Terminal group effects on the fluorescence spectra of Eu(III) nitrate complexes with a family of amide-based 1,10-phenanthroline derivatives

Four ligands 1,10-phenanthroline-5,6-bis(N,N-dibenzyl-1′-oxopropylamide) (L^a) 1,10-phenanthroline-5,6-bis(N-methyl-N-benzyl-1′-oxopropylamide) (L^b) 1,10-phenanthroline-5,6-bis(N-benzyl-1′-oxopropylamide) (L^c) and 1,10-phenanthroline-5,6-bis(N,N-diethyl-1′-oxopropylamide) (L^d), and their lanthanide(III) (La and Eu) complexes were synthesized. The complexes were characterized by elemental analysis, IR, fluorescence spectroscopy and conductivity. The lanthanide atoms are coordinated by O atoms from C=O, Ar–O –C and N atoms from phen With the difference of the ligands, the fluorescent intensities of the Eu(III) complexes vary regularly in the THF solution. Some factors that influence the fluorescent intensity were discussed.     

Solvent isotope effects on the complexation and exchange kinetics of Tl(I), K and Na with 18-crown-6 by competitive NMR spectroscopy: Competition between homo- and heterobimolecular cations exchange

The thermodynamic properties of complexation and exchange kinetics of thallium by 18-crown-6 have been studied by thallium NMR spectroscopy. Effects of solvent isotope, counterion (ClO₄⁻ and NO₃⁻) and presence of competitive cations, such as Na⁺ and K⁺, on the exchange characteristics of the system have been considered. The obvious relationships between the effects of D₂O-H₂O solvent isotope on the thermodynamic properties and activation parameters of complexation have been investigated. In the absence of competitor cations, the mechanism of thallium exchange is unimolecular decomplexation and in the presence of competitor cations, homobimolecular cation exchange is the predominant mechanism at low concentrations of the ligand. At higher concentrations of the ligand, the measured rate constants show that the complexation/decomplexation process obeys a heterobimolecular cation interchange mechanism. The rate constants ratios (k_D2O/k_H2O < 1) for unimolecular mechanisms also show an inverse solvent isotope effect.     

Reassessment of the electronic absorption spectra of Cr(η6-C6H6)2, Cr(CO)6 and Cr(η6-C6H6)(CO)3

The UV absorption bands between approximately 330 and 200 nm have been assigned to Rydberg transitions for the d⁶ complexes Cr(η⁶-C₆H₆)₂, Cr(CO)₆ and Cr(η⁶-C₆H₆)(CO)₃     

铬的羰基络合物及其碳炔衍生物中铬原子的共价

用ＤＶ－Ｘα方法和自然轨道法研究了Ｃｒ（ＣＯ）_６和（ＣＯ）_４ＩＣｒＣＣＨ_３的电子结构和成键情况，并根据共价新定义讨论了其中铬原子的共价。结果表明：在（ＣＯ）_４ＩＣｒＣＣＨ_３中，Ｃｒ－Ｃ_（ｃａｒｂｙｎｅ）之间存在三重键，但其中只有σ键定域在Ｃｒ－Ｃ_（ｃａｒｂｙｎｅ）两原子之间，而两个π键已部分离域到各ＣＯ上；另外，中心铬原子上的价电子未能反馈到Ｃ_（ｃａｒｂｙｎｅ）上。两个因素同时作用，结果使Ｃ_（ｃａｒｂｙｎｅ）上的电荷密度较同一分子中的Ｃ_（ＣＯ）和Ｃ_（Ｍｅ）小．这一计算结果从理论上解释了该分子的~（１３）ＣＮＭＲ谱化学位移Ｃ_（ｃａｒｂｙｎｅ）大于Ｃ_（ＣＯ）和Ｃ_（Ｍｅ）的原因。由于在Ｃｒ（ＣＯ）_６和（ＣＯ）_４ＩＣｒＣＣＨ_３分子中铬原子均接受了１２个有效共享成键电子，根据共价新定义，铬原子共价均为１２。     

固体超强酸催化下的醛酮自身缩合及其溶剂效应的研究

研究了在三种固体超强酸催化下醛(酮)自身的羟醛缩合反应,系统考察了反应时间,催化剂用量等因素对反应的影响,优化了反应条件.同时,对该反应的溶剂效应进行了研究.结果表明,当催化剂用量为2 g/1 mol醛(酮),反应5 h,转化率可达40%,溶剂对该反应有明显的抑制作用.超强酸对各种醛都具有较好的催化活性,其催化醛类化合物自身缩合的转化率都在48%以上,选择性在95%以上,证明固体超强酸对该缩合反应有较好的催化活性和选择性.     

CO和H2分子在Cu(111)面的吸附和溶剂化效应

采用广义梯度近似(GGA)密度泛函理论(DFT)的PW91方法结合周期性模型, 在DNP基组下, 利用Dmol3模块研究了CO和H2在真空和液体石蜡环境下在Cu(111)表面上不同位置的吸附. 计算结果表明, 溶剂化效应对H2和CO的吸附结构参数和吸附能的影响非常显著. 在液体石蜡环境下, H2平行吸附在Cu(111)表面是解离吸附, 而CO 和H2在两种环境下的垂直吸附都是非解离吸附. 相比真空环境吸附, 在液体石蜡环境中, Cu(111)吸附CO时, 溶剂化效应能够提高CO吸附的稳定性, 同时有利于CO的活化. 在真空中, H2只能以垂直方式或接近垂直方式吸附在Cu(111)表面. 当Cu(111)顶位垂直吸附H2, 相比真空环境吸附, 溶剂化效应能够提高H2吸附的稳定性, 但对H2的活化没有明显影响. Cu(111)表面的桥位或三重穴位(hcp和fcc)垂直吸附H2时, 溶剂化效应能明显提高H2的活化程度, 但降低H2的吸附稳定性; 在液体石蜡中, 当H2平行Cu(111)表面吸附时, 溶剂化效应使H—H键断裂, 一个H原子吸附在fcc位, 另一个吸附在hcp位.     

Synthesis of [(μ-RS)(μ-S){Fe2(CO)6}2(μ4-S)] and their reactivity toward electrophiles

Reaction of the Et₃NH⁺ salts of the [(μ-RS)(μ-CO)Fe₂(CO)₆]⁻ anions (R=Bu^t, Ph or PhCH₂) with (μ-S₂)Fe₂(CO)₆ gives reactive intermediates [(μ-RS)(μ-S){Fe₂(CO)₆}₂(μ₄-S)]⁻. Reactions of the latter with alkyl halides, acid chlorides and Cp(CO)₂FeI have been studied. X-Ray structure of (μ-Bu^tS)(μ-PhCH₂S)[Fe₂(CO)₆]₂(μ₄-S) was determined.     

Solvent effects on the acid-catalyzed hydrolysis of tetramethylurea

Tetramethylurea was hydrolyzed in aqueous hydrochloric acid at temperatures of 80, 90, and 100°C. All reactions were carried out in an excess of both tetramethylurea and water, with first-order dependence on acid concentration being observed. As the concentration of water was increased, the rate of hydrolysis decreased until equimolar amounts of water and tetramethylurea were present. Subsequent addition of water had no effect on the observed rate.     

Thermal and spectral studies of 5-(phenylazo)-2-thiohydantoin and 5-(2- hydroxyphenylazo)-2-thiohydantoin complexes of cobalt(II), nickel(II) and copper(II)

Complexes of 5-(phenylazo)-2-thiohydantoin (L¹) and 5-(2-hydroxyphenylazo)-2-thiohydantoin (HL²) with Co(II), Ni(II) and Cu(II) salts have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The magnetic and spectral data suggested octahedral geometry for [L¹M(OAc)₂(H₂O)₂]·xH₂O {M=Ni^ll and Cu^ll} and [L¹CuCl₂(H₂O)]·H₂O (dimeric form for the latter), trigonal bipyramidal geometry for [L²Co(OAc)(H₂O)]·2H₂O, square pyramidal geometry for [L²Ni(OAc)(H₂O)]·H₂O and square planar geometry for [L²CuCl]·2H₂O. TG studies confirmed the chemical formulations of these complexes and showed that their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic parameters (n, E^#, A, ΔH^#, ΔS^# and ΔG^#) of the thermal decomposition stages were computed using the Coats-Redfern and other standard equations and are discussed.     

Understanding the enthalpic and entropic contributions to solvent effects on osmium tetroxide complexation with pyridine

Solvent effects on the complex formation of osmium tetroxide (which is the most reliable reagent available for the cis-hydroxylation of alkenes) and pyridine were investigated using spectrophotometric techniques in different solvents (benzene, chloroform, acetone, acetonitrile, anisole, tetrahydrofuran, nitrobenzene and nitromethane). The enthalpy and entropy exhibit opposing effects on stability constant with the change in solvent. In these solvents, the entropy and enthalpy of the reaction are found to be mainly influenced by the donor number (DN) of the solvents.     

Silanolato-Komplexe von Titan und Zirconium. Die Kristallstrukturen von Cp2TiCl(OSiPh3) und Cp2ZrCl(OSiPh3)

Silanolato Complexes of Titanium and Zirconium. The Crystal Structures of Cp₂TiCl(OSiPh₃) and Cp₂ZrCl(OSiPh₃) The title compounds have been prepared by the reaction of Cp₂MCl₂ (M = Ti, Zr) with triphenylsilanole in diethylether in the presence of piperidine. They form only sparingly moisture sensitive orange (Ti) or colourless (Zr) crystal needles, which were characterized by X-ray crystallography. Cp₂TiCl(OSiPh₃): Space group P2₁/n, Z = 4, structure solution with 3961 observed unique reflections, R = 0.057. Lattice dimensions at 20°C: a = 1029.6, b = 1719.3, c = 1388.9 pm, β = 100.69°. The compound forms monomeric molecules with bond lengths TiO of 184.2 pm, SiO of 161.5 pm, and a TiOSi bonding angle of 164.5°. Cp₂ZrCl(OSiPh₃): Space group P3 , Z = 18, structure solution with 2799 observed unique reflections, R = 0.047. Lattice dimensions at ?20°C: a = b = 3518, c = 1058.3 pm. The structure consists of three symmetry-independent monomeric molecules, which differ only slightly. The bond lengths are (in average): ZrO 196.4 pm, SiO 162.1 pm, the ZrOSi bond angle is 173.7°.     

Solvent and guest isotope effects on complexation thermodynamics of alpha-, beta-, and 6-amino-6-deoxy-beta-cyclodextrins

The stability constant (K), standard free energy (DeltaG degrees ), enthalpy (DeltaH degrees ), and entropy changes (TDeltaS degrees ) for the complexation of native alpha- and beta-cyclodextrins (CDs) and 6-amino-6-deoxy-beta-CD with more than 30 neutral, positively, and negatively charged guests, including seven fully or partially deuterated guests, have been determined in phosphate buffer solutions (pH/pD 6.9) of hydrogen oxide (H(2)O) or deuterium oxide (D(2)O) at 298.15 K by titration microcalorimetry. Upon complexation with these native and modified CDs, both nondeuterated and deuterated guests examined consistently exhibited higher affinities (by 5-20%) in D(2)O than in H(2)O. The quantitative affinity enhancement in D(2)O versus H(2)O directly correlates with the size and strength of the hydration shell around the charged/hydrophilic group of the guest. For that reason, negatively/positively charged guests, possessing a relatively large and strong hydration shell, afford smaller K(H2O)/K(D2O) ratios than those for neutral guests with a smaller and weaker hydration shell. Deuterated guests showed lower affinities (by 5-15%) than the relevant nondeuterated guests in both H(2)O and D(2)O, which is most likely ascribed to the lower ability of the C-D bond to produce induced dipoles and thus the reduced intracavity van der Waals interactions. The excellent enthalpy-entropy correlation obtained can be taken as evidence for the very limited conformational changes upon transfer of CD complexes from H(2)O to D(2)O.     

Synthesis and Mossbauer Spectra Studies of Mono-Binuclear Iron(III) Complexes with a Quinquedentate Ligand Derived from Saucylaldehyeds and Diethylenetriamine

Mono- and bi-nuclear iron(III) complexes of general formula [FeXL] and [LFe-Y-FeL](Bph₄)₂ have been prepared, and their spin state of iron atom in the complexes has been studied by means of the temperature dependence of the Mössbauer spectra, electronic spectra and magnetic measurement, where X is a mono- dentate ligand such as Cl-, NCS-, NCO-, N3-, pyridine and L denotes a quinquedentate Schiff base derived from salicylaldehyde and diethylenetriamine, and Y denotes bridged ligand such as pyrazine(pyr), 4,4′-bipyridine(bpy) and 4,4′-vinylenebipyridine(vibpy). On the basis of the Mössbauer and magnetic data, it was concluded that these complexes were all the high-spin (S = 5/2) slate. The effect of gamma ray irradiation for these complexes has been discussed.     

Solvent effects on the nπ* transition of pyrimidine in aqueous solution

A hybrid quantum mechanical and molecular mechanical potential is used in Monte Carlo simulations to examine the solvent effects on the electronic excitation energy for the n→π* transition of pyrimidine in aqueous solution. In the present study, the pyrimidine molecule is described by the semi-empirical AM1 model, while the solvent molecules are treated classically. Two sets of calculations are performed: the first involves the use of the pairwise three-point charge TIP3P model for water, and the second computation employs a polarizable many-body potential for the solvent. The latter calculation takes into account the effect of solvent polarization following the solute electronic excitation, and makes a correction to the energies determined using pairwise potentials, which neglects such fast polarization effects and overestimates the solute-solvent interactions on the Franck-Condon excited states. Our simulation studies of pyrimidine in water indicate that the solvent charge redistribution following the solute electronic excitation makes modest corrections (about −130␣cm⁻¹) to the energy predicted by using pairwise potentials. Specific hydrogen bonding interactions between pyrimidine and water are important for the prediction of solvatochromic shifts for pyrimidine. The computed n→π* blue shift is 2275±110 cm⁻¹, which may be compared with the experimental value (2700 cm⁻¹) from isooctane to water. Received: 14 January 1997 / Accepted: 21 February 1997     

Synthesis and Thermodynamic Investigation of 4-Amino-6-Hydroxy-2-Mercapto Pyrimidine (AHMP) Complexes with Some Selected Divalent Metal(II) Ions

The synthesis and characterization of zinc(II), cadmium(II), lead(II), mercury(II) and phenylmercury(II) complexes of 4-amino-6-hydroxy-2-mercapto pyrimidine (AHMP) are reported. The stoichiometry of the complexes was found to be 1:2 except for the phenylmercury(II) complex where the ratio is 1:1. Characterization of these complexes was carried out by means of elemental analyses, IR and ¹H NMR measurements. In these complexes the ligand is bonded to the metal through its sulfur atom. The potentiometric results showed the formation of 1:1 and 1:2 complexes and the corresponding stability constants were determined for both Zn(II) and Cd(II) ions. The high insolubility of mercury(II), phenylmercury(II) and lead(II) complexes prevented the determination of their stability constants. The concentration distribution of the complexes in solution was evaluated. The effect of temperature on the dissociation constant of AHMP and the formation constants of both the Zn-AHMP and Cd-AHMP complexes were studied and the thermodynamic parameters were calculated.     

Synthesis,spectral, electrochemical and biological studies of Co(II), Ni(II) and Cu(II) complexes with Schiff bases of 8-formyl-7-hydroxy-4-methyl coumarin

A series of Co(II), Ni(II) and Cu(II) complexes have been synthesized with Schiff bases derived from 8-formyl-7-hydroxy-4-methyl coumarin and o-chloroaniline/o-toluidine. The structures of the complexes have been proposed from analytical, spectral (IR, UV-Vis, ESR and FAB-mass), magnetic, thermal and fluorescence studies. The complexes are soluble in DMF and DMSO and molar conductance values indicate the complexes are non-electrolytes. Elemental analyses indicate ML₂ · 2H₂O [M = Co(II), Ni(II) and Cu(II)] stoichiometry. Spectroscopic studies (IR, UV-Vis, ESR and fluorescence) indicate octahedral geometry, in which ligand coordinates through azomethine nitrogen and phenolic oxygen via deprotonation. Thermal studies suggest coordination of water to the metal ion. Redox behavior of the complexes was investigated by cyclic voltammetry. The Schiff bases and their complexes were screened for their antibacterial (E. coli, S. aureus, P. aeruginosa and S. typhi) and antifungal activities (A. niger, A. flavus and Cladosporium) by MIC method.     

Solvent and concentration effects on fluorescence emission in MEH-PPV solution

We systematically studied the excitation and the fluorescence steady-state spectroscopy of poly[2-methoxy-5-(2′-ethylhexoxy)-p-phenylene vinylene] (MEH-PPV) in two solvents and several concentrations. Fluorescence spectra were recorded for solutions in several concentrations (10⁻⁵ mg/ml to 10⁻³ mg/ml), showing that tetrahydrofuran (THF) and toluene solvate the polymer chain differently. Dilute solution (10⁻⁵ mg/ml) in THF exhibit broader fluorescence spectra due to greater conformation disorder. The degree of the aggregation depends on both the solvent and the polymer concentration. Aggregation is promoted in toluene solution and hindered in THF solvent.     

Complexation of phthalides and substituted 3-benzylidene phthalides with Cr(CO)6

The acid-catalysed complexation of various substituted phthalides with Cr(CO)₆ has been studied. Complexation of substituted 3-benzylidene phthalides takes place at the phenyl ring in most cases, but with di-halogeno-substituted 3-benzylidene phthalides the complexation took place at the phthalide moiety. An explanation of this difference is based on molecular modelling quantum chemical calculations.