Wasuke Mori

Comparison between spin restricted and unrestricted post-Hartree—Fock calculations of effective exchange integrals in Ising and Heisenberg models

Abstract Spin-restricted and unrestricted post-Hartree—Fock calculations were carried out for clusters of triplet methylene and nitroxide radicals. The UHF-based methods such as UMP and QCISD followed by approximate spin projection provide reasonable energy differences between the high-and low-spin states of these species. They are close to the corresponding values from spin-restricted multi-reference (MR) approaches such as CASSCF and second-order (SO) CI. Implications of SOCI and MRSDCI results are discussed in relation to the size inconsistency erros involved in ab initio calculations of weak interaction energies, such as the effective exchange integrals in Ising and Heisenberg models.

Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid

Abstract Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 μ B/O2. These results are interpreted by the dimer model of S=½ with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the inter-dimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.

A theoretical explanation of the organic ferromagnetism in the β-phase of para-nitrophenyl nitronyl nitroxide

Abstract Molecular orbital calculations have been carried out for clusters of para-nitrophenyl nitronyl nitroxide ( p -NPNN) extracted from the experimental crystal structure of its β-phase. Three-dimensional effective exchange integrals ( J ab ) are found to be possitive (ferromagnetic). The ferromagnetic transition temperature is estimated by a generalized Langevin—Weiss model combined with the calculated J ab , being consistent with the observed value. A theoretical explanation is presented for the long-range ferromagnetic ordering in the p -NPNN crystal. Implications of the calculated results are also discussed in relation to a theoretical possibility of organic ferromagnetism of other substituted phenyl nitronyl nitroxides.

No-overlap and orientation principle for ferromagnetic interactions between nitroxide groups

Abstract Approximately spin-projected UMP4(2) and UCC SD(T) computations show that ferromagnetic intermolecular interactions are feasible for T-shape and rhombus conformations in parallel interplane orientations for nitroxide pairs because of no-overlap between π ∗ -type SOMOs (no kinetic exchange) and non-zero potential exchange via SOMO-SOMO through-space contact. On the other hand, antiferromagnetic kinetic exchange interactions via SOMO-SOMO overlap are predominant for rectangular conformations. The no-overlap and orientation principle proposed previously is a useful guide for the theoretical understanding of ferromagnetic exchange interactions between nitroxide groups. Implications of the calculated results are discussed in relation to the discovery of ferromagnetic interactions in the crystals of adamantane dinitroxide, TEMPO derivatives and MOTMP.

A MO-theoretical calculation of the antiferromagnetism in the γ-phase of p-nitrophenyl nitronyl nitroxide

Abstract Semi-empirical and ab initio molecular orbital (MO) calculations have been carried out for clusters of p -nitrophenyl nitronyl nitroxide ( p -NPNN) extracted from the experimental crystal structure of its γ-phase. It is found that the intraplane exchange interactions ( J ab ) are ferromagnetic, whereas the interplane one is antiferromagnetic. The antiferromagnetic transition temperature ( T N ) is estimated by a generalized Langevin-Weiss-Neel (GLWN) model combined with the calculated J ab values by the MO methods. The Neel temperature ( T N ) by the mean-field GLWN model is of the order of the experimental value, although the former is much larger than the latter because of the low dimensionality of the γ-phase. A systematic theoretical explanation is presented for the magnetic long-range orderings in the β- and γ-phase crystals of p -NPNN.

Electronic structures of poly-cations and -anions of C60. Possible mechanisms of organic ferromagnetism

Abstract The ORHF and CAS CI calculations by MNDO and PM3 parametrizations are carried out for poly-cation and -anion states of C 60 in order to elucidate bond alternations and changes of ground spin multiplicities by doping of electrons or holes. The singlet state is calculated to be more stable than the triplet state for the dianion of C 60 in accordance with a recent experiment. A three-band model is constructed of the t 1u orbitals of C 60 in order to examine the itinerant ferro- and antiferro-magnetism. Implications of the calculated results are discussed in relation to the organic ferromagnetism observed in the C 60 ·TDAE complex.

The monomeric and dimeric copper(II) complexes containing imidazole and dipeptides

Abstract The mixed ligand copper(II) complexes with imidazole and glycylglycine or glycyl-β-alanine were prepared in neutral and basic solutions. The copper(II) complexes obtained in neutral solutions were mononuclear complexes, while those in basic solutions were binuclear complexes bridged by imidazolate. In the cases of the binuclear complexes, it was found that the two copper(II) ions are antiferromagnetically coupled with -J values of 19–17 cm −1 . It has also been disclosed on the basis of visible and ESR spectral measurements that these dimeric structures are maintained in the concentration of 1.3 × 10 −2 to 1.2 × 10 −3 M /Cu.

Monomeric and dimeric copper(II) complexes composed of some terdentate schiff bases and oxalate, oxamate, azide, thiocyanate or cyanate ions

Abstract Monomeric and dimeric copper(II) complexes containing the Schiff bases derived from 2-pyridinecarbaldehyde and histamine (2-Pcaue5fbHist), 2-(2-aminoethyl)pyridine (2-Pcaue5fb2-Aep), or β-alanine (2-Pcaue5fbβ-Ala), and oxalate (ox), oxamate (om), azide, thiocyanate, or cyanate ions have been prepared and characterized based on their electronic, infrared and electron spin resonance spectra, and magnetic susceptibilities. The structure of the monomeric copper(II) complex, [Cu(2-Pcaue5fbHist)(N3)2] has been determined by the X-ray diffraction method. The crystal of [Cu(2-Pcaue5fbHist)(N3)2] is triclinic, with a = 10.262(8), b = 9.177(6), c = 7.688(5) A, α = 104.42(4), β = 94.09(4), γ = 92.64(4)°, Z = 2, and space group P 1 . The five-coordinate geometry around copper(II) ion is intermediate between trigonal-bipyramid and square-pyramid. The half-field absorption in the ΔMs = 2 region of powdered X-band ESR spectra was scarcely observed for [Cu(2-Pcaue5fb2-Aep)(N3)2], [Cu(2-Pcaue5fb2-Aep)(NCS)2], [Cu(2-Pcaue5fb2-Aep)(NCO)2] and [Cu(2-Pcaue5fbHist(N3)2]. The compounds [Cu2(2-Pcaue5fbHist)2(N3)3]Cl·2H2O and [Cu2(2-Pcaue5fbHist)2(N3)2](ClO4)2 which are considered to have a dimeric structure exhibited the half-field absorption in the same region. However, an exchange interaction was hardly observed down to 4.2 °K in the magnetic susceptibility measurement for [Cu2(2-Pcaue5fbHist)2(N3)3](Cl·2H2O. The susceptibility of an oxalate-bridged copper(II) complex, [Cu2(2-Pcaue5fbHist)2(ox)](ClO4)2, showed an antiferromagnetic interaction (J = −21.5 cm−1) and the X-band ESR spectrum for the powdered sample showed a very weak absorption for the triplet state of such a dimer in the ΔMs = 2 region.

Theoretical Studies of Magnetic Orderings in the β- and γ-Phases of P-NPNN and Related Nitroxides

Abstract Intermolecular spin alignment rules are derived on the basis of ab initio results obtained for clusters of triplet carbenes, free radicals, etc. Interrelationships between several theoretical models are also clarified. The APUHF calculations are performed for radical pairs in the β and γ-phase crystals of para-nitrophenyl nitronyl nitroxide. The magnetic transition temperatures are calculated by the use of Langevin-Weiss type mean-field theory combined with the calculated effective exchange integrals. The origins of ferromagnetic interactions in both the phases are discussed in relation to the intermolecular spin alignment rules.

Structure of the active site of hemocyanin. Cobalt(II)-substituted squid hemocyanin

Abstract Cobalt(II)-substituted squid ( Sepioteuthis lessoniana ) hemocyanin was prepared by dialyzing the apohemocyanin against pH 8.0 Tris-HCl buffer containing 5 m M Co(II) ion. The electronic absorption, circular dichroism and magnetic circular dichroism spectra of Co(II)-substituted hemocyanins containing one mol of Co(II) and 2.6 mol of Co(II) per mol of protein were studied comparatively to characterize the coordination geometry and the ligating groups around the binuclear copper sites in native squid hemocyanin. The two copper sites at one active site in squid deoxyhemocyanin may differ from each other in coordination geometry, and may consist of a tetrahedral-like copper site and a tetragonal-like copper site. Three histidine imidazoles are expected to be coordinated around each copper(II). The structure of the active site of squid and horseshoe crab hemocyanins was comparatively discussed on the basis of spectral data of the respective cobalt(II)-substituted hemocyanins of the two phyla.