Identification of adsorption forms by ir spectroscopy for formaldehyde and formic acid on K3PMo12O40

Interaction of HCOOH and H₂CO with K₃PMo₁₂O₄₀ has been studied by IR spectroscopy. HCOOH adsorbed mainly in molecular form due to hydrogen bonds with surface oxygen ions. Two forms of adsorbed H₂CO were observed depending on the pressure. At low pressures it adsorbed on Br?nsted acid sites with the formation of hydrogen-bonded complexes. Dioxymethylene groups and a small amount of polyoxymethylene groups were formed at higher pressures. In contrast to oxide catalysts, formates were formed only in small amounts in the absence of oxygen. This can be explained by the formation of new surface adsorption sites Mo ions-due to a partial reduction of K₃PMo₁₂O₄₀ during its interaction with HCOOH and H₂CO.     

Thermal behaviour of two new salts of malonic acid: Cu(C3H2O4)·4H2O and Cu(NH4)2(C3H2O4)2

Two new salts of malonic acid have been prepared: the copper(II) malonate tetrahydrate and the copper(II)-ammonium double malonate. Their study by thermal analysis (TG and DTA) leads to the following results:Cu(C₃H₂O₄)·4H₂O: the dehydration is rather complex and it is only under careful conditions that an intermediate hydrate Cu(C₃H₂O₄)·3H₂O could be traced. At about 170°C the dehydration is not ended (the salt holds yet about 0.15H₂O) and the anhydrous salt occurs only at about 240°C. It decomposes immediately leading to residues the composition of which depends upon the surrounding atmosphere; the part played by the gas given off is discussed.Cu(NH₄)₂(C₃H₂O₄)₂: this salt melts and decomposes simultaneously at about 190°C. During the decomposition the copper nitride Cu₃N forms as intermediate compound (as well as copper metal). Concerning the final residues of the decomposition the results and the conclusions are the same as the ones of the previous case.     

PPh3/I2/HCOOH: An efficient CO source for the synthesis of phthalimides

A straightforward and general method has been developed for the synthesis of phthalimide derivatives from 2-iodobenzamides and PPh₃/I₂/HCOOH in the presence of a catalytic amount of Pd(OAc)₂. The reaction results demonstrate that PPh₃/I₂/HCOOH is a facile, efficient and safe CO source. The whole process is carried out in toluene at 80?°C and furnishes the desired products in good to excellent yields.     

Acyl-platinum(II) and -palladium(II) complexes derived from 2-hydroxybenzaldehyde derivatives. X-ray structure of [Pt(OC6H4CO) (P(p-CH3C6H4)3)2]

Platinum(II) and palladium(II) complexes containing chelating acyl ligands have been synthesized from salicylaldehyde, 2-hydroxynaphthaldehyde and 2-hydroxy-3-methoxybenzaldehyde. The platinum(II) complexes [Pt(acyl)L₂], acyl  OC₆H₄CO, OC₁₀H₆CO, O(m-CH₃OC₆H₃CO), L  tertiary phosphine, 1/2 diphenylphosphinoethane, can be isolated with both monodentate and chelating diphosphines, whereas for palladium only the compounds with chelating phosphines are readily obtainable. The reactions of [Pt(OC₆H₄CO)L₂] with HCl afford trans-[PtCl(OHC₆H₄CO)L₂], L  monodentate tertiary phosphine and cis-[PtCl(OHC₆H₄CO)L₂], L2  1,2-bis-diphenylphosphinoethane, in which the metal—carbon bond remains intact. The structure of [Pt(OC₆H₄CO)-(P(p-CH₃C₆H₄)₃)₂] has been determined by X-ray diffraction methods and found to have the expected square planar structure. Some relevant bond lengths and angles are: PtP; 2.271(4) and 2.348(5) Å; PtC; 1.96(2) Å and PtO; 2.07(1) Å; PPtP  101°, CPtO  82°.     

The reaction of trihydrobistriphenylphosphine iridium IrH3(PPh3)2 with diazonium salts

The reaction of IrH₃(PPh₃)₂ with p-substituted aryldiazonium salts gives the compounds [IrH₂(NHNC₆H₄R)(PPh₃)₂]⁺BF₄^- at low temperature (-10°C) and the o-metalated complexes [I$\text{rH(NHN}$C₆H₃R)(PPh₃)₂]⁺BF₄^- (R  F, OCH₃) at 40–50°C. The reactions of the o-metalated complexes with CO, PPh₃, NaI and HCl have been studied.     

Thermal decomposition of (η)-cyclopentadienyl)- tricarbonyl(σ-phenylethynyl)molybdenum and the molecular structure of a molybdenum binuclear complex with a bridging 1,4-diphenylbutadiyne ligand [η- C5H5)(CO)2Mo]2(μ-1,2-η-C6H5CCCCC6H5)

Thermolysis of C₅H₅(CO)₃MoCCC₆H₅ (I) in octane at 110–115°C results in the formation of [(η-C₅H₅)(CO)₂Mo]₂(μ-1,2-η-C₆H₅CCCCC₆H₅) (II). The structure of II was determined by X-ray analysis. The reaction scheme is discussed.     

Rehybridization of C2H2 chemisorbed on W(110)

Chemisorption of C₂H₂ on W(110) has been studied by high resolution electron energy low spectroscopy. At low coverages the molecule dissociates, while at thigh coverage C₂H₂ is di-σ adsorbed with a CC bond order of 0.25 and a CH bond angle of. ≈ 103°.     

The preparation of NbH5(Me2PCH2CH2Me2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4)

MMe₅(dmpe) (M = Nb or Ta, dmpe = Me₂PCH₂CH₂PMe₂) reacts with H₂ (500 atm) and dmpe in THF at 60°C to give MH₅(dmpe)_2? NbH₅(dmpe)₂ readily reacts with two mol of CO or ethylene (L) to give NbHL₂(dmpe)₂. The exchange of the hydride ligand with the ethylene protons in NbH(C₂H₄)₂(dmpe)₂ is not rapid on the ¹H NMR time scale (60 MHz) at 95°C.     

Synthesis and x-ray crystallographic structural determination of the acetylene complex (η5−C5H5)2W2(CO)4(C2H2)

Reaction of photogenerated (η⁵?C₅H₅)₂W₂(CO)₄ with acetylene at 25°C yields a complex of the formula (η⁵-C₅H₅)₂W₂(CO)₄(C₂H₂). The crystal structure of the complex shows it to have a tetrahedrane-like W₂C₂ core. The C—C bond distance of the C₂H₂ unit is 1.33 Å which is close to that of ethylene, considerably longer than the 1.20 Å for acetylenes. The W—W distance is 2.987 Å which is ～0.25 Å shorter than the W—W distance in (η⁵-C₅H₅)₂W₂(CO)₆ but longer than that expected for (η⁵-C₅H₅)₂W₂(CO)₄. By analogy to the parent (η⁵-C₅H₅)₂M₂(CO)₆ species, the near-UV absorption in (η⁵-C₅H₅)₂M₂(CO)₄(C₂H₂) is assigned to a σ_b → σ^* transition. Owing to the shorter M—M bond in the C₂H₂ adducts, the σ_b → σ^* absorption is at higher energy than in the (η⁵-C₅H₅)₂M₂(CO)₆ complexes.     

Syntheses and structural studies on two cycloruthenapentadienyl complexes: [(CO)3RuC4(CH2OH)4]Ru(CO)3·H2O and [(CO)3RuC4(CH2CH2OH)2(C2H5)2]Ru(CO)3

Syntheses and single-crystal X-ray diffraction studies have been completed on two cycloruthenapentadienyl (CO)₆Ru₂L₂ derivatives, with L = CH₂OHC = CCH₂OH and C₂H₅C=CCH₂CH₂OH respectively. Crystal data are as follows: for [(CO)₃RuC₄(CH₂OH)₄]Ru(CO)₃·H₂O, P2₁/c, a 13.72(1), b 9.501(4), c 14.86(1) Å, β 101.10(6)°, R_w = 0.052 for 1911 reflections; for [(CO)₃RuC₄(CH₂CH₂OH)₂(C₂H₅)₂]Ru(CO)₃, P2₁/c, a 9.191(3), b 16.732(4), c 14.903(3) Å, β 113.61(4)°, R_w = 0.042 for 2865 reflections. Both compounds are built up from binuclear units, each unit being regarded as a Ru(CO)₃ fragment π-bonded to a cycloruthenapentadienyl ring. The molecular parameters are compared with those of known cyclometallapentadienyl complexes of transition metals. The presence of a semi-bridging CO group is discussed.     

Conductivity and thermogravimetric studies of HTi2NbO7 · 2H2O and CsTi2NbO7

A detailed study was performed of the interrelationships of the lattice parameters, ionic conductivity, and infrared spectrum of HTi₂NbO₇ · 2H₂O as a function of dehydration. We have shown that the oxide layers in this ion-exchange compound are interespaced with water layers 2-molecules thick, providing a rare example of a bilayer hydrate. Bulk proton transport occurs through these layers, with a conductivity of (8 ± 4) × 10^?6 ohm^?1cm^?1 at 20°C. Upon heating to 55°C, 0.5 H₂O per formula was gradually lost, but the conductivity was essentially retained. Upon further heating to 62°C another 0.5 H₂O was rapidly lost, resulting in a conductivity drop of a factor of 10. Further water was gradually lost until HTi₂NbO₇ was reached at 220°C. The X-ray evidence revealed no discrete, fixed-composition hydrate phases, indicating a single isostructural phase from HTi₂NbO₇ · 2H₂O to HTi₂NbO₇, with a single continuously variable interlayer spacing. The bulk conductivity of CsTi₂NbO₇ was less than 10^?8 ohm^?1cm^?1.     

A study of the reaction Na2SO4·10H2O→Na2SO4+10H2O in the temperature range 0 to 25°C

Thermogravimetry was used to obtain data on the isothermal rate of dehydration and hydration of the reaction Na₂SO₄·10H₂O→Na₂SO₄+10H₂O in the temperature range 10 to 25°C. The thermodynamic functions, ΔH, ΔG and ΔS were calculated and compared with data in the literature. The dissociation pressures of Na₂SO₄·10H₂O at temperatures in the range 0 to 25°C were measured in a volumetric dissociation apparatus. The results obtained were compared with those using thermogravimetry and the accuracy of the two techniques was assessed.     

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

Conformational analysis in diastereoisomer equilibria of square-pyramidal [C5H5(CO)2Mo pyridine-2-imine]PF6 complexes

Synthesis and characterization of sonic new square-pyramidal pyridine-2-imine complexes [C₅,H₅,(CO)₂,MoNC₅,H₄,CX=NCH(R₁)(R₂)]PF₆ with X = CH₃, C₆H₅ and chiral amine, 1-phenyl-isobutylamine and amino acid methyl ester H₂NCH(COOCH₃)(R) with (R) = (CH₂C₆H₅) and (C₂H₅) have been reported. In combination with Mo chirality (R) and (S), mixtures of two diastereoisomeric pairs of enantiomers with racemic amine and amino acids were obtained which were separated by fractional cystallization. The diastereoisomers differ in the chemical shift of most of their ¹H NMR signals and interconvert on heating in acetone-d₆ at 80°C for 80 hr and 40°C for 200 hr. On the basis of three conformational determining effects (i) C-H or C-alkyl of the asymmetric centre eclipses the ligand plane, (ii) MC₅H₅/C₆H₅ attraction and (iii) MC₅H₅/alkyl repulsion in order of decreasing significance, the chemical shifts of the C₅H₅ signals, their differences as well as the diastereoisomer ratio at equilibrium for all the complexes has been rationalised.     

The reaction of Ru3(CO)12 and Os3(CO)12 with PH2Ph; the x-ray crystal structures of HRu3(CO)10(PHPh) and H2Ru3(CO)9(PPh)

Twelve new trinuclear complexes containing terminal PH₂Ph, edge-bridging PHPh and/or capping PPh ligands have been isolated from the reaction of M₃(CO)₁₂ (M = Ru or Os) with PH₂Ph in refluxing solvents. HRu₃(CO)₁₀(PHPh) (IIIa) crystallises in the monoclinic space group P2₁/c with a = 8.761(3), b = 11.402(4), c = 22.041(7) Å,β = 98.89(2)°, and Z = 4. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by blocked-cascade least squares to R = 0.027 for 3676 unique observed intensities. The X-ray analysis shows that one edge of the Ru₃ triangle is bridged by a hydride and the PHPh ligand, and that the phosphorus-bound hydrogen atom lies over the metal triangle and the phenyl group away from it. This provides an explanation for the ready formation of the capped species H₂Ru₃(CO)₉(PPh) (Va) on pyrolysis of the edge-bridged complex as opposed to the previously reported conversion of HOs₃(CO)₁₀(NHPh) to an orthometallated derivative under similar conditions. An X-ray analysis of H₂Ru₃(CO)₉-(PPh) (Va) confirms the capped geometry. the complex crystallises in the monoclinic space group P2₁/n with a = 9.323(4), b = 15.110(6), c = 45.267(15) Å,β = 91.84(3)°, and Z = 12. the structure was solved and refined using the same techniques as described previously. The final residual R is 0.061 for 4839 reflections. Some reactions of Va show that the phosphorous cap is difficult to displace and stabilises the molecule with respect to decomposition to non-cluster species.     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

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.     

Oxidative addition of hydrogen in the “reduced” Mo/Al2O3 catalysts

An X-ray photoelectron spectroscopy study of Mo/Al₂O₃ catalysts prepared via [Mo^V ₂O₄(C₂O₄)₂(H₂O)₂]^2- complexes showed that after heating the catalysts with hydrogen in the spectrometer chamber, the position of the Mo3d line shifted to higher values of binding energy. This shift is interpreted as oxidative addition of hydrogen to the surface Mo species. A similar phenomenon was observed for a CO treated catalyst. A temperature-programmed desorption study has shown that hydrogen is strongly bounded to Mo and can only be removed from the catalysts at temperatures as high as 500°C. This revised version was published online in June 2006 with corrections to the Cover Date.     

The preparation,characterisation and some reactions of Os3(CO)9(μ2-H)(μ3-SR) (R  Me or Et)

The complex Os₃(CO)₉(μ₂-H)₂(μ₃-S) reacts with KOH/MeOH to produce the anionic complex [Os₃(CO)₉(μ₂-H)(μ₃-S)^?, which reacts in turn with RO⁺ (R = Me, Et) to form HOs₃(CO)₉SR. This complex is especially reactive towards ligands L (L = C₂H₄, CO, PR₃ and MeCN) to generate complexes of the type Os₃(CO)₉(μ₂-H)(μ₂-SR)(L). At 125°C the complex Os₃(CO)₉(μ₂-H)(μ₂-SR)(C₂H₄) (in the presence of C₂H₄) ejects RH and CO to form Os₃(CO)₈(μ₂-H)?(μ₃-S)(CHCH₂). The structures of the new complexes are described and the probable reaction pathways discussed.     

A study of the preparation of solid solutions in the system α-Fe2O3Al2O3

In order to elucidate the formation of precipitated iron catalysts for ammonia synthesis, the formation of solid solutions between α-Fe₂O₃ and Al₂O₃ was studied in the temperature range 500–950°C. The Al₂O₃ content in the solid solutions was found to be below 15 mole%. At temperatures of 800–950°C, solid solutions are formed at an appropriate rate. Specimens with relatively large specific surface areas are obtained at 800°C.