Coordination polymers, 1. Magnetic,spectral, and thermal properties of coordination polymers derived from terephthalaldehyde bis(S-benzyldithiocarbazate)

New Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) coordination polymers of Schiff base ligand derived from terephthalaldehyde and S-benzyldithiocarbazate have been synthesized in DMF media. The coordination polymers have been characterized by their elemental analysis, magnetic susceptibility, and by electronic and infrared spectral measurements. The thermal stability of each polymer was found out by thermogravimetric analysis. The thermal stability of coordination polymers obtained from thermograms has the following order: $ {\rm Zn} \simeq {\rm Fe} > {\rm Co} > {\rm Ni} > {\rm Min} \simeq {\rm Cu}$ Mn(II), Fe(II), Co(II), and Ni(II) coordination polymers are of a six-coordinated octahedral structure while Cu(II) and Zn(II) coordination polymers are found to be four-coordinated square planar and tetrahedral structure, respectively. The ligand-field and nephelauxetic parameters have been determined from the spectra, using ligand-field theory of spin-allowed transitions which are found consistent with six-coordinate structure for Mn(II), Fe(II), Co(II), and Ni(II) coordination polymers. Elemental analyses indicates a ligand: metal ratio of 1 : 1 in all the coordination polymers and the association of water molecules with central metal atom in case of Mn(II), Fe(II), Co(II), and Ni(II) coordination polymers.     

Syntheses,structures and photocatalytic properties of two coordination polymers based on bis(1,2,4-triazol-4-ylmethyl)benzene and multicarboxylates

Two coordination polymers {[Cu₄(OH)₂(btrb)₂(btc)₂]·4H₂O}_n (1) and {[Cd₂(btrb)(adc)₂(H₂O)]·H₂O}_n (2) were synthesized with hydrothermal method and characterized (btrb = 1,4-bis(1,2,4-triazol-4-ylmethyl)benzene, btc = 1,3,5-benzenetricarboxylate, adc = 1,3-adamantanedicarboxylate). 1 shows an unusual (3,10)-connected two-dimensional metal–organic framework based on the tetranuclear copper(II) cluster [Cu₄(μ₃-OH)₂]. 2 is an interesting three-dimensional network based on the one-dimensional metal–organic nanotube. 1 shows good photocatalytic activity for the degradation of methyl blue (MB). The luminescence of 2 was investigated.     

Construction of Zn(II)/Cd(II) coordination polymers derived from a tetrazole derivative: Syntheses,structures and luminescent properties

Three new coordination polymers [Zn(Htip)Cl(H₂O)]_n (1), [Zn(Htip)₂]_n (2) and [Cd(Htip)₂]_n·2nH₂O (3) were synthesized by reactions of Zn(II)/Cd(II) salts with a multidentate tetrazole-based ligand 2-(4-(tetrazol-5-yl)phenyl)imidazo(4,5-f)(1,10)phenanthroline (H₂tip). Complex 1 possesses an infinite 1D coordination chain, and further forms the final 3D supramolecule through π⋯π stacking interactions. Complexes 2 and 3 are isomorphous, and both of them feature an 8-fold interpenetrating 4-connected 3D framework with the dia topological net and the Schläfli symbol of {6⁶}. In 1–3, the Htip⁻ ligand links two metal centers through three terminal N-donors. The structural analyses indicate that the anions and solvents can subtly influence the formation of the resulting network. Moreover, the thermal stabilities and photoluminescent properties of 1–3 are investigated in the solid state.     

Effect of orientation on electrical properties of polymers

This article deals with the effect of orientation on the electrical properties (tangent of the angle of dielectric losses tan δ, electric strength E, and lifetime τ) of polymer films. It is shown that the orientational stretching of PVC and PC films leads to the change of the temperature position of dipole segmental losses and reduces the value of tan δ in the maximum of this region. Under the orientation the electric strength of PE and PVC films increases considerably, and the lifetime τ increases under the high strengths of the field, and reduces under the low ones. The mechanical loads causing no orientation only reduce the lifetime of the polymer films.     

Coordination polymers, 4. Electrical properties of some bisphenolic chelate polymers

The electrical properties of Ni(II) and Cu(II) chelate polymers of bis(2,4-dihydroxybenzaldehyde), bis(2,4-dihydroxyacetophenone), bis(2,4-dihydroxybenzophenone), bis(2,4-dihydroxybenzaldehyde)ethylenediimine, bis(2,4-dihydroxyacetophenone)-ethylenediimine, bis(2,4-dihydroxybenzophenone)ethylenediimine and bis(2,4-dihydroxyacetophenoneimine) and aromatic acid chlorides have been studied. The chelate polymers with the most rigid structure were found to have the highest conductivities.     

Synthesis and properties of novel aromatic polyimides derived from bis(p-aminophenoxy)methylphenylsilane

A novel siloxane-containing diamine, bis(p-aminophenoxy)methylphenylsilane (BAMPS), was synthesized from the condensation of dichloromethylphenylsilane with p-aminophenol in the presence of triethylamine. A series of BAMPS-based aromatic polyimides were prepared from BAMPS and various aromatic tetracarboxylic dianhydrides by the usual two-step procedure including ring-opening polyaddition to poly(amic acid)s and subsequent cyclodehydration to polyimides. The inherent viscosities of poly(amic acid)s III_a - III_f ranged from 0.09 to 0.36 dL g⁻¹ in N,N-dimethylacetamide at a concentration of 0.5 g dL⁻¹ at 30°C. The inherent viscosities of polyimides were between 0.06 and 0.32 dL g⁻¹ in various solvents at 30°C. Polyimides, especially IV_c and IV_f , were soluble in a wide range of organic solvents such as N-methyl-2-pyrrolidinone, concentrated H₂SO₄, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide. The polyimides were characterized by elementary analysis, IR spectra, TGA, and DSC. They also had glass transition temperatures ranging from 128 to 181°C. The 10% mass loss temperature was recorded in the range of 404–443°C in nitrogen and of 315–339°C in oxygen. © 1997 John Wiley & Sons, Inc.     

Syntheses,structures and photocatalytic properties of three copper(II) coordination polymers

Three coordination polymers [Cu₂(obtz)₂(tdc)₂]_n (1), {[Cu(obtz)₂(H₂O)₂][Cu₂(obtz)₂(sip)₂]5.5H₂O}_n (2) and [Cu(obtz)(nip)]_n(3) were synthesized by the hydrothermal reaction (obtz = 1.2-bis(1,2,4-triazol-1-ylmethyl)benzene, tdc = 2.5-thiophenedicarboxylate, sip = 5-sulfoisophthalate, nip = 5-nitroisophthalate). 1 shows a ladder-like one-dimensional chain with two side arms. 2 is comprised of two distinct and crystallographically independent polymeric motifs. The first motif in 2 is the ladder-like one-dimensional anionic chain with two side arms. The second motif in 2 is the cationic chain. 3 exhibits the intriguing 2-fold interpenetrated network based on the undulated 2D (4.4) network. 1, 2 and 3 are good photocatalysts for the degradation of methyl orange (MO) under UV irradiation.     

Syntheses,structures and luminescence of two cadmium entangled coordination polymers based on bis(imidazole) and biscarboxylate ligands

Two entangled coordination polymers [Cd₂(bib)(bdc)₂]_n (1) and [Cd₂(bib)(bda)₂]_n (2) were synthesized by the hydrothermal reaction (bib = 1,4-bis(2-methyl-imidazol-1-yl)butane, bdc = 1,2-benzenedicarboxylate, bda = 1,4-benzenediacetate). 1 exhibits an unusual 6-connected self-catenated 3D network based on Cd₂(COO)₂ dimer with the point symbol of (4⁴·6¹⁰·8). 2 exhibits a 3-fold interpenetrating 3D pcu network based on Cd₂(COO)₂ dimer. The different conformations of bib ligands (the anti–anti–anti conformation in 1 and gauche–anti–gauche conformation in 2) play the key role in the construction of different structures in 1 and 2. The luminescence and thermal stability were investigated.     

Two chiral coordination polymers constructed from (1R,2R)-1,2-diaminocyclohexane derivative: Syntheses,structures and properties

Two chiral coordination polymers were synthesized by using a chiral ligand (1R,2R)-1,2-bis(4-(1,2,4-triazolyl))cyclohexane to assemble with Zn(II)/Ag(I) salts. The different coordination modes of the ligand result in two diverse structures, such as a 0D structure for 1 and a 1D chain for 2, respectively. The chiral nature of compounds 1 and 2 was confirmed by circular dichroism spectra (CD) and second harmonic generation (SHG) efficiency measurements. Furthermore, the photoluminescent properties of compounds 1 and 2 have been investigated in the solid state at ambient temperature.     

Fixed helical Cd(II) coordination polymers assembled from diastereopure Schiff-base ligands derived from condensation of acetylacetone with 1S,2S- and 1R,2R-cyclohexanediamine

The 1:1 interaction of the diastereopure Schiff bases (1S,2S)-bis(acetylacetone)-cyclohexanediimine (L¹) and (1R,2R)-bis(acetylacetone)cyclohexanediimine (L²) with CdI₂ yields the new helical metal coordination polymers [CdL¹I₂]_n (1) and [CdL²I₂]_n (2). The respective X-ray structures, as expected, confirmed 1 and 2 to be enantiomeric, existing as right-handed (P) and left-handed (M) helical chains in which both L¹ and L² are formally present in their (unusual) uncharged ketoamine form, with the (protonated) amine nitrogens not coordinated. The Cd(II) centres in 1 and 2 display distorted tetrahedral coordination geometries being bound to two iodo ligands and two oxygen donor atoms from individual ketoamine domains belonging to different Schiff base ligands.     

Coordination polymers. 7. Synthesis and characterization of some polychelates derived from bisphenolic complexes

Chelate polyesters and polysiloxanes derived from bisphenolic complexes with some bivalent ions as copper, nickel, cobalt, iron, zinc have been synthesized. The polychelates are studied in terms of spectral, thermal, magnetic, and electrical properties; the probable structures of these polymers have been proposed.     

Synthesis,luminescence, and structural characterization of Zn and Cd coordination polymers of flexible bis(imidazolyl) derivatives

Coordination polymers [Zn(imc)(L¹)] · H₂O, (1, imc = iminodiacetate, L¹ = bis(N-imidazolyl)methane) [Zn(hba)₂(L²)]₂ · EtOH · 3H₂O, (2, hba = p-hydroxybenzoate, L² = bis(N-benzimidazolyl)methane), [Cd(mal)(H₂O)(L³)](3, L³ = 1,4-bis(N-imidazolyl)butane, mal = maleate) have been prepared and structurally characterized. Complex 1 consists of hexa-coordinated central Zn ions and exhibits 2D network structure. The Zn atoms in 2 have tetrahedral coordination geometry, and are linked by bis(imidazolyl) ligands into 1D chain structure. The cadmium ions in 3 are hepta-coordinated with pentagonal bipyramidal geometry. Complex 3 displays 2D grid structure. The TGA showed that the coordination polymers are stable up to 200 °C. All the three complexes are emissive at room temperature in their solid state.     

The synthesis of selenium condensation polymers using bis(2-hydroxyethyl) selenide and bis(2-aminoethyl) selenide

Procedures were developed for the large-scale synthesis of bis(2-hydroxyethyl) selenide and bis(2-aminoethyl) selenide. These bifunctional selenides were converted into a series of polyesters, polyureas, and polyurethanes. Methods of syntheses and properties of these condensation polymers are described.     

Three new d10 coordination polymers based on 2-(2-pyridyl)benzimidazole ligand: Synthesis,structures and properties

Three coordination polymers containing 2-(2-pyridyl)benzimidazole (PyHBIm) ligand, namely {[Zn₃(PyBIm)₃(PyHBIm)₂(tma)(H₂O)]?H₂O}_n (1), [Zn(PyHBIm)(oba)]_n (2), [Cd(PyHBIm)(oba)]_n (3), (tma = trimesate, oba = 4,4′-oxybis-(benzoate)), have been prepared through hydrothermal reaction. Compound 1 exhibits one-dimensional (1D) helical structure. However, compounds 2 and 3 display 1D meso-helical structure. These 1D structures are further assembled into three-dimensional (3D) networks through aromatic π–π stacking interactions and hydrogen bonding interactions. Moreover they all exhibit strong photoluminescence at room temperature and may be good candidates for potential luminescence materials.     

Effect of Pb doping on the electrical properties of textured Bi-2212 superconductors

Bi_2−xPb_xSr₂CaCu₂O_y textured materials (x = 0.0, 0.2, 0.4, and 0.6) have been successfully prepared by the laser floating zone technique. Microstructure and electrical properties (J_C and T_C) have been clearly affected by Pb addition. From the E–I curves, slope of the transition between the superconducting and the normal state (n) at 77 K reaches a maximum of about 16 for the 0.4 Pb doped samples. This value is much higher than the typical ones for the Bi-2212 materials. Moreover, when the electrical properties of the 0.4 Pb doped samples are measured at lower temperatures (between 65 and 77 K), n values increase when the temperature is decreased. A maximum n value of 32 has been reached at 65 K which makes this material very attractive for its use as resistive fault current limiters.     

Effect of NiO doping on grain growth and electrical properties of ZnO-based varistors

The effects of NiO content on the grain growth and the electrical properties of the ZnO varistors were studied. The effect on the grain growth was characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometer, while the effects on the electrical properties were investigated by varistor tester, pulse surge tester and precision impedance analyzer. The results showed that the growth of the (0002) plane of the ZnO varistors was inhibited by doping NiO, which improved the electrical properties of the varistors, especially the surge shock stability. The sample doped with 1.56 mol% NiO exhibited excellent electrical properties with breakdown voltage gradient of 184.0 V/mm, nonlinear coefficient of 72.7, leakage current of 0.37 µA, clamp voltage ratio of 2.20 under 8/20 μs waveform impact of 20 kA and change rates of positive and negative breakdown voltages of < 4% under 20 times impacts of 20 kA.     

Four coordination polymers derived from 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole and copper sulfate

The reaction of 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole (3-bpt) with copper sulfate in EtOH/H₂O solvent yields four coordination polymers [Cu(3-bpt)(H₂O)₄](SO₄)·H₂O (1), [Cu(3-bpt)(H₂O)₄][Cu(3-bpt)(H₂O)₃(SO₄)](SO₄)·7H₂O (2), [Cu(3-bpt)(H₂O)₃(SO₄)]·2H₂O (3) and [Cu(3-bpt)(H₂O)(SO₄)] (4), showing one-dimensional undulated chain, zigzag chain and two-dimensional network. The formations of compounds 1, 2 and 3 are controlled by the EtOH/H₂O ratio. The synthesis of compound 4 may be controlled by the EtOH/H₂O ratio and the temperature because it is prepared under solvothermal condition. The thermal properties have been investigated.     

Effect of iodine incorporation on the electrical properties of amorphous conducting carbon films

In this work, the influence of iodine incorporation on the electrical properties of amorphous conducting carbon films, prepared by the vapor phase pyrolysis of maleic anhydride, is reported and discussed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies reveal structural changes in the system. The anomalous behavior in the electrical properties of the intercalated system at low temperatures is investigated. The system shows a positive temperature coefficient of resistance (TCR) at low temperatures, which suggests reasons for the induced ordering of the system at low temperatures with the iodine incorporation. Also, a systematic increase in the conductivity of the sample is observed. The crossover temperature depends on the disorder in the system. The results indicate the possibility of metal-insulator (M-I) transition as a function of preparation temperature, iodine concentration and magnetic field.