Synthesis of fluoride garnets {Na3}[M3+2](Li3)F12 (M = Al,Cr, and Fe) from aqueous solution and their properties

The garnet-type fluorides, Na₃M₂Li₃F₁₂ (M = Al, Cr, and Fe) were synthesized as the coprecipitates of ～1 to 10 μm powders from HF solutions. The garnet structures were always obtained under acidic conditions. The incorporation of water molecules into the structure of the Cr and Fe garnets was observed. After heat treatment at 300°C, very small unknown peaks were observed in the X-ray powder pattern in addition to the garnet phase which had a slightly smaller value of the lattice constant than that of hydrous garnets. From the measurement of magnetic properties and Mössbauer effects, the Fe and Cr garnets were found to be paramagnetic with both ions in the trivalent state. Presentation of infrared spectra of the garnets is also included.     

A useful procedure for diiodination of carbazoles and subsequent efficient transformation to novel 3,6-bis(triethoxysilyl)carbazoles giving mesoporous materials

Bis(pyridine)iodonium tetrafluoroborate (IPy₂BF₄) was successfully used as a diiodination reagent for carbazole and its derivatives to give 3,6-diiodocarbazoles in excellent yield. Subsequent rhodium-catalyzed disilylation of 3,6-diiodocarbazoles with triethoxysilane gave the corresponding 3,6-bis(triethoxysilyl)carbazoles, which are precursors for sol-gel polymerization, in good yield.     

Resonance Raman spectra of β-carotene and its molecular structure in the excited electronic state

The resonance Raman spectra of β-carotene have been obtained at low temperature. The excitation profiles of ν₁ (1525 cm^?1) and 2ν₁ (3043 cm^?1) are analysed in terms of the Albrecht theory. The overlap integrals between the vibrational wavefunctions of the ground and the first excited electronic states are shown to be the most important factor in determining the resonance Raman intensities of this molecule. Information on the structure of the electronically excited state has been obtained.     

Separation of N2-ethyl-2'-deoxyguanosine-5'-monophosphate and four native deoxyribonucleoside monophosphates using capillary zone electrophoresis with polyethylene glycol as buffer additive

We investigated the separation of five deoxyribonucleoside monophosphates: 2'-deoxyguanosine-5'-monophosphate (dGMP), 2'-deoxyadenosine-5'-monophosphate (dAMP), 2'-deoxycytosine-5'-monophosphate (dCMP), 2'-deoxythymidine-5'-monophosphate (dTMP) and a dGMP adduct possessing N2-ethyl-guanine, which has been noted in relation to mutagenesis of alcohol, using capillary zone electrophoresis (CZE). The concentration of polyethylene glycol (PEG) as a modifier and the pH of the running solutions can efficiently control the observed separation. Interaction of PEG with analytes was quantitatively evaluated. PEG worked effectively as a hydrophobic selector in these separations. The values of pKa of the acidic-NH-groups in the base moieties of dGMP, dTMP, and the dGMP adduct are close to that of boric acid used as buffer of the running solutions. The control of their charge was facilitated, enabling improved separations. A more sufficient and fast separation was achieved by both optimization of pH of the running solutions and PEG concentration compared with that obtained by pH control alone. On-line concentration using a stacking method followed by the PEG-assisted CZE was briefly studied.     

Xenophilic complexes bearing a Tp(R) Ligand, [Tp(R)M--M'Ln] [Tp(R) = Tp(iPr2), Tp(#) (Tp(Me2,4-Br)); M=Ni, Co, Fe, Mn; M'Ln = Co(CO)4, Co(CO)3(PPh3), RuCp(CO)2]: the two metal centers are held together not by covalent interaction but by electrostatic attraction

A series of dinuclear complexes, [Tp(R)M--M'L(n)] [Tp(iPr(2) )M--Co(CO)(4) (1; M=Ni, Co, Fe, Mn); Tp(#)M--Co(CO)(4) (1'; M=Ni, Co); Tp(#)Ni--RuCp(CO)(2) (3')] (Tp(iPr(2) )=hydrotris(3,5-diisopropylpyrazolyl)borato; Tp(#) (Tp(Me(2),4-Br))=hydrotris(3,5-dimethyl-4-bromopyrazolyl)borato), has been prepared by treatment of the cationic complexes [Tp(iPr(2) )M(NCMe)(3)]PF(6) or the halo complexes [Tp(#)M--X] with the appropriate metalates. Spectroscopic and crystallographic characterization of 1-3' reveals that the tetrahedral, high-spin Tp(R)M fragment and the coordinatively saturated carbonyl-metal fragment (M'L(n)) are connected only by a metal-metal interaction and, thus, the dinuclear complexes belong to a unique class of xenophilic complexes. The metal-metal interaction in the xenophilic complexes is polarized, as revealed by their nu(CO) vibrations and structural features, which fall between those of reference complexes: covalently bonded species [R--M'L(n)] and ionic species [M'L(n)](-). Unrestricted DFT calculations for the model complexes [Tp(H(2) )Ni--Co(CO)(4)], [Tp(H(2) )Ni--Co(CO)(3)(PH(3))], and [Tp(H(2) )Ni--RuCp(CO)(2)] prove that the two metal centers are held together not by covalent interactions, but by electrostatic attractions. In other words, the obtained xenophilic complexes can be regarded as carbonylmetalates, in which the cationic counterpart interacts with the metal center rather than the oxygen atom of the carbonyl ligand. The xenophilic complexes show divergent reactivity dependent on the properties of donor molecules. Hard (N and O donors) and soft donors (P and C donors) attack the Tp(R)M part and the ML(n) moiety, respectively. The selectivity has been interpreted in terms of the hard-soft theory, and the reactions of the high-spin species 1-3' with singlet donor molecules should involve a spin-crossover process.     

Electrochemical formation of stable ferrocene anion and the formal rate constant of the ferrocene0/− electrode

A reversible cyclic voltammogram for the one-electron reduction of ferrocene in 1,2-dimethoxyethane is recorded under experimental conditions that enable the ferrocene anion to exist for a few minutes. The formal rate constant of the ferrocene^0/? electrode, determined by cyclic voltammetry at ?45°C, ca. 10^?3 cm s^?1, is in striking contrast with that of ferrocene^+/0, > 10^?1 cm s^?1. The distortion of the ferrocene molecule caused by reduction may be a reason for this difference in electron-transfer rate.     

Rh(I)-catalyzed Pauson-Khand reaction and cycloisomerization of allenynes: selective preparation of monocyclic, bicyclo[m.3.0], and bicyclo[5.2.0] ring systems

[reaction: see text] Rhodium(I)-catalyzed PKR of allenynes was found to be applicable for constructing azabicyclo[5.3.0]decadienone as well as oxabicyclo[5.3.0]decadienone frameworks. In addition, a reliable procedure for constructing a 10-monosubstituted bicyclo[5.3.0]deca-1,7-dien-9-one ring system by the rhodium(I)-catalyzed PKR of allenynes was developed under the condition of 10 atm of CO. Investigation of the rhodium(I)-catalyzed cycloisomerization of 4-phenylsulfonylnona-2,3-dien-8-ynes under nitrogen atmosphere gave the corresponding cyclohexene derivatives, whereas the C1-homologated allenynes produced cycloheptene derivatives and/or bicyclo[5.2.0]nonene skeletons depending on the substitution pattern at the allenic terminus. Thus, proper choice of the starting allenynes and reaction conditions led to the selective formation of 2-phenylsulfonylbicyclo[5.3.0]deca-1,7-dien-9-ones (Pauson-Khand-type product), 3-alkylidene-1-phenylsulfonyl-2-vinylcycloheptene derivatives, and bicyclo[5.2.0]nonene frameworks.     

Comparisons of glow discharge polymerization between hexamethyldisilazane and trimethylsilyldimethylamine

Glow discharge polymerization between hexamethyldisilazane (HMDSZ) and trimethylsilyldimethylamine (TMSDMA) was compared by means of infrared spectroscopy and ESCA analysis. Infrared spectra pointed out differences in chemical structure between the polymers prepared from the two monomers, although the two polymers were mainly composed of resembling units such as Si? CH₃, Si? CH₂, Si? H, Si? O? Si, and Si? O? C groups: (i) The polymers prepared from TMSDMA contained N → O group, but the polymers from HMDSZ did not contain this group. (ii) Influences of the W/FM parameter (W is the input energy of rf power, F the flow rate of the monomer, and M the molecular weight of the monomer) appeared on decreasing the C? N group and increasing the C?O group in the TMSDMA system, but little influence appeared in the HMDSZ system. ESCA spectra (C_1s, Si_2p, and N_1s core levels) supported the differences between the two polymers elucidated by infrared spectroscopy, and pointed out differences in susceptibility of the Si? N bond to plasma: The N? Si sequence of TMSDMA was completely ruptured in discharge to yield polymers, and the Si? NH? Si sequence of HMDSZ remained in considerable amount.