Metal–metal bonding and structures of trinickel and tricobalt dipyridylamido complexes from surface‐enhanced Raman spectra

We recorded surface‐enhanced Raman scattering (SERS) spectra of metal‐string complexes Co₃(dpa)₄ Cl₂ [di(2‐pyridyl)amido (dpa)], Ni₃(dpa)₄ Cl₂ and the oxidized form of the Ni₃ complex to determine their vibrational wavenumbers and to investigate their structures. For SERS measurements these complexes were adsorbed on silver nanoparticles in aqueous solution to eliminate the constraint of a crystal lattice and the complexes remain in thermal equilibrium. From our analysis of the vibrational normal modes we assigned the SERS lines at 242 and 276 cm⁻¹ to Ni₃ and Co₃ symmetric‐stretching modes of the symmetric form. For Co₃ (dpa)₄Cl₂ a Raman line at 383 cm⁻¹ was assigned to the Co Co stretching mode of the unsymmetric form. The wavenumber of the Ni₃ symmetric‐stretching mode of the oxidized form [Ni₃(dpa)₄]³⁺ is 274 cm⁻¹, greater than that for neutral Ni₃(dpa)₄Cl₂, in agreement with a prediction of delocalized molecular‐orbital theory that an electron is removed from an antibonding orbital after oxidation. The experimental data show that the SERS technique serves as an excellent tool to observe the variation of metal–metal bonding during an oxidation or reduction reaction. Copyright © 2010 John Wiley & Sons, Ltd.     

4-Port polarization-independent wavelength-interleaving bidirectional circulator

This study develops an alternative type of 4-port polarization-independent wavelength-interleaving bidirectional circulator. In this circulator the even- and odd-channels circulate with opposite handedness regardless of the state of polarization of signals. It has a pair of orthogonal holographic spatial- and polarization modules (HSPMs) and a Lyot-Ohman filter (LOF). Each HSPM has two holographic spatial walk-off polarizers (HSWPs), two glass plates and two half-wave plates. The function of the HSWP is firstly described. Next, the structures and the operating principles of the HSPM and the LOF are also described. Then, the operating principle and the performance of this circulator are discussed. It has such merits as polarization-independence, compactness, high isolation, lack of polarization mode dispersion and ease of fabrication.     

Novel chloride-centered discrete CuI8 cubic clusters containing diselenophosphate ligands. Syntheses and structures of [Cu8(mu8-Cl)[Se2P(OR)2](6)](PF6) (R = Et,Pr, iPr)1

Three clusters 1-3, Cu(8)(mu8-Cl)[Se(2)P(OR)(2)](6)(PF(6)) (R= Et, Pr, (i)Pr), were synthesized in high yield from the reaction of [Cu(CH(3)CN)(4)](PF(6)), NH(4)[Se(2)P(OR)(2)], and Bu(4)NCl in a molar ratio of 4:3:1 in diethyl ether. FAB mass spectra show m/z peaks at 2218.10 for 1, 2386.10 for 2, and 2387.34 for 3 which are due to molecular cations, [1-PF(6)]+, [2-PF(6)]+, and [3-PF(6)]+, respectively. (31)P NMR spectra of 1-3 display a singlet at delta 76.48, 76.73, and 69.32 ppm with satellites (J(PSe) = 652, 653, and 648 Hz), respectively. The (77)Se NMR spectra of 1-3 exhibit a doublet peak at -21.7, -16.42, and 2.3 ppm, respectively (J(SeP) = 652 Hz for 1, 653 Hz for 2, and 648 Hz for 3). The X-ray structure (1-3) consists of a discrete cationic cluster in which eight copper ions are linked by six diselenophosphate ligands and a central mu8-Cl ion with a noncoordinating PF(6)(-) anion. The shape of the molecule is a chloride-centered distorted Cu(8) cube in clusters 1 and 2 and a near perfect Cu(8) cube for cluster 3. The dsep ligand exhibits a tetrametallic tetraconnective (mu2, mu2)) coordination pattern, and each occupies a square face of the cube. Each copper atom of the cube is coordinated by three selenium atoms with a strong interaction with the central chloride ion. The observed Cu-Cl distances lie in the range 2.649-2.878 A.     

Capillary zone electrophoretic separation of neutral species of chloro-s-triazines in the presence of cationic surfactant monomers

Chloro-s-triazines are difficult to separate by capillary zone electrophoresis (CZE), due to their low pKa values. However, these analytes can be effectively separated by CZE in the presence of cationic surfactant monomers, such as tetradecylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB). The separation mechanism based on a 1:1 binding of analytes to cationic surfactant monomers is proposed. The binding constants of chloro-s-triazines to cationic surfactant monomers are estimated. The results show that the strength of the interactions of these analytes with TTAB monomers is considerably strong, whereas that of the corresponding analyte with DTAB monomers is about 12- to 14-fold weaker. A linear correlation of binding constants with log P(ow) (the logarithm of the partition coefficient of analytes between 1-octanol and aqueous phases) indicates that the migration order of these chloro-s-triazines depends primarily on their hydrophobicity. Moreover, the skewed peaks of chloro-s-triazines observed may reveal the occurrence of adsolubilization of these analytes in the adsorbed cationic surfactant layer on the capillary surface.     

Synthesis,structure, and reactivity of uranium(vi) nitrides

Uranium nitride compounds are important molecular analogues of uranium nitride materials such as UN and UN₂ which are effective catalysts in the Haber–Bosch synthesis of ammonia, but the synthesis of molecular nitrides remains a challenge and studies of the reactivity and of the nature of the bonding are poorly developed. Here we report the synthesis of the first nitride bridged uranium complexes containing U(vi) and provide a unique comparison of reactivity and bonding in U(vi)/U(vi), U(vi)/U(v) and U(v)/U(v) systems. Oxidation of the U(v)/U(v) bis-nitride [K₂{U(OSi(O^tBu)₃)₃(μ-N)}₂], 1, with mild oxidants yields the U(v)/U(vi) complexes [K{U(OSi(O^tBu)₃)₃(μ-N)}₂], 2 and [K₂{U(OSi(O^tBu)₃)₃}₂(μ-N)₂(μ-I)], 3 while oxidation with a stronger oxidant (“magic blue”) yields the U(vi)/U(vi) complex [{U(OSi(O^tBu)₃)₃}₂(μ-N)₂(μ-thf)], 4. The three complexes show very different stability and reactivity, with N₂ release observed for complex 4. Complex 2 undergoes hydrogenolysis to yield imido bridged [K₂{U(OSi(O^tBu)₃)₃(μ-NH)}₂], 6 and rare amido bridged U(iv)/U(iv) complexes [{U(OSi(O^tBu)₃)₃}₂(μ-NH₂)₂(μ-thf)], 7 while no hydrogenolysis could be observed for 4. Both complexes 2 and 4 react with H⁺ to yield quantitatively NH₄Cl, but only complex 2 reacts with CO and H₂. Differences in reactivity can be related to significant differences in the U–N bonding. Computational studies show a delocalised bond across the U–N–U for 1 and 2, but an asymmetric bonding scheme is found for the U(vi)/U(vi) complex 4 which shows a U–N σ orbital well localised to U N and π orbitals which partially delocalise to form the U–N single bond with the other uranium.

The first examples of molecular compounds containing the cyclic (U(vi)N)₂ and (U(v)U(vi)N)₂ cores were obtained by oxidation of the (U(v)U(v)N)₂ analogue. Different bonding within these complexes yields different stability and reactivity with CO and H₂.     

Molecular Nonlinear Optical Properties of Acceptors Substituted 2,2′‐Bipyridine and 1,10‐Phenathroline Complexes of Nickel Dithiolate

Linear and nonlinear optical properties of two new nickel(diimine)(dithiolate) complexes, nickel(4,4′‐dinitro2,2′‐bipyridyl)(tfd), Ni(NO₂bipy)(tfd) , (tfd = 1,2‐trifluoromethylethene‐1,2‐dithiolate) and nickel(4,7‐diphenyl‐1,10‐phenathroline)(tfd), Ni(dpphen)(tfd) are reported. Ni(NO₂bipy)(tfd) has a potent electronic acceptor substituted on the diimine ligand and exhibits an enhanced molecular first hyperpolarizability (β₀ = ?31 × 10^?30 esu), which is more than three times greater than that (β₀ = ?10 × 10^?30 esu) of Ni(dpphen)(tfd). Ni(NO₂bipy)(tfd) also possesses the longest absorption wavelength, the largest solvatochromic shift, and one of the largest dipole moment changes (‐16 debye from ground to excited state) among nickel(diimine)(dithiolate) complexes. Crystal X‐ray structure of Ni(NO₂bipy)(tfd) is used to compared the π‐bonding structure of central (N=C‐C=N)Ni(S‐C=C‐S) unit with that of previously known nickel(4,4′‐bis(butyloxycarbonyl)‐2,2′‐bipyridyl)(tfd), Ni(CO₂Bubipy)(tfd).     

μ‐Oxo‐bis{{2,2′‐[2,2‐di­methyl­propane‐1,3‐diyl­bis­(nitrilomethyl­idyne)]­diphenolato}­oxo­rhenium(V)}

The title compound, [Re₂O₃(C₁₉H₂₀N₂O₂)₂], is a hexacoordinate complex containing an [Re₂O₃]⁴⁺ core with a linear O=Re—O—Re=O bridge. The distorted octahedral coordination of the Re^V atom is achieved by an N₂O₂ donor set from the tetradentate imine–phenol ligand. The overall charge of the compound is neutral due to deprotonation of the phenol groups, and the terminating and bridging O atoms. The Re=O and Re—O bond distances of the [Re₂O₃]⁴⁺ core are 1.699 (4) and 1.911 (1) Å, respectively. The Re—O and Re—N bond distances of the equatorial plane are in the ranges 2.024 (4)–2.013 (4) and 2.128 (5)–2.120 (5) Å, respectively.     

裂纹尖端场弹塑性分析的加权残数法及塑性应力强度因子的计算

本文以幂强化材料,平面应变情形为例,系统地提出了裂纹尖端场弹塑性分析的加权残数法,并根据此法,得出了裂纹尖端场的解析式弹塑性近似解.在此基础上.对整个裂纹区域,构造了弹塑性解叠加非线性有限元计算塑性应力强度因子的方法,从而为裂纹尖端场和整个裂纹体的分析和计算,提供了一个方法.