Metal framework as a novel approach for the fabrication of electric double layer capacitor device with high energy density using plasticized Poly(vinyl alcohol): Ammonium thiocyanate based polymer electrolyte

High performance electric double-layer capacitors (EDLCs) based on poly (vinyl alcohol) (PVA): ammonium thiocyanate (NH₄SCN):Cu(II)-complex plasticized with glycerol (GLY) have been fabricated. The maximum DC ionic conductivity (σ_DC) of 2.25 × 10^-3 S cm⁻¹ is achieved at ambient temperature. The X-ray diffraction (XRD) patterns confirmed that the addition of both Cu(II)–complex and GLY enhanced the amorphous region within the samples. Through the Fourier transform infrared (FTIR) the interactions between the host polymer and other components of the prepared electrolyte are observed. The FESEM images reveal that the surface morphology of the samples showed a uniform smooth surface at high GLY concentration. This is in good agreement with the XRD and FTIR results. Transference numbers of ion (t_ion) and electron (t_el) for the highest conducting composite polymer electrolyte (CPE) are recognized to be 0.971 and 0.029, respectively. The linear sweep voltammetry (LSV) revealed that the electrochemical stability window for the CPE is 2.15 V. These high values of t_ion and potential stability established the suitability of the synthesized systems for EDLC application. Cyclic voltammetry (CV) offered nearly rectangular shape with the lack of Faradaic peak. The specific capacitance and energy density of the EDLC are nearly constant within 1000 cycles at a current density of 0.5 mA/cm² with average of 155.322F/g and 17.473 Wh/Kg, respectively. The energy density of the EDLC in the current work is in the range of battery specific energy. The EDLC performance was found to be stable over 1000 cycles. The low value of equivalent series resistance reveals that the EDLC has good electrolyte-electrode contact. The EDLC exhibited the initial high power density of 4.960 × 10³ W/Kg.     

Design of plasticized proton conducting Chitosan:Dextran based biopolymer blend electrolytes for EDLC application: Structural,impedance and electrochemical studies

In this work, for the use of an electrical double-layer capacitor (EDLC) device applications, the fabrication and characterization of solid polymer electrolytes (SPEs) based on chitosan-dextran (CS-DN) blended polymer doped and plasticized with ammonium thiocyanate (NH₄SCN) and glycerol are studied, respectively. The Fourier transform infrared (FTIR) spectroscopy method has been used to investigate the structural behavior of electrolytes. It was observed that the FTIR bands are shifted and decreased in their intensities with the increased glycerol plasticizer content and it results in the complex formation. According to the electrical impedance spectra (EIS), the electrolyte incorporated with high contents of plasticizer (42 wt%) revealed the highest ionic conductivity of (3.08 × 10⁻⁴ S/cm). The electrical equivalent circuits (EEC) were used to investigate the circuit elements of the electrolytes further. Increasing glycerol plasticizers verified an improvement in ions density number (n), mobility (μ), and diffusion coefficient (D). The transference number measurements (TNM) indicated that the predominant charge carriers in the conduction process are ions where the (t_ion) is 0.95. According to the linear sweep voltammetry (LSV) study, the uppermost conducting sample was found to have sufficient anode stability with a breakdown voltage of 1.9 V that can be used in electrochemical devices. The absence of peaks in the cyclic voltammetry (CV) demonstrated that the charge storage mechanism within the constructed EDLC is fully capacitive. Based on this finding, the starting specific capacitance (C_s), energy density (E_d), and power density (P_d) have been identified to be 118F/g, 13.2 Wh/kg, and 1560 W/kg, respectively. Throughout its 100 cycles, the equivalence series resistance ESR value was between 53 and 117 Ω.     

The study of EDLC device fabricated from plasticized magnesium ion conducting chitosan based polymer electrolyte

Plasticized biopolymer electrolytes based on chitosan (CS) doped with magnesium acetate (Mg(CH₃COO)₂) and various amounts of glycerol have been prepared for energy storage electrochemical double-layer capacitor (EDLC) application. In this work the dielectric and electrochemical properties have been examined using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). It is confirmed from the frequency changing of the impedance spectra that relatively high dielectric constant has been recorded at low frequency region. From tan δ and M″ spectra, relaxation peaks are clearly seen. It has been found that as the glycerol concentration increased, the DC conductivity increases. In the fabricated system (CS: Mg(CH₃COO)₂: glycerol.), ions are responsible for charge carrying as the ion transference number is higher than the electron transference number. The electrochemical stability of the system extends to 2.4 V as shown in the LSV. The mechanism of the charge storage has been investigated and indicated that the non-Faradaic dominates where the specific capacitance is significantly affected by scan rate. The fabricated EDLC possessed a constant value of specific capacitance (78.2 F/g), energy density (8.8 Wh/kg), and ESR (78.2 F/g). The EDLC has an tremendous cycleability as high number of Columbic efficiency has accomplished. The value of efficiency of the EDLC has been in the range of 97%–99%.     

Investigation of anharmonicity in rotational phonon mode for BaWO4 crystal

Spontaneous Raman spectra in the BaWO₄ were measured in the temperature range from 4 K to 280 K, and the temperature dependence of the linewidth of the A_g (191 cm⁻¹) Raman mode was analyzed using the lattice dynamical perturbative approach and one-phonon density of states (PDOS). The linewidth slope for the 191 cm⁻¹ peak for an external mode is 7.2 times larger than that for the 926 cm⁻¹ peak for a breathing mode. The different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the one-phonon density of states (PDOS) resulting in different anharmonic interactions. The origin may be that the ratio of up-conversion TDOS to down-conversion TDOS for Eg mode (191 cm⁻¹) is more than that for A_g (926 cm⁻¹). The peak of the Eg mode (191 cm⁻¹) is attributed to the coupling mode both a rotation of the Barium and an out-of-phase rotation of the oxygen in x–y plane as a librational mode.     

The chain-shaped coordination polymers based on the bowl-like Ln18Ni24(23.5) clusters exhibiting favorable low-field magnetocaloric effect

The design of assembling high-nuclearity transition-lanthanide (3d-4f) clusters along with excellent magnetocaloric effect (MCE) is one of the most prominent fields but is extremely challenging. Herein, two heterometallic metal coordination polymers are constructed via the “carbonate-template” method, formulated as {[Gd₁₈Ni₂₄(IDA)₂₂(CO₃)₇(μ₃-OH)₃₂(μ₂-OH)₃(H₂O)₅Cl]·Cl₈·(H₂O)₁₄}_n and {[Eu₁₈Ni_23.5(IDA)₂₂(CO₃)₇(μ₃-OH)₃₂(H₂O)₅(IN)(CH₃COO)₂(NH₂CH₂COO)Cl]·Cl₆·(H₂O)₁₇}_n [abbreviated as 1-(Gd₁₈Ni₂₄)_n and 2-(Eu₁₈Ni_23.5)_n respectively; H₂IDA = iminodiacetic acid; HIN = isonicotinic acid]. Concerning the structures, compounds 1-(Gd₁₈Ni₂₄)_n and 2-(Eu₁₈Ni_23.5)_n both feature the one-dimensional (1D) chain-like structure which is rarely reported in high-nuclearity metal complexes. Meanwhile, the large presences of Gd³⁺ ions in compound 1-(Gd₁₈Ni₂₄)_n are conducive to the fantastic MCE, and the value of −∆S_m is 35.30 J kg⁻¹ K⁻¹ at 3.0 K and ∆H = 7.0 T. And more significantly, compound 1-(Gd₁₈Ni₂₄)_n shows the large low-field magnetic entropy change (−∆S_m = 20.95 J kg⁻¹ K⁻¹ at 2.0 K and ∆H = 2.0 T) among the published 3d-4f mixed metal clusters.     

Upper critical solution temperatures for immiscible solvent systems with halide salts,carboxylic acids,surfactants and polynuclear aromatic compounds and benzene derivatives

Upper critical solution temperatures (UCSTs) of (water + phenol) systems are reported with 0.1 mol · kg⁻¹ halide salts, carboxylic acids, 1.0% PEG 200 in water, and 0.01 mol · kg⁻¹ surfactants and polynuclear aromatic compounds namely benzene, naphthalene, anthracene, chrysene; and benzene derivatives namely toluene and xylene solutions in phenol. Valence electrons and shell numbers, basicity, –CH₃ and –CH₂–, hydrophilic, hydrophobic and π conjugated electrons of respective additives have been noted to affect their UCSTs and mutual solubilities. The surfactants decrease the USCTs with higher mutual solubilities due to effective hydrophilic as well as hydrophobic interactions with aqueous and organic phases, respectively. A stronger structure breaking action of 3(-OH) of glycerol outweighs those of the 3(-COO⁻) and 1(-OH) of citric acid and urea does produce almost equal UCSTs as compared to glycerol. A decrease in UCSTs is noted with increasing number of conjugated π electrons of benzene, naphthalene, anthracene and chrysene. In general, dTc/dx₂ values of salts for 0.20 to 0.16 mole fractions of phenol are found positive while for 0.055 to 0.052 mole fractions, the negative.     

New thioether–dithiolate complexes of Cp1Ir and some reactivity features

The reaction of [Cp1IrCl₂]₂ (Cp* = η⁵ − C₅Me₅) with the tridentate 3-thiapentane-1,5-dithiolate ligand, S(CH₂CH₂S⁻)₂ (tpdt), led to the formation of [Cp1Ir(η³ − tpdt)] (1) in 81% isolated yield. Subsequent reactions of 1 with [Cp1IrCl₂]₂ in 2:1 and 1:1 molar equiv ratios resulted in the formation of [Cp1Ir(μ − η²:η³ − tpdt)Cp1IrCl][PF₆] (2) and [Cp1Irμ − η²:η³ − tpdt)Cp1IrCl][Cp1IrCl₃] (3) in 86 and 79% yields, respectively, based on 1, whereas the reactions of 1 with [(COD)IrCl]₂ (COD = 1,5-cyclooctadiene) in 2:1 and 1:1 molar equiv ratios resulted in the formation of the homo-bimetallic derivatives Cp1Ir(μ − η¹:η³ − tpdt)(COD)IrCl (4) (92% yield) and [Cp1Ir(μ − η²:η³ − tpdt)(COD)Ir] [(COD)IrCl₂] (5) (82% yield). Reactions between 1 and [(COD)RhCl]₂, yielded the hetero-bimetallic derivatives Cp1Ir(μ − η¹:η³ − tpdt)(COD)RhCl (6) and [Cp1Ir(μ − η²:η³ − tpdt)(COD)Rh][(COD)RhCl₂] (7), in 92 and 93% yields, respectively. The reaction of 1 with methyl iodide gave mono-methylated derivative [Cp1Ir(η³-C₄H₈S₃Me)]I (8) (93% yield). All these compounds have been comprehensively characterized.     

Synthesis,crystal structure,spectroscopy and magnetism of a trinuclear nickel(II) complex with 3,5-pyrazoledicarboxylic acid as bridge ligands

A new complex of [Ni₃(dcp)₂(H₂O)₁₀] (1) (H₃dcp = 3,5-pyrazoledicarboxylic acid) has been synthesized from H₃dcp and Ni(NO₃)₂·6H₂O by hydrothermal reaction. Complex 1 has the discrete trinuclear structure. Three Ni(II) ions are bridged by two dcp³⁻ ligands, with 10 coordinated water molecules as terminal ligands. The molecules of [Ni₃(dcp)₂(H₂O)₁₀] extend into three-dimensional supramolecular architectures by intermolecular O–H···O hydrogen bonds as well as π-π stacking interactions. Magnetic susceptibility measurement shows that a weak antiferromagnetic interaction is operative between nickel(II) ions and an excellent simulation of the experimental data gives D = 5.27 cm⁻¹, J = −2.19 cm⁻¹ and g = 2.05.     

Study on degrees of mesomorphic zone of polymer.Ⅰ.Determination of degrees of crystallinity of Eucommia ulmoides gum and natural rubber by dynamic mechanical thermal analysis

According to the two-phase model theories of polymer crystallization, the degree of crystallinity of natural rubber (NR) induced to crystallize at −25 °C can be directly determined by dynamic mechanical thermal analysis (DMTA) by testing its tanδ peak areas of crystalline state and 100% amorphous state respectively. The degree of crystallinity is 86% when the induction time increases to 12 h. However, due to the tanδ peak area of 100% amorphous state cannot be measured by DMTA directly, the degree of crystallinity of Eucommia Ulmoides (EU) gum can only be determined indirectly with DMTA by using the tanδ peak areas of 100% amorphous state extrapolated from the linear equation (y = ax + b) which is derived from the relationship between tanδ peak areas and crosslink densities. The degree of crystallinity is 87%, which is very close to NR. The crystallization of NR can be prevented effectively by increasing slightly the crosslink density to the critical crystallization point, which is 6.20 × 10⁻⁵mol/cm⁻³ for vulcanized NR induced to crystallize at −25 °C for 4 h. However, it is very hard for EU gum to prevent the crystallization by crosslinking. Because, with increasing of the crosslink density, the EU gum will firstly show a percolation threshold, which is 53.34 × 10⁻⁵mol/cm⁻³, and the degree of crystallinity is 71.04%. Then, like NR, the degree of crystallinity of EU gum will decrease rapidly to zero by increasing the crosslink density to the critical crystallization point, which is 68.89 × 10⁻⁵mol/cm⁻³. In the end of the paper, the linear relationship of the equation is verified and the influence factors on slope a and intercept b of the linear equation are discussed as well.     

In situ polymerization and reduction to fabricate gold nanoparticle‐incorporated polyaniline as supercapacitor electrode materials

Nanocomposites of gold nanoparticles and polyaniline are synthesized by using HAuCl₄ and ammonium peroxydisulfate as the co‐oxidant involving in situ polymerization of aniline and in situ reduction of HAuCl₄. Through these in situ methods, the synthesized Au nanoparticles of ca. 20 nm embedded tightly and dispersed uniformly in polyaniline backbone. With the Au content in composite increasing from 4.20 to 24.72 wt.%, the specific capacitance of the materials first increased from 334 to 392 F g⁻¹ and then decreased to 298 F g⁻¹. Based on the real content of PANI in composite material, the highest specific capacitance is calculated to be 485 F g⁻¹ at the Au amount of 19.15 wt.%, which remains 55.6% after 5000 cycles at the current density of 2 A g⁻¹. Finally, the asymmetric supercapacitor of AuNP/PANI||AC and the symmetric supercapacitor of AuNP/PANI||AuNP/PANI are assembled. The asymmetric supercapacitor device shows a better electrochemical performance, which delivers the maximum energy density of 7.71 Wh kg⁻¹ with power density of 125 W kg⁻¹ and maximum power density of 2500 W kg⁻¹ with the energy density of 5.35 Wh kg⁻¹.     

Bithiophene triarylborane dyad: An efficient material for the selective detection of CN− and F− ions

A new fluorescent chemosensor based on bithiophene coupled dimesitylborane (BMB-1) was synthesized and characterized. BMB-1 was used for colorimetric and turn-on fluorescent sensing of cyanide (CN⁻) and fluoride (F⁻) ions, in the presence of other competitive anions in an aqueous (CH₃CN–H₂O) medium. BMB-1 showed a hypsochromic shift (blue shift) with addition of CN⁻ and F⁻ ions in absorption studies. The lower detection level of CN⁻ and F⁻ ions is 1.37 × 10⁻⁹ and 1.75 × 10⁻⁹ M, respectively. The BMB-1 binding mechanism is based on the nucleophilic addition of CN⁻ and F⁻ ions in the internal charge transfer transition of bithio moiety to the boranylmesitylene unit, and the color changes were observed under UV light. This result is further confirmed by Fourier transform infrared spectroscopy, mass spectrometry and density functional theory calculations. Also, the BMB-1 probe is found to be a good adsorbent for the removal of F⁻ ions in real water samples using the adsorption technique.     

A mixed-valence Mn6 cluster capped by nitronyl nitroxide units

A mixed-valence Mn₆ cluster, [Mn₆O₂(t-BuCO₂)₁₀(H₂O)(NNPy)₂] (2), has been synthesized by the assembly of [Mn₆O₂(t-BuCO₂)₁₀(THF)₄] · THF (1) with a nitronyl nitroxide radical molecule, 2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NNPy). Complex 2 consists of [Mn₆O₂]¹⁰⁺ core and two NNPy radical attachments, where the [Mn₆O₂]¹⁰⁺ core is composed of two Mn^III ions (i.e., the inner Mn ions) bridged by two μ₄-O²⁻ and four Mn^II ions (i.e., the outer Mn ions) surrounding the inner Mn^III ions via the two μ₄-O²⁻, forming an edge-shared double-tetrahedral polygon (vertices: Mn ions, centers: μ₄-O²⁻). Bridges by pivalate groups in μ₂- and μ₃-modes assist the coordination spheres around these Mn ions. Two of the outer Mn^II ions in trans position are, to the sixth coordination site, occupied by NNPy molecule (pyridine-N coordination). One of the outer Mn^II ions is occupied by a water molecule to complete octahedral geometry, but the rest of them is vacancy taking a square-pyramidal geometry. The variable-temperature direct current (DC) magnetic susceptibility was collected in the temperature range of 1.81 to 300 K at a 1 kOe appled field. The molar magnetic susceptibility (χ_M) steadily increases from 0.053 emu mol⁻¹ at 300 K to 0.29 emu mol⁻¹ at 20 K, showing a kink (peak), and then increases rapidly to 0.70 emu mol⁻¹ at 1.81 K. The profile of this magnetic behavior indicates that the intracluster spin cancellation takes place bellow 20 K to derive an S_Mn6 = 0 by strong antiferromagnetic interaction between Mn ions. This is consequently leading to paramagnetic isolation of only the two nitronyl nitroxide units as if remaining as exchange-uncorrelated spin carriers. The variable-temperature ESR spectra show a sharp signal below 30 K with g = 2.00, proving the presence of free nitronyl nitroxide radical, in which double integral of such signal obeys the Curie–Weiss law that follows the susceptibility result in the low-temperature region.     

Interactions of some amino acids and glycine peptides with aqueous sodium dodecyl sulfate and cetyltrimethylammonium bromide at T=298.15 K: a volumetric approach

The apparent molar volumes V_φ of glycine, alanine, valine, leucine, and lysine have been determined in aqueous solutions of 0.05, 0.5, 1.0 mol · kg⁻¹ sodium dodecyl sulfate (SDS) and 1.0 mol · kg⁻¹ cetyltrimethylammonium bromide (CTAB) by density measurements at T=298.15 K. The apparent molar volumes have also been determined for diglycine and triglycine in 1 mol · kg⁻¹ SDS and CTAB solutions. These data have been used to calculate the infinite dilution apparent molar volumes V₂⁰ for the amino acids and peptides in aqueous SDS and CTAB and the standard partial molar volumes of transfer (Δ_trV_2,m⁰) of the amino acids and peptides to these aqueous surfactant solutions. The linear correlation of V₂⁰ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH₃⁺, COO⁻), CH₂ group and other alkyl chains of the amino acids to V₂⁰. The results on the partial molar volumes of transfer from water to aqueous SDS and CTAB have been interpreted in terms of ion–ion, ion–polar and hydrophobic–hydrophobic group interactions. The volume of transfer data suggests that ion–ion or ion–hydrophilic group interactions of the amino acids and peptides are stronger with SDS compared to those with CTAB. Comparison of the hydration numbers of amino acids calculated in the present studies with those in other solvents from literature shows that these numbers are almost the same at 1 mol · kg⁻¹ level of the cosolvent/cosolute. Increasing molality of the cosolvent/cosolute beyond 1 mol · kg⁻¹ lowers the hydration number of the amino acids due to increased interactions with the solvent and reduced electrostriction.     

Synthesis,crystal structures and properties of three glutarato and adipato bridged manganese(II) coordination polymers under ambient conditions

Three Mn(II) polymers Mn(H₂O)₄(C₅H₆O₄) 1, [Mn(H₂O)₂(C₅H₆O₄)]·H₂O 2 and Mn(H₂O)(C₆H₈O₄) 3 were synthesized (H₂(C₅H₆O₄) = glutaric acid, H₂(C₆H₈O₄) = adipic acid) under mild ambient conditions. The [Mn(H₂O)₂]²⁺ units in 2 are interlinked by the glutarate anions with a η⁴μ₃ bridging mode to form 2D (4·8²) topological networks, which are stacked via interlayer hydrogen bonds into a 3D (4³·6⁵·8²)(4⁷·6³) topological net. Compound 3 crystallizes in the acentric space group P2₁ and exhibits significant ferroelectricity (remnant polarization Pr = 0.371 nC cm⁻², coercive field Ec = 0.028 kV cm⁻¹, saturation of the spontaneous polarization Ps = 0.972 nC cm⁻²). The adjacent MnO₆ octahedrons in 3 are one atom-shared to generate the Mn₂O₁₁ bi-octahedron, leading into 1D metal oxide chains. The resulting chains are interconnected by the η⁵μ₅ adipate anions to form new 2D (4⁸·6²) networks, which are held together via strong interlayer hydrogen bonds into 3D α-Po topological supra-molecular architecture. The temperature-dependent magnetic susceptibility data of 1–3 shows overall anti-ferromagnetic interactions between the metal ions bridged by the carboxylate groups.     

Oxidative addition of MeI to cationic Rh(I) carbonyl complexes with pyridyl bis(carbene) ligands

A series of cationic Rh(I) carbonyl complexes of the form [Rh(CO)(L)]PF₆ (where L = 2,6-bis (alkylimidazol-2-ylidene)-pyridine; alkyl = Me (1a), Et (1b), CH₂Ph (1c)) have been prepared by the reactions of [Rh(CO)₂(OAc)]₂ with diimidazolium pyridine salts in the presence of NEt₃. The ν(CO) values for 1 are ca. 1982 cm⁻¹, indicating that the N-heterocyclic carbene ligands impart high electron density on the Rh(I) centres, despite the overall cationic charge. Each of the Rh(I) complexes reacts with MeI to form two isomeric Rh(III) methyl species, and a third unidentified species. Kinetic measurements on the MeI oxidative addition reactions give second-order rate constants (MeCN, 25 °C) of 0.0927, 0.0633 and 0.0277 M⁻¹ s⁻¹ for 1a, 1b and 1c, respectively. Comparison of these data with those for related Rh(I) carbonyl complexes shows that 1 have remarkably high nucleophilicity for cationic species.     

Crystal structures,luminescence, and thermal properties of lanthanide complexes with 2,3,4-trimethoxybenzoic acid and 1,10-phenanthroline

The complexes of [Ln(2,3,4-tmoba)₃phen]₂ (Ln = Dy (1), Eu (2), Tb (3); 2,3,4-tmoba = 2,3,4-trimethoxybenzoate; phen = 1,10-phenanthroline) were synthesized and characterized by a series of techniques including the elemental analysis, IR and fluorescent spectra and TG/DSC-FTIR technology. The crystal structures were determined by X-ray crystallography. Each complex include two Ln³⁺ ions, six 2,3,4-tmoBA and two phen molecules forming a binuclear structure, giving the coordination number of nine. The three-dimensional IR accumulation spectra of gaseous products for the complexes 1 to 3 are analyzed and the thermal decomposition processes are further authenticated. Through means of differential scanning calorimeter (DSC), two solid-solid phase transition endothermic peaks were found in the complex 2, which was different from the complexes 1 and 3. The heat capacities of these complexes were measured and fitted to a polynomial equation with the least squares method for each complex on the basis of the reduce temperature x (x = [T − (T_max + T_min)/2]/[(T_max − T_min)/2]) over the range from (256.15 to 476.15) K. Subsequently, the smoothed molar heat capacities and thermodynamic functions (H_T−H_298.15 K), (S_T−S_298.15 K), and (G_T−G_298.15 K) of the complexes 1 to 3 were calculated based on the fitted polynomial of the heat capacities. The fluorescent intensity of the complexes 2 and 3 are markedly improved as well.     

Molecular spin ladders self-assembly from [Ni(dmit)2]− building blocks: Syntheses,structures and magnetic properties

Two ion-pair compounds, consisting of 1-(4′-R-benzyl)pyridinium ([RBzPy]⁺, R = NO₂ (1) and Br (2)) and [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithion-4,5-dithiolato), have been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through terminal S⋯S interactions in 1, lateral S⋯S interactions in 2. The weak H-bonding interactions of C–H⋯S were observed in 2, while only weak van de Waals interactions between anion and cations in 1. The magnetic susceptibilities measured in 2–300 K indicate AFM exchange interaction domination both two compounds. A peculiar magnetic transition at ∼100 K was observed in 1. An AFM ordering below ∼11 K was found in 2, and the best fit to magnetic susceptibility above 45 K in this compound, using a dimer model with s = 1/2, give rise to Δ/k_B = 36.1 K, zJ = −0.91 K, C = 3.2 × 10⁻³ emu K mol⁻¹ and χ₀ = −4.0 × 10⁻⁶ emu mol⁻¹ with g of 2.0 fixed.     

Low-dimensional quantum magnetic systems: Synthesis,structure and magnetic behavior of (2,5-dimethylpyrazine)copper(II) chloride and synthesis and magnetic behavior of bis(2,6-dimethylpyrazine)copper(II) chloride

The synthesis, X-ray structure and magnetic susceptibility of (2,5-dimethylpyrazine)copper(II) chloride (1), and the synthesis and magnetic susceptibility of (2,6-dimethylpyrazine)₂copper(II) chloride (2), are reported. Compound 1 crystallizes in the space group P2₁/c as a coordination polymer of Cu(II) ions bridged by 2,5-methylpyrazine. The resulting chains are magnetically linked via short chloride–chloride contacts. The magnetic susceptibility responds as a uniform Heisenberg chain (2J/k = −20(5) K) with a phase transition to three dimensional order near 5 K. Susceptibility data for compound 2 show that the compound is a linear chain coordination polymer with the copper ions linked by bihalide bridges. A fit to the model for a uniform Heisenberg chain yields 2J = −22.7(2) K.     

Spectroscopic and structural studies of chromate ions in zinc complexes with 2,2′-bipyridine. Analysis of the lowest triplet states in the CrO42− entity

Two novel complexes of Zn(II) chromate with 2,2′-bipyridine have been synthesised: [Zn(bpy)₃]CrO₄·7.5H₂O (1) and catena-(μ-CrO₄-O,O′)[Zn(bpy)(H₂O)₂]·2H₂O (2). Complex 1 has been characterised by a structural method. The [Zn(bpy)₃]CrO₄·7.5H₂O crystals have a monoclinic symmetry with space group C2/c and eight chemical units. The chromate ion is not coordinated to the zinc(II) ion. The O(3) and O(4) atoms of CrO₄²⁻ and O(8) of the water molecule statistically occupy their position with k=0.5, which means that the chromate ions execute reorientational motion between two equilibrium arrangements with equal probability. 4 K electronic spectra (1) revealed the vibrational fine structure in ν₃(F₂)=820 cm⁻¹ for the spin-forbidden ¹A₁→³T₁ transition. The pure electronic 0–0 transition in ¹A₁→¹T₁ was found at 20 270 cm⁻¹. In complex 2 the broad low intensity band at ca. 16 800 cm⁻¹ has been assigned to a forbidden ZnOCr transition in the bridge.