Solution Thermolysis Research Articles

Two sides of thermal stability of energetic liquid: Vaporization and decomposition of 3-methylfuroxan

Analysis of thermal behavior of liquids is often accompanied by vaporization. In an extreme case, the calorimetric (DSC) experiment reveals the only endothermic evaporation instead of the more valuable thermal decomposition. 3-Methylfuroxan (MMF) is an energetic monosubstituted 1,2,5-oxadiazole N-oxide that shows the above behavior. We investigate the sample mass and confinement effects and show that the pressure DSC allows observing thermal decomposition of target compound at 2.0 MPa. Advanced model-fitting kinetic analysis reveals two global stages, the first of which is a competition between the noncatalytic reaction and autocatalytic one, whereas the second global stage is a second-order reaction. Analysis of MMF thermolysis in solution in dibutyl phthalate shows the activation energy for noncatalytic reaction to be 145.4 ± 1.7 kJ mol−1. To resolve the gas decomposition products in experiments at 0.1 MPa pressure, where the evaporation is abundant, a gas chromatography–mass spectrometry coupled with thermal analyzer was used. Among the gases that are consistent with a furoxan ring rupture by CC and NO bonds (HNCO, CH3CN), we detect CH3COCN that retains CC bond. The formation of geminal cyanonitro compound in the course of thermolysis is proposed to explain the composition of the gas reaction products. Overall, with the range of thermal analysis tools (DSC, PDSC, GC–MS/TGA, thermokinetic modeling) we performed a detailed analysis of thermal transformations of unexplored simple monosubstituted furoxan. The applied methodological approaches could be transferred to other molecular liquids.

The power of model-fitting kinetic analysis applied to complex thermal decomposition of explosives: reconciling the kinetics of bicyclo-HMX thermolysis in solid state and solution

Thermal decomposition of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (Bicyclo-HMX) both in solid state and in solution has been studied with a set of thermal analysis methods. Differential scanning calorimetry data obtained at several heating rates were analyzed using the model-fitting kinetic technique using the free open-source THINKS thermokinetic software. The kinetic parameters for a noncatalytic stage of thermolysis in solution are found to be Ea = 168.7 ± 1.4 kJ mol−1, log (A, s−1) = 15.7 ± 0.2, to prove the activation energy agrees with the theoretical prediction of the barrier for N–NO2 bond rupture in BC-HMX molecule. Thermal decomposition of solid BC-HMX is a complex process, typical for explosives. A formal three-step kinetic scheme is proposed, which explains the numerous experimental findings (thermal behavior at various confinement degree, morphology changes under heating) and the previous literature results as well. The first step of the process obeys a third-order nucleation-growth model with the Ea = 186.6 ± 1.2 kJ mol−1 and log (A, s−1) = 16.7 ± 0.3. Overall, the power of the model-fitting kinetic analysis is demonstrated and the extension of the proposed methodology to other energetic materials with complex decomposition patterns is suggested.

Frustrated Lewis Pair Chelation as a Vehicle for Low-Temperature Semiconductor Element and Polymer Deposition.

The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, i Pr2 P(C6 H4 )BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2 }] and [PB{GeH2 }] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine-borane ligand (PB) after element deposition, and 2) the single-source precursor [PB{SiH2 }] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2 }] was also prepared, and shown to release poly(dimethylsilane) [SiMe2 ]n upon heating. Overall, this study introduces a "closed loop" deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

Frustrated Lewis Pair Chelation as a Vehicle for Low‐Temperature Semiconductor Element and Polymer Deposition

AbstractThe stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, iPr2P(C6H4)BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2}] and [PB{GeH2}] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine‐borane ligand (PB) after element deposition, and 2) the single‐source precursor [PB{SiH2}] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2}] was also prepared, and shown to release poly(dimethylsilane) [SiMe2]n upon heating. Overall, this study introduces a “closed loop” deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

Quantum Size Effect in Bimetallic Nanoparticles Obtained via Thermolysis of Solid Solutions of Co(II), Ni(II), Zn(II) Salts of Maleic Acid

Powder X-ray diffraction and the thermoanalytical characteristics of solid solutions with compositions [(CoxNi1 – x)(H2O)4(C4H3O4)2], [(CoxZn1 – x)(H2O)4(C4H3O4)2], [(NixZn1 – x)(H2O)4(C4H3O4)2] (0 < x < 1) are compared. The decomposition of solid solutions and their constituents when heated to 500°C in a flow of He is conventionally divided into three stages. Products of the thermolysis of solid solutions are found to be Co/Ni, Co/ZnO, and Ni/Zn bimetallic nanoparticles, respectively, embedded into the polymeric matrix of composites. It is shown that the thermal decomposition of solid solutions in the Curie curve upon a second order phase transition with the formation of the two-phase region found in Co/Ni bimetallic nanoparticles is a quantum size effect. The decomposition of [(Co0.1Zn0.9)(H2O)4(С4H3O4)2] solid solution removes the Co atoms (d = 2.5 A) embedded in channels of the ZnO structure. These atoms also serve as catalysts for the growth of a nanobrush of carbon nanotubes (CNTs) on the composite’s surface at ≤500°C, another consequence of the quantum size effect. It is concluded that using a similar catalyst of CNT growth can appreciably lower the energy of the process.

Di-tert-butylphosphate Derived Thermolabile Calcium Organophosphates: Precursors for Ca(H2PO4)2, Ca(HPO4), α-/β-Ca(PO3)2, and Nanocrystalline Ca10(PO4)6(OH)2.

Thermally and hydrolytically unstable di-tert-butyl phosphate (dtbp-H) has been used as synthon to prepare discrete and polymeric calcium phosphates that are convenient single-source precursors for a range of calcium phosphate ceramic biomaterials. The reactivity of dtbp-H toward two different calcium sources has been found to vary significantly, e.g., the reaction of Ca(OMe)2 with dtbp-H in a 1:6 molar ratio in petroleum ether forms a mononuclear calcium hexa-phosphate complex [Ca(dtbp)2(dtbp-H)4] (1), whereas the change of calcium source to CaH2, in a 1:2 molar ratio under otherwise similar reaction conditions, yields the calcium phosphate polymer, [Ca(μ-dtbp)2(H2O)2·H2O]n(2). Compounds 1 and 2 have been extensively characterized by various spectroscopic and analytical techniques. The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. In discrete molecule 1, the central calcium ion is surrounded by two anionic dtbp and four neutral dtbp-H ligands in an octahedral coordination environment. Compound 2 is a one-dimensional polymer in which adjacent calcium ions are connected through double dtbp bridges. Solid-state thermolysis of bulk 1 in air leads to the exclusive formation of calcium metaphosphate β-Ca(PO3)2 in the entire temperature range of 400-800 °C. Thermal decomposition of polymer 2, however, can be fine-tuned to produce either α-Ca(PO3)2 or β-Ca(PO3)2 depending on the thermolysis conditions employed. Although the sample sintered at 600 °C produces exclusively α-form of Ca(PO3)2, the sample annealed at 800 °C or above produces β-form. Both α- and β-forms can also be successively formed one after other by a slow heating of a freshly prepared 2 on the powder diffractometer sample holder. Additional forms of ceramic phosphates have been prepared by solvothermal conditions because of the highly labile nature of the tert-butoxy groups of dtbp in 1 and 2. Solution decomposition of either 1 or 2 in boiling toluene at 140 °C in a sealed tube produces calcium dihydrogen phosphate [Ca(H2PO4)2·H2O] as the only product in the form of single crystals. Solution thermolysis of 2 in protic solvents such as water and methanol can be biased to produce other calcium phosphate biomaterials such as hydroxyapatite [Ca10(PO4)6(OH)2]and calcium monohydrogen phosphate [Ca(HPO4)] in the presence of additional calcium precursors such as CaO and Ca(OMe)2, respectively.

Gas-phase study of the stability of α-substituted cyclic amino nitriles under electron ionization and electrospray ionization and fragmentation peculiarities of cyclic ketimines.

α-Substituted cyclic amino nitriles show different reactivity and stability in solution depending on their ring size. Mass-spectrometric modeling of the reactions, which normally take place in solution, may shed light on the nature of the studied compounds and explain some observations. The stability of the nitriles in an acidic solution was studied by adding glacial acetic acid. Gas-phase modelling was conducted by gas chromatography/mass spectrometry (GC/MS) with electron ionization mass spectrometry and direct inlet electrospray ionization. QqQ and Orbitrap analyzers were used to carry out tandem mass spectrometry (MS/MS) experiments. The obtained data show that the elimination of HCN from α-substituted cyclic amino nitriles occurs in the same way for an acidic solution, thermolysis and electrospray ionization. According to GC, the most stable were N-formylated nitriles compared with N-benzylated or N-unsubstituted ones. Electrospray ionization demonstrated its advantages for the routine identification of cyclic amino nitriles due to milder conditions than in electron ionization. Fragmentations of cyclic ketimines, formed from N-unsubstituted amino nitriles, are discussed in particular. Similarities in the behavior of the α-substituted cyclic amino nitriles under electron ionization, electrospray ionization, thermolysis and reaction in solution under acidic catalysis were discovered and confirmed by MS/MS experiments. Fragmentation schemes of the studied nitriles and corresponding imines are proposed.

Accessing Mixed-Halide Upconverters Using Heterohaloacetate Precursors

A new type of organic–inorganic hybrid precursor to mixed-halide optical materials is described by using Ba5(CF2ClCOO)10·7H2O as an example. This heterohaloacetate belongs to the family of extended inorganic hybrids in which metal connectivity in three dimensions is achieved via metal–organooxygen–metal bridges. Thermolysis in the solid state and in solution yield crystalline BaFCl at temperatures below 300 °C. Chlorodifluoromethyl groups act as chlorine and fluorine source, making the organic moiety a de facto single-source precursor for the anionic portion of the target mixed halide. Solution thermolysis in the presence of Yb3+–Er3+ sensitizing–activator pairs yields rare-earth-doped BaFCl nanocrystals capable of NIR-to-visible photon upconversion. Analyses of the composition, morphology, structure, and luminescence of these nanocrystals demonstrate that heterohalocetates serve as dual halogen sources for mixed-halide optical materials. Findings presented in this article enlarge the synthetic toolbox to...

Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C-C Multiple Bonds.

A series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [( p- tBu-C6H4)2CH]2M(L n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI2(THF) n ( n = 0-2) and [( p- tBu-C6H4)2CH]-Na+. In complex 1, the benzhydryl ligands are bound to the metal center in η2-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in η3-fashion. In complex 2, one ligand is η3-coordinated while the second one is η4-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C6D6 at 100 °C during 72 h. Complex 1 behaves differently: thermolysis in C6D6 solution at 75 °C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 °C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH2 toward the internal C═C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph2PH and PhPH2 was realized due to the application of Yb(II) complex as a catalyst.

Rubidium-Alkaline-Earth Trifluoroacetate Hybrids as Self-Fluorinating Single-Source Precursors to Mixed-Metal Fluorides.

Three novel bimetallic hybrid crystals featuring rubidium-alkaline-earth metal pairs and trifluoroacetato ligands were synthesized, and their utility as self-fluorinating single-source precursors to the corresponding mixed-metal fluorides was demonstrated. Rb2Mg2(tfa)6(tfaH)2·3H2O, RbCa(tfa)3, and RbSr2(tfa)5 (tfa = CF3COO-; tfaH = CF3COOH) were synthesized in both single-crystal and polycrystalline forms via solvent evaporation. Their crystal structures were solved using single-crystal X-ray diffraction (XRD), and chemical purity was confirmed using thermal analysis (TGA/DTA). Metal-oxygen-metal connectivity in Rb2Mg2(tfa)6(tfaH)2·3H2O was restricted to four-metal building blocks. In contrast, RbCa(tfa)3 and RbSr2(tfa)5 were found to be extended inorganic hybrids ( Cheetham et al. Chem. Commun. 2006 , 0 , 4780 - 4795 ) exhibiting infinite metal connectivity in three and two dimensions, respectively. Systematic analysis of the coordination modes of the trifluoroacetato ligand revealed its ability to bridge alkali and alkaline-earth metals. Rietveld analysis of powder X-ray diffraction data (PXRD) showed that thermal decomposition of Rb2Mg2(tfa)6(tfaH)2·3H2O and RbCa(tfa)3 under inert atmosphere yielded crystalline RbMgF3 and RbCaF3, respectively. This solid-state transformation occurred without the need for an external fluorinating agent because the trifluoromethyl group acted as a built-in fluorine source. Solid-state and solution thermolysis of Rb2Mg2(tfa)6(tfaH)2·3H2O provided access to the hexagonal and cubic polymorphs of the fluoroperovskite RbMgF3, respectively. Findings reported in this article highlight that bimetallic trifluoroacetates offer unique features from the standpoint of both crystal lattice topology and reactivity.

Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts

The complex (μ-Me2C-3,3′){(η5-cyclopentadienyl)[1-Me2Si-(tBuN)](TiMe2)}2 (3) was prepared as a new binuclear catalyst motif for homogeneous olefin polymerization. Complex 3 exists as rac-3 and meso-3 diastereomers, which can be separated and characterized by solution NMR spectroscopy and single-crystal X-ray diffraction. While meso-3 has high thermal stability, rac-3 undergoes thermolysis in solution to quantitatively form the dimeric methylidene complex (μ-Me2C-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)][(μ-CH2)Ti]}2 (rac-4). Activation of rac-3 and meso-3 with 1 equiv of Ph3C+B(C6F5)4– yields [(μ-CMe2-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)(μ-CH3)Ti2]+B(C6F5)4– (5; rac-5 and meso-5, respectively). Interestingly, meso-5 is stable in the presence of an additional 1 equiv of Ph3C+B(C6F5)4–, while rac-5 reacts to yield rac-[(μ-CMe2-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)[(TiCH3)(Ti-η1-Ph3C)]2+[B(C6F5)4–]2 (rac-6) as indicated by multinuclear NMR spectroscopy and DFT computation. meso-3 reacts with 2 equiv of B(C6F5)3 to yield meso-[(μ-CMe2-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)(μ-CH3)Ti2]+MeB(C6F5)3– (meso-7) containing the same meso-5 cation but with a MeB(C6F5)3–counteranion. These findings, along with catalytic results, indicate that rac-3 and meso-3 remain structurally intact during polymerization, consistent with the observed diastereoselectivity effects. Under identical ethylene/1-octene copolymerization conditions, only activated bimetallic rac-3 produces appreciable polymer, with meso-3 exhibiting low activity, but both yield polymer with a branch density >2× that of the monometallic control [(3-tBu-C5H3)SiMe2NtBu]TiMe2 (Ti1). In ethylene/styrene copolymerizations, rac-3 produces polymers with 3.1× higher Mn and 2.1× greater styrene incorporation versus Ti1, while meso-3 catalyzes only ethylene-free styrene homopolymerization. In 1-octene homopolymerizations, meso-3 + B(C6F5)3 (i.e., meso-7) produces highly isotactic poly-1-octene (mmmm 91.7%), while rac-3 + Ph3C+B(C6F5)4– (i.e., rac-5), rac-3 + B(C6F5)3 (i.e., rac-7), and meso-3 + Ph3C+B(C6F5)4– (i.e., meso-5) produce only atactic poly-1-octene. These bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product Mn, tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.

Kinetics of oxidation of 30% TBP solutions in С13 diluent with nitric acid: Effect of temperature and γ-irradiation

The behavior of the two-phase system consisting of a 30% solution of tri-n-butyl phosphate (TBP) in a paraffin diluent (C13) and a 12 M aqueous HNO3 solution was studied in the temperature interval from 70 to 110°С. The parameters of thermolysis of TBP solutions in C13 in the reaction with HNO3 in open vessels were determined with the aim of evaluating the explosion hazard of the system in the course of extraction reprocessing of high-level radioactive materials. Solutions of TBP in C13 in the two-phase systems are characterized in the examined temperature interval by more intense gas evolution compared to that from the singlephase systems.

ChemInform Abstract: Thermolysis of 1‐(Thiophen‐2‐yl)‐1H‐tetrazoles: A Route to Thiophene‐Fused Imidazoles and Pyrimidines.

Abstract Thermal reactions of 1-(thiophene-2-yl)-1H-tetrazoles are reported for the first time. The solution thermolysis of 1-(thiophene-2-yl)-1H-tetrazoles under conventional heating and microwave irradiation afforded the unexpected new thieno[2,3-d]pyrimidines incorporating two thiophene rings, which were obtained as major or only product. The synthesis of these heterocycles was rationalized considering the initial nitrogen elimination to generate imidoylnitrene followed by rearrangement to the corresponding carbodiimide and subsequent cyclization triggered by the nucleophilic attack of the in situ generated 2-aminothiophene. The flash vacuum pyrolysis and solution thermolysis of 1-(thiophene-2-yl)-1H-tetrazoles also gave thieno[2,3-d]imidazoles via intramolecular formal insertion into a C–C bond of the corresponding imidoylnitrene intermediate.

Thermolysis of 1-(thiophen-2-yl)-1H-tetrazoles: a route to thiophene-fused imidazoles and pyrimidines

Thermal reactions of 1-(thiophene-2-yl)-1H-tetrazoles are reported for the first time. The solution thermolysis of 1-(thiophene-2-yl)-1H-tetrazoles under conventional heating and microwave irradiation afforded the unexpected new thieno[2,3-d]pyrimidines incorporating two thiophene rings, which were obtained as major or only product. The synthesis of these heterocycles was rationalized considering the initial nitrogen elimination to generate imidoylnitrene followed by rearrangement to the corresponding carbodiimide and subsequent cyclization triggered by the nucleophilic attack of the in situ generated 2-aminothiophene. The flash vacuum pyrolysis and solution thermolysis of 1-(thiophene-2-yl)-1H-tetrazoles also gave thieno[2,3-d]imidazoles via intramolecular formal insertion into a C–C bond of the corresponding imidoylnitrene intermediate.

Robust Carboxylic Acid-Terminated Organic Thin Films and Nanoparticle Protectants Generated from Bidentate Alkanethiols

A new carboxylic acid-terminated alkanethiol having bidentate character, 16-(3,5-bis(mercaptomethyl)phenoxy)hexadecanoic acid (BMPHA), was designed as an absorbate and protectant to form thermally stable carboxylic acid-terminated organic thin films on flat gold and nanoparticles, respectively. The structural features of the organic thin films derived from BMPHA were characterized by ellipsometry, X-ray photoelectron spectroscopy (XPS), and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and compared to those derived from mercaptohexadecanoic acid (MHA) and 16-(4-(mercaptomethyl)phenoxy)hexadecanoic acid (MMPHA). This study demonstrates that films derived from BMPHA are less densely packed than films derived from MHA and MMPHA. However, the results of solution-phase thermal desorption tests revealed that the carboxylic acid-terminated films generated from BMPHA exhibit an enhanced thermal stability compared to those generated from MHA and MMPHA. Furthermore, as a nanoparticle protectant, BMPHA can be used to stabilize large gold nanoparticles (~45 nm diameter) in solution, and BMPHA-protected gold nanoparticles exhibited a high thermal stability in solution thermolysis studies.

4‐Heptanone cyclic diperoxide: Improved preparation method and solvent effect on its thermolysis in solution

AbstractCyclic organic peroxides have interesting pharmacological properties and are used at industrial level as polyfunctional initiators of polymerization, and so their preparation through novel methods has attracted the attention of numerous researchers. White crystals of 4‐heptanone cyclic diperoxide (HDP) can be obtained in acidic media at −1°C by a reaction between 4‐heptanone and hydrogen peroxide. Its thermal decomposition was studied in acetone, cyclohexane, acetonitrile, ethyl acetate, ethanol, 2‐propanol, 2‐butanol, and 1,4‐dioxane at temperatures higher than 120°C, showing a behavior accordingly with a pseudo‐first‐order kinetic law up to at least 80% HDP conversion. It was demonstrated that an increase in solvent polarity is accompanied by an increase in reaction rates. The effect of solvent polarity on the thermal decomposition rate constant values can be associated with a reaction mechanism involving a more dipolar‐activated complex than the diperoxide initial molecule. The activation parameters varied widely from 31.2 to 46.6 kcal mol−1 and −1.33 to 31.7 cal mol−1 K−1 when going from ethanol to cyclohexane as reaction solvents, respectively. An enthalpy–entropy compensation effect was observed in all solvents. Specific interactions between the oxygen atoms from the peroxidic bond and the hydrogen atom bonded to C2 and/or from the OH group can be taken into account to explain that the existence of the compensation effect does not mean that an isokinetic relationship consequently can be established. The kinetic results showed that an isokinetic relationship is observed only for a group of solvents. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 657–666, 2011

Morphology‐Tailored Synthesis of PbSe Nanocrystals and Thin Films from Bis[N,N‐diisobutyl‐N′‐(4‐nitrobenzoyl)selenoureato]lead(II)

AbstractThe ligand N,N‐diisobutyl‐N′‐(4‐nitrobenzoyl)selenourea (4‐NO2‐C6H4CONHCSeNiBu2) (1) and its complex {bis[N,N‐diisobutyl‐N′‐(4‐nitrobenzoyl)selenoureato]lead(II)} [(4‐NO2‐C6H4CONHCSeNiBu2)PbII] (2) have been synthesized, and their structures determined by single‐crystal X‐ray methods. Compound 2 was employed as a single‐source precursor (SSP) for the deposition of PbSe thin films by aerosol‐assisted chemical vapor deposition (AACVD) in the temperature range 250–500 °C on glass substrates. The films obtained at low temperature consist of globular‐shaped crystallites, whereas at higher temperature (ca. 500 °C) wirelike morphologies are dominant. PbSe nanocrystals were also prepared from compound 2 by solution thermolysis at 200–250 °C. Photoluminescence (PL) life time measurements based on the time‐correlated single‐photon‐counting (TCSPC) technique showed significantly faster PL decay in as‐prepared PbSe nanocrystals relative to previous reports. The purity and elemental composition of the as‐deposited PbSe thin films and nanocrystals were determined by energy‐dispersive X‐ray analysis (EDX).

Interaction of 1,3,2,4-Benzodithiadiazines and Their 1-Se Congeners with Ph3P and Some Properties of the Iminophosphorane Products

Interaction between Ph(3)P and 1,3,2,4-benzodithiadiazine (1); its 6,7-difluoro (2), 5,6,8-trifluoro (3) and 5,6,7,8-tetrafluoro (4) derivatives; and 5,6,8-trifluoro-3,1,2,4-benzothiaselenadiazine (5) proceeded via a 1:1 condensation to give Ph(3)P═N-R iminophosphoranes (1a-5a, R = corresponding 1,2,3-benzodichalcogenazol-2-yls), which are inaccessible by general approaches based on the Staudinger and Kirsanov reactions. In contrast, neither Ph(3)As nor Ph(3)Sb reacted with 1 and 4. Molecular structures of 1a-5a and 5 were confirmed by X-ray diffraction (XRD). The crystals formed by chiral molecules of 2a-5a were racemic, whereas the crystal of 1a was formed by a single enantiomer. In all of the Ph(3)P═N-R derivatives, one of the Ph rings is oriented face-to-face to the hetero ring, R. Upon heating to ∼120 °C in squalane (1a, 3a, 4a) or dissolving in chloroform at ambient temperatures (1a, 2a, 4a), the Ph(3)P═N-R derivatives generated the 1,2,3-benzodithiazolyls (1b-4b, respectively) whose identity was confirmed by electron paramagnetic resonance (EPR). 2,1,3-Benzothiaselenazolyls 5b and 6b were detected by EPR as the main paramagnetic products of solution thermolysis of 5 and its 5,6,7,8-tetrafluoro congener (6), respectively. Passing a chloroform solution of 4a through silica column unexpectedly gave 5-6-6-6 tetracyclic (9) and 6-10-6 tricyclic (10) sulfur-nitrogen compounds, which were characterized by XRD.

New routes to copper sulfide nanostructures and thin films

The copper(II) complex of 1,1,5,5-tetra-iso-propyl-2-thiobiuret [Cu(SON(CNiPr2)2)2], has been synthesized and its single crystal X-ray structure determined. The complex has been used as a single source precursor for the preparation of copper sulfide nanoparticles by solution thermolysis. The nanoparticles synthesized had various morphologies including spherical, hexagonal disks, and trigonal crystallites; depending on the reaction temperature, concentration of the precursor and the growth time. Thermolysis experiments in oleylamine produced Cu7S4 nanoparticles as a mixture of roxbyite (monoclinic) and anilite (orthorhombic) phases. Pure anilite Cu7S4 nanoparticles were obtained when a solution of precursor in octadecene was injected into hot oleylamine whereas, djurleite Cu1.94S nanoparticles were obtained when a solution of the precursor in oleylamine was injected into hot dodecanethiol. The optical properties of the pure anilite Cu7S4 phase and the djurleite Cu1.94S are consistent with indirect band gap materials. The complex was also used for the preparation of copper sulfide thin films by aerosol assisted chemical vapour deposition (AACVD). Powder X-ray diffraction (p-XRD) patterns of the thin films showed the deposition of a mixture of cubic CuS2 and hexagonal Cu2S phases at all temperatures. Scanning Electron Microscopy (SEM) of copper sulfide films showed spherical crystallites from reaction at 280 °C, cuboids at 320 °C and plate like crystallites between 360 and 400 °C. Transmission Electron Microscopy (TEM) of material scratched from thin films showed nanoplates of copper sulfides with 25–30 nm in width.

ChemInform Abstract: Thermal Decomposition of Nitramines: Dimethylnitramine, Diisopropylnitramine, and N-Nitropiperidine.

Kinetics and activation parameters of the solution thermolysis of nitramines dimethylnitramine, diisopropylnitramine, and N-nitropiperidine were determined over the temperature range 200-300 o C. Each formed the corresponding nitrosamine as the only, or major, condensed-phase product. For dimethylnitramine the products were completely characterized. The observations of a large positive activation volume in the thermolysis of dimethylnitramine and of the slowing of the decomposition reaction with increased solvent viscosity both suggest that the rate-determining step is homolysis, the N-NO 2 bond being the most obvious point for this