Structure and energy study of β-diketonates. XV. Composition of superheated vapors and structure of monomeric molecules of <Emphasis Type="Italic">tris</Emphasis>-hexafluoroacetylacetonates of dysprosium,holmium, erbium,and ytterbium

The molecular structure of tris-hexafluoroacetylacetonates of dysprosium, holmium, erbium, and ytterbium (M(hfa)₃, M = Dy, Ho, Er, Yb) is studied in the framework of synchronous electron diffraction and massspectrometric experiment and also quantum-chemically. For all M(hfa)₃ complexes structural parameters r _a , r _g , and r _h1 are found. It is established that the coordination polyhedron LnO₆ has a configuration of D ₃ symmetry. In experiments on superheated vapors of Dy(hfa)₃, Ho(hfa)₃, and Yb(hfa)₃ the molecular forms present in the vapor at different degrees of superheat are determined.     

Synthesis and reactivity of alkenyl- and alkynyl-substituted β,β-dihalo-and β,β,β-trichloroamines

β,β-Dihalo- and β,β,β-trichloroamines, obtained by Lewis acid-promoted Petasis-type reaction of α,α-dichlorinated and α,α,α-trichlorinated imines or reduction of α,α-dihaloaldimines, were subjected to a reactivity study and turned out to be remarkably stable compounds. In general, only the bases KO^tBu and NaOMe cause a 1,2-dehydrochlorination with formation of unsaturated α-chloroimines or unsaturated α,α-dichloroimines. Hydrolysis of the α-chloroimines with aqueous oxalic acid resulted in the formation of the corresponding unsaturated α-chloroketones. The reaction of simple β,β-dihaloamines with NaOMe and KO^tBu generated 2-haloprop-2-enylmines and 2,2-dimethoxypropylamines.     

Synthesis,Structure, and Hydrophosphorylation of π-Complexes of Hexacarbonyltungsten(0) with Cyclohexanone,Cyclohexanethione, and <Emphasis Type="Italic">N</Emphasis>-Cyclohexylideneaniline

New carbonyl π-complexes of tungsten(0) with cyclohexanone, cyclohexanethione, and N-cyclo-hexylideneaniline were synthesized. Geometric and electronic parameters of the ligands, as well as energy parameters of the complex formation process, were determined by quantum-chemical calculations. Hydrophosphorylation with diethyl phosphonate changed the reactivity of coordinated N-cyclohexylideneaniline, while no analogous effect was observed for cyclohexanone and cyclohexanethione.     

Evaluation of bias,precision, and systematic errors in proficiency testing of Cl<Superscript>−</Superscript> and Cu concentration in water

The proficiency testing exercise was conducted to assess the quality of water testing in several laboratories in India. The 11 participants from all over India gathered at one place and attended the workshop organized at NEERI, Nagpur. The test samples were analyzed for Cl⁻ (Chloride) and Cu (Copper) concentration in water. The objective of the study was to determine bias and precision among participants for the analysis of Cl⁻ and Cu concentration. Statistical analysis indicated that most of the measurement results were overestimating the Cl⁻ concentration and underestimating the Cu concentration. The presence of systematic error identified the need for further improvement in determining the Cu concentration in water by the participants.     

Molecular geometries,electronic properties,and vibrational spectroscopic studies of endohedral metallofullerenes TM@C<Subscript>24</Subscript> and TM@C<Subscript>24</Subscript>H<Subscript>12</Subscript> (TM = Cr,Mo, and W)

Molecular geometries, electronic properties, and vibrational spectroscopies of TM@C₂₄ and TM@C₂₄H₁₂ (TM = Cr, Mo, and W) in their different spin configurations have been systematically investigated with the hybrid DFT-(U)B3PW91 functional. The results show that the TM atoms bind over the pentagon ring inside C₂₄ cage, and they move gradually toward the center of C₂₄ cage along with the increasing atomic radii. The most stable Mo@C₂₄H₁₂ and W@C₂₄H₁₂ are in their spin-triplet states. The analyses of dissociation energy and energy gap reveal that TM@C₂₄ (TM = Cr, Mo, and W) and Cr@C₂₄H₁₂ are not only thermodynamically stable, but also considerably stable kinetically. Meanwhile, natural population analyses tell us that the two cages act as electron acceptors, and the transferred charge from the W atom to C₂₄ cage is the largest in the endohedral metallofullerenes. Additionally, the vibrational frequencies and active infrared intensities may be used as evidence to characterize these unknown species.     

Study of optical,dimensional, and catalytic properties of nanodispersed CdS–Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> powders

Composite powders of the CdS–Na₂SiO₃(SiO₂) type were synthesized. It was found that varying the amount of Na₂SiO₃ introduced in the synthesis stage affects both the texture characteristics of the powders obtained and their optical and photocatalytic properties. All the powders absorb electromagnetic radiation in the visible spectral range (~420–620 nm). It was shown for the example of photodestruction of Nile Blue and Rhodamine C dyes that the powders exhibit good photocatalytic properties under exposure to visible light (λ ≥ 410 nm). One of important advantages of the composites used as photocatalysts is that the transfer of cadmium ions under photoirradiation, characteristic of CdS particles, does not occur.     

Theoretical study of the activation barriers of elementary reactions of hydrogenation of aluminide clusters X@Al<Subscript>12</Subscript> and X@Al<Stack><Subscript>12</Subscript><Superscript>−</Superscript></Stack> with dopants X = Al,Si, and Ge

The transition states and activation barriers h of elementary reactions of addition of the H₂ molecule to aluminide clusters Al₁₃, Al ₁₃ ^? , Al₁₃H ₂ ^? , Al₁₃H ₄ ^? , Si@Al₁₂, Ge@Al₁₂, and LiAl₁₃ were calculated within the B3LYP approximation of the density functional theory using 6–31G* and 6–311+G* basis sets. The barriers h for all diamagnetic clusters were found to be high (～30–40 kcal/mol). The outer-sphere cation Li⁺ decreases while the endohedral electronegative dopants Si and Ge increase the barrier by a few kcal/mol. The hydrogenation barrier of the neural paramagnetic cluster Al₁₃, which has free valence, decreases to ～20 kcal/mol. The addition of a hydrogen atom or a Cl₂ molecule to both paramagnetic and diamagnetic aluminum clusters occurs without a barrier. The first stage of the reaction (addition of H₂ to an Al-Al edge) is in all cases the critical stage of aluminide hydrogenation. The barrier h of this reaction is several times higher than the barriers to migration of hydrogen atoms over the metal cage. The migration of H atoms occurs simultaneously with considerable distortions of the Al₁₃ cage even to the extent that it changes its structural motif. The addition of the H₂ molecule to the Al@TiAl₁₁ cluster containing the peripheral titanium atom occurs with a small barrier, whereas the barrier to elimination of H₂ from the dihydride Al@TiAl₁₁H₂ is reduced to ～15 kcal/mol. Based on the calculations, the conclusion was drawn that the elementary reactions of hydrogenation and dehydrogenation for Ti-doped aluminide clusters should occur considerably faster and under milder conditions than for homonuclear aluminides.     

Synthesis,crystal, and molecular structure of coordination polymers constructed by self-assembly of NiN<Subscript>4</Subscript> cores with 2,2′-iminodibenzoate and nitroprusside ions

Two coordination compounds of compositions [Ni(L¹)(idba)(H₂O)]·1.5 H₂O (1) and [Ni(L²)Fe(CN)₅NO]·C₂H₅OH (2) where L¹ is N, N′-bis(3-aminopropyl)ethylenediamine, L² is 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene, and idba^2? is 2,2′-iminodibenzoate have been synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. Complex 1 crystallizes in the monoclinic space group P2₁/n (No. 14) with a=9.810(2) Å, b=10.230(2) Å, c=25.350(5) Å, V=2543.6(9) Å³, Z=4, and R=0.0727. The nickel atom is six-coordinated by four N atoms of amine and two O atoms of water and idba^2?. The molecular packing of the complex comprises of an infinite one-dimensional layered network in which the molecules in the crystal are held together by a system of hydrogen bonding. Complex 2, however, crystallizes in the space group C2/c (No. 15) of the monoclinic system with a=19.7990(4) Å, b=14.9440(3) Å, c=19.8800(3) Å, V=5115.90(17) Å³, Z=4, and R=0.0540. The Ni ion in compound 2 has a slightly distorted octahedral arrangement of the N₄ donor atoms of primary ligand L² and two N-donor atoms of the secondary nitroprusside ligand. The structure of 2 displays an extended one-dimensional network formed by linear [—Ni—NC—Fe—CN—] units. A cyclic voltammetric study shows that compound 1 undergoes a quasireversible oxidation attributable to Ni²⁺ → Ni³⁺ in the range 300–420 mV vs SCE.     

Thermal and BF<Subscript>3</Subscript>⋅Et<Subscript>2</Subscript>O-catalyzed cleavage of 1-hydrohexafluoroisobutenyloxytrimethylsilane. Perfluoromethacrolein,its isomers,dimers, and homopolymers

During vacuum pyrolysis in a quartz or steel tube, 1-hydrohexafluoroisobutenyloxytrimethylsilane (1) eliminates fluorotrimethylsilane to give perfluoromethacrolein, which was detected by NMR. Similar pyrolysis of silane 1 over KF results in E- and Z--hydrotetrafluoromethacryloyl fluorides. At 20 °C, perfluoromethacrolein undergoes homopolymerisation and/or cyclodimerization to yield 4,4-difluoro-2-pentafluoroisopropenyl-5-trifluoromethyl-4H-1,3-dioxin, which rearranges into E-7,7,7-trifluoro-2,6-bis(trifluoromethyl)-4-oxahepta-2,5-dienoyl fluoride under the action of BF₃Et₂O. The same fluoride is also formed, together with fluorotrimethylsilane, directly from silane 1 under the action of BF₃Et₂O.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1629–1635, August, 2004.Deceased     

Study of the formation temperature of mixed LaREO<Subscript>3</Subscript> (RE ≡ Dy,Ho, Er,Tm, Yb,Lu) and NdGdO<Subscript>3</Subscript> oxides

Mixed LaREO₃ (RE ≡ Dy, Ho, Er, Tm, Yb, Lu) and NdGdO₃ oxides were prepared by thermal decomposition of the corresponding co-precipitated mixed oxalates. The decomposition of La/RE and Nd/Gd oxalates was studied by means of differential thermal analysis and thermogravimetric (DTA-TG) measurements; in particular the last step, consisting of the loss of a CO₂ molecule from the corresponding oxycarbonate, has been thoroughly investigated, as it is particularly interesting for the study of the formation temperature of mixed rare earth oxides. After the release of CO₂, the oxides crystallize in a distorted perovskitic cell or one of the structures typical of rare earth sesquioxides, depending on the cationic size difference and on the average cationic radius. The mixed rare earth oxycarbonate decomposition has been studied in comparison to the decomposition of single rare earth oxycarbonates. A trend of the mixed oxides formation temperature as a function both of the average cationic size and of the cationic sizes difference has been observed and compared to the behaviour of single rare earth oxides.     

Synthesis and reactions of sulfur-substituted α,β-unsaturated δ- and γ-lactones

A new synthetic method for the preparation of sulfur-substituted α,β-unsaturated δ- and γ-lactones has been developed by reaction of the allylic bromides of 5,6-dihydro-2-pyridinones with NaOH in refluxing MeOH or t-BuOH. The substituents at C5 and C6 of these substrates are very important for the success of this reaction. Some synthetic transformations of the α,β-unsaturated δ-lactones have also been carried out.     

Synthesis of carbazoles and 1,2-dihydrocarbazoles by domino ‘twofold Heck/6π-electrocyclization’ reactions of di-, tri- and tetrabromoindoles

Di-, tri- and tetra-alkenylindoles were prepared by palladium(0)-catalyzed Heck cross-coupling reactions of di-, tri- and tetrabromo-N-methylindoles. The reactions were carried out at 90 °C using a novel biaryl monophosphine ligand developed by Buchwald and co-workers. 1,2-Dihydrocarbazoles were formed by a domino ‘twofold Heck/6π-electrocyclization’ when the reaction was carried out at higher temperature. The regioselectivity of the Heck reaction of 2,3,6-tribromo-N-methylindoles was in favour of carbon atoms C-2 and C-3. The 1,2-dihydrocarbazoles were transformed, by Pd/C-catalyzed dehydrogenation, into the corresponding carbazoles in high yield.     

Effect of mercaptopropionic acid as linker on structural,thermal, and optical properties of TiO<Subscript>2</Subscript>–CdSe nanocomposites

In this study, we have studied the stability of TiO₂–CdSe nanocomposites in which the individual moieties are linked using a bifunctional linker (mercaptopropionic acid). Nanoparticles of TiO₂ and CdSe are synthesized by sol–gel and one pot methods. The equimolar amount of the above particles is utilized to prepare nanocomposites with and without linker. These samples are characterized for their structural, thermal, and optical properties using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TG), Fourier transform infra-red spectroscopy (FTIR), and UV–Vis spectroscopy. The average particle size of TiO₂ and CdSe are 16 and 23 nm, respectively. The addition of a bifunctional linker shows remarkable effect on the properties of TiO₂–CdSe nanocomposites.     

Synthesis of Derivatives of ω-Isocyanato-α-methylamino, ω-Ureido-α-methylamino,and N<Superscript>α</Superscript>-Methyl-α, ω-diamino Acids

Summary.  Homochiral N^α-methyl-2,3-diaminopropionic and N^α-methyl-2,4-diaminobutyric acid derivatives 8a,b were obtained via a stereoconservative four-step synthesis starting from hexafluoroacetone protected L-aspartic and L-glutamic acid 2a,b, respectively. Hexafluoroacetone protected ω-isocyanato-α-methylamino acids 4a,b– the key intermediates of the synthesis – are versatile building blocks for amino acid and peptide modification and promising candidates for combinatorial chemistry. Upon reaction with alcohols, compounds 4 give activated N ^ω-urethane protected ω-amino-α-methylamino acid derivatives 5–7; upon reaction with amines, ω-ureido-α-methylamino acid derivatives 10–12 and 3-methylamino-pyrrolidin-2-ones 13 are available. Received November 17, 1999. Accepted November 26, 1999     

A theoretical investigation on the structures and stabilities of C<Subscript>60</Subscript>X<Subscript>18</Subscript> and C<Subscript>70</Subscript>X<Subscript>10</Subscript> (X = H,F, Cl,and Br)

A density functional theory study was performed on fullerene derivatives C₆₀X₁₈ and C₇₀X₁₀ (X = H, F, Cl, and Br). The calculated results show that the lowest energy isomers are IPR-satisfying for C₆₀X₁₈ (X = H, F, Cl, and Br). It is found that the addition patterns of X (X = Cl and Br) are different from those of X (X = H and F) for C₆₀, demonstrating that the stability of fullerene derivatives is partly attributed to the steric repulsion and electronegativity of added atoms. However, the lowest energy isomers are IPR-violating for C₇₀X₁₀ (X = H, F, and Cl), suggesting that many more fullerene derivatives may violate the isolated pentagon rule.     

Structure and donor–acceptor properties of Au<Subscript>12</Subscript>M (M = Hf,Ta, W,Re, and Os) intermetallic clusters

Evolution of three-dimensional configurations, electronic properties, and energies of attachment of donor and acceptor ligands to Au₁₂M (M = Hf, Ta, W, Re, and Os) intermetallic clusters were studied by quantum-chemical methods. The attachment of F to clusters Au₁₂Re and Au₁₂Os and the attachment of H to clusters Au₁₂Ta and Au₁₂Hf are found to give rise to more symmetric structures. The energies of attachment of F to >18-electron Au₁₂M clusters and the energies of attachment of H to <18-electron clusters exceed the energies of attachment of the same atoms to 18-electron cluster Au₁₂W and to cluster Au₁₂.     

Are They Linear,Bent, or Cyclic? Quantum Chemical Investigation of the Heavier Group 14 and Group 15 Homologues of HCN and HNC

The singlet potential‐energy surface (PES) of the system involving the atoms H, X, and E (the (H, X, E) system) in which X=N–Bi and E=C–Pb has been explored at the CCSD(T)/TZVPP and BP86/TZ2P+ levels of theory. The nature of the X? E bonding has been analyzed with charge‐ and energy‐partitioning methods. The calculations show that the linear isomers of the nitrogen systems lin ‐HEN and lin ‐HNE are minima on the singlet PES. The carbon compound lin ‐HCN (HCN=hydrogen cyanide) is 14.9 kcal mol^?1 lower in energy than lin ‐HNC but the heavier group 14 homologues lin ‐HEN (E=Si–Pb) are between 64.8 and 71.5 kcal mol^?1 less stable than the lin ‐HNE isomers. The phosphorous system (H, P, E) exhibits significant differences concerning the geometry and stability of the equilibrium structures compared with the nitrogen system. The linear form lin ‐HEP of the former system is much more stable than lin ‐HPE . The molecule lin ‐HCP is the only minimum on the singlet PES. It is 78.5 kcal mol^?1 lower in energy than lin ‐HPC , which is a second‐order saddle point. The heavier homologues lin ‐HPE , in which E=Si–Pb, are also second‐order saddle points, whereas the bent ‐HPE structures are the global minima on the PES. They are between 10.3 (E=Si) and 36.5 kcal mol^?1 (E=Pb) lower in energy than lin ‐HEP . The bent ‐HPE structures possess rather acute bending angles H‐P‐E between 60.1 (E=Si) and 79.7° (E=Pb). The energy differences between the heavier group 15 isomers lin ‐HEX (X=P–Bi) and the bent structures bent ‐HXE become continuously smaller. The silicon species lin ‐HSiBi is even 3.1 kcal mol^?1 lower in energy than bent ‐HBiSi . The bending angle H‐X‐E becomes more acute when X becomes heavier. The drastic energy differences between the isomers of the system (H, X, E) are explained with three factors that determine the relative stabilities of the energy minima: 1) The different bond strength between the hydrogen bonds H? X and H? E. 2) The electronic excitation energy of the fragment HE from the X ²Π ground state to the ⁴Σ^? excited state, which is required to establish a E≡X triple bond in the molecules lin ‐HEX . 3) The strength of the intrinsic X? E interactions in the molecules. The trends of the geometries and relative energies of the linear, bent, and cyclic isomers are explained with an energy‐decomposition analysis that provides deep insight into the nature of the bonding situation.     

Liquid-phase synthesis and physicochemical properties of xerogels,nanopowders and thin films of the CeO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Low-agglomerated xerogels, ultrafine oxide powders with particle sizes of 12–20 nm, and uniform thin films with particle sizes of 8–14 nm are prepared in the CeO₂–Y₂O₃ system using liquid-phase low-temperature methods, namely via coprecipitation of hydroxides and cocrystallization of salts, sol—gel technology. A comparative characterization of the prepared xerogels and nanopowders is performed using a set of physicochemical analytical methods. A dependence of phase composition, microstructure, and particle size on synthetic parameters is elucidated.     

Synthesis and reactions of thiosemicarbazides,triazoles, and <Emphasis Type="Italic">Schiff</Emphasis> bases as antihypertensive α-blocking agents

Methyl 2-(thiazol-2-ylcarbamoyl)acetate was synthesized and used as starting material. It was treated with hydrazine hydrate to afford the hydrazide, which was reacted with nitromethane and formaldehyde to give the saturated nitropyrimidine. The hydrazide was reacted with phenyl isothiocyanate to afford the thiosemicarbazide, which was cyclized with ethyl bromoacetate, sodium hydroxide, or sulfuric acid to afford N-phenylthiazolidinone, N-phenyltriazole, and thiadiazolyl derivatives. The methyl 2-(thiazol-2-ylcarbamoyl)acetate was coupled with diazonium salts of aniline, 4-chloroaniline, 4-bromoaniline, or 4-aminobenzenesulfonamide to afford the carbamoyl acetates, which were reacted with 2-aminobenzimidazole, 1,2,4,5-tetrachlorophthalic anhydride, and hydrazine hydrate to afford the corresponding thiazolylmalonamide, tetrachloroisoindolylimide, and tri-azole derivatives. Schiff bases and imides are newly synthesized candidates obtained via simple condensation of the hydrazide with aldehydes, 2,3-pyridinedicarboxylic anhydride, or 1,8-naphthalenedicarboxylic anhydride. The pharmacological screening showed that many of these compounds have good antihypertensive α-blocking activity and low toxicity. Correspondence: Abd El-Galil E. Amr, National Research Center, Applied Organic Chemistry, Dokki, Cairo, Egypt.