Synthesis of heterometal cluster complexes by the reaction of cobaltadichalcogenolato complexes with groups 6 and 8 metal carbonyls

Metalladichalcogenolate cluster complexes [{CpCo(S2C6H4)}2Mo(CO)2] (Cp = eta(5)-C5H5) (3), [{CpCo(S2C6H4)}2W(CO)2] (4), [CpCo(S2C6H4)Fe(CO)3] (5), [CpCo(S2C6H4)Ru(CO)2(P(t)Bu3)] (6), [{CpCo(Se2C6H4)}2Mo(CO)2] (7), and [{CpCo(Se2C6H4)}(Se2C6H4)W(CO)2] (8) were synthesized by the reaction of [CpCo(E2C6H4)] (E = S, Se) with [M(CO)3(py)3] (M = Mo, W), [Fe(CO)5], or [Ru(CO)3(P(t)Bu3)2], and their crystal structures and physical properties were investigated. In the series of trinuclear group 6 metal-Co complexes, 3, 4, and 7 have similar structures, but the W-Se complex, 8, eliminates one cobalt atom and one cyclopentadienyl group from the sulfur analogue, 4, and does not satisfy the 18-electron rule. 1H NMR observation suggested that the CoW dinuclear complex 8 was generated via a trinuclear Co2W complex, with a structure comparable to 7. The trinuclear cluster complexes, 3, 4, and 7, undergo quasi-reversible two-step one-electron reduction, indicating the formation of mixed-valence complexes Co(III)M(0)Co(II) (M = Mo, W). The thermodynamic stability of the mixed-valence state increases in the order 4 < 3 < 7. In the dinuclear group 8 metal-Co complexes, 5 and 6, the CpCo(S2C6H4) moiety and the metal carbonyl moiety act as a Lewis acid character and a base character, respectively, as determined by their spectrochemical and redox properties. Complex 5 undergoes reversible two-step one-electron reduction, and an electron paramagnetic resonance (EPR) study indicates the stepwise reduction process from Co(III)Fe(0) to form Co(III)Fe(-I) and Co(II)Fe(-I).     

Carbon monoxide ligand-exchange reaction of triruthenium cluster complexes induced by photosensitized electron transfer: a new type of photoactive CO color sensor

Oxo-acetato-bridged triruthenium cluster complexes ([Ru3(mu3-O)(mu-CH3CO2)6(L1)(L2)2](+/0)) show various color changes with variations of the total charge of the cluster complexes and terminal ligands. After photosensitized electron transfer via the triplet excited state of zinc tetraphenylporphyrin, the change of the formal oxidation state of the ruthenium ion allowed coordination with the carbon monoxide ligand accompanying the color changes.     

Prolongation of the lifetime of the charge-separated state at low temperatures in a photoinduced electron-transfer system of [60]fullerene and ferrocene moieties tethered by rotaxane structures

A rotaxane tethering both fullerene (C60) and ferrocene (Fc) moieties (abbreviated as (C60;Fc)rotax+) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ether-secondary amine motif. In (C60;Fc)rotax+, the C60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C60 and Fc in (C60;Fc)rotax+ have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Nanosecond transient absorption measurements of the rotaxane demonstrated that the charge-separated state (C60*-;Fc*+)rotax+ is formed mainly via the excited triplet state of C60 in polar solvents. The lifetime of (C60*-;Fc*+)rotax+ was evaluated to be 20 ns in dimethylformamide (DMF) at room temperature. With lowing temperature, the lifetime of (C60*-;Fc*+)rotax+ extends to 270 ns in DMF at -65 degrees C, due to the structural changes leaving C60*- and Fc*+ at a relatively long distance in the low-temperature region.     

A photoelectrochemical device with a nanostructured SnO2 electrode modified with composite clusters of porphyrin-modified silica nanoparticle and fullerene

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.     

Inclusion Behavior of 4-Nonylphenol into Cyclodextrin Derivatives

The solubilities of 4-nonylphenol in five kinds of hydroxypropyl-cyclodextrin (HP-CDs) solutions were investigated in order to evaluate them for soil remediation. The relative aqueous-phase concentration of 4-nonylphenol linearly increased with the increasing HP-CD concentration. The addition of HP-beta-CD (degree of substitution, D.S.=0.6) produced the largest change because the inner core of HP-beta-CD is the most hydrophobic. The solubility of 4-nonylphenol in the HP-CD solutions depended upon the cavity diameter and the degree of HP-CD substitution. Both ozone and activated carbon treatments have been using for removing organic compounds and foul odor compounds from tap water. As the inclusion complexes moved into the groundwater, the ozone degradation of the inclusion complexes was estimated. The 4-nonylphenol-HP-CD inclusion complexes were easily degraded by ozone. The degree of degradation increased with the increasing ozonization time. Weakly acidic compounds were produced from the 4-nonylphenol-HP-CD inclusion complexes by ozonization. HP-CDs could be used for the removal of 4-nonylphenol from soil. Copyright 2001 Academic Press.     

Spectral, electrochemical, and photophysical studies of a magnesium porphyrin-fullerene dyad

A covalently linked magnesium porphyrin-fullerene (MgPo-C60) dyad was synthesized and its spectral, electrochemical, molecular orbital, and photophysical properties were investigated and the results were compared to the earlier reported zinc porphyrin-fullerene (ZnPo-C60) dyad. The ab initio B3LYP/3-21G(*) computed geometry and electronic structure of the dyad predicted that the HOMO and LUMO are mainly localized on the MgP and C60 units, respectively. In o-dichlorobenzene containing 0.1 M (n-Bu)4NClO4, the synthesized dyad exhibited six one-electron reversible redox reactions within the potential window of the solvent. The oxidation and reduction potentials of the MgP and C60 units indicate stabilization of the charge-separated state. The emission, monitored by both steady-state and time-resolved techniques, revealed efficient quenching of the singlet excited state of the MgP and C60 units. The quenching pathway of the singlet excited MgP moiety involved energy transfer to the appended C60 moiety, generating the singlet excited C60 moiety, from which subsequent charge-separation occurred. The charge recombination rates, k(CR), evaluated from nanosecond transient absorption studies, were found to be 2-3 orders of magnitude smaller than the charge separation rate, k(CS). In o-dichlorobenzene, the lifetime of the radical ion-pair, MgPo*+-C60*-, was found to be 520 ns which is longer than that of ZnPo*+-C60*- indicating better charge stabilization in MgPo-C60. Additional prolongation of the lifetime of MgPo*+-C60*- was achieved by coordinating nitrogenous axial ligands. The solvent effect in controlling the rates of forward and reverse electron transfer is also investigated.     

Electronic interplay on illuminated aqueous carbon nanohorn-porphyrin ensembles

Tetracationic water-soluble porphyrin (H(2)P(4+)) has been immobilized by pi-pi stacking interactions onto the skeleton of carbon nanohorns (CNH), without disrupting their pi-electronic network. The stable aqueous solution of the CNH-H(2)P(4+) nanoensemble was examined by both electron microscopy and spectroscopic techniques. The efficient fluorescence quenching of the H(2)P(4+) moiety in the CNH-H(2)P(4+) nanoensemble was probed by steady-state as well as time-resolved fluorescence emission spectroscopy, suggesting charge separation from the photoexcited H(2)P(4+) to CNH. In the presence of methyl viologen dication (MV(2+)) and a hole trap, accumulation of the reduced species of methyl viologen was observed by the photoillumination of CNH-H(2)P(4+), suggesting that the electron migration from the initially formed charge-separated state takes place. Transient absorption spectroscopy gave further insights on the transient species such as the charge-separated state (CNH(*-))-(H(2)P(4+))(*+), which was consumed in the presence of MV(2+) and hole shifter, leaving the reduced methyl viologen.     

Growth of isotopically enriched Si nanowires

The isotopically enriched silicon (²⁸Si) nanowires have been fabricated by using the floating-zone (FZ) melting vapour method. The growth of the nanowires was performed in the top area, 1.52 cm from the floating melting zone (2 mm width) of a raw material bar under a flow of Ar gas. Field emission scanning electron microscopy and transmission electron microscopy analyses revealed that the nanowires of isotopically enriched ²⁸Si crystalline had diameters ranging from 2050 nm and lengths of several hundreds of micrometres. The special structure of the tip of the isotopically enriched ²⁸Si nanowires was observed.     

Absorption and Luminescence Spectra of Tetra (3-Pyridyl)Porphyrazine: A Convergent Spectroscopic Method for the Elucidation of Association Reactions in Solution

Tetra(3-pyridyl)porphyrazine is soluble in trifluoroethanol yielding intense blue solutions. The electronic spectra exhibit the characteristic Soret and Q bands around 330 and 610 nm, respectively; however, the absorption profile is strongly dependent on the concentration, reflecting the occurrence of an association process. The system has been elucidated by solving the equilibrium and the absorbance-concentration equations for all the wavelengths in the spectral range, according to a variational procedure. In this way the consistent spectra of the individual species have been generated. The study has also been extended to the luminescence properties of the porphyrazine molecule, and discussed in terms of the ground state association and the exciplex formation involving the monomeric species.