Linking of the trinuclear pivalate fragment Fe2CoO(Piv)6 by the redox-active bridge Ni(L)2 (compound 1; LH is Schiff base from hydrazide of 4-pyridinecarboxylic acid and 2-pyridinecarbaldehyde, Piv– ...= pivalate) led to formation of a new porous coordination polymer (PCP) {Fe2CoO(Piv)6}{Ni(L)2}1.5 (2). X-ray structures of 1 and 2 were determined. A crystal lattice of compound 2 is built from stacked 2D layers; the Ni(L)2 units can be considered as bridges, which bind two Fe2CoO(Piv)6 units. In desolvated form, 2 possesses a porous crystal lattice (S BET = 50 m2 g–1, V DR = 0.017 cm3 g–1 estimated from N2 sorption at 78 K). At 298 K, 2 absorbed a significant quantity of methanol (up to 0.3 cm3 g–1) and chloroform. Temperature dependence of molar magnetic susceptibility of 2 could be fitted as superposition of χM T of Fe2CoO(Piv)6 and Ni(L)2 units, possible interactions between them were taken into account using molecular field model. In turn, magnetic properties of the Fe2CoO(Piv)6 unit were fitted using two models, one of which directly took into account a spin–orbit coupling of CoII, and in the second model the spin–orbit coupling of CoII was approximated as zero-field splitting. Electrochemical and electrocatalytic properties of 2 were studied by cyclic voltammetry in suspension and compared with electrochemical and electrocatalytic properties of a soluble analogue 1. A catalytic effect was determined by analysis of the catalytic current dependency on concentrations of the substrate. Compound 1 possessed electrocatalytic activity in organic halide dehalogenation, and such activity was preserved for the Ni(L)2 units, incorporated into the framework of 2. In addition, a new property occurred in the case of 2: the catalytic activity of PCP depended on its sorption capacity with respect to the substrate. In contrast to homogeneous catalysts, usage of solid PCPs may allow selectivity due to porous structure and simplify separation of product.
Flickering in FU Orionis Kenyon, Scott J; Kolotilov, E. A; Ibragimov, M. A ...
The Astrophysical journal,
03/2000, Volume:
531, Issue:
2
Journal Article
Metathesis of the isomorphous 15‐metallacrown‐5 complexes {LnCu5(GlyHA)5(SO4)(H2O)6.5}2(SO4)·6H2O (LnIII = Pr, Nd, Sm, Eu; GlyHA2– = glycinehydroxamate) with excess p‐bdc2– (p‐bdc2– = terephthalate) ...gave pairs of isomorphous complexes {LnCu5(GlyHA)5(CO3)(H2O)42(p‐bdc)}·15H2O Ln = Pr (1) and Nd (2) and {LnCu5(GlyHA)5(SO4)(H2O)x2(p‐bdc)}·yH2O Sm (3) x = 5, y = 12; Eu (4), x = 4, y = 14 as outcomes of partial sulfate replacement. Complexes 1–4 are discrete dimers with two 15‐metallacrown‐5 blocks {LnCu5}3+, a bridging p‐bdc2– and a bidentate capping anion on each Ln3+. The anion caps in 1 and 2 are carbonates from atmospheric CO2 capture, while in 3 and 4 the anion caps are sulfates. Between 3 K and 300 K, intrametallacycle antiferromagnetic exchange interactions amongst the Cu2+ dominate the magnetic properties of 1–4, while for the Ln3+, spin‐orbit coupling and crystal field effects are significant, the former being greater for Sm3+ and Eu3+. The experimental χMT vs. T data were fitted with an additive model reflecting the dominance of the Cu···Cu superexchange, while Ln3+···Cu2+ exchange interactions were taken into account through a molecular field approach. The best‐fit values (–2JCu–Cu) for the intercopper superexchange interactions range from 88 to 120 cm–1; the g‐factors, spin‐orbit coupling (λ) and axial crystal field splitting (Δ) parameter values are typical for LnIII.
Structural and magnetic studies of two pairs of discrete isomorphous 15‐MC‐5 dimers containing {LnCu5}3+ units (Ln = Pr, Nd, Sm, Eu) bridged by terephthalates were performed. The χMT vs. T data obtained were fitted with an additive model, which considers exchange interactions JCu–Cu in the {LnCu5}3+ units to be dominant. All possible weak exchange interactions were included with a molecular field approach.
Complexes {LnCu5(GlyHA)5(m-bdc)(H2O)4–x 2LnCu5(GlyHA)5(SO4)(m-bdc)(H2O)42}·(30 + 2x)H2O (where GlyHA2– = glycinehydroxamate, m-bdc2– = m-phthalate; Ln = Pr and x = 0.21 for compound 1, or Ln = Sm ...and x = 0.24 for 3) and one-dimensional (1D) coordination polymers {NdCu5(GlyHA)5(H2O)5(m-bdc) nnNdCu5(GlyHA)5(H2O)4(μ-CO3)(m-bdc)}·13nH2O (2) and {EuCu5(GlyHA)5(H2O)3(m-bdc)2EuCu5(GlyHA)5(m-bdc)(H2O)3} n ·17nH2O (4) were obtained starting from the 15-metallacrown-5 complexes {LnCu5(GlyHA)5(SO4)(H2O)6.5}2(SO4)·6H2O (Ln = Pr, Nd, Sm, Eu) by the partial or complete metathesis of sulfate anions with m-phthalate. Compounds 1 and 3 contain unprecedented quadruple-decker neutral metallacrown assemblies, where the LnCu5(GlyHA)53+ cations are linked by m-phthalate dianions. In contrast, in complexes 2 and 4, these components assemble into 1D chains of coordination polymers, the adjacent {NdCu5(GlyHA)5(H2O)5(m-bdc)+} n 1D chains in 2 being separated by discrete NdCu5(GlyHA)5(H2O)4(μ-CO3)(m-bdc)}− complex anions. The crystal lattices of 2 and 4 contain voids filled by solvent molecules. Desolvated 4 is able to absorb up to 0.12 cm3/g of methanol vapor or 0.04 cm3/g of ethanol at 293 K. The isotherm for methanol absorption by compound 4 is consistent with a possible “gate opening” mechanism upon interaction with this substrate. The χM T vs T data for complexes 1–4 and their simpler starting materials {LnCu5(GlyHA)5(SO4)(H2O)6.5}2(SO4)·6H2O (Ln(III) = Pr, Nd, Sm, Eu) were fitted using an additive model, which takes into account exchange interactions between lanthanide(III) and copper(II) ions in the metallamacrocycles via a molecular field model. The exchange interactions between adjacent Cu(II) ions in metallacrown fragments were found to fall in the range of −47 < J Cu–Cu < −63 cm–1. These complexes are the first examples of a Ln(III)-Cu(II) 15-metallacrowns-5 (Ln(III) = Pr, Nd, Sm, Eu), for which values of exchange parameters have now been reported.
We present the results of our analysis of the spectrophotometric and photometric data for the symbiotic nova PU Vul acquired in 2001–2008. The continuum in the optical observed in 2006–2008 cannot be ...reconciled with a standard model including light from the cool component, hot component, and nebula. The hot component’s temperature increased to 194 000 K by 2008, while its luminosity decreased by a factor of ten compared to the plateau of 1979–1991. The evolution of the hot component as reflected by the Hertzsprung-Russell diagram does not agree with a theoretical model describing the evolution of a thermonuclear outburst in a white-dwarf envelope. We estimate the mass of the hot component to be 0.5
M
⊙
based on the luminosity of the hot component during the plateau stage. Our spectroscopy reveals periodic continuum-flux variations due to brightness variability of the cool component, with an amplitude of at least 2
m
at 7000 Å. The spectral type of the cool component in 2008 was M6.3.
The safety and effectiveness of endoscopic rhinological operations in the treatment of chronic inflammatory diseases, as well as neoplasms of the paranasal sinuses, are largely achieved by reducing ...bleeding in the area of the surgical field. Even a small amount of blood can disrupt the view during endoscopy and prevent the intervention from being performed, thereby increasing the risk of complications.
The review presents modern methods of reducing the risk of intraoperative bleeding under general anesthesia. Each approach has its own characteristics, therefore, the benefit-risk ratio should be assessed for each patient before choosing a specific method for controlling intraoperative bleeding.
With maleate, Cu5(ahpha)42+ gives two complexes, Cu5(ahpha)4(DMF)2(MalH)2·2DMF (1) and Cu5(ahpha)4(MalH)2 (2) (ahpha2– is 3‐amino‐3‐hydroximinopropane hydroxamate; MalH2 is maleic acid). Both 1 and 2 ...contain non‐oligomerized Cu5(ahpha)42+ metallacrown blocks; in 1, two MalH– are bound to Cu5(ahpha)42+ only via H‐bonds, while in 2, they coordinate to Cu2+. The X‐band EPR of 1 was observed at 20 K, 100 K, and 295 K. The EPR at 20 K was of an S = 1/2 ground state, while at room temperature anisotropic |ΔMs| = 1 and |ΔMs| = 2 resonances around 3200 G (g ≈ 2.19) and 1600 G (g ≈ 4.25) were observed for the Cu5 system, due to partial occupation of an S = 3/2 state. The room temperature EPR of 1 was simulated as the weighted sum of the spectra of its various S = 1/2, 3/2, and 5/2 states. Its magnetic behavior was fitted with a χMT vs. T model using a spin Hamiltonian accounting for central–peripheral (J1), peripheral–peripheral (J2) Cu2+–Cu2+ and intercrown (zJ′) spin interactions, yielding J1 = –156(4) cm–1, J2 = –63(1) cm–1, and zJ′ = –4.5(3) cm–1. For sorption of methanol and ethanol vapors at 293 K by a desolvated polycrystalline sample of 1, the shape of the adsorption and desorption isotherms indicated a “gates opening” phenomenon.
ESI‐mass spectra evidence the dependence of copper 12‐MC‐4 crown aggregation on counter‐anion charge, and an EPR analysis elucidates the populations of the crown's spin states.
A dimeric complex of trivalent europium Eu2Cl4(bc)2(ptpy)2 (1), containing the separate ligands 4'‐phenyl‐2,2':6',2''‐terpyridine (ptpy) and benzoate (bc–) and a one‐dimensional double strand ...coordination polymer of the composition 1∞EuCl2(cptpy) (2) with 4‐2,2':6',2''‐terpyridin‐4'‐yl‐benzoate (cptpy–) were obtained. The products exhibit structural similarities despite the character of joint and separate functionality of the ligands. The dimer 1 shows photoluminescence with high quantum yield 61(2) %. Eu3+ emission lifetime is 1.493(1) ms at room temperature and rises to 1.649(1) ms upon cooling to 77 K.
We present the results of our spectroscopic and photometric observations of the classical symbiotic star V1413 Aql in 2003–2007, which cover the transition phase of its hot component from activity to ...quiescence. Various quiescence criteria for the hot component of the system are analyzed. Judging by its photometric characteristics, the system had not yet returned to quiescence by 2007, although a fairly strong He II λ4686 Å line observed previously during quiescence in 1993 appeared in its spectrum. We model the continuum energy distribution for V1413 Aql based on a standard three-component model and a model with an accretion disk. Analysis of the forbidden O III and Ne III lines shows that the neon abundance in V1413 Aql may be enhanced with respect to the oxygen abundance. The cool component of V1413 Aql has been found to be a variable M5-type red giant, with the variability amplitude at λ = 7500 Å being at least 2
m
.
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