A calorimetric method has been employed to measure the heat of dilution of atactic poly(methyl methacrylate), v= 26,000, in both toluene and chloroform at 303·15 K. Further measurements in toluene with polymer of v= 41,500 are also are reported. The apparent enthalpy parameter χH and the concentration-independent enthalpy parameter χ1 have been calculated. For chloroform solutions χH is negative and for toluene solutions is positive over the range of average volume fractions examined. The results are discussed in relation to reported experimental data and the recent theories of polymer solutions.
The reduction of nitrobenzene, nitrosobenzene, and azoxybenzene by potassium borohydride is catalysed by hydroxocobalamin. The products of the reaction with nitrobenzene include aniline and azobenzene. The cobalt(I) cobalamin, vitamin B12s, reacts with nitrobenzene, nitrosobenzene, azoxybenzene, and azobenzene but not with phenylhydroxylamine or hydrazobenzene. A mechanism for the reduction is proposed.
Two series of compounds (chelate)PtCl(MMe3)(I) and (chelate)Pt(MMe3)2(II)[chelate =(Ph2PCH2)2; M = Si, Ge, or Sn] have been isolated. For M = Si or Ge both are obtained by the reaction of (chelate)PtCl2 with (Me3M)2Hg. Trimethylstannyl–platinum compounds have been isolated (a) by exchange reactions e.g. Pt–MMe3+ Me3SnH → Pt–SnMe3+ Me3MH (M = Si, Ge) and (b) from the oxidative addition of Me3SnH to (chelate)2Pt. Trimethylstannane adds reversibly to (I) and (II) when M = Sn yielding the octahedral complexes (chelate)Pt(H)(Cl)(SnMe3)2 and (chelate)Pt(H)(SnMe3)3 respectively. Stepwise hydrogen chloride cleavage of Pt–MMe3 groups has been investigated: the products from (chelate)Pt(MMe3)2 are (chelate)PtCl(MMe3) and (chelate)PtCl2. Hydrogenolysis of Pt–MMe3 bonds proceeds readily when M = Si or Ge (1 atmos. H2 and 25°). For the reaction (chelate)Pt(SiMe3)2+ H2→(chelate)PtH(SiMe3) the rate constant at 25° is ca. 5·0 × 10–2 l mol–1 s–1, the reaction being first-order with respect to H2 and (II). At 70° and 1 atoms. H2 the second Me3Si–Pt bond is hydrogenated to Me3SiH and a platinum cluster compound, formulated as (chelate)3Pt4. Equilibrium constants have been derived for the hydrogenolysis of trans-(Et3P)2PtCl(SiMe3). Exchange reactions of the types: Pt–SiMe3+ Me3GeH → Pt–GeMe3+ Me3SiH and Pt–GeMe3+ Me3SnH → Pt–SnMe3+ Me3GeH have been investigated; the position of equilibrium favours R3M–Pt products in the order, Sn Ge > Si. Cleavage of Pt–M bonds by 1,2-dibromoethane is considered to involve an octahedral intermediate. 1H n.m.r., i.r. and mass spectra of the various compounds and reactions are discussed.
Silver carbonate prepared by precipitation from very dilute solutions of AgNO3 and NaHCO3 decomposes at 170 °C to yield Ag2O which is particularly active for the uptake of CO2. In contrast to other oxide adsorbents prepared from carbonates, the high activity is not a consequence of the development of a high surface area. The decomposition of Ag2CO3 leads to only a small increase in surface area, the oxide product having an area less than 1 m2 g–1. The activity in this system is linked instead with the presence of water. Co2 absorption depends upon the continuing availability of water at the reacting interface. Ag2O rapidly loses activity towards CO2 uptake in absorption–regeneration cycles if dry CO2 is employed. There is, in addition, a slow loss of activity during cycling which is independent of the presence of water. The results are discussed by use of a model in which water is considered to be incorporated in the oxide as OH– and in the carbonated solid as OH– and HCO3– ions.
Reaction of [M(dien)(acac)](M = Rh or Ir; diene = 1,5-C8H12 or bicyclo[2,2,1]heptadiene) with Ph3C+BF4– in the presence of an excess of diene affords [M(diene)2]+BF4–, from which diene is readily displaced by acetonitrile to form [M(diene)(CH3CN)2]+BF4–. Reaction of [M(diene)(CH3CN)2]+BF4– with phosphines and bipyridyl are described; complexes of the type [M(diene)L2]+BF4– and [ML4]+BF4– being formed depending on the nucleophilicity of the ligand L. Reaction of [M(1,5-C8H12)2]+BF4– with sodium iodide in acetone affords [M(1,5-C8H12)I]2. Methanol reacts with [Ir(1,5-C8H12)2]+BF4– in the presence of sodium carbonate to give [Ir(1,5-C8H12)OMe]2; a mixture of syn- and anti-isomers.
The kinetic parameters for the reaction between hydroxide and acetylmandelate ions have been determined in water, 20% ethanol–water, and two sets of isodielectric ethanol–water mixtures having dielectric constants (D) 63·77 and 40·98 respectively. One set of isodielectric media (D= 63·77) comprising ethylene glycol–water mixtures has also been used. The components due to the electrostatic and nonelectrostatic factors have been computed by dissecting each parameter. An analysis of the activation energy and the entropy of activation indicates that the presence of water as well as ethanol in optimum proportions in the medium leads to enhanced solvation and hence stabilisation of the activated complex. Solvation of the transition state is greater in ethanol–water than in glycol–water of the same dielectric constant (63·77). The free energy of activation is in general little affected by a change in the medium.
The transference number of the ammonium ion in iodide solutions in liquid ammonia at –40 °C (t+°= 0·3957) is found to be almost independent of the concentration.
The title complex exhibits a temperature-dependent 1H n.m.r. spectrum indicative of proton averaging between –25 and 75 °C. The stable molecular conformation was inferred from the limiting spectrum below –25 °C. The averaging of diene protons was interpreted in terms of a planar rotation of the ligand and the energy barrier calculated from the temperature dependence was about 14 kcal mol–1.
Potassium fluoride is very soluble in glacial acetic acid and the solutions have several unusual properties. These have been studied by cryoscopic, spectroscopic, thermochemical, and electrochemical methods. The collected data have been interpreted in terms of fluoride ion solvation being the most important factor in such solutions. This anion solvation is thought to be by the initial formation of a strong hydrogen bond F ⋯ H–OAc. This bond is the second strongest hydrogen bond known and solvation and i.r. measurements suggest that it has a bond energy of about 120 kJ mol–1(29 kcal mol–1).
Hexacyanoferric(II) acid readily absorbs boron trifluoride (but not boron trichloride) to form the adduct Fe(CNH)4(CN)2,2BF3. The trans-dicyanotetrakis(alkyl isocyanide)iron(II) complexes Fe(CNMe)4(CN)2 and Fe(CNEt)4(CN)2 readily absorb either of these boron trihalides to form adducts Fe(CNR)4(CN)2,2BX3. The i.r. and Mössbauer spectra of these adducts are interpreted in terms of structures Fe(CNR)4(CN,BX3)2 with the Lewis acids linked to the nitrogen atoms of the cyanide group. The spectra are consistent with local octahedral symmetry at iron, indicating the similar π-acid ligand properties of the groups CNR and CNBX3, although in the cyanide stretching region the two i.r. bands appropriate for D4h symmetry are observed.
The electron paramagnetic resonance spectra of copper-doped tetracetatocadmium(II) hexahydrate have been observed. The co-ordination of the copper(II) ion in this molecule is a distorted dodecahedron. The phenomenological spin-Hamiltonian parameters have been determined at both room and liquid nitrogen temperatures. A temperature-dependence of the spin-Hamiltonian parameters has been tentatively ascribed to variation in the 4p orbital admixture in the ground and excited states. The orbital reduction for the cupric ion is found to be large and anisotropic in accord with previous results.
Compounds of the types M(CO)4L2 and Mo(CO)3L2Y have been prepared where M = Cr, Mo, and W, L2=Z-pyridine-2-aldehyde 2′-pyridylhydrazone and Y = PPh3, AsPh3, SbPh3, Ph3PSe and SO2. The E-isomer of the hydrazone can be stabilised in the compounds Mo(CO)4L2, Mo(CO)3L2(PPh3) and Mo(CO)2L2I2. Some results of the halogen oxidations of Mo(CO)4L2 where L2= either E- or Z-hydrazone are presented, compounds such as Mo(CO)3(L2)X2, where L2=Z-hydrazone and X = Br, I, and [L2H2]MoOX5, where X = Cl, Br, having been isolated.
A series of compounds, Fe(isoquinoline)4X2, Fe(pyridine)4X2, and Fe(phenanthroline)2X2, (X = Cl, Br, or l) and Fe(phenanthroline)2(N3)2 were prepared and their magnetic susceptibilities were measured at temperatures in the range 20–300 K. The observed temperature dependence of the magnetic moment was used to evaluate the magnitude of the orbital reduction factor k, the low symmetry distortion parameter, Δ, and the extent of the reduction in spin–orbit coupling. The temperature dependence of the experimental magnetic moments for the isoquinoline and pyridine complexes was found to be in agreement with the theoretically predicted dependence for a complex with D4h symmetry. In all of these compounds, except Fe(isoquinoline)4l2, the results indicate an orbitally nondegenerate (5B2g) ground state. The same successful agreement was not found for all of the lower symmetry phenanthroline complexes. The derived crystal-field parameters are discussed and related to the structural properties of the complexes.
The polarised single-crystal electronic spectra and e.s.r. spectra of dichloroaquo-(2,9-dimethyl-1,10-phenanthroline)copper(II), [Cu(dmp)Cl2(H2O], are reported and are interpreted in C2v effective symmetry. A comparison of the crystal structure with that of [Cu(dien)(HCO2)]HCO2(dien = diethylenetriamine) and a study of the electronic properties provide reasons for preferring a distorted square-pyramidal description of the stereochemistry of [Cu(dmp)Cl2(H2O)] rather than a distorted trigonal-bipyramidal description.
Infrared spectroscopy has been employed to study the cis–trans-equilibria and ΔH values in secondary amides and thioamides. Based on these results, several generalizations have been made regarding the structural factors affecting the configurations. Solvent effects on the cis–trans-equilibria and on the barrier height to rotation in secondary amides have been investigated by i.r. and n.m.r. spectroscopy; the barrier height increases with solvent polarity. Proton-donor or -acceptor solvents significantly affect the cis–trans equilibrium in amides. Solvent effect and temperature effect studies on the n.m.r. and i.r. spectra of 8-, 9- and 13-lactams and their N-methyl derivatives show that in 9-lactam and N-methyl-13-lactam both cis- and trans-isomers are present. Molecular orbital calculations satisfactorily predict relative stabilities of the different configurations of secondary amide derivatives; oxygen protonation of amides is favoured over nitrogen protonation. In the O-protonated amides, the barrier height to rotation is appreciably larger than in the parent amides.
K2Mo4O13 crystallises in the triclinic system, space group P, with Z= 2 in a unit cell of dimensions a= 7·972, b= 8·352, c= 10·994 Å, α= 119·4, β= 62·7, and γ= 109·8°. Its structure, determined by three-dimensional Patterson and Fourier methods and refined by least-squares techniques, contains subunits of eight distorted MoO6 octahedra sharing edges, joined by a common edge to form infinite chains, with adjacent chains having no common oxygen atoms. The potassium ions occupy irregular eight-co-ordinate interchain sites. Rb2Mo4O13 is isomorphous with K2Mo4O13. The tetramolybdate chain structure is compared with those of some other anhydrous polymolybdates(VI), and the similarity of the subunit of eight octahedra to the basic units found in a number of complex molybdates, and to the hepta- and octa-molybdate polyanions, is discussed. The possible existence of polyanions in molybdate melts is considered, and the ability to predict polymolybdate structures from i.r. absorption spectra critically assessed.
The kinetics of oxidation of iodine to iodate by peroxydisulphate ion in aqueous solution has been studied by a spectrophotometric technique at 25·0°C and at ionic strength 0·5M. The rate equation, obtained by a statistical treatment, is (i). Catalysis by copper(II) and silver(I) ions and inhibition by oxygen are observed and the effect, –d[I2]/dt=kA[S2O82–]½[I2]½+kB[S2O82–][I2]½(i) of several added salts is also tested. The mechanism is discussed.
The pseudo-Jahn–Teller formalism is used to devise a partitioning of vibrational force constant, particularly applicable to the study of transition-metal complexes. Parameters derived from this Valence Shell Force Field (VSFF) are readily correlated with the molecular orbital scheme of the complex. The scheme is used to investigate the relationship between π-bonding, the bond–bond interaction constant of the General Quadratic Force Field, and i.r. intensities in metal hexacarbonyls and hexacyanides.
Far-i.r. reflectance spectra of M2IMCl6 complexes where M = Sn, Pt, or Te, have been used to estimate the half-bandwidths of the v3 vibration of the [MCl6]2– ions. The values are substantially lower than those found from absorption spectra of powdered samples but those for the tellurates are greater than those for the platinates and stannates. An earlier interpretation of the mull i.r. spectra is supported by these results.
The complex InL3(L = 3-hydroxy-2-methyl-4-pyronato-anion) has been prepared, and its n.m.r., i.r. and Raman spectra compared with those of the parent ligand. Polarographic reduction of this complex, and of In(trop)3(trop = tropolonato-anion) takes place in successive one-electron steps, as in the case of complexes of indium with bidentate sulphur-donor ligands. One-electron polarographic reduction of In (acac)3(acac = acetylacetonato-anion) and In(oxine)3(oxine = quinolin-8-olato-anion) has also been observed, and may be a general property of complexes of indium(III) with bidentate chelating ligands.
