Coordination Numbers of Central Atoms in Coordination Compounds

A sample of structurally characterized 10000 complexes (X-ray diffraction data) was carefully selected from available databases for analysis of coordination numbers (CNs) of their central atoms (complexing agents). The coordination numbers of various chemical elements are tabulated for their different oxidation numbers (ONs). Variations in CN with the ordinal number of an element in the Periodic Table were followed. A general distribution of the sample complexes over the CNs of the central atom, as well as their distributions for particular ONs, is displayed. References to particular coordination compounds are given for extreme and very uncommon CNs of a central atom with different ONs. A general pattern of the observed variations in the CN of chemical elements can be useful for predicting the properties of complexes, constructing their stability models, designing compounds with rich and unique properties, and developing retrieval and graphic tools for chemical databases.     

Redistribution of Water and Gelatin between Contacting Liquid Phases According to the IR Spectroscopy Data: The Role of Lecithin

The spontaneous redistribution of components between two contacting liquid phases, an aqueous gelatin solution and a micellar lecithin solution in a hydrocarbon (heptane), is studied by infrared spectroscopy at various phospholipid concentrations and contact times of the liquid phases. It is noted that lecithin plays the key role in the transfer of the water and gelatin molecules from the aqueous phase to heptane. The transfer of these components of the aqueous phase through the interface resulted from their inclusion into phospholipid reverse micelles via hydrogen bonding. Phosphate and carbonyl groups of lecithin make the largest contribution to the formation of hydrogen bonds. The time of the establishment of the equilibrium component distribution between the two liquid phases is determined.     

Structural and Anion Coordination Features of Macrocyclic Polyammonium Cations in the Solid,Solution and Computational Phases

Abstract

The crystal structures of two hexaaza macrocycles 1,4,7,12,15,18-hexaazacyclodocosane ([22]N₆:1-6H⁺, 6C1^?) and 1,13-dioxa-4,7,10,16,19,22-hexaazacyclotetraeicosane ([24]N₆O₂:2-6H⁺,6CI^?) as their hexa-hydrochloride salts have been determined. 1-6H⁺ binds specifically two CI^? anions above and below the almost planar hexaammonium macrocycle yielding a dinuclear CI^? complex. The hexacation 2-6H⁺ on the other hand interacts preferentially with three CI^? anions of the six present in the solid state. Among the three closest anions, one of them, interacting with four ammonium groups, is located in the centre of the macrocycle which adopts a “pocket-like” conformation. Potentiometric and ³⁵CI NMR experiments demonstrate that 2-6H⁺ also binds CI^? in aqueous solution. Subsequent extensive molecular dynamics computational studies starting from X-ray coordinates show that the solid state structure is representative of the solution conformations for I-6H⁺, whereas the conformations of 2-6H⁺ are strongly affected by intramolecular interactions between the ammonium centres and O-atoms of the ether linkage as well as by intermolecular interactions with H₂O molecules and CI^? counterions.     

Polymerization of Transition Metal Complexes in Solid Polymer Electrolyte Membranes

Prussian blue (PB), which is a mixed-valent polynuclear metal complex, was formed in the presence of the solid polymer electrolyte membrane Nafion (Nf). According to the stepwise dipping method, in which either Fe²⁺ or Fe(CN)₆ ^3? of the component ions of PB was first incorporated into the matrix membrane and then the membrane was immersed into a solution containing the other component ion, a thin layer of PB was deposited on the surface of Nf or inside Nf depending upon the sequence of incorporation of the component ions. A dissipative structure of periodic PB layer deposit inside Nf was found to be formed under a specific condition of the stepwise method. PB was also formed inside Nf as a broader line by the countercurrent diffusion method in which both component ions were incorporated into Nf from opposite surfaces. The position of PB in Nf varied with the concentration ratio of Fe²⁺ to Fe(CN)₆ ^3? in this case.     

Calculating the Entropy of Solid and Liquid Metals,Based on Acoustic Data

The entropies of iron, cobalt, rhodium, and platinum are studied for the first time, based on acoustic data and using the Debye theory and rigid-sphere model, from 298 K up to the boiling point. A formula for the melting entropy of metals is validated. Good agreement between the research results and the literature data is obtained.     

The Mechanism of Low-Temperature Ammonia Oxidation on Metal Oxides According to the Data of Spectrokinetic Measurements

Low temperature ammonia oxidation on MoO₃, Fe₂O₃, Cr₂O₃, and ZnO is studied by the spectrokinetic method. It is shown that the following adsorbed species are intermediates in this reaction: NH₃ and N₂O on Fe₂O₃ and ZnO; NH₃, N₂O, and NO on Cr₂O₃. All of the detected intermediates are used to construct the mechanism of the process. In the framework of the proposed mechanism, stationary and nonstationary spectral and kinetic data are quantitatively processed. The dependence of the rate constants of the same steps on different oxides on their physicochemical properties is discussed.     

Thermotropic Ionic Liquid Crystals VI. Structural Parameters of Solid and Liquid Crystal Phases of Anhydrous Short-Chain Sodium Alkanoates

Unit cell constants were determined from powder X-ray diffraction photographs taken of several anhydrous short-chain sodium alkanoates at room temperature. The temperature dependence of the bilayer spacing in the alkanoates was determined over the range 25-300°C. Overall changes in bilayer spacings between the solid and the neat phase were found to be much smaller than in long-chain alkanoates. A correspondence was noted between the room temperature lateral packing area and the ²³Na quadrupole coupling constant in the mesophase. The mcsophase bilayer spacing was consistent with a structural model in which the tilted anion chain rotates on a cone.     

The Coordination and Transformation of Arene Rings by Transition Metal Carbonyl Cluster Complexes

A survey of the synthetic pathways and of the reactivity and catalytic activity of transition metal carbonyl clusters substituted with benzyne (and, for comparison, benzene and diene) ligands is given. Cluster-surface analogies are helpful in gaining an understanding of the homogeneous and heterogeneous catalytic behaviour of the clusters.     

Spectral,Antimicrobial, and Thermal Studies of Some Transition Metal Complexes Derived from Bidentate Ligands Containing N and S Donor Atoms

Abstract

Bidentate ligands have been synthesized by the reaction of 2,4-dichlorobenzaldehyde with 4-amino-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole. The ligands react with acetates of Co(II), Ni(II), Cu(II), and Zn(II) to yield 1:2 [metal:ligand] complexes. The newly synthesized compounds were characterized by elemental analyses, spectral (UV-Vis, IR, ¹H NMR, fluorescence, ESR) studies, thermal techniques, and magnetic measurements. Thermal studies of the complexes showed a multistep decomposition pattern. A square planar geometry for Cu(II) and octahedral geometry for Co(II), Ni(II), and Zn(II) complexes have been proposed. The synthesized complexes exhibit enhanced antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Aspergillus niger, and A. flavus compared to parent ligands. However, tested compounds did not exhibit any activity against Escherichia coli and Pseudomonas aeruginosa.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

借多波长量测数据测定二元配合物组成

本文提出利用多波长量测数据测定二元配合物组成的新方法。首先以线性最小二乘求得各吸收组分吸收系数；继而应用多元线性回归获取各组分平衡浓度并据物料平衡求得配合物组成比及稳定常数。运用单纯形方法对５个体系测定结果进行了检验。     

Structure and Dynamics of 1-Butyl-3-methylimidazolium Hexafluorophosphate Phases on Silica and Laponite Clay: From Liquid to Solid Behavior

Solid-state NMR experiments show that the behavior of supported 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid phases depends on the type of support and the phase thickness. A mobile nearly liquid phase is obtained on silica, on the basis of the line widths of the bands in (1)H, (31)P, and (13)C spectra. However, the mobility is somehow restricted, as shown by the possibility of using the cross-polarization technique, although with slow dynamics. On laponite clay, a layered material with a negatively charged surface, a truly solid phase is obtained at low coverage, whereas the increase in ionic liquid loading leads to a second liquid phase, as shown by the presence of two contributions with very different line widths. These two phases seem to coexist without exchange in the NMR time frame. Heteronuclear correlation experiments evidence different relative dispositions of the imidazolium-surface-PF(6) system, with only aromatic protons involved in all the interactions on silica but participation of the benzylic groups (N-CH(3) and/or N-CH(2)) in the case of laponite clay.     

First-Principles Studies of the Adsorption and Catalytic Properties for Gas Molecules on h-BN Monolayer Doped with Various Transition Metal Atoms

Catalysis Surveys from Asia - The adsorption properties for some gas molecules (H2, N2, CO, NO and CO2) on pristine and transition metal-doped h-BN monolayer are investigated by using density...     

Metal Sorption,Solid Phase Extraction and Preconcentration Properties of Two Silica Gel Phases Chemically Modified with 2-Hydroxy-1-Naphthaldehyde

Active silica gel phase (I) was chemically modified to the corresponding amino- (SiNH₂) and chloro- (SiCl) derivatives via silylation reactions. These were used to synthesize two newly modified silica gel phases (II, III) by direct chemical reaction with 2-hydroxynaphthaldehyde (2-HNA). The surface coverage values are 370, 432µmolg^–1 and 320, 355µmolg^–1 for (II) and (III), on the basis of thermal desorption and metal probe testing method, respectively. The metal sorption properties of silica gel phases (II, III) were studied and compared with active silica gel phase (I). The maximum determined metal capacity values were found to be 10–110, 20–290 and 20–370µmolg^–1 for phases I, II and III, respectively. The distribution coefficient values (K_d) were also determined for a series of metal ions, and the results showed that the two new chemically modified phases (II and III) were highly selective for Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺. The potential applications of silica gel phases (II, III) as solid phase extractors for the same five metal ions spiked in drinking tap water (1.000µgmL^–1) were found to give percentage recovery values in the range of 90.2–96.3±4.1–6.3%, while pre-concentration of the same five metal ions spiked in drinking tap water (50.0ngmL^–1) was successfully accomplished with a percentage recovery range of 92.6–95.8±4.8–5.7%.Received December 16, 2002; accepted May 14, 2003 published online September 1, 2003     

Structure of Dimethylsulfoxide Water Solutions,According to Static Inductivity Data

Russian Journal of Physical Chemistry A - The static permittivity of water–DMSO mixtures is measured in the interval of 293–323 K throughout the range of concentrations of...     

Fluorescence Enhancement of Levosulpiride Upon Coordination with Transition Metal Ions and Spectrophotometric Determination of Complex Formation

Abstract

Absorbance and fluorescence spectral pattern of levosulpiride in absence and presence of first row transition metal ions (Mn-Zn) has been studied at room temperature under physiological condition. The fluorescence spectra of the drug in presence of different concentrations of transition metal ions showed enhancement in fluorescence intensity of levosulpiride. The photophysical changes owing to the direct interaction between metal ion and the amide nitrogen of levosulpiride has been described in terms of CHEF (chelating enhancement fluorescence) effect. The absorption spectra of the drug at different pH exhibited two isosbestic points at 255 and 275 nm respectively, indicating the presence of three chemical species in solution. The ratio of the drug to metal ions is found to be 2:1 and the log K of the resulting complex was determined spectrophotometrically and potentiometrically. The apparent ionization constant of levosulpiride is found to be 8.98. The low value of stability constant suggests that complexes may dissolve and the drug can be absorbed.