Tetragonal distortions in the jahn-teller active copper pyridine-N-oxide complexes

The Jahn-Teller (JT) and the E.P.R. parameters of the trigonal, JT-active hexakispyridine-N-oxide complex Cu(C₅H₅NO)₆ ^2- are calculated from the results of extended Hückel molecular orbital calculations on a series of distorted geometries of this complex. These geometries are obtained from a recent, low temperature, neutron diffraction study and compared with a monoclinic, static, modification of the corresponding nitrate complex. For two different distortion models, the JT minimum is obtained for a tetragonally elongated octahedron. The JT parameters are in very reasonable agreement with the experimental ones. The EPR parameters are compared with newly determined experimental values obtained by a re-evaluation, using matrix diagonalization instead of a perturbation treatment, of earlier measurements on Cu(C₅H₅NO)₆(BF₄)₂ at 4·2 K and on Cu(C₅H₅NO)₅DMF(ClO_{4 2} at room temperature. On the basis of these computations, the E.P.R. parameters, and especially the very small isotropic copper hyperfine coupling, can be understood.     

Origin of accidental degeneracy in ligand-field splittings of substituted octahedral complexes

Accidental degeneracy seems to be the rule rather than an exception amongst thed orbital energies of substituted octahedral complexes ofd ¹ configuration. By using symmetry and physical arguments, in conjunction with first-order and second-order degenerate perturbation theory, it is shown that such accidental degeneracies arise in crystal-field theory due to the choice of an inflexible basis set of metal orbitals which neglects the polarisation of metal orbitals by the ligand charges.     

Least-squares analysis. Correlated data in treatment of frequency splittings

It is pointed out that when the splittings between measured frequencies of spectral multiplets are used as data in a least-squares analysis, the data are not statistically independent but are correlated, and the least-squares procedure should be modified accordingly. The ordinary and correct least-squares solutions are compared, and a criterion presented for determining whether the parameters of the two solutions differ significantly. A convention for choosing splittings is given for a common class of splitting problems for which the generalization to the correct least-squares equations is particularly simple and requires little additional computation.     

Exponentially small splittings in Hamiltonian systems

Families of area preserving analytical maps, depending on a small parameter epsilon, are considered, with the case epsilon=0 corresponding to an integrable map. The asymptotic formulas for the splittings of separatrices are derived by the method of analytical continuation of the separatrices to the complex domain. The main terms of the asymptotics are exponentially small with respect to the size of the perturbation. As epsilon tends to zero, the intersection angle of the separatrices can oscillate. The exponent and the oscillatory multiplier of the asymptotic formulas are determined by the position of poles of the homoclinic (heteroclinic) orbit of the limiting flow. Pre-exponential coefficients in the asymptotic formulas contain a multiplier obtained by the numerical study of separatrices of "model" maps in the complex domain.     

A remark on eigenvalue splittings for one-dimensional double-well Hamiltonians

It is shown that the bound obtained by the WKB-method gives a correct lower bound on eigenvalue splittings for one-dimensional double-well Hamiltonians in the semiclassical limit. A modified version of the argument of Kirsch and Simon is employed.     

Shape and chemical shifts of the cobalt K-absorption discontinuity in some complexes

X-ray K-absorption edges of cobalt (II) in its three complexes with para-amino salicylic acid have been recorded. The coordination symmetries of the three complexes have been established on the basis of the shapes of the absorption discontinuities. The coordination symmetries of the three complexes have been established on the basis of the shapes of the absorption discontinuities. The chemical shifts have been determined, and these shifts are employed to determine the effective nuclear charge on the central atom due to its chemical combination and the percentage covalency of the metal ligand bonds. The results are discussed.     

光诱导下系列钴配合物的表面电子行为对比研究

通过水热方法合成了6种Co(Ⅱ/Ⅲ)配合物Co(H2O)6·H2btec(1);{[Co2(HCOO)6]·CH3OH}n(2);([Co(4,4'-bipy)2(H2O)4]·suc·4H2O}n(3);Co(NA)2(H2O)4(4);[Co(mal)(4,4'-bipy)H2O]n(5);[Co(HCOO)4Co(H2O)4]n(6)(H4btec=均苯四甲酸,H2suc=丁二酸,HNA=娴酸,H2mal=丙二酸,bipy=联吡啶)},测试了配合物的UV-Vis吸收光游和表面光电压光谱(SPS),并通过X-ray单晶衍射确定了配合物的结构.它们的表面光电压光谱在300～800 nm范围内均表现出正的光伏响应,并将其与UV-Vis吸收光谱进行了分析和对比,发现SPS中表面光伏响应带与UV-Vis吸收光谱的吸收峰具有良好的对应关系.通过对比6种配合物的SPS可以看出,中心金属离子的价态、配位模式及配位微环境均对SPS响应带的位置和形状有一定影响.     

DFT calculations as a tool to analyse quadrupole splittings of spin crossover Fe(II) complexes

Density functional methods have been applied to calculate the quadrupole splitting of a series of iron(II) spin crossover complexes. Experimental and calculated values are in reasonable agreement. In one case spin–orbit coupling is necessary to explain the very small quadrupole splitting value of 0.77 mm/s at 293 K for a high-spin isomer.     

The optical activity of cobalt(III) chelate diamine complexes

The optical activity of the tris-diamine complexes of cobalt (III) in the visible region is accounted for quantitatively by a coulombic correlation between the components of the electric hexadecapole moment of the ¹ A ₁→¹ T ₁ d-electron transition of the cobalt(III) ion in the [CoN₆] chromophore and a transient electric dipole induced in each ligand group. The correlated electric dipole of the ligand group forms a non-zero scalar product with a component of the magnetic dipole moment of the cobalt(III) ion d-electron transition in the first order employing either an O or a D ₃ effective chromophoric symmetry. The calculated first-order rotational strengths account largely for the observed optical activity due to the chiral puckered conformation of the chelate rings and for the axial single-crystal circular dichroism of a cobalt(III) tris-diamine complex in a uniaxial crystal. The second-order rotational strengths improve the agreement and accommodate the observed circular dichroism of randomly-oriented cobalt(III) tris-diamine complexes. The increase in the dipole strength of the ¹ A ₁→¹ T ₁ transition in a tris-diamine complex, relative to [Co(NH₃)₆]³⁺, is explained by the model in the first order.     

Macroscopic tunnel splittings in superconducting phase qubits

Prototype Josephson-junction based qubit coherence times are too short for quantum computing. Recent experiments probing superconducting phase qubits have revealed previously unseen fine splittings in the transition energy spectra. These splittings have been attributed to new microscopic degrees of freedom (microresonators), a previously unknown source of decoherence. We show that macroscopic resonant tunneling in the extremely asymmetric double-well potential of the phase qubit can have observational consequences that are strikingly similar to the observed data.     

Singlet-triplet splittings in free and self-trapped excitons

We discuss the available experimental data for the singlet-triplet splitting of free and self-trapped excitons in alkali halides. These data are analysed quantitatively using the pseudopotential method of Bartram, Stoneham and Gash. The predictions confirm the trend emerging from the observed data, namely that the splittings are systematically lower for the self-trapped systems. This difference comes principally from the spread of the self-trapped hole onto two ions, and would not be expected, for example, if the hole were localised on a single site.     

Orientational Relaxation in Ferroelectrics of Tetragonal Symmetry

The energy absorption caused by rotation of the spontaneous and induced polarization vectors in external longitudinal alternating-sign stress field is calculated for the barium titanate ferroelectric of tetragonal symmetry. The acoustic absorption coefficient, the internal friction, and the E effect together with their frequency and orientational dependences are derived in terms of elastic and piezoelastic constants, components of the electrostriction tensor, and rotational dissipation coefficients. The given dissipation type can dominate in ferroelectric magnets with strong coupling of their elastic, electrical, and magnetic subsystems.