state, for which the ligands function essentially as pure donors. The νCN stretching frequencies for these divalent metal isocyanides are at or above that of the free ligand. Relative to FeII, in the structure containing iron in the formally zero-valent oxidation state, the Fe-C bond lengths have shortened, the C[triple-bond]N bond lengths have elongated, the (M)C-N-C(Xyl) angles of the terminal CNXyl ligands are more bent, and the νCN stretching frequencies have shifted to lower energies, all indicative of substantial M(dπ)→π* backbonding.

Ruthenium-cymene containing pyridine-derived aldiimine ligands: Synthesis, characterization and application in the transfer hydrogenation of aryl ketones and kinetics studies

Five electron-rich NN′−pyridylimine ligands, which form five-membered chelate ring when coordinate to a metal center, have been synthesized by the easily accessible condensation between 2-pyridinecarboxyaldhehyde and the corresponding substituted aniline in diethyl ether solution, in the presence of catalytic amount of p-toluenesulfonic acid. The reaction of NN′–pyridylimine ligands with [RuCl2(p-cym)]2(1) in the presence of excess of KPF6 led to the formation of mononuclear adducts with general formula [RuCl(p-cym)(NN′)]PF6, where NN′ = N-phenyl-1-(pyridin-2-yl)methanimine (Amp) (2), N-(4-chlorophenyl)-1-(pyridin-2-yl)methanimine (Clmp) (3), N-(4-methylphenyl)-1-(pyridin-2-yl)methanimine (Memp) (4), N-(4-tert-butylphenyl)-1-(pyridin-2-yl)methanimine (Tbump) (5), N-(2,6-diethylphenyl)-1-(pyridin-2-yl)methanimine (Diemp) and N-[2,6-bis(propan-2-yl)phenyl]-1-(pyridin-2-yl)methanimine (Diipmp) (7). Additionally, the reaction of 2-acetylbenzenolate (OO′) with (1) produces a less bulky neutral congener [RuCl(p-cym)(OO′)] (8). All complexes were isolated and fully characterized by molar conductivity, elemental analysis, cyclic voltammetry and spectroscopic methods, including single crystal X-ray diffraction of (4), (7) and (8). The structures (2)–(7) were also optimized with the Density Functional Theory (DFT) and theoretical absorption spectra were obtained with TD-DFT formalism. The complexes (2)–(8) were applied as pre-catalyst in the transfer hydrogenation of the acetophenone and 4-methylacetophenone, showing good catalytic activity, with productivity up to 90%, and TOF up to 302 h−1 within 3 h of reaction; except for (8), which has no activity for the catalytic reduction performed in this work. A kinetic investigation using (3) and (7) as pre-catalysts showed that the time dependence for the production of 1-phenylethanol has a sigmoidal shape, with an induction time of 20 min. The catalytic activity of (3) is more sensitive to the temperature variation and its rate constant (k) increases faster than for (7). An Arrhenius plot reveals a smaller activation barrier (Ea) for the rate-determining step for (7) than for (3), Ea = 14.75 and 49.38 kJ mol−1, respectively. The ΔS≠ values obtained from an Eyring plot suggest an associative mechanism in the transition state of the catalytic reactions.

Two quasi-stable lead(ii) hydrides at ambient temperature.

Simple reactions of their terphenyl lead bromide precursors with DIBAL-H in diethyl ether solution at ca. -78 °C leads to the isolation of the hydrides {Pb(μ-H)ArPri4}2 (ArPri4 = C6H3-2,6-(C6H3-2,6-Pri2)2) (1) and {Pb(μ-H)ArMe6}2 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) (2) in good yield (60-80%). The isolated solids are stable at up to 5 °C for several weeks but are thermally labile in solution. Hydride 1 decomposes to the diplumbyne ArPri4PbPbArPri4, while 2 decomposes to the plumbylene Pb(ArMe6)2. The decomposition of 1 was determined to be zero order with a rate constant of ca. 2.0 × 10-5 M min-1 at 298 K.

Reactions of cyclochlorotriphosphazatriene with 2-mercaptoethanol. Calorimetric and spectroscopic investigations of the derived products

The reactions of hexachlorocyclotriphosphazatriene, N3P3Cl6 (1) with 2-mercaptoethanol, 2-HS-CH2-CH2-OH (2), in (1:1, 1:2 and 1:3) mole ratios, in excess of NaH, in THF and diethylether solutions yield a total of 6 novel products: one mono spiro, N3P3Cl4[O-CH2-CH2-S] (3); one mono-substituted open chain, N3P3Cl5[S-CH2-CH2-OH] (4); one dispiro, N3P3Cl2[O-CH2-CH2-S]2 (5); one tri-substituted open chain, N3P3Cl3[S-CH2-CH2-OH]3 (6); one tris-spiro, N3P3[O-CH2-CH2-S]3 (7) and one disubstituted open chain, N3P3Cl4[S-CH2-CH2-OH]2 (8) derivatives. The spiro products (3, 5 and 7) are formed as the major products in this system and all of the synthesized compounds are found to be stable at room temperature. The structures of the derived compounds were elucidated by elemental analysis, TLC-MS, 31P and 1H NMR spectral data. For evaluation of melting behavior of derivatives (6) and (7), thermal transition peaks and their corresponding enthalpies were determined via DSC technique.

Controlled Release of DEET Loaded on Fibrous Mats from Electrospun PMDA/Cyclodextrin Polymer.

Electrospun beta-cyclodextrin (βCD)-based polymers can combine a high surface-to-volume ratio and a high loading/controlled-release-system potential. In this work, pyromellitic dianhydride (PMDA)/βCD-based nanosponge microfibers were used to study the capability to host a common insect repellent (N,N-diethyl-3-toluamide (DEET)) and to monitor its release over time. Fibrous samples characterized by an average fibrous diameter of 2.8 ± 0.8 µm were obtained and subsequently loaded with DEET, starting from a 10 g/L diethyl ether (DEET) solution. The loading capacity of the system was assessed via HPLC/UV–Vis analysis and resulted in 130 mg/g. The releasing behavior was followed by leaving fibrous DEET-loaded nanosponge samples in air at room temperature for a period of between 24 h and 2 weeks. The releasing rate and the amount were calculated by thermogravimetric analysis (TGA), and the release of the repellent was found to last for over 2 weeks. Eventually, both the chemical composition and sample morphology were proven to play a key role for the high sample loading capacity, determining the microfibers’ capability to be applied as an effective controlled-release system.

Isolation of Mn(I) Compounds Featuring a Reduced Bis(imino)pyridine Chelate and Their Relevance to Electrocatalytic Hydrogen Production.

We report the preparation and electronic structure determination of chelate-reduced Mn(I) compounds that are relevant to electrocatalytic proton reduction mediated by [(Ph2PPrPDI)Mn(CO)][Br]. Reducing [(Ph2PPrPDI)Mn(CO)][Br] with excess Na-Hg afforded a neutral paramagnetic complex, (Ph2PPrPDI)Mn(CO). This compound was found to feature a low spin Mn(I) center and a PDI radical anion as determined by magnetic susceptibility measurement (1.97 μB), EPR spectroscopy ( S = 1/2), and density functional theory calculations. When [(Ph2PPrPDI)Mn(CO)][Br] was reduced with K-Hg, Mn(I) complexes with highly activated CO ligands were obtained. Recrystallization of the reduced product from diethyl ether solution allowed for the isolation of dimeric [(κ4-Ph2PPrPDI)Mn(μ-η1,η1,η2-CO)K(Et2O)]2 (νCO = 1710 cm-1, 1656 cm-1), while methyl tert-butyl ether treatment afforded dimeric [(κ4-Ph2PPrPDI)Mn(μ-η1,η1-CO)K(MTBE)2]2 (νCO = 1695 cm-1, MTBE = methyl tert-butyl ether). Addition of 18-crown-6 to these products, or conducting the K-Hg reduction of [(Ph2PPrPDI)Mn(CO)][Br] in the presence of 18-crown-6, allowed for the isolation of a monomeric example, (κ4-Ph2PPrPDI)Mn(μ-η1,η2-CO)K(18-crown-6) (νCO = 1697 cm-1). All three complexes were found to be diamagnetic and were characterized thoroughly by multinuclear 1D and 2D NMR spectroscopy and single crystal X-ray diffraction. Detailed analysis of the metrical parameters and spectroscopic properties suggest that all three compounds possess a Mn(I) center that is supported by a PDI dianion. Importantly, (κ4-Ph2PPrPDI)Mn(μ-η1,η2-CO)K(18-crown-6) was found to react instantaneously with either HBF4·OEt2 or HOTf to evolve H2 and generate the corresponding Mn(I) complex, [(Ph2PPrPDI)Mn(CO)][BF4] or [(Ph2PPrPDI)Mn(CO)][OTf], respectively. These products are spectroscopically and electrochemically similar to previously reported [(Ph2PPrPDI)Mn(CO)][Br]. It is believed that the mechanism of [(Ph2PPrPDI)Mn(CO)][Br]-mediated proton reduction involves intermediates that are related to the compounds described herein and that their ambient temperature isolation is aided by the redox active nature of Ph2PPrPDI.

The role of solvent and neutral organophosphorus extractant structure in their organization and association

The choice of organic solvent is known to impact metal ion partitioning in solvent extraction systems, although an understanding based on molecular interactions has been largely qualitative. To provide a more quantitative and molecular scale understanding of extractant and solvent association in liquid-liquid solvent extraction systems, molecular dynamics studies of binary extractant/solvent systems are conducted for several organophosphorus solvating extractants across a range of organic solvents. Classical molecular dynamics potentials for the extractants are optimized in pure phase simulations. These potentials are then validated with binary extractant/solvent solutions by comparison to experimental data for percent volume change on mixing and mixing enthalpies. Trends in association free energy, mixing enthalpy and deviations from ideal mixing volume are reported for each extractant and solvent binary mixture. Contributions to those properties depending on extractant and solvent molecular structure are investigated, including the relative enthalpic favorability of extractant solutions in toluene, diethyl ether or n-hexane. Inclusion of the ether group in diethyl ether lowered the enthalpy of mixing to a similar degree as reducing the alkane solvent chain length from n-dodecane to n-hexane owing to dipole-dipole interactions with the “head” and “tail” regions of the extractant molecules, which depend on extractant alkyl chain length. Despite similar percent volume changes on mixing with n-hexane or diethyl ether, extractant/toluene mixtures were significantly more enthalpically favorable with an enthalpy of mixing minimum controlled by stoichiometry rather than volume fraction, as observed for alkane solvents.

Insertion of a Transient Tin Nitride into Carbon-Carbon and Boron-Carbon Bonds.

A simple exchange reaction between [AriPr4Sn(μ-Cl)]2 (1) and sodium azide afforded the doubly bridged Sn(II) azide, [AriPr4Sn(μ-N3)]2 (2) (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) in 85% yield. Photolysis of a diethyl ether solution of 2 for ca. 16 h yielded an azepinyl-substituted insertion product, [C6H3-2-(C6H3-2,6-iPr2)-6-(C6H3N-3,7-iPr2)Sn]2 (3). The reaction of the Lewis acid, B(C6F5)3 (BCF), or the Lewis base, pyridine, with 2 dissociates the dimer to afford the corresponding complexed monomeric Sn(II) azide, AriPr4SnN3BCF (4) in which BCF coordinates the α-nitrogen, or AriPr4Sn(pyridine)N3 (6) in which pyridine coordinates to the tin atom. Photolysis of 4 in diethyl ether for 12 h results in the insertion of the α-nitrogen of the azide group into one of the B-C bonds of the BCF acceptor to yield the tin(II) amide, AriPr4SnN(C6F5)B(C6F5)2 (5). In contrast, photolysis of 6 for over 36 h afforded no apparent reaction. A highly reactive Sn nitride intermediate, AriPr4Sn≡N, is proposed as part of the mechanistic pathway for the formation of 3 and 5 as a result of trapping the tin-centered radical isomers. This was effected by immediate freezing the samples of 2 or 4 after ca. 30 min of UV photolysis and recording their electron paramagnetic resonance spectra. These exhibited a rhombic g tensor of [g1, g2, g3] = [2.029, 1.978, 1.933]. This radical intermediate could be related to the valence isomers of the nitride [-SnIV≡N] intermediate, in isomeric equilibrium with the nitrene [-SnII-N] and nitridyl [-SnIII═N·] forms, but with the spin density on the nitrogen being quenched, possibly by the H atom abstraction to form an S = 1/2 species of formula -Sn·═N(H).

Crystal structure of 2,4,6-tri-methyl-benzoic anhydride.

The title compound, C20H22O3, was formed in the reaction between 2,4,6-tri-methyl-benzoic acid and N,N-diiso-propyl-ethyl-amine in the presence of 1,3-di-chloro-1,3-bis-(di-methyl-amino)-propenium hydrogen dichloride, and was recrystallized from diethyl ether solution. It is the first exclusively alkyl-substituted benzoic anhydride to have been structurally characterized. The asymmetric unit consists of a half mol-ecule, the other half of which is generated by twofold rotation symmetry; the dihedral angle between the symmetry-related aromatic rings is 54.97 (3)°. The geometric parameters of the aromatic ring are typical of those for 2,4,6-tri-methyl-phenyl substituted groups. The C=O and C-O bond lengths are 1.1934 (12) and 1.3958 (11) Å, respectively, and the angle between these three atoms (O=C-O) is 121.24 (9)°. In the crystal, mol-ecules are linked by weak C-H⋯O hydrogen bonds and C-H⋯π inter-actions. The packing features wavy chains that extend parallel to [001].