Anomalous magnetic properties of tetraphenylporphinato Co(II) complex in the solid state

The α,β,γ,δ-tetraphenylporphinatocobalt(II) complex is found to exist in two distinct, but interconvertible, polycrystalline forms. The one with a tetragonal crystal symmetry (species B) gives the EPR spectrum which has been attributed to the low-spin electronic configuration of Co(II) ion in an axial crystal field. The other form (species A) having a triclinic crystal symmetry shows no easily detectable EPR signal even at liquid helium temperature.Magnetic susceptibility and magnetization meaurements demonstrated that the complex is paramagnetic in both forms, but the species (A) is characterized by ferromagnetic exchange coupling, while the species (B) behaves as a normal paramagnet.The experimental susceptibility versus 1/T curve can be reproduced quite well by using the Ising method. The g values thus obtained (g_| = 5.2,g_⊥ = 0) can not be explained by a low-spin electronic configuration, but are consistent with a high-spin ground state. Assigning a high-spin state to the species (A), the first such case in Co(II) porphine complexes, can not only explain the absence of EPR signal, but is also supported by the results of X-ray structural analyses.     

Structure and properties of poly-2,5-distyrylpyrazine

Poly-2,5-distyrylpyrazine (poly-DSP) was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and measurements of dynamic viscoelastic and electrical properties. From DTA and TGA studies it was confirmed that poly-DSP melts at 321°C and depolymerizes rapidly to the monomer at temperatures between 335°C and 345°C in helium. The polymer is affected by oxygen above 200°C. The E′ value from dynamic viscoelasticity measurements on amorphous film is 2 × 10¹¹ dyne/cm² at room temperature. It decrease abruptly in the temperature range 140–150°C; but the net decrease of E′ within this temperature range is relatively small. The electrical properties of amorphous poly-DSP are characterized by a small temperature dependence of the dielectric constant between room temperature and 100°C. The dielectric loss tangent was observed to be small, and the dc conductivity was extremely small. It is concluded that rotation of the phenyl branches in the polymer occurs above ?30°C and the glass transition occurs at about 150°C. These properties are discussed in some detail in relation to the polymer structure.     

Thermodynamics of polymerization. Part IV. Free energy changes of binary copolymerization systems

Using a statistical thermodynamic method we discuss the general shape of a free energy change versus composition curve for a binary copolymerization system. This simple theoretical approach gives reasonable agreement with the experimental results.     

Claisen rearrangements—VII : Novel reactions of the coumarin,tomentin

The structure of tomentin has been confirmed as 5-hydroxy-6,7-dimethoxycoumarin (2), the derived 3,3-dimethylallyl ether giving a para-Claisen rearrangement product. Relief of strain in the corresponding 1,1-dimethylallyl ether has been found to result in a novel regiospecific ortho-Claisen rearrangement occurring on silica at room temperature. The structure 18 of the stable ortho-dienone formed has been confirmed by conversion of the corresponding dehydrodienone (15), obtained from the rearrangement of tomentin 1,1-dimethylpropargyl ether, to alloxanthoxyletin (25).     

Effect of solvents and substituents on the distribution coefficients of alkyl-substituted β-diketones and their copper chelates

The distribution ratios of alkyl-substituted β-diketone derivatives and their copper(II) chelates between water and a number of common water-immiscible solvents were investigated, in order to establish the effect of substituents and solvents on the extraction. A plot of the logarithms of the distribution coefficients of the β-diketones and of their copper chelates as a function of the number of carbon atoms in the molecule, gave a linear relationship. The relationship between the distribution coefficients of the copper chelate (P_CuA2) and those of β-diketone (P_HA) was shown to be log P_CuA2=2 log P_HA +const.