Syntheses and characterizations of four metal coordination polymers constructed by the pyridine-3,5-dicarboxylate ligand

A series of metal-organic frameworks, namely [Ni(PDB)(H₂O)]_n (1), [Pb(PDB)(H₂O)] · (H₂O) (2), [Co₂(PDB)₂(bpy)₂(H₂O)₄] · 4H₂O (3) and [Co₂(PDB)₂(phen)₂]_n (4) (H₂PDB = pyridine-3,5-dicarboxylic acid, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), have been synthesized based on pyridine-3,5-dicarboxylate acid and two neutral chelate ligands, with different metal ions such as Ni^II, Co^II and Pb^II, under hydrothermal conditions. The framework structures of these polymeric complexes have been determined by the X-ray single crystal diffraction technique. In the four complexes, the pyridine-3,5-dicarboxylate acid ligand exhibits diverse coordination modes, which play an important role in the construction of metal-organic frameworks. The thermal analyses of these four complexes have been measured and discussed. In addition, complex 2 shows strong phosphorescent emission at room temperature and the magnetic measurement of the polymer of 4 reveals a typical antiferromagnetic exchange.     

Evidence for single-chain magnet behavior in a Mn(III)-Ni(II) chain designed with high spin magnetic units: a route to high temperature metastable magnets

We herein present the synthesis, crystal structure, and magnetic properties of a new heterometallic chain of MnIII and NiII ions, [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (saltmen2- = N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate) and pao- = pyridine-2-aldoximate). The crystal structure of 1 was investigated by X-ray crystallographic analysis: compound 1 crystallized in monoclinic, space group C2/c (No. 15) with a = 21.140(3) A, b = 15.975(1) A, c = 18.6212(4) A, beta = 98.0586(4) degrees , V = 6226.5(7) A3, and Z = 4. This compound consists of two fragments, the out-of-plane dimer [Mn2(saltmen)2]2+ as a coordination acceptor building block and the neutral mononuclear unit [Ni(pao)2(py)2] as a coordination donor building block, forming an alternating chain having the repeating unit [-Mn-(O)2-Mn-ON-Ni-NO-]n. In the crystal structure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of 10.39 A and with the absence of interchain pi overlaps between organic ligands. These features ensure a good magnetic isolation of the chains. The dc and ac magnetic measurements were performed on both the polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility of this one-dimensional compound was successfully described in a mean field approximation as an assembly of trimers (Mn...Ni...Mn) with a NiII...MnIII antiferromagnetic interaction (J = -21 K) connected through a ferromagnetic MnIII...MnIII interaction (J'). However, the mean field theory fails to describe the magnetic behavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between 5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading to the same value of J'. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In the same range of temperature, combined ac and dc measurements show a slow relaxation of the magnetization. This result indicates the presence of a metastable state without magnetic long-range order. This material is the first experimental design of a heterometallic chain with ST = 3 magnetic units showing a "single-chain magnet" behavior predicted in 1963 by R. J. Glauber for an Ising one-dimensional system. This work opens new perspectives for one-dimensional systems to obtain high temperature metastable magnets by combining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.     

Chemo- and stereoselective monobenzoylation of 1,2-diols catalyzed by organotin compounds

A new facile method for monoacylation of diols has been developed. A variety of cyclic and acyclic diols, in particular 1,2-diols, were selectively monobenzoylated in good yields by the reaction with benzoyl chloride in the presence of a catalytic amount of dimethyltin dichloride and inorganic bases such as potassium carbonate. Furthermore, the method was successfully applied to a kinetic resolution of racemic 1-phenyl-1,2-ethanediol using a chiral organotin catalyst. The ee was dependent on the kind of base, water as an additive, and the reaction temperature.     

Synthesis of optically active heterocyclic compounds via deracemization of 1,2-diol monotosylate derivatives bearing a long aliphatic chain by a combination of enzymatic hydrolysis with Mitsunobu inversion

We have succeeded in accomplishing the deracemization of (±)-2-acetoxydecyl and (±)-acetoxy-6-benzyloxyhexyl tosylates, which have a long substituent, via an enzyme-mediated enantioselective hydrolysis with a Mitsunobu inversion using polymer-supported triphenylphosphine to afford the corresponding (S)-enantiomer. Enantiomerically pure (S)- and (R)-γ-dodecalactones, a fruit flavor, were synthesized from (S)-2-acetoxydecyl tosylate as the mutual starting material. The poisonous alkaloid (S)-coniine was also synthesized using enantiomerically pure allyl amine as the key intermediate derived from (S)-acetoxy-6-benzyloxyhexyl tosylate.     

Diversity in magnetic properties of 3D isomorphous networks of Co(II) and Mn(II) constructed by napthalene-1,4-dicarboxylate

Two novel 3D isomorphous organic-inorganic hybrid frameworks, [M(1,4-napdc)]n ( M = Co(II), and Mn(II), ; 1,4-napdcH2 = napthalene-1,4-dicarboxylic acid) have been hydrothermally synthesized and structurally characterized, and the magnetic results exhibit metamagnetic behaviour (TC = 5.5 K), and a weak antiferromagnetic interaction, which are structurally correlated.     

Two chiral mononuclear and one-dimensional cadmium(II) complexes constructed by (1R,2R)-N1,N2-bis(pyridinylmethyl)cyclohexane-1,2-diamine derivatives: Effect of positional isomerism

Reactions of (1R,2R)-N¹,N²-bis(pyridinylmethyl)cyclohexane-1,2-diamine derivatives, (1R,2R)-2-bpcd and (1R,2R)-3-bpcd [(1R,2R)-2-bpcd = (1R,2R)-N¹,N²-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine, (1R,2R)-3-bpcd = (1R,2R)-N¹,N²-bis(pyridin-3-ylmethyl)cyclohexane-1,2-diamine], with CdI₂ in an analogous way led to the formation of a chiral discrete mononuclear complex and a chiral one-dimensional polymeric chain, respectively, which may be attributed to the positional isomerism of the ligands. The chiral organic ligands and complexes display luminescent properties indicating that they may have a potential application as optical materials. Powder second-harmonic generation (SHG) efficiency measurement shows that the SHG efficiency of the complexes is approximately 0.3 and 0.45 times that of KDP, respectively.     

Kinetics of photosensitized chain reaction of 1,2-dichloroethane induced by a cw CO2 laser

The photosensitized chain reaction of 1.2-dichloroethane induced by a cw CO₂ laser produced vinyl chloride with high purity. The initiation of the chain reaction is strictly dependent on the irradiated laser frequency. Kinetics of the chain reaction has been studied on the basis of the effects of laser frequency, laser incident power and the pressure of sensitizer on reaction rate. Arrhenius plot shows an activation energy of 21.8 kcal per mole. Generating the active centers by infrared laser can allow the reactions of chain propagation with low activation energy to proceed at a lower temperature, which is of significance in cutting down the energy expenditure and formation of by-products in the process.     

Synthesis,crystal structure and magnetic properties of a new 3D coordination polymer constructed by Co(II) with pyridine-3,4-dicarboxylate and 4,4’-bipyridine

A metal-organic framework, [Co₂(pydc)₂(bpy)₂] _n · 2nH₂O (1) (H₂pydc = pyridine-3,4-dicarboxylic acid, bpy = 4,4′-bipyridine), was synthesized under hydrothermal conditions. X-ray diffraction experiments reveal that (1) exhibits a chiral 3D metal-organic framework, which represents the rare example of 3D chiral coordination polymers containing two kinds of organic ligands. Temperature-dependent magnetic susceptibility for (1) was also studied. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Anion-modulated reversible conversion of molecular assembly between a macrocycle and a linear chain

Interaction of a flexible thioether ligand with mercury(II) acetate and iodide, respectively, yielded two compounds with structural motifs of a macrocycle and a 1D polymer, whose structural patterns were dominated by anions and could be reversibly changed.     

Photoisomerization of 1,2-diphenylcyclopropane sensitized by polypeptides containing naphthalene groups in their side chain

Poly(γ-1-naphthylmethyl L - and DL -glutamate) (PNLG and PNDLG) and copolypeptides of γ-1-naphthylmethyl L -glutamate and γ-benzyl-L -glutamate were used as sensitizers for isomerization of trans-1,2-diphenylcyclopropane. Quantum yields relative to that of 1-methylnaphthalene were measured in dichloroethane (DCE) and dichloroacetic acid (DCA). The relative quantum yield in DCE was smaller than unity for PNLG, but greater than unity for PNDLG and copolypeptides. The result is discussed in terms of increased effective collisional radius and energy trapping by excimer formation. The relative quantum yields in DCA were close to unity except for the copolypeptides of higher γ-benzyl L -glutamate content. This suggests that the naphthalene groups act in the same manner as their monomeric counterparts in the random conformation and that the greater proportion of γ-benzyl L -glutamate in the copolypeptides lowers the quantum efficiency because trans-1,2-diphenylcyclopropane must penetrate through the polymeric medium in order to encounter the excited naphthalene.     

Syntheses and characterization of energetic compounds constructed from alkaline earth metal cations (Sr and Ba) and 1,2-bis(tetrazol-5-yl)ethane

Two new energetic compounds, [M(BTE)(H₂O)₅]_n (M=Sr(1), Ba(2)) [H₂BTE=1,2-bis(tetrazol-5-yl)ethane], have been hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that they are isomorphous and exhibit 2D (4,4) net framework, generated by 4-connected Sr₂(H₂O)₁₀/Ba₂(H₂O)₁₀ SBUs linked up by two independent binding modes of H₂BTE, and the resulting 2D structure is interconnected by hydrogen-bond and strong face to face π-π stacking interactions between two tetrazole rings to lead to a 3D supramolecular architecture. DSC measurements show that they have significant catalytic effects on thermal decomposition of ammonium perchlorate. Moreover, the photoluminescence properties, thermogravimetric analyses, and flame colors of the as-prepared compounds are also investigated in this paper.     

Probing the pH-dependent chain dynamics of poly(acrylate acid) in concentrated solution by using a cationic AIE fluorophore

We report a novel strategy to study the chain dynamics of poly(acrylic acid) (PAA) in a relative concentrated solution (1.0 g/L). The strategy is based on the fluorescent probe (DCTPE) with unique aggregation-induced emission (AIE) characteristics. Free DCTPE molecules are non-emissive in aqueous solution, but they become highly emissive when trapped in polymer coils. The fluorescence intensity is proportional to the efficiency of trapping DCTPE molecules in polymer coils. By correlation the change of fluorescence intensity with the variation of pH value (from 1.78 to 12.06), the PAA chain’s dynamics in the relatively concentrated solution have been elucidated into three processes. In the pH range from 12.06 to 6.0, PAA chains take an extended and non-folding conformation. Changing pH from 6.0 to 3.86, PAA chains are partially protonated and loosely packed polymer coils are formed. Further lowering the pH value of the solution (from 3.86 to 1.78), protonated segments dominate the PAA chains, and at the same time, the intermolecular hydrogen bonding takes effect, thus the polymer chains posses in the conformation of more compact coils.     

Synthesis of gramicidin S and its analogues via an on-resin macrolactamization assisted by a predisposed conformation of the linear precursors

A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance.     

Generalized structural and kinetic relationships for 1,2-shifts of a hydrogen atom in carbocations and neutral compounds

Dynamic PMR has been used in a kinetic study of degenerate rearrangement of 5,6-X₂-1-H-1, 2-dimethylacenaphthylenonium ions (X=CH₃, Br), accomplished by means of a 1,2-shift of the hydrogen atom. It has been found that the free energy of activation of the 1,2-shift of the H atom in the 5,6-X₂-1-H-1,2-dimethylacenaphthylenonium cation (X=H, CH₃, Br), in the 1-H-1,2-dimethylcyclopentyl cation, and in 5-H-1,2, 3,4,5-pentamethyl-1,3-cyclopentadiene exhibits a linear correlation with parameters characterizing the electron density on the atom to which the migrant is shifted.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1352–1358, June, 1991.     

On a quantity describing the degree of chain entanglement in linear polymer systems

In the present paper we define a quantity which describes how strong a polymer system is entangled. In MD computer simulations we apply this definition to samples of polymer melts which were generated with a specific large-scale structure, as characterized by their radius of gyration, end-to-end distance and the “degree” of mutual entanglement of the chains. The quantities mentioned above are monitored over the relaxation of the samples towards equilibrium.     

Control of peptide chain conformation by photoisomerising chromophores: Enzymes and model compounds

Literature data about enzymatic proteins and synthetic polymers containing azo or spirobenzopyran photochromic compounds are discussed.In enzymes, the catalytic activity can be photomodulated by means of the attached photochromic molecules as well as by microenvironmental changes when they are embedded in photoresponsive membranes. In synthetic polymers, large light-induced conformational changes can be obtained in solution, the most pronounced effects being observed in systems with labile fold structures.The mechanisms responsible for the conformational variations can be the changes in intramolecular and solvational interactions brought about both by the structural change of the chromophore after photoisomerisation and by the charge separation.The data about enzymes, when brought into correlation with those about model compounds, support the hypothesis that the above mechanisms are also operative in the photomodulation of enzyme activity.     

Polyyn-diyls capped by diruthenium termini: a new family of carbon-rich organometallic compounds and distance-dependent electronic coupling therein

Polyyn-diyls capped by Ru(2)(ap)(4) termini (ap = 2-anilinopyridinate), that is, [Ru2(ap)4](mu-C,C'-C2m)[Ru2(ap)4] (compounds 1-5 with m = 1-4 and 6), were synthesized through either a metathesis reaction between Ru2(ap)4Cl and LiC(2m)Li or a Glaser homocoupling reaction of Ru2(ap)4(CmH) under Eglinton/Hay conditions. X-ray diffraction studies of compounds 2 and 4 revealed both the linear rigid rod topology of these compounds and the fine structural details about the Ru2 cores and polyyn-diyl chains. Cyclic and differential pulse voltammetric (CV and DPV) measurements and spectroelectrochemical studies show that reduced and oxidized forms of 1, 2, 4, and 5 are donor-acceptor systems in which the Ru2 termini are coupled to varying degrees depending upon the length of the polyyn-diyl bridge.     

Green,mild and efficient bromination of aromatic compounds by HBr promoted by trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane in water as a solvent

A combination of HBr and trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane as anew and powerful oxidant was found effective for facile brotnination of different aromatic compounds at room temperature in water as a green solvent.Mild reaction conditions,high selectivity and yield,high reaction rate and non-toxicity are some of the major advantages of this synthetic protocol.