Syntheses,structures and photoluminescent property of coordination complexes with 2-(1H-1,2,4-triazol-1-yl)acetic acid

Reactions of ligand 2-(1H-1,2,4-triazol-1-yl)acetic acid (HL) with varied metal salts of Cu(II), Co(II), Ni(II), Zn(II), Cd(II) and Ag(I) result in formation of six new coordination complexes, {[Cu(L)₂] · 3H₂O}_n (1), [Co(L)₂(H₂O)₂]_n (2), [Ni(L)₂(H₂O)₂]_n (3), [Zn(L)₂(H₂O)₂]_n, (4), [Cd(L)₂]_n (5) and [Ag(L)]_n (6), and their structures were determined by X-ray crystallography. Complexes 1, 2, 3 and 4 with square-planar or octahedral metal centers have similar two-dimensional (2D) network structure with (4, 4) topology, while complex 5 displays a 2D structure with (6, 3)-connected topology. Complex 6 has a three-dimensional (3D) structure, in which the Ag(I) has tetrahedral coordination geometry. Ligand L^? acts as a 2-connected rod (bridging ligand) in 1, 2, 3 and 4, and acts as 3-connected nodes in 5 and 6. The results indicate that the coordination modes of the ligand and metal centers have great influence on the structures of the complexes. In addition, the photoluminescent properties of ligand HL and complexes 4 and 5 were studied in the solid state at room temperature.     

Synthesis,spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(3-pyme)2(H2O)2] and polymeric [Cu{3,5-(NO2)2bz}2(3-pyme)2]n

Two new complexes of composition [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] (1) and/or [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂] (2) (3-pyme = 3-pyridylmethanol, ronicol or 3-pyridylcarbinol, 2-NO₂bz = 2-nitrobenzoate and 3,5-(NO₂)₂bz = 3,5-dinitrobenzoate) have been prepared and studied by elemental analysis, electronic, infrared and EPR spectroscopy, magnetic susceptibility measurements and the structure of both complexes has been solved. Complex (1) shows an unusual molecular type of structure consisting of the [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] molecules held together by hydrogen bonds and van der Waals interactions. Complex (2) exhibits a polymeric chain-like structure [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂]_n with copper atoms doubly bridged by two 3-pyridylmethanol molecules and the polymeric molecules are held together by van der Waals interactions. Complex (1) exhibits a magnetic moment μ_eff = 1.84 B.M. at 300 K that remains nearly constant within the temperature region (5–300 K). Further cooling results in lowering the magnetic moment to μ_eff = 1.82 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.423 cm³ K mol⁻¹ and with Weiss constant of −0.06 K. The magnetic moment of (2) exhibits a small increase with a decrease in the temperature (μ_eff = 1.80 B.M. at 300 K and μ_eff = 1.85 B.M. at 1.8 K) with Curie constant of 0.409 cm³ K mol⁻¹ and with Weiss constant of +1.1 K, which can indicate a very weak ferromagnetic interaction between the copper atoms within the chain. Applying the molecular field model resulted in obtaining zJ′ values −0.08 cm⁻¹ for complex (1), and −0.07 cm⁻¹ for complex (2), respectively, that could characterize intermolecular and interchain interactions transmitted through π–π stacking.     

Syntheses,structures and properties of Zn(II) and Co(II) complexes of N-benzesulfonyl-l-glutamic acid ligand

The reaction of N-benzesulfonyl-l-glutamic acid (Bs-glu) with Zn(CH₃COO)₂ · 2H₂O or Co(CH₃COO)₂ · 4H₂O in the presence of imidazole (Im) produced two novel complexes [Zn(Im)₂(Bs-glu)]_n (1) and [Co(Im)₂(Bs-glu)]_n (2). Both of the complexes exhibit similar one-dimensional structural motif and coordination environment. Bs-glu adopts the bis-monodentated coordination mode linking two adjacent metal ions. The complex 1 shows intense photoluminescence in the solid state. Magnetic measurements for 2 show that the exchange interaction of the two Co(II) ions is antiferromagnetic.     

Photoprocesses and magnetic behavior of photochromic transition metal indoline[phenanthrolinospirooxazine] complexes: Tunable photochromic materials

We have synthesized a series of M(IPSO)₃(BPh₄)₂ complexes consisting of first row transition metals and a photochromic phenanthroline ligand: (M = Mn(II), Fe(II), Co(II), Ni(II), Zn(II), and Cu(II), IPSO = spiro[indole-phenanthrolinoxazine]). The optical properties associated with photochromic behavior were evaluated by determination of the (i) equilibrium constants (K) for the thermal and photostationary states, (ii) rates of photochemical ring-opening and ring-closure, and (iii) rates of thermal ring-closure. The photocolorability values associated with conversion from the colorless spirooxazine to the colored photomerocyanine isomer are greatly enhanced upon metal coordination. Variable temperature magnetic susceptibility experiments suggest deviations from cubic symmetry associated with desymmetrization induced by a dependence of ligand field strength on the photochromic state of IPSO.     

Synthesis,structures and magnetic properties of pentanuclear and trinuclear heterometallic complexes with bended and linear cyano-bridges (tren = tris(2-aminoethyl)amine)

The reaction of [Cu(tren)(OH₂)](ClO₄)₂ with KCN gave a mononuclear complex [Cu(tren)(CN)](ClO₄) (1) (tren = tris(2-aminoethyl)amine). Using 1 as a building block, one pentanuclear compound, [{Cu(tren)(NC)}₄Ni](ClO₄)₆ (2) and two trinuclear complexes, [{Cu(tren)NC}₂Co(tren)](ClO₄)₅ · 2H₂O (3), [{Cu(tren)CN}₂NiL](ClO₄)₄ (4) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) were prepared and characterized by single crystal X-ray analysis. In 1, Cu(II) atom adopts a distorted trigonal bipyramidal (TBP) geometry. In 2, the Ni(II) atom occupies the center of the pentanuclear compound with a square-planar coordination geometry. In 3, the six-coordinated Co(III) atom presents a distorted octahedral geometry with four nitrogen atoms from tren and two carbon atoms of bridged cyano groups in cis-positions. In 4, the nickel atom is located in an inversion center and coordinated with two [(tren)CuCN]⁺ moieties through cyano-bridging ligands. Magnetic susceptibility measurements of 2–4 show that the magnetic interactions between the heterometallic ions are antiferromagnetical coupling through the cyano bridges with g = 2.25, J = −0.142 cm⁻¹ and J′ = −0.167 cm⁻¹ for 2, g = 2.06, J = −0.094 cm⁻¹ for 3, and g = 2.20, J = −33.133 cm⁻¹ for 4. The correlations between the structures and the J values are discussed.     

Calorimetric and spectroscopic investigations of the binding of metallated porphyrins to G-quadruplex DNA

BackgroundThe human telomere contains tandem repeat of (TTAGG) capable of forming a higher order DNA structure known as G-quadruplex. Porphyrin molecules such as TMPyP4 bind and stabilize G-quadruplex structure.MethodsIsothermal titration calorimetry (ITC), circular dichroism (CD), and mass spectroscopy (ESI/MS), were used to investigate the interactions between TMPyP4 and the Co(III), Ni(II), Cu(II), and Zn(II) complexes of TMPyP4 (e.g. Co(III)-TMPyP4) and a model human telomere G-quadruplex (hTel22) at or near physiologic ionic strength ([Na⁺] or [K⁺] ≈ 0.15 M).ResultsThe apo-TMPyP4, Ni(II)-TMPyP4, and Cu(II)-TMPyP4 all formed complexes having a saturation stoichiometry of 4:1, moles of ligand per mole of DNA. Binding of apo-TMPyP4, Ni(II)-TMPyP4, and Cu(II)-TMPyP4 is described by a “four-independent-sites model”. The two highest-affinity sites exhibit a K in the range of 10⁸ to 10¹⁰ M^− 1 with the two lower-affinity sites exhibiting a K in the range of 10⁴ to 10⁵ M^− 1. Binding of Co(III)-TMPyP4, and Zn(II)-TMPyP4, is best described by a “two-independent-sites model” in which only the end-stacking binding mode is observed with a K in the range of 10⁴ to 10⁵ M^− 1.ConclusionsIn the case of apo-TMPyP4, Ni(II)-TMPyP4, and Cu(II)-TMPyP4, the thermodynamic signatures for the two binding modes are consistent with an “end stacking” mechanism for the higher affinity binding mode and an “intercalation” mechanism for the lower affinity binding mode. In the case of Co(III)-TMPyP4 and Zn(II)-TMPyP4, both the lower affinity for the “end-stacking” mode and the loss of the intercalative mode for forming the 2:1 complexes with hTel22 are attributed to the preferred metal coordination geometry and the presence of axial ligands.General significanceThe preferred coordination geometry around the metal center strongly influences the energetics of the interactions between the metallated-TMPyP4 and the model human telomeric G-quadruplex. This article is part of a Special Issue entitled Microcalorimetry in the BioSciences — Principles and Applications, edited by Fadi Bou-Abdallah.     

Magnetic properties of six-coordinated high-spin cobalt(II) complexes: Theoretical background and its application

In this contribution we study and analyse the influence of the different parameters involved in the magnetic susceptibility of six-coordinated high-spin Co(II) complexes. We propose an empirical expression to fit the magnetic susceptibility of polycrystalline samples of mononuclear Co(II) complexes with an axial distortion, the variable parameters being Δ (axial distortion), α (orbital reduction factor) and λ (spin–orbit coupling). This expression avoids solving the 12 × 12 matrix associated to the distortion of the ⁴T_1g term. In order to take into account the magnetic coupling (J) in the polynuclear Co(II) complexes, a perturbational approach is proposed to describe their magnetic susceptibility in the whole temperature range (2–300 K) as a function of J, Δ, α and λ. This approach is valid in the limit of the weak magnetic coupling as compared to the spin–orbit coupling, |J/λ| < 0.1. The model allows the treatment of each cobalt(II) ion in axial symmetry as an effective spin S_eff = 1/2. That causes a drastic reduction of the matrix size of the polynuclear compounds from 12ⁿ × 12ⁿ to 2ⁿ × 2ⁿ, n being the number of Co(II) ions in the complex. The main advantage of the model is to make possible the fit of the magnetic susceptibility data of those polynuclear Co(II) complexes whose high nuclearity involved intractable matrices.     

Syntheses,characterization, antimicrobial and cytotoxic activities of pyridine-2,5-dicarboxylate complexes with 1,10-phenanthroline

In this study, four mononuclear M(II)-pyridine-2,5-dicarboxylate (M = Co(II), Ni(II), Cu(II) and Zn(II) complexes with pyridine-2,5-dicarboxylic acid or isocinchomeronic acid, 1,10-phenanthroline (phen), [Co(Hpydc)₂(phen)]·H₂O (1), [Ni(pydc)(phen)₂]·6.5H₂O (2) [Cu(pydc)(phen)(H₂O)₂] (3) and [Zn(pydc)(phen)(H₂O)₂]·H₂O (4) have been synthesized. Elemental, thermal and mass analyses, molar conductance, magnetic susceptibilities, IR and UV/vis spectroscopic studies have been performed to characterize the complexes. Subsequently, these ligands and complexes were tested for antimicrobial activity by disc diffusion method on Gram positive, negative bacteria and yeast. In addition, cytotoxic activity tests were performed on rat glioma (C6) cells by MTT viability assay for 24 and 48 h. Antimicrobial activity results demonstrated that when compared to the standard antibiotics, phen displayed the most effective antimicrobial effect. The effect of synthesized complexes was close to phen or less. Cytotoxic activity results showed that IC₅₀ value of phen was determined as 31 μM for 48 h. (1) and (2) compared to the alone ligand had less toxic activity. IC₅₀ values of (3) for 24 and 48 h treatments were 2.5 and 0.6 μM, respectively. IC₅₀ value of (4) for 48 h was 15 μM. In conclusion, phen, (3) and (4) may be useful as antibacterial and antiproliferative agents in the future.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

Synthesis,characterization and magnetic properties of six new copper(II) complexes with aminoacids as bridging ligand,exhibiting ferromagnetic coupling

The synthesis, crystallographic analysis and magnetic studies of six new copper(II) complexes of formulae [Cu(μ-ala)(im)(H₂O)]_n(ClO₄)_n (1), [Cu(μ-ala)(pz)(μ-ClO₄)] (2), [Cu(μ-phe)(im)(H₂O)]_n(ClO₄)_n (3), [Cu(μ-gly)(H₂O)(ClO₄)]_n (4), [Cu(μ-gly)(pz)(ClO₄)]_n(5) and [Cu(μ-pro)(pz)(ClO₄)]_n (6) have been carried out (ala = alanine; phe = phenylalanine; gly = glycine; pro = proline; im = imidazole; pz = pyrazole). In all cases, the deprotonated aminoacid ligand acts as chelate through the N(amine) and one O(carboxylato), whereas the second O atom of the same carboxylato acts as a bridge to the neighbouring copper(II) ion. The coordination of copper(II) ions is square-pyramidal in all complexes but 2 (elongated O_h). All complexes (1–6) are uniform chains with syn–anti (equatorial–equatorial) coordination mode of the carboxylato bridging ligand, exhibiting intrachain ferromagnetic interactions.     

Removal of Zn(II) ions from aqueous solution using Moringa oleifera Lam. (horseradish tree) biomass

The removal of Zn(II) ions from aqueous solution using pure and chemically pretreated biomass of Moringa oleifera was investigated at 30 ± 1 °C in this study. The experimental results explored that the maximum pH (pH_max) for efficient sorption of Zn(II) was 7 ± 0.1 at which evaluated biosorbent dosage and biosorbent particle size, were 0.5 g/L, <0.255 mm, respectively. The cellular Zn(II) concentration increased with the concentrations of Zn(II) in solution. Pretreatment of M. oleifera biomass affected the sorption process and the uptake capacity (mg/g) of biomass for Zn(II) uptake was in following order: NaOH (45.76) > H₂SO₄ (45.00) > CTAB (42.80) > Ca(OH)₂ (42.60) > Triton X-100 (42.06) > H₃PO₄ (41.22) > Al(OH)₃ (41.06) > SDS (40.41) > HCl (37.00) > non-treated biomass (36.07). There was significant increase in uptake capacity of M. oleifera biomass, which suggested that affinity between metal and sorbent can be increased after some sort of pretreatment. Both Langmuir and Freundlich isotherm model fitted well to data of Zn(II) biosorption as represented by high value of their correlation coefficient (i.e. R² ≈ 1). Kinetic studies revealed that Zn(II) uptake was fast with 90% or more of uptake occurring with in 40 min of contact time and the equilibrium was reached in 50 min of contact time. The sorption rates were better described by a second order expression than by a more commonly applied Lagergren equation. Finally it was concluded that pretreatment of M. oleifera biomass can achieve superior Zn(II) uptake capacity in comparison to non-pretreated biomass.     

Structures and magnetic properties of Mn(hfac)2 complexes derived from Bis-TEMPO-substituted diamines

Structures and properties of three Mn(hfac)₂ (hfac = hexafluoroacetylacetonate) complexes derived from two kinds of bis-TEMPO (2,2,6,6-tetramethylpiperdinyl-1-oxy)-substituted diamines are reported. In a complex derived from bis-TEMPO-substituted ethylenediamine, the unit is coordinated to the manganese atom to afford a spin system with weak antiferromagnetic intermolecular interactions, while apparent ligations of both TEMPO groups to the metal atom are observed in a couple of Mn(hfac)₂ complexes derived from bis-TEMPO-substituted piperadine to result in spin systems with fairly large antiferromagnetic interactions.     

Copper and zinc in Elodea canadensis from rivers with various pollution levels

The anthropogenic impact of xenobiotics contributes to environmental risk for the aquatic environment and thus, must be controlled. Elodea canadensis, a cosmopolitan aquatic macrophyte with an important role in the ecology of many littoral zones, may provide an integrated record of pollution. Therefore, it was interesting to investigate the accumulation of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in this species and in water and bottom sediments collected from rivers with various levels of contamination. Of these rivers one control and one polluted was selected for the collection of E. canadensis for an experiment to compare the ability of this species to accumulate Cu and Zn. These elements were supplemented at concentrations (mg L⁻¹) of 0.01, 0.02, 0.03, 0.05, 0.08 and 0.14 as CuSO₄·5H₂O, and 0.4, 0.6, 0.9, 1.4, 2.03 and 3.04 as ZnSO₄·7H₂O and in a mixture containing (mg L⁻¹) 0.01Cu + 0.4Zn, 0.02Cu + 0.6Zn, 0.03Cu + 0.9Zn, 0.05Cu + 1.4Zn, 0.08Cu + 2.03Zn and 0.14Cu + 3.04Zn. After the experiment, E. canadensis from the polluted river contained significantly higher Cu and Zn concentrations when applied separately and also significantly higher Cu and Zn concentrations when applied as a mixture compared to the control river. These higher concentrations in E. canadensis from the polluted river were found in all combinations in the experiment. Thus, E. canadensis habituated in polluted sites to the exposure, and long-term influence of elevated metal levels appeared to be better adapted, and it also exhibited a higher increase in biomass than plants from the control river in all the experimental Cu and Zn solutions. Younger leaves of E. canadensis were more resistant to the effects of Cu and Zn than older leaves. Both Cu and Zn negatively affected the cell structure of older leaves, although the influence of Cu on plasma membrane integrity and chloroplast distribution was stronger than that of Zn. The influence of the Cu + Zn mixture on E. canadensis resulted in less pronounced cell disintegration than the influence of Cu added separately.The explanation of differences in the E. canadensis biomass increase and metal concentrations under the binary Cu and Zn impact needs further examination.     

Characterization and DNA-interaction studies of 1,1-dicyano-2,2-ethylene dithiolate Ni(II) mixed-ligand complexes with 2-amino-5-methyl thiazole, 2-amino-2-thiazoline and imidazole. Crystal structure of [Ni(i-MNT)(2a-5mt)2]

A series of mixed-ligand neutral nickel(II) complexes of the general formula [Ni(i-MNT)(2a-5mt)₂] (1), [Ni(i-MNT)(2a-2tzn)₂] (2) and [Ni(i-MNT)(Im)₂] (3), [where i-MNT^2? = the dianion of 1,1-dicyano-2,2-ethylenedithiolate, 2a-5mt = 2-amino-5-methyl thiazole, 2a-2tzn = 2-amino-2-thiazoline and Im = imidazole] were prepared and characterized with elemental analyses, spectroscopic (IR, UV–vis) methods, magnetic susceptibility, molar conductivity and cyclic voltammetry measurements. The magnetic data, the electronic spectra and the electrical conductivity measurements indicated mononuclear neutral complexes with square-planar geometry. The X-ray analysis of [Ni(i-MNT)(2a-5mt)₂] shows the nickel atom being fourfold coordinated with the two sulfur atoms of the dithiolate (i-MNT) ligand and the endocyclic nitrogen atoms from the two 2a-5mt ring giving rise to a slightly distorted square-planar arrangement. The cyclic voltammograms of the complexes have been recorded and the corresponding redox potentials have been estimated. The DNA-binding studies of the complexes has been evaluated by examining their ability to bind to calf-thymus DNA (CT DNA) with UV spectroscopy and cyclic voltammetry. Both studies have shown that the complexes can bind to CT-DNA by the intercalative and the electrostatic binding mode. Competitive binding studies with ethidium bromide (EB) with fluorescence spectroscopy have also shown that the complexes exhibit the ability to displace the DNA-bound EB indicating that they can bind to DNA in strong competition with EB.     

Synthesis,X-ray structures,and magnetic properties of heterometal dinuclear Cr(III)–M(II) complexes

New 3,5-bis(2-pyridyl)pyrazolato (bpypz) bridged heterometal dinuclear complexes [(nta)Cr(μ-bpypz)M^II(picen)]⁺ (M = Mn(II), Ni(II)) and [(acac)₂Cr(μ-bpypz)Ni^II(picen)]²⁺ (nta = nitrilotriacetate, picen = N,N′-bis(2-pyridylmethyl)ethylenediamine, acac = acetylacetate) were synthesized and characterized by the X-ray analysis, ESI-MS and the magnetic measurements, and/or ²H NMR spectra. The molecular structures were compared from a viewpoint of the conformation of the picen depending on M^II ionic radii or different modes of hydrogen bonds. The picen in [(nta)Cr(μ-bpypz)Mn^II(picen)]BF₄ takes an abnormal conformation with intramolecular bifurcated three-center hydrogen bonds between two carboxylate oxygens of nta and an amine proton of the picen as found for the previously reported corresponding Fe(II) complex [K. Ni-iya, A. Fuyuhiro, T. Yagi, S. Nasu, K. Kuzushita, S. Morimoto, S. Kaizaki, Bull. Chem. Soc. Jpn. 74 (2001) 1891]. On the other hand, for both Ni(II)-nta and Ni(II)-acac complexes, the picen takes a normal conformation with only a two-center hydrogen bond between non-bridging ligands. The magneto-structural relation is discussed for the Cr(III)–Ni(II) complexes in connection with the orthogonality or orbital overlap arising from the difference in distortion around Cr(III) moiety.     

Structure and magnetic properties of a trinuclear nickel(II) complex with benzenetricarboxylate bridge

Novel trinuclear Ni(II) complex [Ni₃(pmdien)₃(btc)(H₂O)₃](ClO₄)₃ · 4H₂O, 1 where pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine, H₃btc = 1,3,5-benzenetricarboxylic (trimesic) acid, has been prepared and structurally characterized. Three nickel atoms are bridged by btc trianion and their coordination sphere is completed by three N atoms of pmdien and O atom of the water molecule. The three nickel(II) magnetic centers are equivalent and their coordination spheres are completed to deformed octahedrons. Magnetic susceptibility was measured over the temperature range 1.8–300 K and zJ′ = ?0.19 cm^?1, D = 3.79 cm^?1, g = 2.18 parameters were calculated.     

Crystal structures and coordination-site exchange reactions of palladium(II) and platinum(II) complexes containing tris[2-(tert-butylthio)ethyl]amine

Palladium(II) and platinum(II) complexes, [PdX(NS₃ ¹Bu)]BPh₄ (X=Cl, Br, I; NS₃ ¹Bu=tris[2-(tert-butylthio)ethyl]amine) and [PtCl(NS₃ ¹Bu)]BPh₄, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS₃ ¹Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The ¹H NMR spectrum of [PdCl(NS₃ ¹Bu)]BPh₄ in acetone-d₆ exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS₃ ¹Bu)]BPh₄ are in equilibrium in acetone-d₆. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The ¹H NMR spectra for [PdX(NS₃ ¹Bu)]BPh₄ (X=Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS₃ ¹Bu)]BPh₄ seems to occur more slowly than that of the palladium(II) analogue.     

Synthesis,characterization and bioactivity of four novel trinuclear copper(II) and nickel(II) complexes with pentadentate ligands derived from N-acylsalicylhydrazide

Four novel trinuclear copper(II)/nickel(II) complexes with four trianionic pentadentate ligands, N-(3-t-butylbenzoyl)-5-nitrosalicylhydrazide (H₃3-t-bbznshz), N-(3,5-dimethylbenzoyl)salicylhydrazide (H₃3,5-dmbzshz), N-(phenylacetyl)-5-bromosalicylhydrazide (H₃pabshz) and N-(3-t-butylbenzoyl)salicylhydrazide (H₃3-t-bbzshz) have been synthesized and characterized by X-ray crystallography. These trinuclear compounds all have an M–N–N–M–N–N–M core formed by three metal ions and two ligands. The geometries of three Cu(II) ions in compound Cu₃(3-t-bbznshz)₂(H₂O)(DMF)(py)₂ · DMF (1) alternate between distorted square pyramidal and square planar, while in compound Cu₃(3,5-dmbzshz)₂(py)₂ (2), they are all square planar. Three Ni(II) ions in compound Ni₃(pabshz)₂(DMF)₂(py)₂ (3) and Ni₃(3-t-bbzshz)₂(py)₄ · 2H₂O (4) follow square-planar/octahedral/square-planar coordination geometry. Compounds 1, 2 and 4 are bent trinuclear, with the bend angles of 156.4°, 141.49° and 127.1°, respectively, while the three nickel ions in compound 3 are strictly linear, with an angle of 180°. Studies on the trinuclear Ni(II) complexes show that the β-branched N-acylsalicylhydrazide ligands with sterically flexible Cα methylene groups are easier to yield linear trinuclear Ni(II) complexes, while α-branched N-acylsalicylhydrazides ligands tend to form bent trinuclear Ni(II) complexes. Antibacterial screening data indicate that the trinuclear Cu(II) compound 2 is more active than 1 and mononuclear Cu(II) compound, bent trinuclear Ni(II) compound 4 is more active than linear compound 3 and less active than tetranuclear nickel compound in the previous study.     

A ratiometric fluorescent detection of Zn(II) in aqueous solutions using pyrene-appended histidine

A fluorescent chemosensor, Py-His, based on histidine was easily synthesized in solid phase synthesis. Py-His displayed a highly sensitive ratiometric response to Zn(II) with potent binding affinity (K_a = 1.17 × 10¹³ M^?2) in aqueous solutions. The detection limit of Py-His for Zn(II) was calculated as 80.8 nM. Moreover, Py-His distinguished Zn(II) and Hg(II) by different ratiometric response type; the chemosensor showed a more enhanced increase of excimer emission intensity to Zn(II) than Hg(II). Upon addition of Ag(I) and Cu(II), Py-His showed a turn-off response mainly due to the quenching effect of these metal ions. The binding stoichiometry (2:1 or 1:1) of Py-His to target metal ions played a critical role in the fluorescent response type (ratiometric and turn off response) to target metal ions. The role of imidazole group of Py-His for ratiometric detection of Zn(II) was proposed by pH titration experiments.     

Diverse magnetic and electrical properties of molecular solids containing the thiazyl radical BDTA

We have examined the crystal structures and the electrical and magnetic properties of the molecular compounds of a thiazyl radical, 1,3,2-benzodithiazolyl (abbreviated as BDTA). BDTA was found to be a useful building block for molecular conductors and magnets because it can operate as a counter cation, a donor or a ligand, depending on its charge. (i) A charge-transfer complex, [BDTA][TCNQ], crystallizes into a uniform segregated stacking structure with a short contact between the donor and acceptor columns. In spite of the partial charge transfer between the two components, this complex exhibits semiconductive behaviour, probably due to a large electron correlation on BDTA. (ii) The crystal structure of [BDTA][Ni(mnt)₂] (mnt = maleonitriledithiolate) consists of alternating stacking columns of S = 0 [BDTA]⁺ and S = 1/2 [Ni(mnt)₂]^?, in which a ferromagnetic coupling operates between the [Ni(mnt)₂]^? anions through the [BDTA] ⁺ cation. (iii) [BDTA]₂[Cu(mnt)₂] consists of an alternating stack of a head-to-head [BDTA]⁺ dimer and a planar [Cu(mnt)₂]^2? dianion. Short intermolecular S?S contacts between the stacks give rise to an ideal 1D Heisenberg antiferromagnetic chain of [Cu(mnt)₂]^2? with a coupling constant of J/k_B = 16–17 K. (iv) The crystal structure of [BDTA]₂[Co(mnt)₂] is similar to that of [BDTA]₂[Cu(mnt)₂] at 253 K, but this salt undergoes a phase transition at 190 K, below which a partial electron transfer occurs from [Co(mnt)₂]^2? to one of the [BDTA]⁺ cations along with formation of a coordination bond. (v) [BDTA][Ni(dmit)₂]₂ (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) exhibits room-temperature conductivity of 0.1 S cm^?1 and semiconductive behaviour over the range 80–200 K, which can be interpreted in terms of multi-conducting bands.