Fujiko Iwasaki

Synthesis and structure of a hexacoordinate carbon compound

In an exploration of six coordination and hypervalence in carbon compounds, steric constraints have been employed to bring four ether O atoms in close proximity to an allenic carbon atom. The dimethylated dication 2 is confirmed to have hexacoordinate carbon by experimental charge density analysis and DFT calculations and is arguably hypervalent.

Magnetic properties of pyrimidine-bridged copper(II) complexes

Abstract The magnetic measurements of [PM2·Cu(NO3)]n (PM = pyrimidine) showed ferromagnetic interaction between the Cu(II) spins with J/kB = +0.89 K. On the other hand, those of PM2·Cu(NO3)2·(H2O)2 and [PM·CU(NO3)2·(H2]n showed para- and antiferromagnetic behaviors respectively. The magnetic properties of pyrimidine-bridged Cu(hfac)2 and Cu(ClO4)2 complexes are also reported.

Synthesis, Reactions, and Electronic Properties of 16 π-Electron Octaisobutyltetraphenylporphyrin

The reaction of the doubly oxidized beta-octaisobutyl-meso-tetraphenylporphyrin (OiBTPP, 4), which has a 16 pi-electronic structure at the porphyrin core, with a variety of metal reagents was investigated. The reaction of 4 with SnCl(2) followed by ethanolysis afforded an 18 pi-electron tin complex, (OiBTPP)Sn(OEt)(2) (5), in a redox manner. No reactions were observed using zerovalent metals (Zn, Cu, and Pd). However, the reaction of 16pi [(OiBTPP)Li](+)[BF(4)](-) (6), which was easily derived from 4, with Zn, Cu, and Pd(2)(dba)(3) gave the corresponding 18pi metalloporphyrins (OiBTPP)M (7, M = Zn(EtOH); 8, M = Cu; and 9, M = Pd). One-electron oxidation of the copper complex 8 by AgSbF(6) afforded a 17 pi-electron cation radical complex, [(OiBTPP)Cu](*+)[SbF(6)](-) (10). The UV-visible and electron spin resonance spectra of 10 were quite similar to those of previously reported beta-octaethyl-meso-tetraphenylporphyrin (OETPP) derivatives, [(OETPP)Cu](*+)X(-) (X = ClO(4), I). In contrast to the reaction of 6 with Zn to give the 18pi complex 7, the reaction of 4 with divalent ZnCl(2) enabled us to isolate a new 16pi porphyrin-zinc(II) complex, [(OiBTPP)Zn(Cl)](+)[ZnCl(3)](-) (11), in 92% yield. The solid-state structures of 5 and 7-11 were unambiguously determined by single-crystal X-ray crystallography. The porphyrin cores of 10 (17pi) and 11 (16pi) are much more distorted than those of the 18pi derivatives 5 and 7-9. Furthermore, the bond distances of 10 and 11 clearly showed the presence of bond alternation in contrast to aromatic 18pi species 8 and 7, respectively. Nucleus-independent chemical shift calculations of 4 and some metalated porphyrins indicated that the highly distorted 16pi porphyrins are essentially nonaromatic, with only weak antiaromaticity. Magnetic circular dichroism studies in conjunction with ZINDO/S calculations assisted in identifying the electronic transitions of the UV-vis spectra of key porphyrins. Electrochemical and thin-layer UV-vis spectroelectrochemical experiments on 4 (16pi) and 11 (16pi) indicated that both compounds can be electroreduced to give the 18pi species, with the 16pi/18pi transition being reversible in the case of [(OiBTPP)Zn(Cl)](+)[ZnCl(3)](-) (11).

Preparation of 2,5-disilylated thiophene derivatives and their conversion to 2,5-dihalo derivatives

2,5-Disilylated thiophenes were prepared and readily oxidized with m-chloroperbenzoic acid (m-CPBA) to give the corresponding 1,1-dioxides. The thiophene dioxide was converted to 2,5-dihalogenothiophene dioxides with halogenating agents

Dipyrimidine-copper(II) dinitrate complexes showing magnetic interactions.

Crystals of Cu(II)(NO(3))(2)(pm)(3) (1), and two crystalline forms of Cu(II)(NO(3))(2)(H(2)O)(2)(pm)(2), (2) and (3), showed ferromagnetic, antiferromagnetic and paramagnetic interactions at extremely low temperatures, respectively. Crystal structure analyses revealed that the complexes were catena-dinitrato[mu-pyrimidine-kappaN(1):kappaN(3)]-(pyrimidine-N(1))copper(II), [Cu(NO(3))(2)(pm)(2)](n), catena-diaquadinitrato[mu-pyrimidine-kappaN(1):kappaN(3)]copper(II), [Cu(NO(3))(2)(H(2)O)(2)(pm)](n), and diaquadinitratodipyrimidinecopper(II), Cu(NO(3))(2)(H(2)O)(2)(pm)(2) for (1), (2) and (3), respectively. In (1) the Cu atom is coordinated by the two nitrates and N atoms of the non-bridging pyrimidine and bridging pyrimidine to form a one-dimensional coordination polymer. The complex is a five-coordinated square pyramid and can be regarded as a pseudo-seven-coordinated complex, since other short non-bonding Cu.O contacts are observed. In the crystals of (2) the pyrimidine bridges the Cu atoms to form a one-dimensional coordination chain. On the other hand, complex (3) is not a coordination polymer. It is important to form a coordination polymer for the appearance of the magnetic interactions. Types of coordination of the bridging organic moieties should also play an important role in magnetic properties. Magnetic measurements of (1) and (2) show that they are good examples of uniform S = 1/2 ferro- and antiferromagnetic Heisenberg chains with exchange parameters 2J/kB = +1.8 and -36 K, respectively.

Ferromagnetism of Organic Radical Crystals of Tempo Derivatives

Abstract Several TEMPO-based radicals were found to be bulk ferromagnets with T C of 0.2–0.4 K, as indicated by the measurements of ac magnetic susceptibilities and magnetization curves. On the basis of the X-ray crystal structure analysis, a possible mechanism of ferromagnetic interactions between neighboring N-O sites is proposed, in which the methyl or methylene groups play a role of ferromagnetic exchange couplers. New organic ferromagnets, 4-(p-methylthiobenzylideneamino)-TEMPO, 4-(benzylamino)-TEMPO, and 4-(hydroxyimino)-TEMPO as well as several metamagnets are reported.

An organic metamagnet: 4-(2-naphtylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl

Abstract Magnetic measurements on the organic radical crystal of 4-(2-naphtylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl exhibited a Neel transition at about 0.12 K ( T N ) and a metamagnetic transition below T N (the coercive field was around 180 Oe at 40 mK). X-ray crystallographic analysis revealed that the molecules were arranged to give an almost columnar structure with the nearest intermolecular O…O distance of 5.70 A. The magnetic property was analyzed on the basis of the crystal structure.

Magnetic Interaction Via β-Hydrogen Atoms in Tempo Derivatives

Abstract Theoretical studies of the ferromagnetic property of phenyl-CH=N-TEMPO were carried out. The effective exchange integrals (J ab) were calculated for the nearest neighbour molecules in the crystal and the ferromagnetic interaction was revealed. To study the role of the hydrogen atoms, modified pair models were considered. It was concluded that the bridged β-hydrogen atoms dominantly contribute to the ferromagnetic interaction in the phenyl-CH=N-TEMPO crystal.

New organic ferromagnets: 4-arylmethyleneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (aryl = phenyl, 4-biphenylyl, 4-chlorophenyl, and 4-phenoxyphenyl)

Abstract The title radicals were found to be bulk ferromagnets, as indicated by the sharp divergence of the susceptibility. Their transition temperatures were found in the range of 0.2–0.4 K. The X-ray crystal structure analysis of the phenyl, biphenylyl, and chlorophenyl derivatives at room temperature revealed that the crystal consisted of an almost two-dimensional network of the N-O sites. In the case of aryl = 2-naphthyl, metamagnetic behavior was observed below about 0.3 K.

Intermolecular ferromagnetic interaction in the crystal of a diphenyl nitroxide derivative. The role of spin-polarized hydrogen atoms located near a neighboring N–O site

Abstract The crystal of 9,9-dipropyl-9,10-dihydroacridin-10-yloxyl exhibited a positive Weiss constant (+0.77 K) ascribable to a three-dimensional network of ferromagnetic interactions. The orbital orthogonality between the antibonding N–O π∗ and H 1s orbitals was found in a nearly isosceles triangle geometry of neighboring H atoms and the N–O site. The following spin polarization scheme is proposed: N(↑)–C(↓)Co(↑)–Cm(↓)–Hm(↑)⋯ ⋅ O (↑)–N, where o- and m-positions are defined with respect to the N–O group.