A model for the plane to plane variations in catalytic activity seen during nitric oxide decomposition on platinum

Previous work has shown that the reactivity of platinum for nitric oxide decomposition varies significantly with the geometry of the exposed surface of the platinum. Here, the available data are compared to the predictions of a model, which is based on conservation of orbital symmetry and a simplified picture of the band structure of the surface. The model predicts that the (100) face of platinum should be more active than either the (111) or the (110). The (410) should be more active still. These predictions agree with recent experiment. The model makes several other predictions which need to be tested experimentally. These results suggest that symmetry conservation methods, similar to the ones developed by Woodward and Hoffmann for organic reactions, could yield many valuable insights into the relative activity of various catalyst structures.     

Preparation and properties of a soluble polymeric aquo ion of molybdenum(V)

An orange/brown ionic and polymeric Mo(V) ion (Mo to Na ratio 2.3:1), soluble in H₂O to give stable solutions at pH～6, with UV visible spectrum λ_max 318nm, ?(per Mo) 330OM^?1 cm^?1, has been prepared and partially characterised. Various properties are described, including the conversion to the well established Mo(V) aquo dimer, MO₂O₄²⁺, on adjustment of [H⁺] to 0.17–0.50 M, I=0.50 M (H/LiClO₄). First-order rate constants, k_obs(25°C), determined by conventional spectrophotometry give a good fit to the empirical rate law,     

Mixed-ligand lanthanide complexes—II : Complexes of β-diketone and heterocyclic amine. Synthesis and spectroscopic studies

The imidazole adducts of tris(heptafluorooctanedionato)lanthanide(III), [Ln(fod)₃ · im] have been synthesized and characterized. The electronic spectra in the visible region have been analysed and spectral parameters ($\text{β}$, b^1/2, δ and T_λ) and oscillator strengths calculated and discussed. These complexes are more covalent than the analogous [Ln(fod)₃ · pz] complexes, pz = pyrazole. The covalency is more in solution than in the solid state. The experimental and the calculated oscillator strengths are in good agreement. The band shape for the hypersensitive transition in the solid and solution spectra is compared with the other known systems and discussed. The difference in the band shape of the hypersensitive transition in the solid and in solution is indicative of solvent molecule coordination. The Mössbauer spectrum of [Eu(fod)₃ · im] is reported. The dipolar shift produced in the NMR spectrum of [Eu(fod)₃ · im] is upfield in comparison to the signal of the organic moiety itself as well as in its diamagnetic analogues. The coordinated base does not dissociate even in DMSO solution. Due to their poor solubility these compounds are not suitable for use as induced NMR shift reagents.     

Synthesis and spectral studies of mixed copper(II) dipeptide complexes of imidazole and related nitrogen donors

Eight mixed copper(II) complexes of the type [Cu(II)(D)(HL)], where D = anion of glycylglycine, glycyl-L-tyrosine or glycyl-L-phenylalanine, and HL = imidazole, 1-methylimidazole, 2-methylimidazole or benzimidazole have been prepared and characterised. The visible and EPR spectral studies of these complexes indicate that they are monomeric having five coordinate square pyramidal geometry (possibly distorted) about Cu(II). The dipeptide behaves as terdentate ligand in these complexes with amino, ionised amide nitrogen and carboxylate oxygen donor atoms approximately tetragonally disposed about Cu(II). The magnetic and bonding parameters obtained by detailed EPR spectral analysis coupled with electronic absorption spectral data suggest that imidazole, 1-methylimidazole, 2-methylimidazole or benzimidazole occupies the fourth position in the tetragonal plane and water molecule occupies an axial position about Cu(II) in solid state and in solution.     

Preparation of niobium and tantalum organoimido complexes from reactions of the pentahalides with amines: The crystal and molecular structure of bis(t-butylamine)bis(t-butylimido)bis(μ-ethoxy)tetrachloroditantalum

MCl₅ (M = Nb, Ta) reacts with 2 equivalents of Me₃SiNHCMe₃ to give [M(NCMe₃)Cl₃(NH₂CMe₃)] from which [M(NCMe₃)Cl₃(PMe₃)₂] is obtained on addition of PMe₃. One equivalent of Me₃SiNHCMe₃ reacts with MCl₅ in the presence of 3 equivalents of PMe₃ to give [M(NCMe₃)Cl₃(PMe₃)₂] and PMe₃HCl. MCl₅ reacts with excess RNH₂ (R = CMe₃, CHMe₂, CH₂Me) to give [M(NR)(NHR)Cl₂(NH₂R)] and 3 equivalents of RNH₃Cl. One equivalent of alcohol replaces the amido ligand in [M(NCMe₃)(NHCMe₃)Cl₂(NH₂CMe₃)] to give [M(NCMe₃)(OR)Cl₂(NH₂CMe₃)]₂ (M = Nb, R = OCMe₃; M = Ta, R = OEt). The structure of [Ta(NCMe₃)(μ-OEt)Cl₂(NH₂CMe₃)]₂ was determined by single-crystal X-ray diffraction methods. Crystals are triclinic, space group P$\text{1}$ with a = 9.900(5), b = 10. 161(17), c = 9.017(6) Å and α = 103.91(8), β = 97.77(4), γ = 64.40(7)°. The structure was solved by Patterson and Fourier methods and refined to an R value of 0.062 for 1319 observed data. The TaN_imido and TaN_amino bond lengths are 1.70(2) Å and 2.28(2) Å, respectively; the bridging TaO bond lengths are 2.01(2) Å and 2.32(2) Å, the longer one lying trans to the imido function.     

Electrochemical synthesis of copper(II) carboxylates

A number of copper(II) carboxylates have been synthesized by anodic oxidation of copper. The reactions were found to proceed with current efficiencies of 0.95 to 1.00 eq./Faraday. Reaction products have been characterized by infrared spectral studies and analysis of copper.     

Crystalline thiophene. II: a comprehensive study of stable and metastable phases by means of heat capacity,thermally stimulated currents and raman spectroscopy measurements

This calorimetric study of crystalline thiophene between 77 and 250 K reveals the existence of four phase transitions at 174.50, 170.49, 136.8 and 111.26 K, respectively. The transition II-III (170.49 K) is easily avoided during cooling, leading to metastable phases, which, in turn, exhibit their own phase transitions.These findings explain previously confused observations. The existence of stable and metastable phases was confirmed by thermally stimulated current measurements. Intermolecular Raman spectra were observed between 10 and 300 K and assigned to the observed phases. Some predictions are made concerning the low-temperature behaviour of thiophene. Tentative rules are proposed to number metastable phases relative to stable ones.     

Linkage isomerism of the oximato group: The characterization of some mono- and binuclear square planar nickel(II) complexes of vicinal oxime-imine ligands

The reactions of the Schiff-base N,N-ethylenebis-(isonitrosoacetylacetoneimine), (H₂L), with Ni(II) acetate led to the formation of the yellow-orange complex LNi (I) in water and the red complex LNi (II) in ethanol. Both oximato groups in I are coordinated to the metal through the oximino-oxygen whereas in II one group is similarly coordinated while the other is coordinated through the oximino-nitrogen. Complex I was converted to complex II by boiling in chloroform and the conversion was reversed by reacting complex II with either piperidine or ethylenediamine. H₂L neutralized by ammonia reacted with Ni(II) chloride (1:1) and the complex formed was characterized as the red square planar bis-(4-iminopentane-2,3-dione 3-oximato)Ni(II);(III). This trans complex reacted with piperidine (1:4) to produce its cis configuration (IV). Complex III reacted with ethylenediamine (2:1) and 1,3-diaminopropane (1:1) to produce complexes II and V respectively of the identical structure. Attempted similar reaction (1:1) with either 1,4-diaminobutane or 1,5-diaminopentane led to the formation of the binuclear complexes VI and VII in which two molecules of complex III are linked together by -(CH₂)₄- and -(CH₂)₅-Moieties respectively. The suggested structures of the square planar Ni(II) complexes are based on analytical, spectral and magnetic moment evidence.     

The formation of flouride complexes of titanium(IV)

The complex formation equilibria between titanium(IV) and fluoride ions have been studied at 25°C in 3 M(Na)Cl ionic medium by measuring, with an ion selective electrode for F^?, the free HF concentration in acid Ti(IV) solutions. The [H⁺] was kept within 0.25 and I M where the predominant form of uncomplexed metal is the dihydroxotitanium(IV) ion, Ti(OH)²⁺₂. The potentiometric data have been explained by assuming Ti(OH)₂F⁺, TiF₄ and HTiF^?₆, with equilibrium constants given in Table 3. Within the accuracy of the present e.m.f. study, ±0.2 mV, no evidence for intermediate complexes bearing 2, 3 and 5 F^? was found.From a special series of measurements, carried out by replacing a large part of the Cl^? with ClO^?₄, it is concluded that no appreciable amount of Ti(IV)Cl complexes is formed at the 3 M level employed as ionic medium.     

Synthesis and characterization of new complexes between sodium monoalkyl benzeneazophosphonates and dibenzo-18-crown-6

A new series of crystalline complexes of sodium monoethyl ester and sodium monobutyl ester of [α-(4-benzeneazoanilino)-N-benzyl]phosphonic acid,