Fluorescent Switch Behavior of 1, 2-Bis(4-pyridyl) Ethylene Controlled by pH in Aqueous Solution

With the decrease of pH value from 8.45 to -1.0, the UV-Vis absorption and fluorescent spectra of 1,2-bis（4-pyridyl） ethylene（BPE） took on the same changing trend at four different successive pH stages： 8.45--7.20, 7.20--5.62, 5.62--2.60, and 2.60--1.0, namely, no change, decrease, increase, and decrease again. Among these, in a range of 7.20--5.62, the fluorescence wavelength blueshifted from 418 to 359 nm, but the UV-Vis absorption wavelength, in contrast, redshifted from 285 to 298 nm. The fluorescence intensity of BPE had a drop even to quench upon a decline in the pH value from 2.60 to -1.0 probably owing to its cation-re interaction to reduce the π electron cloud density of BPE. Two dissociation constants, pKa1（4.30±0.01） and PKa2（5.65±0.04）, were obtained based on fluorescence data. The changes of fluorescence spectra indicate that BPE has ＂oft-on-off＂ switch behavior. The fluorescent spectra of BPE were nearly independent on the presence of α- and β-cyclodextrins.

Syntheses,Structures and Luminescent Properties of Cd(Ⅱ)/Zn(Ⅱ) Coordination Polymers Based on the Flexible 4-Substituted Bis(1,2,4-triazole) Ligand

Two new cadmium（II） and zinc（II） coordination polymers, {[Cd（btre）0.5- （mip）（H2O）2]·H2O}n （1） and [Zn（btre）（mip）]n （2）, were synthesized at room temperature condition and characterized by IR spectra, elemental analyses, single-crystal and powder X-ray diffractions （btre = 1,2-bis（1,2,4-triazol-4-yl）ethane, H2mip = 5-methyl-1,3-benzenedicarboxylic acid）. Complex 1 belongs to the triclinic system, P space group, with a = 8.9830（6）, b = 10.0579（6）, c = 10.2479（9） , α = 98.837（6）, β = 115.975（8）, γ = 106.370（6）°, V = 756.30（11） 3 and Z = 2; complex 2 crystallizes in monoclinic, space group P21/c, with a = 7.0332（3）, b = 14.9947（7）, c = 15.9689（7） ？, β = 97.1170（10）°, V = 1671.12（13） ？3 and Z = 4. Compounds 1 and 2 based on the same N/O-donor ligands show different structures. The one-dimensional chains of 1 are further linked by hydrogen bonding and π-π interactions to yield a three-dimensional supramolecular structure. The two-dimensional （6,3） networks of 2 are further extended into a 3D framework via π-π interactions. Thermal stabilities and luminescence of 1 and 2 were investigated.

One Dimensional Coordination Polymer Constructed by 1,2-Bis(4-pyridinecarboxamido)ethane and Copper(II)

The ligand [1, 2-bis(4-pyridinecarboxamido) ethane] (L) and the coordination polymer {[Cu(L)(2)(H2O)].(NO3)(2).6H(2)O}(n)(1) have been synthesized and characterized by IR and H-1 NMR, spectra. Their molecular structures and the packing of 1 have been determined by single-crystal X-ray diffraction analysis. The Cu(II) in 1 is bridged by two ligand forming an infinite one-dimensional chain like structure and L in I adopts a different conformation from its free state. 1 belongs to monoclinic, space group P2(1)/n, a = 1.2896(3) nm, b = 1.2552(8) nm, c = 2.2903(19) nm, beta = 93.04(5)degrees, Z = 4, V = 3.702(4) nm(3). The TG and DTG experiments showed that the uncoordinated H2O can be removed at low temperature by heating, and it does not decompose until 250 degreesC.

Syntheses, Crystal Structures, and Fluorescence Properties of Two 2D→2D Coordination Polymers Based on the Flexible 4-Substituted Bis(1,2,4-triazole) Ligand

Two new 2 D → 2 D zinc(II) coordination polymers, [Zn(btre)0.5(nbdc)(H2 O)]n(1) and {[Zn(btre)0.5(Me Oip)(H2 O)2]·H2 O}n(2)(btre = 1,2-bis(1,2,4-triazol-4-yl)ethane, nbdc=3-nitro-1, 2-benzenedicarboxylate, Me Oip=4-methoxybenzene-1, 3-dicarboxylate) were synthesized at room temperature condition and characterized by IR spectra, elemental analyses, single-crystal and powder X-ray diffractions. Three sets of equivalent 2 D(6, 3) networks parallel polycatenated with each other to give a 2 D → 2 D network in 1 and 2. There are strong π-π interactions and hydrogen bonding interactions between adjacent parallel polycatenated 2 D(6, 3) network in 1. Only hydrogen bonding interactions exist in 2. Thermal stabilities and luminescence of 1 and 2 were investigated.

Synthesis,Spectra,X-ray Diffraction and Thermal Studies of New Zn(Ⅱ) Compounds Based on Dibenzoylmethane

Two new zinc（Ⅱ） compounds with dibenzoylmethane and N-donor ancillary ligands,[Zn（μ-pyz）（dbm）_2]_n（1） and [Zn（dbm）_2（μ-bpe）Zn（dbm）_2]（2）（Hdbm = dibenzoylmethane,pyz = pyrazine and bpe = 1,2-bis（4-pyridyl）ethane）,have been prepared and characterized using elemental analysis,IR,~1H NMR and 13 C NMR spectroscopy,and studied by thermal gravimetric analysis as well as single-crystal X-ray diffraction. The crystal and molecular structures of 1 and 2 have been solved by X-ray diffraction and they turned out to be a one-dimensional coordination polymer with linear dispositions of metal atoms and binuclear compound,respectively. These one-dimensional polymers are further connected to form a 3D supramolecular network by C–H···O（only in 2） and π-π interactions.

Synthesis, Structure and Luminescence Property of a New Two-dimensional Znic(Ⅱ) Coordination Polymer

Based on 5-dimethylamino-isophthalic acid(H2dia)and 1,2-bis(4-pyridyl)ethylene(bpe)mixed linkers,a new d10-configuration Zn(Ⅱ)coordination polymer material,[Zn(dia)(bpe)(H2O)]n(1),was synthesized.In the asymmetric unit,there are one Zn2+ion,two dia2-anions,one neutral bpe linker and one free H2O molecule.In the complex,adjacent Zn2+ions are alternately bridged by the dia2-dianions to generate chains which are further connected by flexible bpe ligands to form a two-dimensional(2 D)layer structure.In topology,the structure of 1 represents a non-interpenetrating 4-connected sql topology.Moreover,infrared spectroscopy,elemental analyses,thermogravimetric analysis,powder X-ray diffraction,solid UV-Vis absorption spectra and photoluminescent property of 1 are also investigated.