Motomi Katada

Synthesis, structures, and electronic properties of [8Fe-7S] cluster complexes modeling the nitrogenase P-cluster.

High-yield synthesis of the iron-sulfur cluster [{N(SiMe(3))(2)}{SC(NMe(2))(2)}Fe(4)S(3)](2)(mu(6)-S) {mu-N(SiMe(3))(2)}(2) (1), which reproduces the [8Fe-7S] core structure of the nitrogenase P(N)-cluster, has been achieved via two pathways: (1) Fe{N(SiMe(3))(2)}(2) + HSTip (Tip = 2,4,6-(i)Pr(3)C(6)H(2)) + tetramethylthiourea (SC(NMe(2))(2)) + elemental sulfur (S(8)); and (2) Fe(3){N(SiMe(3))(2)}(2)(mu-STip)(4) (2) + HSTip + SC(NMe(2))(2) + S(8). The thiourea and terminal amide ligands of 1 were found to be replaceable by thiolate ligands upon treatment with thiolate anions and thiols at -40 degrees C, respectively, and a series of [8Fe-7S] clusters bearing two to four thiolate ligands have been synthesized and their structures were determined by X-ray analysis. The structures of these model [8Fe-7S] clusters all closely resemble that of the reduced form of P-cluster (P(N)) having 8Fe(II) centers, while their 6Fe(II)-2Fe(III) oxidation states correspond to the oxidized form of P-cluster (P(OX)). The cyclic voltammograms of the [8Fe-7S] clusters reveal two quasi-reversible one-electron reduction processes, leading to the 8Fe(II) state that is the same as the P(N)-cluster, and the synthetic models demonstrate the redox behavior between the two major oxidation states of the native P-cluster. Replacement of the SC(NMe(2))(2) ligands in 1 with thiolate anions led to more negative reduction potentials, while a slight positive shift occurred upon replacement of the terminal amide ligands with thiolates. The clusters 1, (NEt(4))(2)[{N(SiMe(3))(2)}(SC(6)H(4)-4-Me)Fe(4)S(3)](2)(mu(6)-S){mu-N(SiMe(3))(2)}(2) (3a), and [(SBtp){SC(NMe(2))(2)}Fe(4)S(3)](2)(mu(6)-S){mu-N(SiMe(3))(2)}(2) (5; Btp = 2,6-(SiMe(3))(2)C(6)H(3)) are EPR silent at 4-100 K, and their temperature-dependent magnetic moments indicate a singlet ground state with antiferromagnetic couplings among the iron centers. The (57)Fe Mössbauer spectra of these clusters are consistent with the 6Fe(II)-2Fe(III) oxidation state, each exhibiting two doublets with an intensity ratio of ca. 1:3, which are assignable to Fe(III) and Fe(II), respectively. Comparison of the quadrupole splittings for 1, 3a, and 5 has led to the conclusion that two Fe(III) sites of the clusters are the peripheral iron atoms.

Structure of glasses in the system SnPbPFO

A quantitative structural model of oxyfluoride glasses in the system SnPbPFO is proposed on the basis of IR, XPS, NMR and Mossbauer spectroscopy. The main structure of the glass is that phosphorus tetrahedra [PO4−xFx] (x = 0, 1, 2) including PF bonds connected to each other by intervening Sn(Pb) or SnO(PbO). This gives rise to the network of the OPOSn linkage. Besides, there are Sn(Pb)F bonds in this structure. The existence of covalent and less polar PF bonds results in the molecular nature in the structure of the glasses. This enables one to introduce organic molecules into the glasses.

Preparation, characterization and electric conductivity of CT adducts of crystalline poly(1,1′-ferrocenylene) with electron acceptors

Abstract Crystalline poly(1,1′-ferrocenylene) forms adducts with various electron acceptors such as iodine, 2,2′-(2,5-cyclohexadiene-1,4-diylidene)bis-propanedinitrile (TCNQ), and tetracyanoethylene (TCNE). Magnetic susceptibilities, color, and Mossbauer spectra of the adducts indicate partial oxidation of Fe(II) in poly(1,1′-ferrocenylene) to Fe(III). The adducts of crystalline poly(1,1′-ferrocenylene) with the electron acceptors show much higher electric conductivities (by a factor of 102–106) than the previously reported adducts of amorphous poly(1,1′-ferrocenylene). Among the adducts studied, a TCNQ adducts shows the highest electric conductivity; σ = 4.1 X 10−2 S cm−1 for a 1:0.64 adduct of the polymer with TCNQ at 295 K. An X-ray diffraction pattern of the crystalline poly(1,1′-ferrocenylene) shows peaks at 11.8°, 19.2°, 23.5°, and 25.2°, whereas the TCNQ adducts gives rise to new sharp peaks at quite different positions. In contrast to a high crystallinity of the TCNQ adduct, the adducts of other electron acceptors are amorphous as revealed by their X-ray diffraction patterns which show no peaks. Both the peaks assigned to Fe(II) and Fe(III) found in the Mossbauer spectrum of the TCNQ adduct become broad on raising the temperature from 78 K to 310 K, suggesting the occurrence of a rapid intervalence electron exchange between Fe(II) and Fe(III) on the Mossbauer time scale at higher temperatures.

Structural investigation of SnO–B2O3 glasses by solid-state NMR and X-ray photoelectron spectroscopy

Abstract Local structure of the SnO–B2O3 glasses was investigated using several spectroscopic techniques. 11B MAS-NMR spectra suggested that BO4 tetrahedral units maximized at around the composition with 50 mol% SnO. The BO4 units were still present at compositions with high SnO content (67 mol% SnO), suggesting that SnO acted not only as a network modifier but also as a network former. O1s photoelectron spectra revealed that the addition of small amounts of SnO formed non-bridging oxygens (NBO) (B–O⋯Sn) and the amounts of NBO increased with an increase in SnO content. 119Sn Mossbauer spectra indicated that Sn was present only as Sn(II) in the glasses. The structure of the SnO–B2O3 glasses was compared with that of conventional alkali borate glasses and lead borate glasses. The thermal and viscous properties of these glasses were discussed on the basis of the glass structure revealed in the present study.

New Lanthanoid Metallofullerenes and their HPLC Elution Behavior

Abstract HPLC behaviors of metallofullerenes of 14 lanthanoid elements were studied by use of radiotracers, and the species of some of the metallofullerenes were identified by mass spectroscopy. From the HPLC elution behaviors, 14 lanthanoid elements forming metallofullerenes were found to be grouped into two, namely, Sm, Eu, Tm and Yb as one group and the rest of the elements as another. Some new species of metallofullerenes like La@C74, and M@Cn (M=Eu, Tm, Yb; n=74, 82, 84, 88, 90, 92, 94) have been identified. The observed retention times of metallofullerenes are discussed in terms of the number of carbon atoms of the cage and from consideration of the electron donor and acceptor relation between the fullerene species and the HPLC stationary phases.

Face-to-face fixed ferrocenes. Synthesis and properties of 2,10-diferrocenyl- and 2,5,7,10-tetraferrocenyl-1,6-methano[10]annulenes

Abstract 2,10-Diferrocenyl- and 2,5,7,10-tetraferrocenyl-1,6-methano[10]annulenes, in which the ferrocene nuclei are held proximate and cofacial, have been synthesized by using the palladium-catalyzed cross-coupling reaction of ferrocenylzinc chloride with 2,10-dibromo- and 2,5,7,10-tetrabromo-1,6-methano[10]annulenes. The structures of the face-to-face fixed ferrocene systems were determined by X-ray analysis. Cyclic voltammetric measurements of diferrocenyl- and tetraferrocenyl-1,6-methano[10]annulenes show two and three redox waves, respectively, reflecting the through-space and through-bond interactions of the ferrocene nuclei.

Structural Studies in Lithium Insertion into SnO ­ B 2 O 3 Glasses and Their Applications for All-Solid-State Batteries

The local structure of electrochemically lithium-inserted SnO-B 2 O 3 glasses was investigated by several spectroscopic techniques to clarify a lithium insertion mechanism into the glasses. 50SnO.50B 2 O 3 (mol %) glass showed two plateaus around 1.5 and 0.5 V (vs. Li + /Li) on the lithium insertion process and exhibited a high capacity of 1240 mAh g -1 in the case of using a conventional liquid electrolyte. On the first plateau (1.5 V vs. Li + /Li), metallic Sn with small domains was formed and the coordination environment at boron in the glass network was not changed. On the second plateau (0.5 V vs. Li + /Li), the borate glass network was rearranged by a transformation from tetrahedral BO 4 to trianglar BO3 boron units, which provides an additional free space compensating an increase in volume followed by a formation of Li-Sn alloy domains. Hence, the larger the fraction of tetrahedral BO 4 unit is in the SnO-B 2 O 3 glasses, the higher the charge-discharge capacities are. The SnO-B 2 O 3 glasses are applicable to all-solid-state lithium rechargeable batteries as anode materials with high capacity.

Occupation of tungsten site by iron in sodium tungstate glasses

Abstract 57 Fe Mossbauer spectra of x Na 2 O · (99 − x )WO 3 · 57 Fe 2 O 3 glasses (30 ≤ x ≤ 42) comprised of a doublet due to octahedral iron, Fe 3+ (O h ), and a weak doublet due to Fe 2+ (O h ); a large Debye temperature of 580 K was obtained at low temperatures. Fourier transform infrared spectra of the sodium tungstate glasses showed a gradual increase in the fraction of WO 4 tetrahedra (T d ) when Na 2 O content was increased. Mossbauer spectra of the tungstate glasses irradiated with 60 Co γ-rays showed an increase in the fraction of Fe 2+ , due to electron transfer (scattering) from WO and FeO bonds to Fe 3+ , as the electron spin resonance spectra of iron-free sodium tungstate glass indicated a simultaneous formation of W 5+ and the ‘hole’ trapped on the oxygen atom. From the linear relationship between glass transition temperature, T g , and quadrupole splitting, Δ, of Fe 3+ (‘ T g − Δ rule’), the slope of the straight line was estimated to be 260°C/(mm s −1 ). Mossbauer spectra of heat-treated tungstate glasses showed a gradual change from Fe 3+ (O h ) to Fe 3+ (T d ), along with the precipitation of the Na 2 W 2 O 7 phase composed of W 6+ (O h ) and W 6+ (T d ). These results indicate that iron occupies W 6+ (O h ) sites in glasses, while it occupies W 6+ (T d ) sites in glass-ceramics.

Mixed ligand copper(II) coordination polymers constructed by Cu-bpm-Cu dimer unit (bpm = 2,2′-bipyrimidine) as a building block. Crystal structures and magnetic properties of [Cu(bpm)(SO4)] (H2O)n, [Cu2(bpm)(suc)0.5(ClO4)2(OH)(H2O)2]n and [Cu(bpm)1.5(suc)0.5](ClO4)(H2O)2n (suc = succinate)

Abstract New 2,2′-bipyrimidine (bpm)-based copper(II) coordination polymers have been synthesized and characterized. The structure of [Cu(bpm)(SO4)](H2O)n (1) contains zigzag chains which are constructed of Cu-bpm-Cu units, sulfate ions and additional bridging bpms. Sulfate ions coordinate to copper(II) ions, and link the chains to form a three-dimensional bundle structure. The crystal structure of [Cu2(bpm)(suc)0.5(ClO4)2(OH)(H2O)2]n (2) consists of a chain of bpm-bridged dinuclear copper(II) units linked by a carboxylate group from the succinate anion and a hydroxo group. Coordinated perchlorate ions also bridge the adjacent chains. The chain structure of [Cu(bpm)1.5(suc)0.5](ClO4)(H2O)2n (3) consists of the bpm-bridged dinuclear copper(II) units, amphimonodentate succinate dianions and terminal bpms. The succinate dianion acts as a bridging ligand between the dimers to yield a one-dimensional zigzag chain in the crystal. The terminal bpm stacks with a nearest-neighbor terminal bpm on an adjacent chain to form a linkage for a two-dimensional sheet. The present work affords a new strategy to build multi-dimensional coordination polymers, which is based on the use of [Cu-bpm-Cu]4+ copper(II) dinuclear units as ‘building blocks’. The geometries around the pyrimidyl rings of bpm are similar to each other, whereas the geometry of the copper atoms is different. The additional linking ligand as a peripheral ligand coordinates to the dimer unit to control the plasticity of the coordination sphere of copper(II); this makes the modification of the symmetry of its magnetic orbital easy. The magnetic susceptibilities were measured from 2 to 300 K and analyzed as antiferromagnetic Heisenberg S = 1/2 alternating chains to yield J = −38.8 cm−1, α = 0.93 (1), J = −132.2 cm−1, α = 0.22 (2) and J = −4.5 cm−1, α = 0.60 (3).

Synthesis and some properties of Pd(BF4)2 and Pt(BF4)2 complexes of 1,1′-bis[(alkyl- or phenyl-)chalcogeno]ferrocenes

Abstract 1,1′-Bis(alkylthio and -phenylthio)ferrocenes react with (MeCN)4Pd(BF4)2 in the presence of triphenylphosphine to give stable 1/1 complexes in good yields. 1,1′-Bis(alkylseleno)ferrocenes and 1,1′-bis(phenylthio and phenylseleno)ferrocenes to give similar 1/1 complexes. Some platinum analogs were prepared from the reaction of the corresponding dichloro-complexes with AgBF4 in the presence of triphenylphosphine. The spectral data indicate that there is a dative metal-metal bond between the iron atom of the ferrocene and the palladium(II) or platinum(II) atom in these complexes.