New fluorescent chemosensors for heavy metal ions based on functionalized pendant arm derivatives of 7-anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane

Two new ligands 7-anthracenylmethyl-13-methylpyridyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L4) and 7-anthracenylmethyl-13-(2,2-dimethyl-2-hydroxyethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L(5)) have been synthesized and characterized. Both derive from 7-anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane (L(3)) and differ for having a differently functionalized pendant arm covalently attached to the remaining secondary nitrogen donor of the macrocyclic framework. The protonation and coordination behavior of L(4), L(5), and the unbranched L(3) with metal ions have been studied in MeCN/H2O (1:1 v/v, 298.1 K, I = 0.1 M) using potentiometric methods. The crystal structures of L(3), [(H2L(3))(HL(3))](ClO4)3, and the complex [CdL(3)(NO3)2] have been determined by single-crystal X-ray methods. The fluorescent behavior of L(3)-L(5) in the presence of Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been studied as a function of pH in MeCN/H2O (1:1 v/v). The presence of Cu(II), Hg(II), or Pb(II) does not affect the fluorescent behavior observed for the three free ligands upon changing the pH. Interestingly, the fluorescent emission of L(3) and L(5) is selectively enhanced only in the presence of Cd(II) at basic pH. The same effect is observed for L4 in the presence of Cd(II) or Zn(II) at about pH 7.     

On (q 2 + q + 1)-sets of class [1, m,n]2 in PG(3, q)

A characterization of cones in PG(3, q) as sets of points of PG(3, q) of size q ² + q + 1 projecting from a point V a set of q + 1 points of a plane of PG(3, q) and with three intersection numbers with respect to the planes is given.     

Gold(III) Complexes of Asymmetrically Aryl‐Substituted 1,2‐Dithiolene Ligands Featuring Potential‐Controlled Spectroscopic Properties: An Insight into the Electronic Properties of bis(Pyren‐1‐yl‐ethylene‐1,2‐dithiolato)Gold(III)

The electrochemical, UV/Vis–NIR absorption, and emission‐spectroscopic features of (TBA⁺)( 1 ⁻) and the corresponding neutral complex 1 were investigated (TBA⁺=tetrabutylammonium; 1 ⁻=[Au^III(Pyr,H‐edt)₂]⁻; Pyr,H‐edt²⁻=pyren‐1‐yl‐ethylene‐1,2‐dithiolato). The intense electrochromic NIR absorption (λ_max=1432 nm; ε=13000 M ⁻¹ cm⁻¹ in CH₂Cl₂) and the potential‐controlled visible emission in the range 400–500 nm, the energy of which depends on the charge of the complex, were interpreted on the grounds of time‐dependent DFT calculations carried out on the cis and trans isomers of 1 , 1 ⁻, and 1 ²⁻. In addition, to evaluate the nonlinear optical properties of 1 ^x− (x=0, 1), first static hyperpolarizability values β_tot were calculated (β_tot=78×10⁻³⁰ and 212×10⁻³⁰ esu for the cis isomer of 1 ⁻ and 1 , respectively) and compared to those of differently substituted [Au(Ar,H‐edt)₂]^x− gold dithiolenes [Ar=naphth‐2‐yl ( 2 ), phenyl ( 3 ); x=0, 1].     

Effect of SiO2 on the dynamics of proton conducting [Nafion/(SiO2)X] composite membranes: a solid-state 19F NMR study

Composite membranes, consisting of Nafion and inorganic oxide additives, are frequently discussed alternative materials to overcome the known low conductivity of pure Nafion at temperatures above 100 °C and at low relative humidity. It has been reported that under dry conditions, these membranes show enhanced water uptake and diffusion as compared to filler-free Nafion. This work focuses on the polymer mobility in Nafion/SiO(2) composites and on the impact of the silica particles on the polymer dynamics. [Nafion/(SiO(2))(X)] composite membranes (with X ranging from 0 to 15 wt%) in the dry and wet states were investigated by variable temperature solid-state (19)F NMR spectroscopy. (19)F T(1) and T(1ρ) relaxation times, and NMR lineshapes (linewidths and spinning sideband intensities) were analyzed to get information about the polymer mobility. It is found that Nafion composite membranes, in general, possess a higher mobility as compared to recast Nafion which is in agreement with previous results from conductivity studies. These findings are attributed to the ability of the SiO(2) particles to keep more water inside the composite membranes which also leads to a higher mobility of the polymer component. The results are further supported by the experimental (19)F{(1)H} CP/MAS NMR spectra. It is also shown that the structure of the composite membranes is more stable after dehydration, and possible condensation reactions are diminished in these membranes. In addition, the decrease in ionic exchange capacity after dehydration is less pronounced for the composite membranes as compared to filler-free Nafion.     

Speciation of the Vanadium (III) Complexes with 6-Methylpicolinic Acid,Salicylic Acid and Phthalic Acid

The complex species formed in aqueous solutions (25 °C, I=3.0 mol⋅dm⁻³ KCl ionic medium) between the V(III) cation and the ligands 6-methylpicolinic acid (MePic, HL), salicylic acid (H₂Sal, H₂L) and phthalic acid (H₂Phtha, H₂L) have been studied by potentiometric and spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the experimental emf(H) data, taking into account the hydrolytic species and hydrolysis constants of V(III), indicates that under the employed experimental conditions the complexes [VL]²⁺, [V(OH)L]⁺, [V(OH)₂L], [V(OH)₃L]⁻, [VL₂]⁺, [VL₃] and [V₂OL₄] form in the vanadium(III)–MePic system. Were observed the complexes [VL]⁺, [VL₂]⁻, [V(OH)L₂]²⁻ and [VL₃]³⁻ in the vanadium(III)–H₂Sal system, and the species [VHL]²⁺, [VL]⁺, [V(OH)L], [VHL₂], [VL₂]⁻, [V(OH)L₂]²⁻, [V(OH)₂L₂]³⁻ and [VL₃]³⁻ in the vanadium(III)–H₂Phtha system. The stability constants of these complexes were determined by potentiometric measurements, and spectrophotometric measurements were made in order to perform a qualitative characterization of the complexes formed in aqueous solution.     

Speciation of the Ternary Complexes of Vanadium(III)–Dipicolinic Acid and the Amino Acids Cysteine,Histidine, Aspartic and Glutamic Acids in 3.0 mol⋅dm<Superscript>−3</Superscript> KCl at 25 °C

In this work we present results for the speciation of the ternary complexes formed in the aqueous vanadium(III)–dipicolinic acid and the amino acids cysteine (H₂cys), histidine (Hhis), aspartic acid (H₂asp) and glutamic acid (H₂glu) systems (25 °C; 3.0 mol⋅dm⁻³ KCl as ionic medium), determined by means of potentiometric measurements. The potentiometric data were analyzed with the least-squares program LETAGROP, taking into account the hydrolysis of vanadium(III), the acid-base reactions of the ligands, and the binary complexes formed. Under the experimental conditions (vanadium(III) concentration = 2–3 mmol⋅dm⁻³ and vanadium(III): dipicolinic acid: amino acid molar ratio 1:1:1, 1:1:2 and 1:2:1), the following species [V(dipic)(H₂asp)]⁺, [V(dipic)(Hasp)], [V(dipic)(asp)]⁻, [V(dipic)(asp)(OH)]²⁻, and [V(dipic)(asp)(OH)₂]³⁻ were found in the vanadium(III)–dipicolinic acid–aspartic acid system. In the vanadium(III)–dipicolinic acid–glutamic acid system [V(Hdipic)(H₂glu)]²⁺, [V(dipic)(H₂glu)]⁺, [V(dipic)(Hglu)], [V(dipic)(Hglu)(OH)]⁻, and [V(dipic)(Hglu)(OH)₂]²⁻ were observed. In the vanadium(III)–dipicolinic acid–cysteine system the complexes [V(dipic)(H₂cys)]⁺, [V(dipic)(Hcys)], [V(dipic)(cys)]⁻, and [V(dipic)(cys)(OH)]²⁻ were present. And finally, in the vanadium(III)–dipicolinic acid–histidine system the complexes [V(Hdipic)(Hhis)]²⁺, [V(dipic) (Hhis)]⁺[\mathrm{V}(\mathrm{dipic}) (\mathrm{Hhis})]^{+}, [V(dipic)(his)], [V(dipic)(his)(OH)]⁻, and [V(dipic)(his)(OH)₂]²⁻ were observed. The stability constants of these complexes were determined. The species distribution diagrams as a function of pH are briefly discussed.     

A characterization of Buekenhout-Metz unitals in PG(2, q 2), q even

The known examples of embedded unitals (i.e. Hermitian arcs) in PG(2, q ²) are B-unitals, i.e. they can be obtained from ovoids of PG(3, q) by a method due to Buekenhout. B-unitals arising from elliptic quadrics are called BM-unitals. Recently, BM-unitals have been classified and their collineation groups have been investigated. A new characterization is given in this paper. We also compute the linear collineation group fixing the B-unital arising from the Segre-Tits ovoid of PG(3, 2 ^r ), r3 odd. It turns out that this group is an Abelian group of order q ².Research supported by MURST.     

LSb(μ‐I)2(μ‐S)SbL: a Neutral Triply Bridged Complex obtained from Sb Powder and Diiodine activated by Tetraphenyldithioimidodiphosphine (HL)

The synthesis of the complex LSb(μ‐I)₂(μ‐S)SbL ( 1 ) was accomplished by reacting antimony powder with diiodine activated by tetraphenyldithioimidodiphosphine (SPPh₂NHPPh₂S) (H L ). X‐ray diffraction (tetragonal, M = 1426.30, space group I 4₁/a (No. 88), Z = 8, a = 18.020(2) Å, c = 33.037(4) Å) shows that ( 1 ) is a dinuclear Sb^III complex, in which the two metal ions are bridged by one sulphide and two iodide anions. An anionic bidentate L ligand completes the coordination sphere of each metal with its two sulphur atoms, leading to a slightly distorted pyramidal coordination geometry, since each metal ion shows the presence of a sterically active lone‐pair in trans position to the bridging sulphide. ³¹P CP‐MAS NMR and IR spectroscopies are in accordance with the structural features of the complex.     

(1,3‐Dimethylimidazolidine‐2‐selone‐κSe)bis(1,10‐phenanthroline‐κ2N,N′)copper(II) bis(perchlorate) and bis(2,2′‐bipyridyl‐κ2N,N′)(imidazolidine‐2‐thione‐κS)copper(II) bis(perchlorate)

In the first title salt, [Cu(C₁₂H₈N₂)₂(C₅H₁₀N₂Se)](ClO₄)₂, the Cu^II centre occupies a distorted trigonal–bipyramidal environment defined by four N donors from two 1,10‐phenanthroline (phen) ligands and by the Se donor of a 1,3‐dimethylimidazolidine‐2‐selone ligand, with the equatorial plane defined by the Se and by two N donors from different phen ligands and the axial sites occupied by the two remaining N donors, one from each phen ligand. The Cu—N distances span the range 1.980 (10)–2.114 (11) Å and the Cu—Se distance is 2.491 (3) Å. Intermolecular π–π contacts between imidazolidine rings and the central rings of phen ligands generate chains of cations. In the second salt, [Cu(C₁₀H₈N₂)₂(C₃H₆N₂S)](ClO₄)₂, the Cu^II centre occupies a similar distorted trigonal–bipyramidal environment comprising four N donors from two 2,2′‐bipyridyl (bipy) ligands and an S donor from an imidazolidine‐2‐thione ligand. The equatorial plane is defined by the S donor and two N donors from different bipy ligands. The Cu—N distances span the range 1.984 (6)–2.069 (7) Å and the Cu—S distance is 2.366 (3) Å. Intermolecular π–π contacts between imidazolidine and pyridyl rings form chains of cations. A major difference between the two structures is due to the presence in the second complex of two N—H...O hydrogen bonds linking the imidazolidine N—H hydrogen‐bond donors to perchlorate O‐atom acceptors.