Aggregation properties of bis(salicylaldiminato)zinc(II) Schiff-base complexes and their Lewis acidic character

The synthesis, characterization, (1)H NMR, optical absorption and fluorescent properties of a series of amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complexes are reported. Detailed (1)H NMR, DOSY NMR, optical absorption and fluorescence spectroscopy studies indicate the existence of aggregate species in solutions of non-coordinating solvents. The degree of aggregation is related to the nature of the bridging diamine. Chloroform solutions of complexes where the bridging diamine contains a naphthalene or the pyridine nucleus are always characterized by the presence of defined dimer aggregates, whereas oligomeric aggregates are likely formed by complexes where the bridging diamine contains a benzene ring. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the complexes occurs, because of the axial coordination to the Zn(II) ion, accompanied by considerable changes in the (1)H NMR and optical absorption spectra. The effect of the alkyl chains length seems to play a minor role in the aggregation properties, as noticed by (1)H NMR data, optical absorption and fluorescence spectra, which remain almost unaltered on changing the chain length.     

Paramagnetic NMR shift,spectroscopic and molecular modeling studies of lanthanide(III)-morin complexes

Studies on nine-coordinate lanthanide complexes of morin are described. The complexes were characterized by elemental analysis, molar conductance, UV–Vis spectra, IR spectra, thermal analysis and NMR spectra. Molecular modeling studies were also carried out. The complexes are non-electrolytes in DMSO. TGA showed anhydrous nature of the complexes. The electronic spectra of the complexes were recorded in methanol. ¹H NMR spectra of lanthanum, praseodymium, neodymium, samarium and dysprosium complexes have been studied in DMSO-d₆. The complexes do not dissociate in DMSO and retain their coordination. ¹H NMR spectra of paramagnetic and diamagnetic complexes exhibit downfield as well as upfield shifts of morin resonances that shows change in geometry during coordination.     

Preparation and characterization of inclusion complexes of pefloxacin mesylate with three kinds of cyclodextrins

The ability of alpha-cyclodextrin, beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin (alpha-CD, beta-CD and HP-beta-CD) to break pefloxacin mesylate (PM) aggregates by forming inclusion complexes has been studied using 1H NMR (nuclear magnetic resonance spectroscopy), 13C NMR and fluorescence spectra. The inclusion constants are determined to compare the corresponding inclusion capacity. Solid-inclusion complexes of PM with CDs are synthesized by coprecipitation method, and all the inclusion ratios are found to be 1:1. Additionally, spatial characterization of complexes has been proposed based on two-dimensional nuclear magnetic resonance technique (2D NMR) and spatial conformation is also investigated to propose two possible models between PM and CDs.     

Effect of cyclodextrins on the physicochemical properties of chlorophyll a in aqueous solution

The interactions between chlorophyll a and two beta-cyclodextrins, that have the same cavity size but different substituents, were studied in aqueous solutions. These supramolecular host-guest complexes were examined by a combination of UV/vis absorption, circular dichroism, NMR, and steady-state and time-resolved fluorescence measurements. The results indicate that all cyclodextrins solubilize the pigment mainly in monomeric form in water. The pigment forms 1:1 complexes with the heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin and 1:2 complexes with the hydroxypropyl-beta-cyclodextrin. In such complexes the methyl groups of the cyclodextrin inner cavity are involved in the interaction with the pigment as evidenced by NMR measurements. We also measured the luminescence of singlet oxygen photosensitized by chlorophyll a in the inclusion complexes.     

Solution NMR studies of iron(II) spin-crossover complexes

The 1H NMR spectra of a series of mono- and dinuclear pyridine complexes [FeL1(R1/R2)(py)2] and [Fe2L2(R1/R2)(py)4] have been investigated in a mixed toluene-d8/pyridine-d5 solution. The equatorial tetradentade Schiff base like ligands L1(R1/R2) and L2(R1/R2) with a N2O22- coordination sphere for each metal center have been obtained by condensation of a substituted malonodialdehyde (R1/R2 are Me/COOEt, Me/COMe, or OEt/COOEt) with o-phenylenediamine (L1(R1/R2)) or 1,2,4,5-tetraaminobenzene (L2(R1/R2)). The 1H NMR resonances were assigned by comparison of differently substituted complexes in combination with a line-width comparison. The 1H NMR shifts from 188 to 358 K show a strong influence of the spin state of the iron center. The behavior of the pure high-spin iron(II) complexes is close to ideal Curie behavior. Analysis of the resonance shifts of the spin-transition complexes can be used for determining the high-spin mole fraction of the complex in solution at different temperatures. Magnetic susceptibility measurements in solution using the Evans method were made for all six complexes. Significant differences between the spin-transition behavior of the complexes in solution of those in the solid state were found. However, the plots of microeff as a function of temperature obtained using the Evans method and those obtained by interpretation of the NMR shifts were virtually identical. The isotropic shifts of protons in the complexes proved to be suitable tools for following a spin transition in solution. Comparison of the microeff plots of the mono- and dinuclear complexes in solution reveals slight differences between the steepness of the curves that may be attributable to cooperative interactions between the metal centers in the case of the dinuclear complexes.     

Preparation and characterization of the crystalline inclusion complexes between cyclodextrins and poly(1,3-dioxolane)

The preparation and characterization of the crystalline inclusion complexes between a polymeric guest, poly(1,3-dioxolane) (PDXL), and small-molecular hosts, cyclodextrins (CDs) are reported. It is observed that the polymer guest can form crystalline inclusion complexes with three kinds of cyclodextrins, which may be attributed to the high oxygen atom density in PDXL chain. The crystalline inclusion complexes were characterized with FTIR , TGA, X-ray diffraction, SEM, 1H NMR and 13C CP/MAS NMR spectroscopes. It was found that the crystalline inclusion complexes have higher temperature stability than the pure CDs. The X-ray powder diffraction patterns of the crystalline inclusion complexes proved that they have columnar structures. 13C CP/MAS NMR spectra of the crystalline inclusion complexes indicate that CDs adopt a more symmetrical conformation in the complexes, while pure CDs assume a less symmetrical conformation in the crystal without a guest inside their cavities. The morphology of the crystal was     

Solid-state NMR of endohedral hydrogen-fullerene complexes

We present an overview of solid-state NMR studies of endohedral H(2)-fullerene complexes, including (1)H and (13)C NMR spectra, (1)H and (13)C spin relaxation studies, and the results of (1)H dipole-dipole recoupling experiments. The available data involves three different endohedral H(2)-fullerene complexes, studied over a wide range of temperatures and applied magnetic fields. The symmetry of the cage influences strongly the motionally-averaged nuclear spin interactions of the endohedral H(2) species, as well as its spin relaxation behaviour. In addition, the non-bonding interactions between fullerene cages are influenced by the presence of endohedral hydrogen molecules. The review also presents several pieces of experimental data which are not yet understood, one example being the structured (1)H NMR lineshapes of endohedral H(2) molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H(2)-fullerene complexes, especially in the cryogenic regime.     

Complete assignments of NMR data of salens and their cobalt (III) complexes

Salens, derived from 1,2‐ethylenediamine and salicylaldehydes, have been widely used as ligands for metal complexes which have been showing enormous potential in chemical properties of asymmetric catalysts as well as biological properties such as anticancer agents. Almost all of the salen–metal complexes with their corresponding metal (II)‐complexes show the evidences of chelation of two oxygens in salens. However, several metal (II) complexes, especially cobalt (II) complexes, could not show NMR spectra due to their paramagnetism. Recently, it has been reported that one of the cobalt (III) complexes was used for NMR spectroscopy to evaluate its stereoselectivity as a catalyst. Even though many salen ligands are known, their NMR data are not assigned completely. It was possible that modification in northern part of salen with 2‐hydroxyphenyl group afforded another oxygen chelation site in salen ligand. Here we report that synthesis and full NMR assignment of new salen ligands, which form meso 1,2‐bis(2‐hydroxyphenyl)ethylenediamine) and their cobalt (III) complexes. The assignments of ¹H and ¹³C NMR data obtained in this experiment can help us to predict the NMR data of other salen ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

1,2-双烷基(芳基)硫代乙烷对金的萃取性质和配合物的研究

本文研究了1,2-双烷基(芳基)硫代乙烷(L)——1,2-双(正辛基硫代)乙烷(BOTE)、1,2-双(正戊基硫代)乙烷(BATE)、1,2-双(苯基硫代)乙烷(BPTE)对金的萃取及其配合物的性质.双烷基硫代乙烷对金具有很强的萃取能力,可定量地萃取金.在溶液中,当[L]≥[Au~(3 )]时,Au与L形成1∶1Au-L配合物,而在[L]<[Au~(3 )]时,则为2∶1Au-L配合物.固态时,Au(Ⅲ)、Au(Ⅰ)与L只形成2∶1配合物(AuCl_3)_2L和AaCl)_2L.讨论了BOTE和BATE与Au(Ⅲ)、Au(Ⅰ)配合物的IR和~1H NMR谱.IR谱证实了关于Au(Ⅰ)配合物为线型结构的推断,并借助金原子的交换机理,解释了配合物与配位体的~1H NMR谱外观相似的原因.详细分析了Au(Ⅲ)配合物低频区的IR数据,提出了配合物有离子型结构的新证据.     

Novel Monomeric Phenanthroline—Thallium（Ⅲ） Complexes Multinuclear NMR Characterization in Organic Solvents

A novel complex of monomeric thallium (Ⅲ） with the nitrogen donor ligand phenanthroline (phen) has been prepared and characterized by multimuclear NMR(^1H,^13C,^205Tl). The three complexes exist in equilibria in DMSO and acetonitrile solution, which was proved by the ^205Tl NMR spectra. The ^1H and ^13C NMR spectra of tris-phen T1(Ⅲ） complex have been measured, where the spin-spin coupling between T1(I=1/2) and ^13C or ^1H signals were observed with the ^1H and ^13C NMR spectroscopy in acetonitrile. The coupling constants are presented and the chemical shifts of complexes are discussed in detail.