Syntheses and crystal structures of hydrated complexes of strontium and barium bromides with 18-crown-6

Two complexes, namely, triaqua(18-crown-6)strontium dibromide monohydrate (I) and diaquabromo(18-crown-6)barium bromide (II), are synthesized. Their crystal structures are determined by X-ray diffraction analyses. For complex I, space group C2/c, a = 17.547 Å, b = 10.246 Å, c = 14.786 Å, β = 123.08°, Z = 4. For complex II, space group Pnma, a = 17.753 Å, b = 17.465 Å, c = 6.629 Å, Z = 4. The structures are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.056 (I) and 0.042 (II) for 2696 (I) and 2440 (II) independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). Both complex cations—randomly disordered [Sr(18C6)(H₂O)₃]²⁺ in complex I and [BaBr(18C6)(H₂O)₂]⁺ in complex II—are of the host-guest type. The Sr²⁺ (Ba²⁺) cation resides in the cavity of the 18-crown-6 ligand and coordinated by all six O atoms. In the structures complexes I and II, the coordination polyhedra of the Sr²⁺ and Ba²⁺ cations (coordination number 9) can be described as distorted hexagonal bipyramids with one apex at the O atom of the water molecule in complex I or at the Br^? ligand in complex II and the other split apex at the O atoms of two water molecules.     

Neutral paddlewheel diruthenium complexes with tetracarboxylates of large pi-conjugated substituents: facile one-pot synthesis, crystal structures, and electrochemical studies

A one-pot reaction of a cationic diruthenium complex, [Ru(2)(II,III)(O(2)CCH(3))(4)(THF)(2)](BF(4)), with arylcarboxylic acids, ArCO(2)H, (PhCO(2)H = benzoic acid, NapCO(2)H = 1-naphthoic acid, AntCO(2)H = 9-anthracenecarboxylic acid) in NDMA (NDMA = N,N-dimethylaniline) has led to isolation of neutral paddlewheel-type diruthenium complexes, [Ru(II)(2)(O(2)CAr)(4)(THF)(2)] (Ar = Ph (1), Nap (2), Ant (3)). Paramagnetic variable temperature (VT) (1)H NMR studies and GC-MS studies show that the reaction consists of two steps: a one-electron reduction of the Ru(2) core by NDMA and a simple carboxylate-exchange reaction. All compounds 1-3 were structurally characterized by X-ray crystallography. While the structural features of the Ru(2) core are very similar in all the compounds, the dihedral angles between the carboxylate plane and the aromatic ring are larger with the expanding of aryl groups from phenyl to anthracene. The effect of pi-pi stacking leads to the formation of a 1-D chain structure in compound 3, whereas compounds 1 and 2 are fully isolated from each other. The electrochemical measurements show that the quasireversible one-electron oxidation step is observed at +0.06, +0.09, and +0.17 V (vs Ag/Ag(+)) for 1-3, respectively, assigned to the Ru(II)(2)/Ru(II,III)(2) redox couple. These potentials are found to demonstrate a linear relationship with the substituent constants for aryl compounds,.     

Zinc halide complexes of imidazolidine-2-thione and its derivatives: X-ray structures,solid state,solution NMR and antimicrobial activity studies

The preparation and characterization of zinc complexes of formula ZnL₂X₂ (X?=?Cl and Br), with L?=?1,3-diazinane-2-thione (Diaz), 1,3-diazipane-2-thione (Diap), imidazolidine-2-thione (Imt) and its methyl and n-propyl substituted derivatives, are described. The complexes dichlorobis(1-methylimidazolidine-2-thione-S)-zinc(II) (1) and dichlorobis(1-propylimidazolidine-2-thione-S)-zinc(II) (2) have been characterized by single-crystal X-ray methods. Both complexes adopt distorted tetrahedral geometry. Only intramolecular hydrogen bonding interactions are observed in 1 and 2. Solution and solid state ¹³C NMR show a significant shift of the C=S carbon resonance of the ligands, while other resonances are relatively unaffected, indicating that most likely the solid state structure is maintained in solution. Antimicrobial activity studies of the free ligands and their complexes show that ligands exhibit substantial antibacterial activities compared to the complexes.     

Pentadienyls vs cyclopentadienyls and reversal of metal-ligand bonding affinity with metal oxidation state: synthesis, molecular structures, and electronic structures of high-valent zirconium pentadienyl complexes

Molecules of the form Cp(6,6-dmch)ZrX(2) (Cp = eta(5)-cyclopentadienyl, X = Cl, Br, I; 6,6-dmch = eta(5)-6,6-dimethylcyclohexadienyl) have been synthesized, and the molecular and electronic structures have been investigated. These molecules allow direct comparison of the bonding and properties of pentadienyl and cyclopentadienyl ligands in the same high-oxidation-state metal complexes. Unlike the well-known Cp(2)ZrX(2) analogues, these Cp(6,6-dmch)ZrX(2) molecules are intensely colored, indicating significantly different relative energies of the frontier orbitals. Also unusual, the average Zr-C distances to the 6,6-dmch pentadienyl ligand are about 0.1 A longer than the average Zr-C distances to the cyclopentadienyl ligand for these Zr(IV) complexes, opposite of what is observed for the Zr(II) complex Cp(2,6,6-tmch)Zr(PMe(3))(2) (tmch = eta(5)-2,6,6-trimethylcyclohexadienyl), reflecting a dramatic reversal in the favorability of the bonding depending on the metal oxidation state. The experimental and computational results indicate that the color of the Cp(6,6-dmch)ZrX(2) complexes is due to a 6,6-dmch ligand-to-metal charge-transfer band. Compared to the Cp(2)ZrX(2) analogues, the Cp(6,6-dmch)ZrX(2) molecules have a considerably less stable HOMO that is pentadienyl-based and an essentially unchanged metal-based LUMO. Also, the lowest unoccupied orbital of pentadienyl is stabilized relative to cyclopentadienyl and becomes a better potential delta electron acceptor, thus contributing to the differences in structure and reactivity of the low-valent and high-valent metal complexes.     

Syntheses, structures, and photoluminescence properties of metal(II) halide complexes with pyridine-containing flexible tripodal ligands

Seven coordination compounds, [Zn(L3)Cl2] . MeOH . H2O (1), [Mn(L3)2Cl2] . 0.5EtOH . 0.5H2O (2), [Cu3(L2)2Cl6] . 2DMF (3), [Cu3(L2)2Br6] . 4MeOH (4), [Hg2(L4)Cl4] (5), [Hg2(L4)Br4] (6), and [Hg3(L4)2I6] . H2O (7), were synthesized by the reactions of ligands 1,3,5-tris(3-pyridylmethoxyl)benzene (L3), 1,3,5-tris(2-pyridylmethoxyl)benzene (L2), and 1,3,5-tris(4-pyridylmethoxyl)benzene (L4) with the corresponding metal halides. All the structures were established by single-crystal X-ray diffraction analysis. In complexes 1 and 2, L3 acts as a bidentate ligand using two of three pyridyl arms to link two metal atoms to result in two different 1D chain structures. In complexes 3 and 4, each L2 serves as tridentate ligand and connects three Cu(II) atoms to form a 2D network structure. Complexes 5 and 6 have the same framework structure, and L4 acts as a three-connecting ligand to connect Hg(II) atoms to generate a 3D 4-fold interpenetrated framework, while the structure of complex 7 is an infinite 1D chain. The results indicate that the flexible ligands can adopt different conformations and thus can form complexes with varied structures. In addition, the coordination geometry of the metal atom and the species of the halide were found to have great impact on the structure of the complexes. The photoluminescence properties of the complexes were investigated, and the Zn(II), Mn(II) and Hg(II) complexes showed blue emissions in solid state at room temperature.     

Polarographic study of mixed ligand complexes of Pb(II) with carboxylate ions and imidazole

Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart^2?), malonate (mal^2?) and citrate (citr^3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO₃) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β₁₁ = 4.19; with mal^2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)₂] and [Pb(mal)₂(im)]^2? with stability constants log β₁₁ = 4.3, log β₁₂ = 7.3 and log β₂₁ = 5.5 respectively are formed. With citr^3? and im a single mixed species, [Pb(citr)(im)]^? with stability constant log β₁₁ = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed.     

Electrochemical reduction of cobalt and nickel complexes with ligands stabilizing metal in low oxidation state

Electrochemical reduction of cobalt(ii) complexes containing -acceptor ligands (L = bpy, Ph₂Ppy) proceeds through three consecutive reversible steps: one-electron transfer to form a more stable Co^IL complex, transfer of two electrons at more negative potentials to form an anionic [NiL]^– complex, and reduction of the ligand to the radical anion. The stability of the cobalt complexes with different ligands decreases in the series Ph₂Ppy > Ph₃P > bpy.     

Quantum chemical investigation on structures of pyrrolic amides functionalized (5,5) single-walled carbon nanotube and their binding with halide ions

The structures of mono- and di-podal pyrrolic amides functionalized (5,5) single-walled carbon nanotubes (SWCNTs) and their complexes with fluoride, chloride, and bromide ions were obtained using the two-layered ONIOM(MO:MO) and density functional theory (DFT) methods. The binding energies between halide ions and all the receptors and their charge transfers were obtained using DFT method. The computational results indicate that the pyrrolic amide functionalized on the SWCNT affects to the density of state and energy gap of SWCNT. All the free receptors, mono-, di-podal pyrrolic amides and the functionalized SWCNT forming the strongest complexes were found.     

A polarographic study of the mixed complexes of Pb(II) with oxalate and malonate ions

The coordinated mixed Pb(II)-oxalate-malonate system has been polarographically studied in aqueous medium. The ionic strength has been maintained constant at μ = 1.0 by using NaClO₄. Application of the Schaap and McMasters method detected only the existence of the [Pb-ox-mal]_2? complex, the overall stability constant of which was β₁₁ = 4.1 x 10⁵.The various coordination equilibria are discussed on the basis of statistical aspects.     

Relationship between the catalytic properties of the products of the oxidative thermolysis of certain complexes and the porous structures of samples in the oxidation reactions of volatile organic compounds

The rate of the gas-phase oxidation of ethanol, 2-propanol, acetone, ethyl acetate, dioxane, and benzene with atmospheric oxygen is studied on surfaces of bimetallic oxide catalysts Co–Fe, Cu–Fe, Cr–Co, and Ni–Fe, prepared via thermal decomposition of double complex compounds in air. It is found that the rate of oxidation of volatile compounds depends on the volume of the transient pores in the catalyst sample. The rate of oxidation on the same catalyst at 350°C depends on the nature of the substance in the order: acetone > ethyl acetate > ethanol > propanol > dioxane, benzene.     

Solid state and solution structures of alkaline-earth complexes with lariat ethers containing aniline and benzimidazole pendants

Herein we report the synthesis and structural characterization of Mg(II), Ca(II), Sr(II) and Ba(II) complexes with bibracchial lariat ethers derived from 1,7-diaza-15-crown-5 and 1,7-diaza-12-crown-4 containing aniline or benzimidazole pendant arms. The solid state structures of most of them have been determined by using single crystal X-ray crystallography. A coordination number of seven was observed for the Mg(II) complexes in the solid state, while the Ca(II), Sr(II) and Ba(II) complexes are 8-, 9- and 11-coordinate, respectively. The Ca(II), Sr(II) and Ba(II) complexes show a syn conformation, with the two pendant arms of the ligand disposed on the same side of the macrocyclic mean plane. However, the Mg(II) complex with the largest ligand derived from 1,7-diaza-15-crown-5 containing benzimidazole pendants presents an anti conformation in the solid state. ¹H and ¹³C NMR spectroscopy reveal that this conformation is maintained in acetonitrile solution.     

Synthesis, properties and structures of eight-coordinate zirconium(IV) and hafnium(IV) halide complexes with phosphorus and arsenic ligands

Eight-coordinate [MX(4)(L-L)(2)] (M = Zr or Hf; X = Cl or Br; L-L = o-C(6)H(4)(PMe(2))(2) or o-C(6)H(4)(AsMe(2))(2)) were made by displacement of Me(2)S from [MX(4)(Me(2)S)(2)] by three equivalents of L-L in CH(2)Cl(2) solution, or from MX(4) and L-L in anhydrous thf solution. The [MI(4)(L-L)(2)] were made directly from reaction of MI(4) with the ligand in CH(2)Cl(2) solution. The very moisture-sensitive complexes were characterised by IR, UV/Vis, and (1)H and (31)P NMR spectroscopy and microanalysis. Crystal structures of [ZrCl(4)[o-C(6)H(4)(AsMe(2))(2)](2)], [ZrBr(4)[-C(6)H(4)(PMe(2))(2)](2)], [ZrI(4)[o-C(6)H(4)(AsMe(2))(2)](2)] and [HfI(4)[o-C(6)H(4)(AsMe(2))(2)](2)] all show distorted dodecahedral structures. Surprisingly, unlike the corresponding Ti(iv) systems, only the eight-coordinate complex was found in each system. In contrast, the ligand o-C(6)H(4)(PPh(2))(2) forms only six-coordinate complexes [MX(4)[-C(6)H(4)(PPh(2))(2)]] which were fully characterised spectroscopically and analytically. Surprisingly the tripodal triarsine, MeC(CH(2)AsMe(2))(3), also produces eight-coordinate [MX(4)[MeC(CH(2)AsMe(2))(3)](2)] in which the triarsines bind as bidentates in a distorted dodecahedral structure. There is no evidence for seven-coordination as found in some thioether systems.     

Syntheses, structures, and properties of tetrakis(mu-acetato)dirhodium(II) complexes with axial pyridine nitrogen donor ligands with or without assistance of hydrogen bonds

Eight adducts of Rh2(O2CCH3)4 with axial pyridine derivatives that contain hydrogen-bonding amino and/or steric methyl substituents in the 2- and 6-positions have been prepared and examined by electronic absorption and 1H NMR spectroscopy in solution and by elemental, IR, thermogravimetric, and X-ray diffraction analyses in the solid state. The results indicated that strong hydrogen bonding interactions between Rh2(O2CCH3)4 and axially coordinated pyridine derivatives with a 2- or 6-amino group occur in both solution and the solid state and contribute to the higher thermal stability of the molecular assembly of dirhodium complexes. It was demonstrated that such a combination of coordinate and hydrogen bonds is useful as a building tool in designing and constructing new organic-inorganic hybridized compounds and supramolecular architectures.     

Gas-phase reactions of electrons,halide ions and radicals with (meso-tetraphenylporphinato)metal(II) complexes under negative ion chemical ionization conditions

The negative ion chemical ionization mass spectra of a series of (meso-tetraphenylporphinato)metal(II) (metal = Mg, Co, Ni, Cu, Zn) complexes obtained with the electron-energy-moderating/reagent gases argon, NF₃, CF₂Cl₂ and CF₃Br are presented. Formation of the negative ions identified in the mass spectra is accounted for in terms of the chemistry which occurs in the gaseous plasmas. In argon plasmas, the metal complexes undergo resonance electron capture with comparable facility to produce stable molecular ions. In the NF₃, CF₂Cl₂ and CF₃Br plasmas, ionization occurs as a result of ion–molecule reactions as well as resonance electron capture, and is quite selective. Only fluoride ions react with each of the metal complexes, producing metal-containing ions by nucleophilic addition and proton abstraction as well as by inducing ring closure. The less reactive chloride and bromide ions react readily by nucleophilic addition only with the magnesium and zinc complexes. Negative ions are also produced in the plasmas by radical-molecule reactions followed by ionization of the neutral products of these encounters.     

Role of nitrogen dioxide in the oxidation of diesel soot on promoted mixed catalysts with fluorite and perovskite structures

The oxidation of soot on catalysts with the perovskite and fluorite structures (including platinum-promoted catalysts) in the presence and in the absence of NO₂ was studied using in situ IR spectroscopy and temperature-programmed techniques (TPR, TPD, and TPO). It was found that, as a rule, the temperature of the onset of soot oxidation considerably decreased upon the addition of NO₂ to a flow of O₂/N₂, whereas the amount of oxygen consumed in soot oxidation considerably increased. To explain these facts, we hypothesized that the initiation of soot combustion in the presence of NO₂ was related to the activation of the NO₂ molecule through the formation (at a low temperature) and decomposition (at a high temperature) of nitrate structures on the catalyst. Superequilibrium amounts of NO₂ resulted from the decomposition of nitrate complexes immediately on the catalyst for soot combustion. Based on a comparison between catalyst activities and data obtained by TPR and the TPD of oxygen, a conclusion was drawn that the presence of labile oxygen in the catalyst is a necessary but insufficient condition for the efficient occurrence of a soot oxidation reaction in the presence of NO₂. The introduction of platinum as a constituent of the catalyst increased the amount of labile oxygen and, as a consequence, increased the amount of highly reactive nitrate complexes. As a result, this caused a decrease in the temperature of the onset of soot combustion.     

The solid-state structures of the ethanol solvated complexes of para-sulphonato-calix[4]arene with magnesium and calcium ions

The structures ethanol solvated complexes of para-sulphonato-calix[4]arene with magnesium and calcium have been determined. Both show the classical bilayer structure of para-sulphonato-calix[4]arene. The cations are situated between the bilayers. In the case of the magnesium complex the cation is octahedrally coordinated by six water molecules, however for the calcium complex the cation is coordinated in two different geometries by water molecules, bridging oxygen atoms of the sulphonate anions and an oxygen of an ethanol molecule. Both complexes contain an ethanol molecule embedded in the macrocyclic cavity.     

Formation and thermodynamic properties of mixed complexes of Cd(II) with thiourea and nitrite or thiosulphate ions as ligands

Formation and thermodynamic parameters of mononuclear mixed complexes Cd(SCN₂H₄)_n(NO₂)^2?p_p and Cd(SCN₂H₄)_n(S₂O₃)^2(1?p_p in aqueous solution were investigated by potentiometric measurements at different temperatures and μ = 1 for KNO₃.