A comparative study of surface acidity in the amorphous, high surface area solids, aluminium fluoride, magnesium fluoride and magnesium fluoride containing iron(III) or aluminium(III) fluorides

The behaviour of the sol–gel prepared, amorphous solids, high surface area (HS) aluminium fluoride and magnesium fluoride in promoting room temperature dehydrochlorination of tert-butyl chloride (Bu^tCl), in their catalytic activity for the dismutation of chlorodifluoromethane and in the temperature programmed desorption of ammonia is similar, indicating that, unexpectedly, both solids exhibit significant surface Lewis acidity. Using a similar approach, it has been demonstrated that surface Lewis acidity in HS-MgF₂ is enhanced by the incorporation of amorphous iron(III) fluoride and probably also by amorphous aluminium(III) fluoride. A second, unexpected feature is the substantial retention of anhydrous hydrogen chloride by all the solids, which is observed by the use of chlorine-36 labelling, when they are exposed at room temperature either to Bu^tCl or to HCl directly. The detailed behaviour of H³⁶Cl towards HS-AlF₃ depends on the fluorinating agent, dichlorodifluoromethane or anhydrous hydrogen fluoride, which is used in the second stage of HS-AlF₃ synthesis. This observation and the pattern of the results obtained overall lead to the proposal that strongly adsorbed HCl behaves as an unconventional Lewis base towards these solids.     

Improvement of stability and luminescence properties in water of Eu(III) and Tb(III) complexes photosensitized by a bipyridine antenna

The convenient synthesis of a new macrocyclic octadentate chelate based on 2,2′-bipyridine chromophore and diethylenetriaminetriacetic acid core is described. In aqueous solutions, the corresponding Eu(III) and Tb(III) neutral complexes are kinetically inert and show very bright luminescence when excited with UV radiation (Φ=11 and 25% respectively). We also report the potentiality of these complexes to act as donors in delayed fluorescence resonance energy transfer (DEFRET).     

锰(III)5,10,15-三(五氟苯基)-Corrole配合物的DFT计算

在6-31G*水平上采用DFT(UB3LYP)方法对锰(III)5,10,15-三(五氟苯基)-corrole [(TPFC)MnIII]及其咪唑轴向配位加合物(TPFC)MnIII(Im)进行了几何结构全优化. 计算结果表明, 咪唑的配位作用不会改变其基态的高自旋(s=2)特性. (TPFC)MnIII与咪唑配位形成轴向加合物后, 其中心金属Mn原子偏离平面结构, 与corrole大环N4平均平面的距离达到0.02734 nm. NBO分析显示(TPFC)MnIII和(TPFC)MnIII(Im)中心金属锰的电子组态为(dxz)1(dyz)1(dz2)1(dx2-y2)1(dxy)0. (TPFC)MnIII(Im)前线分子轨道能级明显上升, 从其β-(LUMO+3)轨道可见咪唑配位N原子的py轨道与中心金属Mn原子dyz轨道形成了d-pπ轨道. TD-DFT计算发现, (TPFC)MnIII和(TPFC)MnIII(Im)电子光谱Q带的“四轨”特征比B 带明显; (TPFC)MnIII的CT带主要源自β-(HOMO-1)→β-(LUMO+5)和β-HOMO→β-(LUMO+4)的跃迁, (TPFC)MnIII(Im)的CT带则主要源自β-(HOMO-1)→β-(LUMO+3)和β-HOMO→β-(LUMO+4)的跃迁.     

Determination of cerium(III) ions in soil and sediment samples by Ce(III) PVC-based membrane electrode based on 2,5-dioxo-4-imidazolidinyl

2,5-Dioxo-4-imidazolidinyl was used as an excellent sensing material in the preparation of a PVC membrane for a Ce(III)-selective sensor. The electrode shows a good selectivity for the Ce(III) ion with respect to most common cations including alkali, alkaline earth, transition, and heavy metal ions. The developed sensor exhibits a wide linear response with a slope of 19.6?±?0.3 mV per decade over the concentration range of 1.0?×?10^?6 to 1.0?×?10^?1 M, while the illustrated detection limit is 5.7?×?10^?7 M of Ce(III) ions. Moreover, it is concluded that the sensor response is pH-independent in the range of 3.1–9.8. The applications of the recommended electrode include the determination of concentration of Ce(III) ions in soil and sediment samples, validation with CRM's, and the Ce(III) ion potentiometric titration with EDTA as an indicator electrode.     

Voltammetric response of the interface between single-crystal cerium fluoride and metallic microelectrodes

The processes occurring at the interface between single-crystal fluoride-conducting solid electrolyte CeF₃: Sr²⁺ and metallic microelectrodes of Bi, Sn, Sb, and Ag are studied by the method of cyclic voltammetry with use of traditional silver-silver chloride electrode or solid-phase reference electrode Sn, SnF₂. Responses of solid-phase reactions involving mobile fluoride ions of the solid electrolyte and the microelectrode material are obtained. It is suggested that signals relating to the reduction of fluorinated metals be used for local qualitative assay of metal traces contained in quantities of about a few nanograms on the surface of conducting solids in air.     

Voltammetric and spectroscopic studies of water/formamide ratios in the production of the cerium (III) hexacyanoferrate (II) nanoparticles

The present study describes the simple and fast preparation of Cerium (III) hexacyanoferrate (II) (CeHCF) solid nanoparticles at three different water/formamide (%) ratios used as solvent (v/v) (100:0, 80:20, 0:100). CeHCF nanoparticles (Nps) were characterized by fourier transform infrared pectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), zeta potential and cyclic voltammetry (CV). Electrodes modified with CeHCF presented a well-defined redox pair with formal potential (E^o′) of approximately 0.29 V (vs. Ag/AgCl(sat) attributed to the Fe^{2 +}/Fe³⁺ redox pair in the presence of cerium (III)). The Nps in the three systems investigates, presents a random size distribution to different surface, where most were distributed between 20 and 160 nm. Considering the three investigated systems, only CeHCF-1 (100:0) was sensitive to L-dopamine, presenting a linear signal region as a function of L-dopamine concentrations, with a limit of detection (LD) of 0.125 mmol L⁻¹, limit of quantification (LQ) of 0.419 mmol L⁻¹ and amperometric sensitivity (S) of 148.16 μA mmol L⁻¹.     

Structures and Chemical Bonding in Antimony(III) Bromide Complexes with Pyridine

Weakly or “partially” bonded molecules are an important link between the chemical and van der Waals interactions. Molecular structures of six new SbBr₃-Py complexes in the solid state have been determined by single-crystal X-ray diffraction analysis. In all complexes all Sb atoms adopt a pseudo-octahedral coordination geometry which is completed by additional Sb⋅⋅⋅Br contacts shorter than the sum of the van der Waals radii, with Br−Sb⋅⋅⋅Br angles close to 180°. To reveal the nature of Sb–Br and Sb–N interactions, the DFT calculations were performed followed by the analysis of the electrostatic potentials, the orbital interactions and the topological analysis. Based on Natural Bond Orbital (NBO) analysis, the Sb–Br interactions range from the covalent bonds to the pnictogen bonds. A simple structural parameter, non-covalence criterion (NCC) is defined as a ratio of the atom-atom distance to the linear combination of sums of covalent and van der Waals radii. NCC correlates with E(2) values for Sb−N, Sb−Cl and Sb−Br bonds, and appears to be useful criterion for a preliminary evaluation of the bonding situation.     

铽（III）-噻吩甲酰三氟丙酮-电化学聚合漆酚配合物的研究

研究了铽（III）和噻吩甲酰三氟丙酮（HTTA）形成的配合物与电化学聚合方 法得到的聚合漆酚（EPU）发生配位反应及pH = 10.2时形成配合物Tb(III)-TTA- EPU的组分和结构。红外光谱、X光电子能谱的测试表明Tb~(3+)分别与EPU,TTA~- 发生配位。元素分析和电感偶合等离子体发射光谱（AES）测定结果证明了每个 Tb~(3+)分别与EPU分子中1个链节单元的羟基和3个TTA~-发生配位,从而得到配合 物的结构。动态机械热分析（DMTA）表明发生配位反应后该配合物进一步交联,从 而难溶于大部分有机溶剂,其玻璃化转变温度和耐热性能均得到很大提高。我们对 其荧光性质进行了研究,发现常温下配合物在紫外光下发生强的荧光,主要是Tb~ (3+)离子的~5D_4→~7F_5的跃迁。讨论了溶剂、pH值对配合物荧光强度的影响。当 pH = 10.2时,合成的配合物有最好的荧光性质。     

芳基与烷基亚砜钯(II)配合物π反馈效应的DFT研究

应用DFT方法对二苯基亚砜(DPSO)和二己基亚砜(DHSO)的钯(II)配合物进行了理论计算。结果表明中心金属钯与亚砜之间存在d-π^*反馈键，而且二苯基亚砜钯(II)配合物中的π反馈键比二己基亚砜钯(II)配合物强，即亚砜的取代基对其钯(II)配合物的π反馈键有显著的影响。以BHandH/6-31+G^**(Pd，3-21G^*)//BHandH/6-31G^*(Pd，3-21G^*)方法对相应的亚砜钯(II)配合物进行单点计算时，配合物trans-PdCl₂(DPSO)₂ 的π反馈键轨道能为-10.695 eV，而trans-PdCl₂(DHSO)₂的π反馈键轨道能量为-10.320 eV。利用电子给体NH₃或电子受体CO配位体置换亚砜钯(II)配合物里的一个亚砜配体后，Pd(II)-DHSO配合物的Pd-S配位键长的变化明显小于Pd(II)-DPSO配合物的Pd-S配位键长变化值，进一步说明在Pd-DPSO配合物中的π反馈效应强于相应的Pd-DHSO配合物。     

DFT/TD‐DFT investigation on Ir(III) complexes with N‐heterocyclic carbene ligands: Geometries,electronic structures,absorption, and phosphorescence properties

Iridium(III) complexes with N‐heterocyclic (NHC) ligands including fac‐Ir(pmb)₃ (1), mer‐Ir(pmb)₃ (2), (pmb)₂Ir(acac) (3), mer‐Ir(pypi)₃ (4), and fac‐Ir(pypi)₃ (5) [pmb = 1‐phenyl‐3H‐benzimidazolin‐2‐ylidene, acac = acetoylacetonate, pypi = 1‐phenyl‐5H‐benzimidazolin‐2‐ylidene; fac = facial, mer = meridional] were investigated theoretically. The geometry structures of 1–5 in the ground and excited state were optimized with restricted and unrestricted DFT (density functional theory) methods, respectively (LANL2DZ for Ir atom and 6‐31G for other atoms). The HOMOs (highest occupied molecular orbitals) of 1–3 are composed of d(Ir) and π(phenyl), while those of 4 and 5 are contributed by d(Ir) and π(carbene). The LUMOs (lowest unoccupied molecular orbitals) of 1, 2, 4, and 5 are localized on carbene, but that of 3 is localized on acac. The calculated lowest‐lying absorptions with TD‐DFT method based on Perdew‐Burke‐Erzenrhof (PBE) functional of 1 (310 nm), 2 (332 nm), and 3 (347 nm) have ML_carbeneCT/IL_{phenyl→carbene}CT (MLCT = metal‐to‐ligand charge transfer; ILCT = intraligand charge transfer) transition characters, whereas those of 4 (385 nm) and 5 (389 nm) are assigned to ML_carbeneCT/IL_{carbene→carbene}CT transitions. The phosphorescences calculated by TD‐DFT method with PBE0 functional of 1 (386 nm) and 2 (388 nm) originate from ³ML_carbeneCT/³IL_{phenyl→carbene}CT excited states, but those of 4 (575 nm) and 5 (578 nm) come from ³ML_carbeneCT/³IL_{carbene→carbene}CT excited states. The calculated results showed that the carbene and phenyl groups act as two independent chromophores in transition processes. Compared with 1 and 2, the absorptions of 4 and 5 are red‐shifted by increasing the effective π‐conjugation groups near the C_carbene atom. We predicated that (pmb)₂Ir(acac) is nonemissive, because the LUMO of 3 is contributed by the nonemissive acac ligand. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Semiempirical PM5 molecular orbital study on chlorophylls and bacteriochlorophylls: comparison of semiempirical, ab initio, and density functional results

The semiempirical PM5 method has been used to calculate fully optimized structures of magnesium-bacteriochlorin, magnesium-chlorin, magnesium-porphin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), and d, and bacteriochlorophylls a, b, c, d, e, f, g, and h with all homologous structures. Hartree-Fock/6-31G* ab initio and density functional B3LYP/6-31G* methods were used to optimize structures of methyl chlorophyllide a, chlorophyll c(1), and methyl bacteriochlorophyllides a and c for comparison. Spectroscopic transition energies of the chromophores and their 1:1 or 1:2 solvent complexes were calculated with the Zindo/S CIS method. The self-consistent reaction field model was used to estimate solvent shifts. The PM5 calculations predict planar structure of the porphyrin ring and central position of the four coordinated magnesium atoms in all pigments studied, in accord with the experimental, ab initio, and density functional results, a significant improvement as compared to the older semiempirical PM3 approach. Only small differences in PM5 and B3LYP/6-31G* or Hartree-Fock/6-31G* minimum energy geometries of the reference molecules were observed. Calculations show that in 1:1 solvent complexes, where the magnesium atom is five coordinated, the magnesium atom is shifted out of the plane of the porphyrin ring towards the solvent molecule, while the hexa coordinated 1:2 complexes are again planar. The PM5 method gives atomic charges that are comparable with those obtained from the Hartree-Fock/6-31G* and B3LYP/6-31G* calculations. The single point ZINDO/S CIS calculations with PM5 minimum energy structure gave excellent correlations between calculated and experimental transition energies of the chlorophylls and bacteriochlorophylls studied. Such correlations may be used for prediction of transition energies of the chromophores in protein binding sites. Calculations also predict existence of dark electronic states below the main Soret absorption band in all chromophores studied. The results suggest that the semiempirical PM5 method is a fairly reliable and computationally efficient method in predicting molecular parameters of porphyrin-like molecules.     

A direct nitrogen-15 NMR study of cerium(III)-nitrate complexes in aqueous solvent mixtures

A study of the complex formation which occurs between cerium(III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low-temperature, nitrogen-15 (¹⁵N) NMR technique. At temperatures in the range of –95 to –110°C, ligand exchange is slow enough to permit the observation of separate¹⁵N NMR signals for bulk nitrate, and this anion in the cerium(III) principal coordination shell. In water-acetone-Freon-12 mixtures, the spectra reveal the nitrato complexes do not form consecutively. Rather, signals are observed for Ce(NO₃)²⁺, Ce(NO₃) ₂ ¹⁺ , and only two other higher order complexes, even at very high NO ₃ ^– to Ce(III) mole ratios. Signal area evaluations were used to identify the possible higher order complexes. At comparable salt concentrations in aqueous-methanol mixtures, only Ce(NO₃)²⁺ and Ce(NO₃) ₂ ¹⁺ are formed, reflecting a decreased tendency for complexation in media of higher dielectric constant.     

Effect of chlorides on cerium(III) and samarium(III) ionic flotation

The ionic flotation of cerium(III) and samarium(III) from nitrate solutions with sodium dodecylsulfate as a collector and sodium chloride addition was studied. Dependences of distribution coefficients and a separation factor on the aqueous phase pH at various concentrations of chloride ions were determined.     

Luminescent Eu(III) and Gd(III) trisbipyridine cryptates: experimental and theoretical study of the substituent effects.

Synthesis, absorption spectra and luminescebce properties of a series of lanthanide trisbipyridine cryptates Ln within R-Bpy x R-Bpy x R-Bpy, where Ln = Eu, Gd and R = H, COOH, COOCH3, CONH(CH2)2NH2 are described. Comparison of the unsubstituted parent compound with the substituted compounds shows that bipyridine substitution doesn't alter significantly the photophysical properties of the lanthanide cryptate. The absorption maximum is slightly red-shifted when three bipyridines are substituted, whereas substituting one bipyridines has a negligible effect on the absorption spectra. The experimental triplet state energy is between 21600 and 22 100 cm(-1) for the series of compounds and the luminescence lifetimes at 77 K are between 0.5 and 0.8 ms in HO2 and equal to 1.7 ms in D2O. The experimental characterizations are completed by DFT and TD-DFT calculations to assess the ability of these approaches to predict absorption maxima, triplet state energies and structural parameters of lanthanide cryptates and to characterize the electronic structure of the excited states. The calculations on the unsubstituted parent and substituted compounds show that absorption maxima and lowest 3pipi* triplet state energies can be accurately determined from density functional theory (DFT) and time-dependent (TD) DFT calculations.     

Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

A study on the fluoride complexes of plutonium(III), samarium(III) and bismuth(III) using fluoride ion-selective potentiometry

Stability constants of the fluoride complexes of Pu(III), Sm(III) and Bi(III) in 1.0M NaClO₄/HClO₄ medium at 23±1°C have been determined by potentiometry using a fluoride ion-selective electrode. Plutonium was reduced to the trivalent state using quinhydrone with an excess to serve as holding reductant. The log values of concentration stability constants log ₁, log ₂, and log ₃ are 3.58, 6.40 and 12.61 for Pu(III), 3.23, 5.81 and 10.54 for Sm(III) and 3.69, 6.13 and 11.04 for Bi(III), respectively. The log ₂ values in all these cases have very large deviation and may be taken only as rough estimates.     

The Thermokinetics of the Formation Reactions of Cerium(III) n-dodecylbenzene Sulfonate and Cerium(III) Stearate

The thermokinetics of the formation reactions of cerium(III) n-dodecylbenzene sulfonate and cerium(III) stearate are studied by using a microcalorimeter. On the basis of experimental and calculated results, three thermodynamics parameters (the activation enthalpies, the activation entropies, the activation free energies), the rate constant, three kinetic parameters (the activation energies, the pre-exponential constant and the reaction order) and the enthalpies of the reaction of preparing cerium(III) n-dodecylbenzene sulfonate in the temperature range of 20–35°C and cerium(III) stearate in the temperature range of44.6–62.8°C are obtained. The results showed that the title reactions easily took place in the studied temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

DFT studies,spectral and biological activity evaluation of binary and ternary sulfamethazine Fe(III) complexes

[FeL₃]·H₂O (1) and [FeL₂Q]·3H₂O (2) (HL = sulfamethazine and HQ = 8-hydroxyquinoline) have been synthesized, characterized (elemental analysis, FT IR, UV–vis, TGA, magnetic and conductivity), and tested for their antibacterial activity against Staphylococcus aureus and Escherichia coli. Theoretical calculations involving geometry optimization, natural orbital analysis, electronic spectra, and molecular electrostatic potential have been done at the DFT/B3LYP level of theory. The high 3d-electron contribution of 6.71 is accounted to L?→?d_Fe charge transfer. Coordination of HL to Fe(III) in 1 led to a significant decrease in the antibacterial activity, and presence of a secondary ligand in 2 completely abolished it.