Coordination chemistry of Group 12 metals with phosphorodiselenoates: syntheses, structures and VT 31P NMR study of monomer-dimer exchange equilibrium

The reactions of diselenophosphates, [dsep, (RO)2PSe2-; R = Et, (n)Pr and (i)Pr] with cadmium(II) and mercury(II) perchlorates in a 2 : 1 molar ratio formed compounds of stoichiometry M[Se2P(OR)2]2{M = Cd, R = Et (1), (n)Pr (2), (i)Pr (3); Hg, Et(4), (n)Pr (5), (i)Pr (6)}, and with zinc(II) perchlorates, chalcogen centered tetranuclear clusters, [Zn4(micro4-E){Se2P(OR)2}6]{E = Se, R = Et (7), (n)Pr (8), (i)Pr (9); E = O, R = Et (10), (n)Pr (11), (i)Pr (12)} were formed. All these complexes have been characterized with the help of analytical data, X-ray crystallography (1, 3, 6, 10, 11 and 12), and FAB-mass spectrometry (7-12). Compound 1 is a linear double-chain polymer, in which each pair of Cd atoms is bridged by two dsep ligands; the mercury 6 polymer has a helical chain structure, in which two Hg atoms are bridged by one dsep ligand, and the other ligand chelates the Hg atom. The chelating dsep ligands lie on either side of the helical chain. Compound 3 exists as a dimer in which two cadmium atoms are connected by two bridging dsep ligands, and each cadmium atom is further chelated by a dsep ligand. The metal atoms in 1, 3 and 6 are each coordinated by four selenium atoms in a distorted tetrahedral geometry. Clusters 10-12 have tetrahedral array of zinc atoms with an oxygen atom in the center with edge-bridging dsep ligands. Positive FAB-mass spectra support the formation of selenium-centered clusters,7-9, of which the cluster 8 was structurally confirmed earlier. The solution state behavior of compounds 1-12 has been studied by using multinuclear NMR spectroscopy. Dimer 3 in CD2Cl2 showed monomer-dimer exchange equilibrium in the temperature range 20 to -90 degrees C and the free energy of activation is calculated from the coalescence temperature as DeltaG++(223 K)= 38.5 kJ mol(-1). Polymer undergoes depolymerization in CDCl3 and exhibits monomer-dimer exchange equilibrium in the temperature range 20 to -60 degrees C.     

Mononuclear [NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- (L = thiolate, selenolate, PPh3, and Cl) complexes with intramolecular [Ni...S...H...S]/[Ni...H...S] interactions modulated by the coordinated ligand L: relevance to the [NiFe] hydrogenases

The shift of the IR nu(S)(-)(H) frequency to lower wavenumbers for the series of complexes [Ni(II)(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- (L = PPh3 (1), Cl (6), Se-p-C6H4-Cl (5), S-C4H3S (7), SePh (4)) indicates that a trend of increasing electronic donation of the L ligands coordinated to the Ni(II) center promotes intramolecular [Ni-S...H-S] interactions. Compared to the Ni...S(H) distance, in the range of 3.609-3.802 A in complexes 1 and 4-7, the Ni...S(CH3) distances of 2.540 and 2.914 A observed in the [Ni(II)(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] complexes (8a and 8b, two conformational isomers with the chemical shift of the thioether methyl group at delta 1.820 (-60 degrees C) and 2.109 ppm (60 degrees C) (C4D8O)) and the Ni...S(CH3) distances of 3.258 and 3.229 A found in the [Ni(II)(L)(P(o-C6H4S)2(o-C6H4-SCH3))]1- complexes (L = SPh (9), SePh (10)) also support the idea that the pendant thiol protons of the Ni(II)-thiol complexes 1/4-7 were attracted by both the sulfur of thiolate and the nickel. The increased basicity (electronic density) of the nickel center regulated by the monodentate ligand attracted the proton of the pendant thiol effectively and caused the weaker S...H bond. In addition, the pendant thiol interaction modes in the solid state (complexes 1a and 1b, Scheme 1) may be controlled by the solvent of crystallization. Compared to complex 1a, the stronger intramolecular [Ni-S...H-S] interaction (or a combination of [Ni-S...H-S]/[Ni...H-S] interactions) found in complexes 4-7 led to the weaker S-H bond strength and accelerated the oxidation (by O2) of complexes 4-7 to produce the [Ni(Y)(L)(P(o-C6H4S)3)]1- (L = Se-p-C6H4-Cl (11), SePh (12), S-C4H3S (13)) complexes.     

Neutral {Fe(NO)2}9 dinitrosyliron complex (DNIC) [(SC6H4-o-NHCOPh)(Im)Fe(NO)2] (Im = imidazole): interconversion among the anionic/neutral {Fe(NO)2}9 DNICs and Roussin's red ester

A neutral {Fe(NO)2}9 dinitrosyliron complex (DNIC) [(SC6H4-o-NHCOPh)(Im)Fe(NO)2] (Im = imidazole; 2) was prepared by the reaction of [Fe(mu-SC6H4-o-NHCOPh)(NO)2]2 (1) and 2 equiv of imidazole. In the synthesis of the anionic {Fe(NO)2}9 DNIC [(SC6H4-o-NHCOPh)2Fe(NO)2]- (3), thiolate [SC6H4-o-NHCOPh]- triggers ligand substitution of DNIC 2 to yield DNIC 3. At 298 K, complexes 2 and 3 exhibit well-resolved nine- and five-line electron paramagnetic resonance (EPR) signals at g = 2.031 and 2.029, respectively, the characteristic g value of DNICs. The facile interconversions among the neutral {Fe(NO)2}9 complex 2, the anionic {Fe(NO)2}9 complex 3, and Roussin's red ester 1 were demonstrated. The EPR spectrum (the pattern of hyperfine splitting) in combination with the IR nu(NO) (the relative position of the nu(NO) stretching frequencies) spectrum may serve as an efficient tool for the discrimination of the anionic {Fe(NO)2}9 DNICs, the neutral {Fe(NO)2}9 DNICs, and Roussin's red ester.     

Rank one perturbations and singular integral operators

We consider rank one perturbations Aα=A+α(⋅,φ)φ of a self-adjoint operator A with cyclic vector φ∈H−1(A) on a Hilbert space H. The spectral representation of the perturbed operator Aα is given by a singular integral operator of special form. Such operators exhibit what we call ‘rigidity’ and are connected with two weight estimates for the Hilbert transform. Also, some results about two weight estimates of Cauchy (Hilbert) transforms are proved. In particular, it is proved that the regularized Cauchy transforms Tε are uniformly (in ε) bounded operators from L²(μ) to L²(μα), where μ and μα are the spectral measures of A and Aα, respectively. As an application, a sufficient condition for Aα to have a pure absolutely continuous spectrum on a closed interval is given in terms of the density of the spectral measure of A with respect to φ. Some examples, like Jacobi matrices and Schrödinger operators with L² potentials are considered.     

A restricted sum formula among multiple zeta values

For positive integers α₁,α₂,…,αr with αr?2, the multiple zeta value or r-fold Euler sum is defined as

     

Wavelength-dependent Faraday–Tyndall effect on laser-induced microbubble in gold colloid

The cavitation microbubbles in dilute gold colloids of different concentrations (2–10 ppm) induced by a focused nanosecond-pulsed laser beam were measured and characterized at different wavelengths by using the passive and active ultrasound measurements. Three colloids with gold nanoparticles (GNPs) of different sizes (10, 45, and 75 nm) were used for experiment. The results show that the lifespan of the microbubble is reduced as the concentration of GNP increases, particularly at the wavelength of 532 nm, the surface plasmon resonance (SPR) of GNP. In contrast, at the off-resonant wavelength (e.g. 700 nm), the lifespan reduction is relatively small. This wavelength-dependent cavitation is attributed to the Faraday–Tyndall effect, a strong light scattering by GNPs. A slight defocusing of the Gaussian beam in gold colloid was proposed. Hence, the waist of the focused beam increases to reduce the optical breakdown in gold colloid. For simplicity, a linear relation between the incremental waist radius of Gaussian beam and the concentration of GNP was assumed. According to this formulation, the theoretical results are consistent with the experimental ones. In addition, the dynamics of the microbubble in gold colloid measured by the active ultrasound method agree with the Rayleigh–Plesset model.     

Linear-cavity fiber laser in nearly single-frequency operation using Faraday rotator mirror

A nearly single-frequency selection is realized in a linear-cavity fiber laser constructed using a Faraday rotator mirror (FRM) and a partial reflectance fiber Bragg grating (FBG) as the cavity ends. At 1552.46 nm wavelength, the measured optical signal-to-noise-ratio (OSNR) is 58.5 dB with a linewidth less than 400MHz obtained using a subring cavity and a polarization controller as the mode filters. The pumping efficiency is improved by 10% by recycling the residual pump power to the gain medium.     

Synthesis and characterization of new soluble polyamides containing phthalimide pendent group

A dicarboxylic acid monomer, 5-phthalimidoisophthalic acid, containing a phthalimide pendent group was prepared by the condensation of 5-aminoisophthalic acid and phthalic anhydride in glacial acetic anhydride. The monomer was reacted with various aromatic diamines to produce polyamides using triphenyl phosphite and pyridine as condensing agents. These polyamides were produced with inherent viscosities of 0.64–1.14 dL · g⁻¹. All the polymers, characterized by wide-angle X-ray diffraction, revealed an amorphous nature resulting from the presence of the bulky pendent group. These polyamides exhibited excellent solubility in a variety of solvents such as N- methyl-2-pyrrolidinone, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, dimethyl sulfoxide, pyridine, and cyclohexanone. These polyamides showed glass-transition temperatures (T_g's) between 247 and 273 °C (by DSC) and 248 and 337 °C (by a dynamic mechanical analyzer). The thermogravimetric analytic measurement revealed the decomposition temperature at 10% weight-loss temperatures (Td₁₀) ranging from 442 to 530 °C in nitrogen. The polyamides containing phthalimide groups exhibited higher T_g and Td₁₀ values than those having no phthalimide groups. Transparent, tough, and flexible films of these polyamides could be cast from the DMAc solutions. These casting films had tensile strengths ranging from 81 to 126 MPa, elongations at break ranging from 7 to 13%, and tensile moduli ranging from 2.0 to 2.9 GPa. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1557–1563, 2001     

Polymerization of 1-methoxy-1-ethynylcyclohexane by transition metal catalysts

The polymerization of 1-methoxy-1-ethynylcyclohexane (MEC) was carried out by various transition metal catalysts. The catalysts MoCl₅, MoCl₄, and WCl₆ gave a relatively low yield of polymer (≤ 16%). The catalytic activity of Mo-based chloride catalyst was greater than that of W-based chloride catalyst. However, catalyst tungsten carbene complex (I) gave a larger molar mass and higher yield in the presence of a Lewis acid such as AlCl₃ than in the absence of a Lewis acid. The activity of the tungsten carbene complex was obviously affected by Lewis acidity. The catalyst PdCl₂ was a very effective catalyst for the present polymerization and gave polymers in a high yield. The structure of the resulting poly(MEC) was identified by various instrumental methods as a conjugated polyene structure having an α-methoxycyclohexyl substituent. The poly(MEC)s were mostly light-brown powders and completely soluble in various organic solvents such as tetrahydrofuran (THF), chloroform (CHCl₃), ethylacetate, n-butylacetate, dimethylformamide, benzene, xylene, dimethylacetamide, 1,4-dioxane, pyridine, and 1-methyl-2-pyrrolidinone. Thermogravimetric analysis showed that the polymer started to lose mass at 125°C and that maximum decomposition occurred at 418°C. The x-ray diffraction diagram shows that poly(MEC) has an amorphous structure. © 1997 John Wiley & Sons, Inc.     

Synthesis of polyphosphates by the polyaddition of bisphenol-S diglycidyl ether and aryl phosphorodichloridates

In this study, we synthesized polyphosphates with reactive pendant chloromethyl groups by an addition reaction of the diglycidyl ether of bisphenol-S (bisphenol-S epoxy, BPSE) with aryl phosphorodichloridates. The polyphosphates obtained were characterized by IR, ¹H NMR spectra, elemental analysis, TGA, DSC, X-ray diffraction, and molar mass measurement. The polyaddition proceeded very smoothly in aromatic solvents catalyzed by quaternary ammonium or phosphonium salts such as tetrabutylammonium bromide and tetrabutylphosphonium bromide to produce a polymer having a high molecular weight. Polymer B, containing a bromine atom in the phenyl ring side chain, has the higher T_g value (T_g = 58°C) than the polyphosphate derived from phenoxy dichlorophosphate (PDCP). Polymer A derived from PDCP begins to lose 10% of its mass at 278°C, and the mass percentage remaining at 700°C is 44% under nitrogen. X-ray diffraction patterns revealed that all the subsequent polyphosphates are amorphous. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2365–2369, 1997