Thermodynamic study of Cd(II) complex formation with tripodal N-donor ligands in DMSO

The complex formation of Cd(II) with N-donor ligands in dimethylsulfoxide (DMSO) is investigated by means of potentiometry and titration calorimetry. The ligands considered in this work are tripodal polyamines and polypyridines: 2,2′,2″-triaminotriethylamine (TREN), tris(2-(methylamino)ethyl)amine (Me₃TREN), tris(2-(dimethylamino)ethyl)amine (Me₆TREN), tris[(2-pyridyl)methyl]amine (TPA) and 6,6′-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine (BTPA). These ligands are characterized by a systematic modification of the donor groups to relate their structure to the thermodynamics of the complexes formed. The TREN and Me₃TREN ligands form highly stable species. The stability of the complex formed with the fully methylated Me₆TREN is much lower than with other polyamines and the enthalpic and entropic terms suggest an incomplete coordination to the metal ion. In general, the TPA ligand forms complexes less stable than TREN and Me₃TREN as a result of the combination of higher structural rigidity of TPA and lower basicity of pyridine moiety with respect to primary and secondary amines. Pyridine-containing ligands display, in general, a less unfavorable formation entropy than tripodal polyamines here considered. In particular, TPA forms a more stable 1:1 species with respect to Me₆TREN due to the entropic term, being the enthalpy less negative. The ligand BTPA is able to form only a monometallic complex, where the metal ion is likely to be encapsulated as indicated by the obtained thermodynamic parameters.     

Affinity of Tripodal and Linear Tetraamines for Silver(I) in Dimethyl Sulfoxide

The thermodynamic functions of the complexation of Ag(I) by the tripodal ligands, tris(2-(methylamino)ethyl)amine (Me₃tren) and tris(2-(dimethylamino)ethyl)amine (Me₆tren) (L), are determined in dimethyl sulfoxide (DMSO) by potentiometric and calorimetric techniques at 298.0 K and 0.1 mol⋅dm⁻³ ionic strength (Et₄NClO₄). A comparison is made between previous data concerning Ag(I) complex formation with the non-alkylated tripodal 2,2′,2″-triaminotriethylamine (tren), in order to analyze the influence of N-methylation on this type of branched donor, and with those relative to the linear triethylenetetramine (trien) and 1,1,4,7,10,10-hexamethyltriethylenetetramine (Me₆trien). The results are discussed taking into account different σ-donating properties, geometric arrangement of the ligands, steric repulsions and solvation effects.     

Mimicking a Superoxide Dismutase (SOD) Enzyme by copper(II) and zinc(II)-complexes

Mimicking the Superoxide Dismutase Enzyme (SOD), several imidazolato-bridged copper(II)-zinc(II) complexes were prepared, characterised by IR spectroscopy and their SOD enzyme activity was determined. 2,2′-Bipyridine, 2,2′:6′,2″-terpyridine and tris(2-aminoethyl)amine molecules were used on both metal sides, as coordinating ligands. The complex, containing the 2,2′:6′,2″-terpyridine ligand on copper side has the smallest SOD activity, which indicates the importance of the rigidity of the copper complex in SOD activity.     

Syntheses,structures, and properties of two binuclear cadmium(II) iodides containing a bis(tridentate) Schiff base/tetradentate tripodal amine: control of coordination numbers by varying ligand matrices

Two binuclear cadmium(II) iodide compounds of the types [Cd₂(L1)(I)₄] (1) and [(L2)Cd(μ-I)CdI₃] (2) [L1 = N,N′-(bis(pyridine-2-yl)formylidene)triethylenetetramine and L2 = tris(2-aminoethyl)amine] are synthesized and characterized. X-ray structural study shows that each cadmium(II) in 1 has a distorted square pyramidal geometry with a CdN₃I₂ chromophore and that L1 behaves as a binucleating bis(tridentate) ligand bridging the metal centers with iodides remaining as terminals. In 2, one cadmium(II) adopts a distorted tetrahedral geometry with a CdI₄ chromophore surrounded by four iodides, while the other has a distorted trigonal bipyramidal environment with CdN₄I chromophore bound by four N atoms of L2 and one bridging iodide. Weak C–H···π interactions in 1 result in an infinite 1D chain; however, such weak non-covalent interactions are absent in 2. The Schiff base complex, 1, shows high-energy intraligand ¹(π–π*) fluorescence in DMF solution at room temperature, whereas compound 2 containing tripodal amine is fluorescent-inactive.     

Thermal Studies of New Cu(I) and Ag(I) Complexes with Bipyridine Isomers

The complexes of the general formula MLSCN (M=Cu(I), Ag(I), L=2,2′-bipyridine=2-bipy, 4,4′-bipyridine=4-bipy or 2,4′-bipyridine=2,4′bipy) have been prepared and their IR spectra examined. The nature of metal-ligand coordination is discussed. Thermal decomposition in air of these complexes occurred in several successive endothermic and exothermic processes and the residue was Cu₂O and Ag, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and direct interactions of silver colloidal nanoparticles with pollutant gases

Silver nanoparticles (NPs) were synthesized in organic solvents. Spontaneous reduction of silver salts takes place in N,N′-dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) at room temperature. The formed colloids are not stable without a stabilizing agent, hence rarely used, and inexpensive organic molecules (β-cyclodextrin and cholic acid) were used as surface modifiers in DMF. The stabilization was successful; the Ag NPs remained stable for more than 3 months. Additionally, Ag NPs were prepared using Ag-2-ethylhexanoate and Na-citrate as capping agent in DMSO. The resulting NPs are stable, of 4.4 nm average size, and at the same time reactive for catalytic purposes. The interaction of Ag NPs with pollutant atmospheric gases (NO and SO₂) was studied. UV–visible spectra show the oxidation of silver and the very efficient reduction of NO at room temperature. SO₂ molecules are adsorbed on the NPs surface, causing their aggregation and precipitation.     

Copper(0)‐mediated living radical polymerization of acrylonitrile: SET‐LRP or AGET‐ATRP

Cu(0)‐mediated living radical polymerization was first extended to acrylonitrile (AN) to synthesize polyacrylonitrile with a high molecular weight and a low polydispersity index. This was achieved by using Cu(0)/hexamethylated tris(2‐aminoethyl)amine (Me₆‐TREN) as the catalyst, 2‐bromopropionitrile as the initiator, and dimethyl sulfoxide (DMSO) as the solvent. The reaction was performed under mild reaction conditions at ambient temperature and thus biradical termination reaction was low. The rapid and extensive disproportionation of Cu(I)Br/Me₆‐TREN in DMSO/AN supports a mechanism consistent with a single electron transfer‐living radical polymerization (SET‐LRP) rather than activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). ¹H NMR analysis and chain extension experiment confirm the high chain‐end functionality of the resultant polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

氮烃基化tren银配合物的合成及二维超分子结构

合成了氮烃基化三角架tren配体L·3HCl(L= [N, N′, N″ 三(4 甲氧苄基) 三(2 氨乙基)胺] ),并得到了其单核Ag(I)配合物 [AgL]NO3.晶体结构研究表明Ag(I)离子被三角架配体L四齿螯合,与罕见的笼形结构相似,NOˉ根没有参加配位,而作为氢键的受体将分子组装成二维超分子结构.     

A kinetic investigation into the rate of chloride substitution from chloro terpyridine platinum(II) and analogous complexes by a series of azole nucleophiles

The substitution kinetics of the complexes [Pt(terpy)Cl]Cl·2H₂O (PtL1), [Pt(^tBu₃terpy)Cl]ClO₄ (PtL2), [Pt{4′-(2′′′-CH₃-Ph)terpy}Cl]BF₄ (PtL3), [Pt{4′-(2′′′-CF₃-Ph)terpy}Cl]CF₃SO₃ (PtL4), [Pt{4′-(2′′′-CF₃-Ph)-6-Ph-bipy}Cl] (PtL5) and [Pt{4′-(2′′′-CH₃-Ph)-6-2′′-pyrazinyl-2,2′-bipy}Cl]CF₃SO₃ (PtL6) with the nucleophiles imidazole (Im), 1-methylimidazole (MIm), 1,2-dimethylimidazole (DIm), pyrazole (Pyz) and 1,2,4-triazole (Trz) were investigated in a methanolic solution of constant ionic strength. Substitution of the chloride ligand from the metal complexes by the nucleophiles was investigated as a function of nucleophile concentration and temperature under pseudo first-order conditions using UV/Visible and stopped-flow spectrophotometric techniques. The reactions follow the rate law k_\textobs = k₂ [ \textNu ] + k _{- 2} k_{\text{obs}} = k_{2} \left[ {\text{Nu}} \right] + k_{ - 2} . The results indicate that changing the nature or distance of influence of the substituents on the terpy moiety affects the π-back-donation ability of the chelate. This in turn controls the electrophilicity of the metal centre and hence its reactivity. Electron-donating groups decrease the reactivity of the metal centre, while electron-withdrawing groups increase the reactivity. Placing a strong σ-donor cis to the leaving group greatly decreases the reactivity of the complex, while the addition of a good π-acceptor group significantly enhances the reactivity. The results indicate that the metal is activated differently by changing the surrounding atoms even though they are part of a conjugated system. It is also evident that substituents in the cis position activate the metal centre differently to those in the trans position. The kinetic results are supported by DFT calculations, which show that the metal centre is less electrophilic when a strong σ-donor is cis to the leaving group and more electrophilic when a good π-acceptor group is part of the ring moiety. The temperature dependence studies support an associative mode of activation. An X-ray crystal structure of Pyz bound to PtL3 was obtained and confirmed the results of the DFT calculations as to the preferred N-atom as a binding site.     

TREN versus Me6‐TREN as ligands in SET‐LRP of methyl acrylate

The commercially available tris(2‐aminoethyl)amine (TREN) was used as ligand to mediate the single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl acrylate in dimethyl sulfoxide initiated with the bifunctional initiator bis(2‐bromopropionyl)ethane and catalyzed by both nonactivated and activated Cu(0) wire. A comparative study between TREN and tris(2‐dimethylaminoethyl)amine (Me₆‐TREN) ligand, that is more commonly used in SET‐LRP, demonstrated that TREN provided a slower polymerization but the chain‐ends functionality of the resulting bifunctional poly(methyl acrylate) was near quantitative and comparable to that obtained when Me₆‐TREN was used as a ligand. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

Thin-layer chromatography of tris(1,10-phenanthroline)iron(II) and tris(2,2′-bipyridine)iron(II) on Sephadex G gels

Summary Gel chromatographic behaviour of tris(1, 10-phenanthroline)iron(II), tris(2,2′-bipyridine)iron(II) and tris(glycinato)cobalt(III) on Sephadex G-10 or G-25 was investigated by TLC with 0.001–1.0M NaCl as the eluent. The zone shapes and R_M values of tris(1,10-phenanthroline)iron(II) and tris(2,2′-bipyridine)iron(II) were appreciably dependent on the sample and eluent concentration, while the neutral complex, tris(glycinato) cobalt(III), exhibited the round zones with constant R_M values. The order of R_M values was found to be tris(glycinato)cobalt(III<tris(2,2∔pyridine)iron(II)<tris-(1,10-phenanthroline)iron(II) in all systems studied, although the reverse trend was expected when assuming the chromatographic behaviour of solute compounds to be controlled by the “sieving effect”. The comparison of the behaviour on Sephadex G gels with that on CM-cellulose revealed that the predominant mechanism involved is not the sieving effect, but ion-exchange and/or hydrophobic interaction.     

Catalytic effect of dimethyl sulfoxide in the Cu(0)/tris(2‐dimethylaminoethyl)amine‐catalyzed living radical polymerization of methyl methacrylate at 0–90 °C initiated with CH3CHClI as a model compound for α,ω‐di(iodo)poly(vinyl chloride) chain ends

A variety of conditions, including catalysts [CuCl, CuI, Cu₂O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me₆‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH₃CHClI, CH₂I₂, CHI₃, and F(CF₂)₈I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH₃CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me₆‐TREN at 90 °C, whereas the second involved Cu(0)/Me₆‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me₆‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me₆‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005     

Quantum-chemical study of <Emphasis Type="Italic">trans</Emphasis> influence in gold(I) linear complexes

Theoretical study of trans influence of ligands in Au(I) and Ag(I) complexes is based on quantumchemical calculations fulfilled within the limits of density functional theory. Metal-ligand bond orders and their σ- and π-components were analyzed for several series of [L-M(I)-X] ^q complexes; the participation of s, p, and d metal orbitals in binding was characterized. The π dative interactions metal→ ligand in Ag(I) and Au(I) complexes are weakened, and trans influence is caused by a competition of σ-donor ligands for the electronic density transfer from lone pairs of ligands onto $ 0.9s + 0.4d_{z^2 } $ 0.9s + 0.4d_{z^2 } hybrid orbitals of gold.     

Low-fluorinated homopolymer from heterogeneous ATRP of 2,2,2-trifluoroethyl methacrylate mediated by copper complex with nitrogen-based ligand

We report the preparation of low-fluorinated homopolymer via heterogeneous atom transfer radical polymerization (ATRP) of 2,2,2-trifluoroethyl methacrylate (TFEMA) using 2,2′-bipyridine (bpy), N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA), and tris(2-(dimethylamino)ethyl)amine (Me₆TREN) as representatives for di-, tri-, and tetradentate amine ligands, respectively. The ATRP was better controlled, yielding polymers with controlled molecular weights and low polydispersities (M_w/M_n ca. 1.11) when bpy was used as a ligand than when PMDETA was used. This was further supported by the results of our kinetic and chain extension studies. However, the ATRP of TFEMA had lower monomer conversions and gel formation when Me₆TREN was used as the ligand. Further reported are the thermal-properties, as well as the surface properties of the films from the resulting polymers with different molecular weights.     

Crystal structures and luminescence of two zinc(II) complexes with benzimidazole ligands

Two new zinc(II) complexes have been synthesized and studied by single crystal X-ray diffraction method: [Zn(L1)Cl₂]·2DMF (1) and [Zn(L2)Cl₂]·DMF (2) (L1 = 3,3′-bis(2-benzimidazolyl)-2,2′-dipyridine, L2 = 3,3′-bis[2-bis(2-ethylbenzimidazolyl)]-2,2′-dipyridine). Compound 1 is monoclinic, C2/c, a = 23.142(3) ?, b = 11.845(1) ?, c = 14.735(3) ?; compound 2 is orthorhombic, C222₁, a = 12.140(7) ?, b = 16.283(9) ?, c = 16.51(1) ?. In both compounds, Zn(II) cations are coordinated by two chlorine atoms and two benzimidazole nitrogen atoms in a slightly distorted tetrahedron fashion. Structural features responsible for fluorescent properties of the complexes are discussed.     

Influence of organic carboxylic acids on self-assembly of silver(I) complexes containing 1,2-bis(4-pyridyl)ethane ligands

Four silver(I) complexes, namely [Ag₂(bpe)₂](bdc)·8H₂O (1), [Ag₂(bpe)₂(da)]·4H₂O (2), [Ag₄(bpe)₃(bptc)]·9H₂O (3), and Ag(bpe)₂(bpdc)₂ (4), have been successfully synthesized by the reactions between AgNO₃, 1,2-bis(4-pyridyl)ethane (bpe) and different carboxylic acids, including 1,3-benzenedicarboxylic acid (H₂bdc), diphenic acid (H₂da), 3,3′,4,4′-biphenyltetracarboxylic acid (H₄bptc), and 2,2′-bipyridine-3,3′-dicarboxylic acid (H₂bpdc). All four compounds were characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. In (1), the Ag(I) atoms, in linear geometry, are joined into 1-D infinite cationic bpe-silver chains, and discrete bdc²⁻ anions compensate the charge of the crystal structure. In (2), the Ag(I) atoms, adopting tetrahedral and trigonal geometries, are linked by bpe and da²⁻ ligands into neutral double chains. In (3), the Ag(I) atoms, in T-shaped and linear environments, are coordinated by bpe and multidentate bptc⁴⁻ ligands to construct a 2-D network. And in (4), the Ag(I) atoms, with trigonal and T-shaped coordination geometries, are coordinated by bpe and bpdc²⁻ ligands to build up a 3-D framework. The different anions play different and important roles in directing the final crystal structures.     

Zinc(II) as an allosteric regulator of liposomal membrane permeability induced by synthetic template-assembled tripodal polypeptides

Three copies of peptide sequences from the peptaibol family, known to affect the permeability of the lipid bilayer of membranes, were connected to tris(2-aminoethyl)amine (TREN), a tripodal metal ion ligand, to prepare functional peptides capable of modifying the permeability of liposomal membranes. Some of the resulting tripodal polypeptide derivatives are very effective in promoting carboxyfluorescein (CF) leakage from CF-loaded unilamellar vesicles composed of a 70:30 phosphatidylcholine/cholesterol blend. The activity of these novel compounds was shown to be tunable upon metal ion coordination of the TREN subunit; the tripodal apopeptide was far more effective than its ZnII complex. Leakage experiments showed that a minimum number of five amino acids per peptide chain is required to form active systems. A mechanism is proposed in which the ZnII ion changes the conformation of the template from extended to globular and thus acts as an allosteric regulator of the activity of the systems. Molecular modeling studies indicate that when the three peptide chains are connected to the template in the extended conformation, the resulting tripodal polypeptide is able to span across the membrane, thus allowing the formation of permeable channels made of a cluster of molecules. The same change of conformation induces, to some extent, fusion of the membranes of different liposomes.     

Construction of novel coordination polymers with simple ligands

Three different types of metal-organic polymers have been prepared by a solution diffusion process carried out at room temperature. Crystals of the copper coordination polymers [CuX(4,4′-bipy)] _n (X = Cl, Br, I) have been obtained by the reaction of 4,4′-bipyridine ligands with Cu₂X₂ fragments to yield a three-dimensional network consisting of four interlocking planar lattices. Single crystals of [Cu₂(1,2,4,5-BTC)(DMF)₂] _n (1,2,4,5-BTC = 1,2,4,5-benzene tetracarboxylate) have been grown by slow diffusion from solutions of a mixture of CuBr₂, 2,2′-dithiosalicylic acid, and sodium azide plus a mixture of 1,2,4,5-H₄BTC and 4-cyanopyridine. The complex [Co(1,3,5-BTC)(4,4′-bipy)] _n (1,3,5-BTC = 1,3,5-benzene tricarboxylate) has a 3D open framework structure involving terminal cobalt atoms plus bridging 1,3,5-BTC and 4,4′-bipyridine ligands.     

Activation of alkyl halides at the Cu0 surface in SARA ATRP: An assessment of reaction order and surface mechanisms

The external order in reagents for the activation of alkyl halides by Cu⁰ was investigated in supplemental activator and reducing agents (SARA) ATRP. Using methyl 2-bromopropionate (MBrP) or ethyl α-bromophenylacetate (EBPA) and tris(2-(dimethylamino)ethyl)amine (Me₆TREN) in DMSO and MeCN, it was determined that the rate of activation scaled with (S/V)^0.9 in both solvents. For MBrP, the rate was first order with respect to [MBrP]₀ until a saturation in the rate was observed around 33 and 110 mM in DMSO and MeCN, respectively. For EBPA, the reaction was also first order until a maximum rate was observed at 33 mM in DMSO, whereas an inverse order was observed for concentrations above 66 mM in MeCN. At saturated concentrations of MBrP, it was found that the rate increased linearly with respect to [Me₆TREN]₀ for all systems but became asymptotic with a maximum rate of 2 × 10⁻⁶ and 4 × 10⁻⁵ M s⁻¹ in DMSO and MeCN, respectively. Model polymerizations in the absence of ligand showed slow reaction rates, indicating the necessity for ligand. The results allow more accurate modeling and understanding of SARA ATRP under a large range of initiator concentrations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3048–3057     

Structural studies of spiroarsoranes derived from 2-aminophenols

This paper describes the structural studies of 2-phenyl-9,9′-dimethyl-2,2′-spirobis(1,3,2-λ⁵-benzoxazarsoline) 5, 2-phenyl-8,8′-dimethyl-2,2′-spirobis(1,3,2-λ⁵-benzoxazarsoline) 6 by ¹H,¹³C,¹⁵N NMR in [²H₆]DMSO and CDCl₃. The solid state studies were made by X-ray experiments. Infrared spectroscopy was obtained in CDCl₃ and the vibrational signals were assigned using DFT calculations. The nature of the As–N, As–C and As–O bonds in these compounds was established by NBO studies.