Structure of tri-aqua-tris-(1,1,1-tri-fluoro-4-oxo-pentan-2-olato)cerium(III) as a possible fluorescent compound.

Luminescence due to the d-f transition of Ce3+ is quite rare in metal-organic complexes where concentrate quenching frequently occurs. One of the possible ways to avoid this is to design an architecture with elongated metal-metal distances. In the structure of the title complex, tri-aqua-tris-(1,1,1-tri-fluoro-4-oxo-pentan-2-olato-κ2O,O')cerium(III), [Ce(C5H4F3O2)3(H2O)3], the CeIII complex is linked to neighbouring ones by hydrogen bonding. Within the complex, the CeIII atom is coordinated by nine O atoms from three 1,1,1-tri-fluoro-4-oxo-pentan-2-olate (tfa) anions as bidentate ligands and three water mol-ecules as monodentate ligands. Thus, the coordination number of CeIII atom is nine in a monocapped square-anti-prismatic polyhedron. The F atoms of all three independent CF3 groups in tfa are disordered over two positions with occupancy ratios of about 0.8:0.2. The inter-molecular hydrogen bonds between the ligands involve tfa-water inter-actions along the [110] and [1-10] directions, generating an overall two-dimensional layered network structure. The presence of the F atoms in the tfa anion is responsible for an increased inter-molecular metal-metal distance compared to that in the analogous acetyl-acetonate (acac) derivatives. Fluorescence from Ce3+ is, however, not observed.

A new lanthanum(III) complex containing acetyl-acetone and 1H-imidazole.

In the title complex, di-aqua-(1H-imidazole-κN3)(nitrato-κ2O,O')bis-(4-oxo-pent-2-en-2-olato-κ2O,O')lanthanum(III), [La(C5H7O2)2(NO3)(C3H4N2)(H2O)2], the La atom is coordinated by eight O atoms of two acetyl-acetonate (acac) anions acting as bidentate ligands, two water mol-ecule as monodentate ligands, one nitrate anions as a bidentate ligand and one N atom of an imidazolate (ImH) molecule as a monodentate ligand. Thus, the coordination number of the La atom is nine in a monocapped square anti-prismatic polyhedron. There are three types of inter-molecular hydrogen bonds between ligands, the first involving nitrate-water O⋯H-O inter-actions running along the [001] direction, the second involving acac-water O⋯H-O inter-actions along the [010] direction and the third involving an Im-nitrate N-H⋯O inter-action along the [100] direction (five inter-actions of this type). Thus, an overall one-dimensional network structure is generated. The mol-ecular plane of an ImH molecule is almost parallel to that of a nitrate ligand, making an angle of only 6.04 (12)°. Inter-estingly, the ImH plane is nearly perpendicular to the planes of two neighbouring acac ligands.

Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells.

Leptothrix species, aquatic Fe-oxidizing bacteria, excrete nano-scaled exopolymer fibrils. Once excreted, the fibrils weave together and coalesce to form extracellular, microtubular, immature sheaths encasing catenulate cells of Leptothrix. The immature sheaths, composed of aggregated nanofibrils with a homogeneous-looking matrix, attract and bind aqueous-phase inorganics, especially Fe, P, and Si, to form seemingly solid, mature sheaths of a hybrid organic-inorganic nature. To verify our assumption that the organic skeleton of the sheaths might sorb a broad range of other metallic and nonmetallic elements, we examined the sorption potential of chemically and enzymatically prepared protein-free organic sheath remnants for 47 available elements. The sheath remnants were found by XRF to sorb each of the 47 elements, although their sorption degree varied among the elements: >35% atomic percentages for Ti, Y, Zr, Ru, Rh, Ag, and Au. Electron microscopy, energy dispersive x-ray spectroscopy, electron and x-ray diffractions, and Fourier transform infrared spectroscopy analyses of sheath remnants that had sorbed Ag, Cu, and Pt revealed that (i) the sheath remnants comprised a 5-10 nm thick aggregation of fibrils, (ii) the test elements were distributed almost homogeneously throughout the fibrillar aggregate, (iii) the nanofibril matrix sorbing the elements was nearly amorphous, and (iv) these elements plausibly were bound to the matrix by ionic binding, especially via OH. The present results show that the constitutive protein-free exopolymer nanofibrils of the sheaths can contribute to creating novel filtering materials for recovering and recycling useful and/or hazardous elements from the environment.

Tubular nitrogen-doped TiO2 samples with efficient photocatalytic properties based on long-lived charge separation under visible-light irradiation: synthesis, characterization and reactivity.

A nitrogen-doped TiO2 sample was prepared at 413 K by direct hydrothermal treatment of titanium isopropoxide in an aqueous solution of NH3. This new material has a large specific surface area of ca. 220 m2 g-1 because of its tubular structure and it exhibits a prominent absorption feature in the region between 400 and 650 nm. It responds strongly to light in the visible region, which is key to its potential performance as a photocatalyst that may improve the efficiency for utilization of solar energy. Actually, this sample exhibits very efficient activity in the decomposition of CH3COOH under visible light among the samples prepared. This effective photocatalysis of the present sample was substantiated by characteristic spectroscopic features, such as: (1) an optical absorption band with λ > 400 nm because of the doped nitrogen species; (2) the formation of EPR-active, long-lived N˙ and O2- species, as well as N2- species, under visible-light irradiation in the O2 or N2 adsorption process at 300 K by way of the monovalent nitrogen ions in the bulk (both substitutional and interstitial); (3) the existence of IR-active O2 species adsorbed on the nitrogen-doped TiO2 sample even without light irradiation; and (4) an XPS N1s band around 399.6 eV that is assignable to the N- species. The amounts of N˙ and O2- species formed in the nitrogen-doped TiO2 sample under visible-light irradiation correlated well with the levels of reactivity observed in the decomposition of CH3COOH on the samples with varying amounts and types of doped nitrogen species. We conclude that the photoactive N˙ and O2- species created in the present sample are responsible for the decomposition of organic materials assisted by visible light irradiation. These features may be attributable to the interface between the sample's tubular structure and anatase with poor crystallinity, which probably causes the resistance to the recombination of electron-hole pairs formed by irradiation.

Material Exhibiting Efficient CO2 Adsorption at Room Temperature for Concentrations Lower Than 1000 ppm: Elucidation of the State of Barium Ion Exchanged in an MFI-Type Zeolite.

Carbon dioxide (CO2) gas is well-known as a greenhouse gas that leads to global warming. Many efforts have been made to capture CO2 from coal-fired power plants, as well as to reduce the amounts of excess CO2 in the atmosphere to around 400 ppm. However, this is not a simple task, particularly in the lower pressure region than 1000 ppm. This is because the CO2 molecule is chemically stable and has a relatively low reactivity. In the present study, the CO2 adsorption at room temperature on MFI-type zeolites exchanged with alkaline-earth-metal ions, with focus on CO2 concentrations <1000 ppm, was investigated both experimentally and by calculation. These materials exhibited a particularly efficient adsorption capability for CO2, compared with other presented samples, such as the sodium-form and transition-metal ion-exchanged MFI-type zeolites. Ethyne (C2H2) was used as a probe molecule. Analyses were carried out with IR spectroscopy and X-ray absorption, and provided significant information regarding the presence of the M(2+)-O(2-)-M(2+) (M(2+): alkaline-earth-metal ion) species formed in the samples. It was subsequently determined that this species acts as a highly efficient site for CO2 adsorption at room temperature under very low pressure, compared to a single M(2+) species. A further advantage is that this material can be easily regenerated by a treatment, e.g., through the application of the temperature swing adsorption process, at relatively low temperatures (300-473 K).

Nanospace-enhanced photoreduction for the synthesis of copper(I) oxide nanoparticles under visible-light irradiation.

Nanoparticles of copper(I) oxide (cuprous oxide; Cu2O) were able to be synthesized from nano-restricted copper acetate (Cu(OAc)2) in micropores of single-wall carbon nanotubes (SWNTs) by visible-light photoreduction. The specific structure of confined Cu(OAc)2 in the micropore is indispensable for the reduction process to Cu2O by the irradiation, because, in general, aqueous solution of Cu(OAc)2 can be reduced under UV-light irradiated conditions. The present results strongly suggest that the micropore of SWNTs whose pore width is in the micropore-size range can play as nanoreactor space for the synthesis of Cu2O through the nano-restricted precursor whose reactivity is different from that in the bulk phase.

Success in making Zn+ from atomic Zn(0) encapsulated in an MFI-type zeolite with UV light irradiation.

For the first time, the paramagnetic Zn(+) species was prepared successfully by the excitation with ultraviolet light in the region ascribed to the absorption band resulting from the 4s-4p transition of an atomic Zn(0) species encapsulated in an MFI-type zeolite. The formed species gives a specific electron spin resonance band at g = 1.998 and also peculiar absorption bands around 38,000 and 32,500 cm(-1) which originate from 4s-4p transitions due to the Zn(+) species with paramagnetic nature that is formed in MFI. The transformation process (Zn(0) → Zn(+)) was explained by considering the mechanism via the excited triplet state ((3)P) caused by the intersystem crossing from the excited singlet state ((1)P) produced through the excitation of the 4s-4p transition of an atomic Zn(0) species grafted in MFI by UV light. The transformation process was well reproduced with the aid of a density functional theory calculation. The thus-formed Zn(+) species which has the doublet spin state exhibits characteristic reaction nature at room temperature for an O2 molecule having a triplet spin state in the ground state, forming an η(1) type of Zn(2+)-O2(-) species. These features clearly indicate the peculiar reactivity of Zn(+) in MFI, whereas Zn(0)-(H(+))2MFI hardly reacts with O2 at room temperature. The bonding nature of [Zn(2+)-O2(-)] species was also evidenced by ESR measurements and was also discussed on the basis of the results obtained through DFT calculations.

Further evidence for the existence of a dual-Cu+ site in MFI working as the efficient site for C2H6 adsorption at room temperature.

We have recently clarified the following point: a dual-type site, which is composed of a pair of monovalent copper ions (Cu(+)) formed in a copper-ion-exchanged MFI-type zeolite (CuMFI), functions as the active center for strong ethane (C2H6) adsorption even at room temperature rather than a single-type site composed of a Cu(+) ion. However, the character of the dual-Cu(+) site in a CuMFI is not yet fully understood. In this study, we have elucidated the nature of the active sites for C2H6 based on infrared (IR) and calorimetric data. On the basis of the results obtained, we came to the conclusion that the dual-Cu(+) site composed of Cu(+) ions giving the adsorption energy of 100 kJ mol(-1) and the absorption band at 2151 cm(-1) for carbon monoxide (used as a probe molecule) at room temperature functions as an adsorption site for C2H6. We also evaluated, for the first time, the interaction between the dual-Cu(+) site and C2H6 energetically, by the direct measurement of heat of adsorption. The value of 67 kJ mol(-1) that we recorded was higher than that for the single-Cu(+) site in this sample and also for other samples, such as NaMFI and HMFI.

Nano-micrometer-architectural acidic silica prepared from iron oxide of Leptothrix ochracea origin.

We prepared nano-micrometer-architectural acidic silica from a natural amorphous iron oxide with structural silicon which is a product of the iron-oxidizing bacterium Leptothrix ochracea. The starting material was heat-treated at 500 °C in a H2 gas flow leading to segregation of α-Fe crystalline particles and then dissolved in 1 M hydrochloric acid to remove the α-Fe particles, giving a gray-colored precipitate. It was determined to be amorphous silica containing some amount of iron (Si/Fe = ~60). The amorphous silica maintains the nano-microstructure of the starting material-~1-µm-diameter micrometer-tubules consisting of inner globular and outer fibrillar structures several tens of nanometer in size-and has many large pores which are most probably formed as a result of segregation of the α-Fe particles on the micrometer-tubule wall. The smallest particle size of the amorphous silica is ~10 nm, and it has a large surface area of 550 m(2)/g with micropores (0.7 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, we found that it has relatively strong Brønsted and Lewis acidic centers that do not desorb pyridine, even upon evacuation at 400 °C. The acidity of this new silica material was confirmed through representative two catalytic reactions: ring-opening reaction and Friedel-Crafts-type reaction, both of which are known to require acid catalysts.

Highly compressed nanosolution restricted in cylindrical carbon nanospaces.

We shed light on the specific hydration structure around a zinc ion of nanosolution restricted in a cylindrical micropore of single-wall carbon nanotube (SWNT) by comparison with the structure restricted in a cylindrical mesopore of multi-wall carbon nanotube (MWNT) and that of bulk aqueous solution. The average micropore width of open-pore SWNT was 0.87 nm which is equivalent to the size of a hydrated zinc ion having 6-hydrated water molecules. We could impregnate the zinc ions into the micropore of SWNT with negligible amounts of ion-exchanged species on surface functional groups by the appropriate oxidation followed by heat treatment under an inert condition. The results of X-ray absorption fine structure (XAFS) spectra confirmed that the proportion of dissolved species in nanospaces against the total adsorbed amounts of zinc ions on the open-pore SWNT and MWNT were 44 and 61%, respectively, indicating the formation of a dehydrated structure in narrower nanospaces. The structure parameters obtained by the analysis of XAFS spectra also indicate that the dehydrated and highly compressed hydration structure can be stably formed inside the cylindrical micropore of SWNT where the structure is different from that inside the slit-shaped micropore whose pore width is less than 1 nm. Such a unique structure needs not only a narrow micropore geometry which is equivalent to the size of a hydrated ion but also the cylindrical nature of the pore.

Acidic amorphous silica prepared from iron oxide of bacterial origin.

Microporous and mesoporous silica derived from biogenous iron oxide is an attractive catalyst for various organic reactions. Biogenous iron oxide contains structural silicon, and amorphous silica remains after iron oxide is dissolved in concentrated hydrochloric acid. The amorphous silica containing slight amounts of iron (Si/Fe = ∼150) is composed of ∼6-nm-diameter granular particles. The amorphous silica has a large surface area of 540 m(2)/g with micropores (1.4 nm) and mesopores (<3 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, it was found that this material has strong Brønsted and Lewis acid sites. When the catalytic performance of this material was evaluated for reactions including the ring opening of epoxides and Friedel-Crafts-type alkylations, which are known to be catalyzed by acid catalysts, this material showed yields higher than those obtained with common silica materials.

Unprecedented reversible redox process in the ZnMFI-H2 system involving formation of stable atomic Zn(0).

In its element: Zn(2+) at the M7 site of MFI-type zeolites activates H(2), via ZnH and OH species, and leads to Zn(0) species. The Zn(0) species returns to its original state, a Zn(2+) ion, upon evacuation of the zeolite at 873 K (see picture). The formation of the Zn(0) species is supported by DFT calculations.

Silicon and phosphorus linkage with iron via oxygen in the amorphous matrix of Gallionella ferruginea stalks.

Bacterial species belonging to the genus Gallionella are Fe-oxidizing bacteria that produce uniquely twisted extracellular stalks consisting of iron-oxide-encrusted inorganic/organic fibers in aquatic environments. This paper describes the degree of crystallinity of Gallionella stalks and the chemical linkages of constituent elements in the stalk fibers. Transmission electron microscopy revealed that the matrix of the fiber edge consisted of an assembly of primary particles of approximately 3 nm in diameter. Scanning transmission electron microscopy revealed the rough granular surfaces of the fibers, which reflect the disordered assembly of the primary particles, indicating a high porosity and large specific surface area of the fibers. This may provide the surface with broader reactive properties. X-ray diffractometry, selected-area electron diffraction, and high-resolution transmission electron microscopy together showed that the primary particles had an amorphous structure. Furthermore, energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy detected the bands characteristic of the vibrational modes assigned to O-H, Fe-O-H, P-O-H, Si-O-H, Si-O-Fe, and P-O-Fe bonds in the stalks, suggesting that the minor constituent elements P and Si could affect the degree of crystallinity of the fibers by linking with Fe via O. This knowledge about the mutual associations of these elements provides deeper insights into the unique inorganic/organic hybrid structure of the stalks.

Visible-light-derived photocatalyst based on TiO(2-δ)Nδ with a tubular structure.

We succeeded in achieving visible-light responsiveness on a tubular TiO(2) sample through the treatment of a tubular TiO(2) that has a large surface area with an aqueous solution of ammonia or triethylamine at room temperature and subsequent calcination at 623 K, which produced a nitrided tubular TiO(2) sample. It was found that the ease of nitridation is dependent on the surface states; washing the tubular TiO(2) sample with an aqueous acidic solution is very effective and indispensable. This treatment causes the appearance of acidic sites on the tubular TiO(2), which was proved by the following experiments: NH(3) temperature-programmed desorption and two types of organic reactions exploiting the acid properties. The prepared samples, TiO(2-δ)N(δ), efficiently absorb light in the visible region, and they exhibit a prominent feature for the decomposition of methylene blue in an aqueous solution at 300 K under irradiation with visible light, indicating the achievement of visible-light responsiveness on the tubular TiO(2) sample. This type of tubular TiO(2-δ)N(δ) sample has merit in the sense that it has a large surface area and a characteristic high transparency for enabling photocatalytic reactions because it has a tubular structure and is composed of thin walls.

Existence of dual species composed of Cu(+) in CuMFI being bridged by C(2)H(2).

The interaction of ethyne (C(2)H(2)), as well as of carbon dioxide (CO(2)), with copper-ion-exchanged MFI zeolite (CuMFI) at room temperature was examined. It was found that CuMFI preferentially adsorbs C(2)H(2), while this material does not respond to CO(2). To clarify the specificity of CuMFI, a combination of various experimental techniques and theoretical calculations was adopted. Distinctive interaction energies of 140 and 110 kJ mol(-1) were clearly observed at the initial stage of C(2)H(2) adsorption on CuMFI, suggesting the presence of two types of adsorbed C(2)H(2). Two distinct IR bands at 1620 and 1814 cm(-1) appeared, which were assigned to the C[triple bond]C stretching vibration modes of C(2)H(2) differing in their adsorbed state. Both photoluminescence and X-ray absorption spectra showed that cuprous ions (Cu(+)) in CuMFI act as efficient sites for a marked C(2)H(2) adsorption. From the analysis of the latter spectra and the calculational results based on the density functional theory, the formation of dual Cu(+)...(C(2)H(2))...Cu(+) complexes was indicated for the first time for CuMFI, and such a special configuration of the Cu(+) sites contributed to the extremely strong adsorption of C(2)H(2). In contrast, it was necessary for the linear CO(2) molecule to take a bent structure to be adsorbed on Cu(+) in CuMFI. It was concluded that the difference in the adsorption response of Cu(+) in CuMFI towards C(2)H(2) and CO(2) is due to the chemistry between the nature of electron donation of Cu(+) and the hybrid orbitals of the respective molecules. This work promotes further understanding of the states of active centres in CuMFI for C(2)H(2) activation, as well as for N(2) fixation.

On the possibility of AgZSM-5 zeolite being a partial oxidation catalyst for methane.

A silver-ion-exchanged HZSM-5 zeolite sample (Ag(H)ZSM-5) evacuated at 573 K exhibited prominent catalytic behavior in the partial oxidation of CH(4) at temperatures above 573 K, exceeding the performance of Ag/SiO(2)Al(2)O(3) and Ag/SiO(2) catalysts. From the infrared (IR) and X-ray absorption fine structure (XAFS) spectra, as well as the dioxygen adsorption measurement, it was concluded that the simultaneous existence of Ag(+) ions and small clusters of Ag particles leads to the partial oxidation of methane. Taking the magnitude of the formation enthalpy (per oxygen atom) of Ag(2)O (DeltaH=26 kJ/mol) into consideration, we propose the interpretation that the dioxygen activated on small Ag metal clusters formed in ZSM-5 elaborates a surface oxide layer on small Ag clusters and the thus-formed species is simultaneously and easily decomposed at 573 K or above, and the oxygen activated in this way on the Ag metal spills over and can react with methane that has been activated by the Ag(+) ions exchanged in ZSM-5, resulting in the high catalytic activity of the Ag(H)ZSM-5 sample in the partial oxidation of methane. This interpretation is also well evidenced by XAFS and IR data. It is anticipated that this material has the potential to be a promising catalyst in the conversion of natural gas into higher value-added chemicals and fuels.

Identification of two types of exchangeable sites for monovalent copper ions exchanged in MFI-type zeolite.

Three different approaches have been used to characterize the state of exchanged copper ions in copper-ion-exchanged MFI (CuMFI) samples. (1) Two types of an ion-exchangeable site with different adsorption properties for N(2) or CO molecules were identified depending on the pre-treatment temperature (723 or 873 K) of a sample prepared by using an aqueous solution of CuCl(2). (2) The state of the active sites formed by the evacuation of a sample at 873 K that had been prepared using a mixture solution of aqueous NH(4)CH(3)COO and Cu(CH(3)COO)(2) was analysed utilizing both (13)C(18)O and (12)C(16)O to identify the two types of active adsorption sites for CO molecules. (3) CuMFI samples prepared by the ion-exchange method employing anhydrous CuCH(3)COO showed a surprising adsorption feature characterized by a single IR band occurring at 2159 cm(-1) due to the adsorbed CO molecules, but there was no corresponding IR band due to adsorbed N(2) molecules. A successful preparation of CuMFI, in which the monovalent copper ions exclusively occupied another one of the two types of ion-exchangeable sites, was also carried out utilizing the solid-ion exchange method using Cu(CH(3)COO)(2).H(2)O. This site exhibits an IR band occurring at 2151 cm(-1) for CO molecules and also acts as an active site for N(2) molecules. These experimental data correlate, and clearly indicate that there are at least two types of exchangeable sites for copper ions in MFI-type zeolites.

Al-pillared montmorillonite clay minerals: low-pressure CO adsorption at room temperature.

Three kinds of Al-pillared montmorillonite clay minerals (AlPMON) ion-exchanged with cobalt(II), nickel(II), or copper(II) ions were prepared (abbreviated as CoAlPMON, NiAlPMON, or CuAlPMON, respectively). For the 673-K- and 873-K-treated samples, carbon monoxide (CO) adsorption measurement was performed at room temperature under an atmosphere of low CO pressure. The 873-K-treated CuAlPMON sample exhibited more efficient adsorption properties for CO molecules, in comparison with both-temperatures-treated CoAlPMON and NiAlPMON samples and the 673-K-treated CuAlPMON sample. In addition, irreversibly adsorbed CO was present only on the CuAlPMON sample that had been treated at 873 K; the sites responsible for strong CO adsorption were formed in the sample after the pretreatment at the higher temperature.

Observation of characteristic IR band assignable to dimerized copper ions in montmorillonite.

Copper ion-exchanged montmorillonite clays, which had been prepared by ion exchange in an aqueous solution of CuCl(2) at a temperature above 323 K, exhibited the characteristic IR band in the region 3360-3310 cm(-1). No such bands were observed for the samples prepared by using different ion-exchange solutions and at different temperatures. From the spectroscopic observations, it was revealed that the ion-exchanged copper ions (Cu(2+)) are in the form of dimerized species by bridging two hydroxyls, [Cu(2+) <(OH(-)(2) > Cu(2+)], in montmorillonite.