Akira Fuyuhiro

Direct two-step spin-crossover through [HS–HS]⋯[LS–LS] at the plateau in dinuclear diiron(II) complex [{Fe(NCBH3)(4phpy)}2(μ-bpypz)2]

The variable temperature magnetic susceptibility, X-ray crystallography, and IR and Raman spectra of a new dinuclear complex [{Fe(II)(NCBH(3))(4-phpy)}(2) mu-bpypz)(2)] demonstrated the first two-step spin-crossover associated with a 1 : 1 mixture of high-spin pair [HS-HS] and low-spin pair [LS-LS] at the plateau.

Magnetic behavior and Mössbauer spectra of spin-crossover pyrazolate bridged dinuclear diiron(II) complexes: X-ray structures of high-spin and low-spin [{Fe(NCBH3)(py)}2(μ-bpypz)2]

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear [(FeII(NCS)(py))2(mu-bpypz)2] and the corresponding cyanotrihydroborato-kappaN complexes are described together with the X-ray crystal analysis of the latter in both the high-spin and low-spin states as well as the variable temperature magnetic susceptibility and/or Mossbauer spectra demonstrating the spin-crossover which exhibits an one-step process, but not a two-step one characteristic of the known bpym bridged dinuclear complexes.

Dinuclear single-molecule magnets with porphyrin–phthalocyanine mixed triple-decker ligand systems giving SAP and SP coordination polyhedra

Two terbium ions in a triple-decker complex (Pc)Tb(Pc)Tb(T(p-OMe)PP) (Pc = phthalocyaninato, T(p-OMe)PP = tetra-p-methoxyphenylporphyrinato) have shown sharply different magnetic behaviours depending on symmetry of the coordination polyhedron. The fast quantum tunnelling relaxation process in a square-prismatic site has been revealed to be hindered by magnetic-dipolar coupling between the f-electronic systems.

Cyclic Hexamer with a Cubic Cavity: Crystal Structure of [{Rh(6-Purinethione Ribosido)(Cp*)}6](CF3SO3)6

The stereoselective formation of a pseudo-S6 hexamer resulted from the self-assembling reaction between [Rh(Cp*)(H2 O)3 ]2+ and 6-purinethione riboside (see left structure; Cp*=C5 Me5 ). The schematic representation (right) shows the direction of the coordination to the S6 and N(7) donor atoms. C (clockwise) and A (anticlockwise) indicate the chirality of each unit complex.

Construction of a novel topological frustrated system: a frustrated metal cluster in a helical space.

A novel topologically frustrated pentanuclear cluster helicate [{Cu(II)(μ-L)(3)}(2)Cu(II) (3)(μ(3)-OH)](3+) (L(-)=3,5-bis(2-pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky-Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high-field/multi-frequency (HF/MF)-ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu(5)-cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system.

Electronic-spin and columnar crystal structures of stable 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl radical

Abstract 1,3-Diazaphenalenyl is a typical example of the isoelectronic mode of heteroatomic modification for phenalenyl. Recently, we have designed and isolated 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl (6) as the first example of stable azaphenalenyl. For further elucidation of the electronic and solid-state structures of 6, 15N atoms incorporated 1,3-diazaphenalenyl 7 was designed. New nitration reaction by K15NO3 of 2,7-di-tert-butylnaphthalene has enabled us to accomplish effective introduction of 15N atoms and synthesis of 7. The spin structure of 1,3-(15N2)diazaphenalenyl 7 was unequivocally determined by the ratio of the hfcc for 14N and 15N (A14N/A15N=0.292/0.409=0.714), which was equal to the ratio of each gyromagnetic ratio (γ14N/γ15N=0.713). Under an air atmosphere, the radical 7 decomposes slowly, but most of it remains unchanged for weeks. By comparing the spin densities of 7 with those of parent phenalenyl radical 2, it appears that the spin densities of the 1- and 3-positions decrease appreciably, while those of the 4-, 6-, 7-, and 9-positions increase. The radical 7 forms the syn-dimer with gable structure in the crystal, and the dimer stacks in a columnar structure motif.

Synthesis and crystal structures of cobalt(III) complexes containing pyridine-2-selenolato and its oxidation products

Abstract A series of mixed cobalt(III) complexes [Co(pySe)3−n(NN)n]n+ [pySe=pyridine-2-selenolato (1−); NN=1,2-ethanediamine (en) and 2,2′-bipyridine (bpy); n=0, 1 and 2] was prepared. The geometrical preference and trans influence of pySe are fairly different from those of pyridine-2-thiolate. These selenolato complexes were oxidized by peracetic acid to give the corresponding pyridine-2-seleninato (pySeO2) and pyridine-2-selenonato (pySeO3) complexes. The crystal structures of the pySeO2 and pySeO3 complexes revealed that the coordination mode change from an original N,Se-four-membered to the N,O-five-membered chelate ring occurred during oxidation and intramolecular hydrogen bonds between the non-coordinated oxygen of pySeO2 or pySeO3 and the amine protons of en stabilize the N,O-coordination mode.

Hexaazaphenalene derivatives: one-pot synthesis, hydrogen-bonded chiral helix, and fluorescence properties.

Symmetric hexaazaphenalenes (R = phenyl and tert-butyl) have been synthesized by one-pot condensations of corresponding amidine hydrochlorides with tricyanomethanide. The hexaazaphenalenes are linked with each other by a N-H···N hydrogen-bonding interaction in the crystalline states. Interestingly, a planar and achiral tert-butylated derivative was crystallized in a chiral space group with assembly of one-handed helical hydrogen-bonded chains. Hexaazaphenalenyl anions were isolated as air- and water-stable tetraethyl ammonium salts.

Cobalt(III) promoted ligand fusion reactions of thiobarbituric acid and 4,6-diamino-2-thiouracil (or 4-amino-2-thiouracil)

Abstract Novel cobalt(III) complexes containing three kinds of assembled ligands, L1L2=dapymt–tbba(2-), tbba–dapymt(1-) and apymt–tbba(1-) (H3tbba=thiobarbituric acid; Hdapymt=4,6-diamino-2-thiouracil; Hapymt=4-amino-2-thiouracil), were prepared from the mixed ligand systems, where L2 indicates the coordinated ligand to the Co(III) ion and L1 is a pendant ligand bonded to L2. These complexes were characterized by UV–Vis absorption spectra and NMR spectroscopy. The crystal structures of [Co(Htbba)(en)2]ClO4·2H2O (2) (en=ethane-1,2-diamine), [Co{dapymt–tbba(2-)}(en)2]ClO4·3H2O (3) and [Co{apymt–tbba(1-)}(en)2](ClO4)Cl·3H2O (5′) revealed that coordination occurs through the S(1) and N(1) donors of tbba and the latter complexes 3 and 5′ have an assembled ligand; a new bond is formed between the C(5) atom of tbba and the S(2) atom of dapymt or apymt. An intramolecular hydrogen bond between O(1) of tbba and NH of en was found in all crystals. An interesting intermolecular π–π stacking interaction was found in 5′.

Synthesis, X-ray structures and NIR chiroptical properties of a series of dinuclear lanthanide(III) complexes [Ln2{μ-(S- or RS-pba)}4(HBpz3)2]; novel configurational chirality due to non-bonding Ln⋯O interactions

Two series of mononuclear [LnIII(S- or RS-pba)(HBpz3)2] (Ln = Tm, Er, Ho ) and dinuclear [Ln2{μ-(S- or RS-pba)}4(HBpz3−)2] (Ln = Yb, Ho, Gd, Dy, Nd ) complexes (pba = RS- and/or S-2-phenyl butyrate, HBpz3 = hydrotris(pyrazol-1-yl)borate) were prepared and their X-ray structures and NIR chiroptical properties investigated. Synthesis with a molar ratio 1 ∶ 2 ∶ 1 of Ln ∶ KHBpz3 ∶ pba results in the formation of either mono- or dinuclear complexes, depending on the Ln(III) ionic radii: mononuclear complexes from Yb(III) to Ho(III) and dinuclear ones from Dy(III) to Nd(III). Only the dinuclear complexes for all of the Ln(III) studied were formed with a molar ratio 1 ∶ 1 ∶ 2 of Ln ∶ KHBpz3 ∶ pba. X-Ray structural analysis confirmed dinuclear structures with CH⋯π interactions and linear B⋯Ln⋯Ln⋯B arrangements for the Ln(μ-RS-pba)4Ln(HBpz3)2 (Yb , Ho , Dy, Gd and Nd) complexes and a skew bent arrangement of B⋯Ln⋯Ln⋯B leading to configurational chirality in the Dy(μ-S-pba)4Dy(HBpz3)2 complex. Comparison of NIR chiroptical spectra in the 4f–4f transitions with those of the corresponding Cr–Ln complexes, [(acac)2Cr(ox)Ln(HBpz3)2] suggests that the 4f–4f CD intensities arise from configurational chirality, probably due to the skew bent B⋯Ln⋯Ln⋯B disposition.