A unique case of oxidative addition of interhalogens IX (X=Cl, Br) to organodiselone ligands: nature of the chemical bonding in asymmetric I-Se-X polarised hypervalent systems.

The reactivity of the imidazoline-2-selone derivatives 1,1'-methylenebis(3-methyl-4-imidazoline-2-selone) (D1) and 1,2-ethylenebis(3-methyl-4-imidazoline-2-selone) (D2) towards the interhalogens IBr and ICl has been investigated in the solid state with the aim of synthesising "T-shaped" hypervalent chalcogen compounds featuring the extremely rare linear asymmetric I-E-X moieties (E=S, Se; X=Br, Cl). X-ray diffraction analysis and FT-Raman measurements provided a clear indication of the presence in the compounds obtained of discrete molecular adducts containing I-Se-Br and I-Se-Cl hypervalent moieties following a unique oxidative addition of interhalogens IX (X=Cl, Br) to the organoselone ligands. In all asymmetric hypervalent systems isolated, a strong polarisation was observed, with longer bond lengths at the selenium atom involving the most electronegative halogen. A topological electron density analysis on model compounds based on the quantum theory of atoms-in-molecules (QTAIM) and electron localisation function (ELF) established the three-centre-four-electron (3c-4e) nature of the bonding in these very polarised selenium hypervalent systems and new criteria were suggested to define and ascertain the hypervalency of the selenium atoms in these and related halogen and interhalogen adducts.

A selective, nontoxic, OFF-ON fluorescent molecular sensor based on 8-hydroxyquinoline for probing Cd(2+) in living cells.

In spite of the fact that cadmium(II) has been recognized as a highly toxic element and that excessive exposure to this metal ion has been reported to have many adverse effects on human health, very few selective and specific fluorescent probes are available for imaging Cd(2+) in living cells. Herein, we report the spectroscopic and photochemical characterization of 5-(5-chloro-8-hydroxyquinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a fluorescent sensor for the selective imaging of Cd(2+) in living cells. In particular, the response of L to Cd(2+) was first assessed in aqueous solutions, sodium dodecyl sulfate micelles, and liposomes, and subsequently in living cells by fluorescence microscopy techniques. Cytofluorimetric analyses of leukemic HL-60 cells loaded with L also allowed evaluation of the toxicity of the probe and the selective analysis of its intracellular fluorescence in the presence of Cd(2+). Furthermore, the 1:1 complex species [Cd(L)H(2)O](2+) responsible for the OFF-ON chelation enhancement of fluorescence (CHEF) effect on L was structurally characterized; time-dependent DFT calculations allowed the prediction of theoretical excitations, which were comparable with the experimental ones.

Synthesis and coordination properties of quinoline pendant arm derivatives of [9]aneN(3) and [9]aneN(2)S as fluorescent zinc sensors.

The coordination chemistry of three new quinoline pendant arm derivatives of [9]aneN(3) (L(1), L(2)) and [9]aneN(2)S (L(3)) toward Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in solution and in the solid state. The protonation constants for L(1)-L(3) and stability constants with the aforementioned metal ions have been determined potentiometrically in 0.10 M NMe(4)Cl MeCN/H(2)O (1:1 v/v) solution at 298.1 +/- 0.1 K; the measured values show that Cu(II) has the highest affinity for all three ligands, followed by Zn(II), Hg(II), Pb(II), and Cd(II). For each metal ion considered, 1:1 complexes with L(1)-L(3) have also been isolated in the solid state and [Cu(L(1))](BF(4))(2) (1), [Zn(L(1))](BF(4))(2) (2), [Cd(L(1))](ClO(4))(2) (3), [Hg(L(1))](NO(3))(2) (4), [Pb(L(1))](ClO(4))(2) x MeCN (5), [Zn(2)Cl(2)(L(2))(2)](BF(4))(2) x 1/2 MeNO(2) x H(2)O (6), [Cu(L(3))](ClO(4))(2) (7), [Zn(L(3))(NO(3))]NO(3) (8), [Cd(L(3))(NO(3))(0.82)Cl(0.18)]NO(3) (9), and [Hg(L(3))](ClO(4))(2) x MeCN (10) have also been characterized by X-ray crystallography. The optical response of L(1)-L(3) to the presence of the above-mentioned metal ions has been investigated in MeCN/H(2)O (1:1 v/v) and H(2)O solutions. All three ligands show a stronger "OFF-ON" CHEF (chelation enhancement of fluorescence) effect in the Zn(II) complexes than in the Cd(II) complexes in both media. The results have been examined by considering the ratio I(rel)(Zn(II))/I(rel)(Cd(II)), within the emerging idea that the relative strength of the CHEF effect for the small Zn(II) ion as compared to larger Cd(II) ion might be determined by steric crowding in the corresponding complexes with quinoline-based fluorescent chemosensors.

Interaction of mixed-donor macrocycles containing the 1,10-phenanthroline subunit with selected transition and post-transition metal ions: metal ion recognition in competitive liquid-liquid solvent extraction of Cu(II), Zn(II), Pb(II), Cd(II), Ag(I), and Hg(II).

Two new mixed aza-thia crowns 5-aza-2,8-dithia[9]-(2,9)-1,10-phenanthrolinophane (L(4)) and 2,8-diaza-5-thia[9]-(2,9)-1,10-phenanthrolinophane (L(7)) have been synthesized and characterized. The coordination behavior of L(4) and L(7) toward the metal ions Cu(II), Zn(II), Pb(II), Cd(II), Hg(II), and Ag(I) was studied in aqueous solution by potentiometric methods, in CD3CN/D2O 4:1 (v/v) by (1)H NMR titrations and in the solid state. The data obtained were compared with those available for the coordination behavior toward the same metal ions of structurally analogous mixed donor macrocyclic ligands L(1)-L(3), L(5), L(6): all these contain a phenanthroline subunit but have only S/O/N(aromatic) donor groups in the remaining portion of the ring and are, therefore, less water-soluble than L(4) and L(7). The complexes [Cd(NO3)2(L(5))], [Pb(L(7))](ClO4)2 x 1/2MeCN, [Pb(L(4))](ClO4)2 x MeCN, and [Cu(L(7))](ClO4)2 x 3/2MeNO2 were characterized by X-ray crystallography. The efficacy of L(1)-L(7) in competitive liquid-liquid metal ion extraction of Cu(II), Zn(II), Cd(II), Pb(II), Ag(I), and Hg(II) was assessed. In the absence of Hg(II), a clear extraction selectivity for Ag(I) was observed in all systems investigated.

An unprecedented example of a cis-phosphonodithioato nickel(II) complex built by an extensive hydrogen bonding supramolecular network.

The P-N bond hydrolysis of the 4-methoxyphenyl-ammonium ethylamido-phosphonodithioato ligand during its complexation to NiII leads to the first example of phosphonodithioato nickel(II) complex having a cis configuration; this complex is stabilised in the solid state by an extensive and intricate network of hydrogen bondings involving the released ethylenediamine and a water molecule.

First example of an infinite polybromide 2D-network.

The reaction of the neutral dithiolene [Pd(Et2timdt)2] (Et2timdt = formally monoreduced diethylimidazolidine-2,4,5-trithione) with an excess of Br2 yielded few crystals of [1(Et) x 2Br](2+)(Br-)2(Br2)3 as a by-product (1(Et) = 4,5,9,10-tetrathiocino-[1,2-b:5,6-b']-1,3,6,8-tetraethyl-diimidazolyl-2,7-dithione); X-ray diffraction analysis showed that this compound represents the first example of a polybromide 2D-network templated by [1(Et) x 2Br](+2) dications, and featuring all the Br-Br distances shorter than those found in solid state bromine.

Monoreduced [M(R,R'timdt)2]- dithiolenes (M = Ni, Pd, Pt; R,R'timdt = disubstituted imidazolidine-2,4,5-trithione): solid state photoconducting properties in the third optical fiber window.

Electrochemically monoreduced [M(R,R'timdt)(2)](-) dithiolenes, showing unprecedented wavelength selective photoconducting properties in the third optical fiber window (1500-1800 nm), fine-tunable through modifications in the chemical structure, allowed for the fabrication of a test photodetector with a bit rate of about 85 kbit s(-1).

Synthesis, Characterization, and Crystal Structures of New Dications Bearing the -Se-Se- Bridge.

Starting from 1,3-dimethyl-4-imidazoline-2-selone (1), 1,2-bis(2-selenoxo-3-methyl-4-imidazolinyl-2-)ethane (3) and 1,3-dimethylimidazolidine-2-selone (4), the following six compounds, [(C(5)H(8)N(2)Se-)(2)](2+).2Br(-) (I), [(C(5)H(8)N(2)Se-)(2)](2+).2I(-) (II), [(C(5)H(8)N(2)Se-)(2)](2+).Cl(-).I(3)(-) (III) [(C(5)H(10)N(2)Se-)(2)](2+).Br(-).IBr(2)(-) (IV), [(C(5)H(7)N(2)Se-)(2)](2+).I(3)(-).(1)/(2)I(4)(-) (V) and [(C(5)H(7)N(2)Se-)(2)](2+).2I(-).CH(3)CN (VI), in which the selenium compounds are oxidized to dications bearing the uncommon -Se-Se- bridge, have been prepared, and I-V crystallographically characterized. I and III were obtained by reacting 1 with IBr and ICl respectively, while II was obtained by reduction of previously described hypervalent selenium compound of 1 (5) bearing the I-Se-I group with elemental tellurium. These three compounds contain the same [(C(5)H(8)N(2)Se-)(2)](2+) dication balanced by two bromides in I, two iodides in II, and Cl(-) and I(3)(-) in III. However, on the basis of the Se-Cl bond length of 2.778(5) Å, III can also be considered as formed by the [(C(5)H(8)N(2)Se-)(2)Cl](+) cation, with I(3)(-) as counterion. Similarly to III, compound IV, which was obtained by reacting 4 with IBr, can be considered as formed by [(C(5)H(10)N(2)Se-)(2)Br](+) cations and IBr(2)(-) anions. As in II, compound V has been prepared by reduction of the hypervalent selenium compound of 3 (6) bearing two I-Se-I groups with elemental tellurium. In V, the [(C(5)H(7)N(2)Se-)(2)](2+) cation is balanced by I(3)(-) and half I(4)(2-) anions. The structural data show that all the cations are very similar, with Se-Se bond lengths ranging from 2.409(2) to 2.440(2) Å. FT-IR and FT-Raman spectra of I-VI allow one to identify two bands around 230 +/- 10 and 193 +/- 5 cm(-1) that are common to all compounds. These bands are generally strong in the FT-Raman and weak in the FT-IR spectra and should contain a contribution of the nu(Se-Se) stretching vibration. The spectra are also in good agreement with the structural features of the polyhalide anions present in the crystals. Crystallographic data are as follows: I is monoclinic, space group P2(1), with a = 9.849(6) Å, b = 11.298(5) Å, c = 7.862(6) Å, beta = 106.44(2) degrees, Z = 2, and R = 0.0362; II is monoclinic, space group P2(1), with a = 8.063(6) Å, b = 11.535(5) Å, c = 10.280(5) Å, beta = 107.13(2) degrees, Z = 2, and R = 0.0429, III is monoclinic, space group P2(1)/n, with a = 10.431(7) Å, b = 18.073(5) Å, c = 11.223(6) Å, beta = 100.76(2) degrees, Z = 4, and R = 0.0490; IV is monoclinic, space group P2(1)/n, with a = 10.298(5) Å, b = 18.428(7) Å, c = 11.475(6) Å, beta = 104.10(4) degrees, Z = 4, and R = 0.0300; V is triclinic, space group P&onemacr;, with a = 7.456(6) Å, b = 11.988(5) Å, c = 12.508(5) Å, alpha = 79.32(2) degrees, beta = 85.49(2) degrees, gamma = 80.62(2) degrees, Z = 2, and R = 0.0340.

Syntheses, X-ray Crystal Structures, and Spectroscopic Properties of New Nickel Dithiolenes and Related Compounds.

The direct addition of nickel powder to the reaction mixtures of 1,3-dialkyl-4,5-dioxoimidazolidine-2-thione (1) with the thionation Lawesson reagent produces [Ni(II)(R(2)timdt(-))(2)] (R(2)timdt = 1,3-dialkylmidazolidine-2,4,5-trithione). These complexes belong to a new class of nickel-dithiolenes, showing remarkably high absorption (epsilon approximately 80 000 dm(3) mol(-)(1) cm(-)(1), lambda approximately 1000 nm) in the near-infrared region (near-IR), accompanied by high photochemical stability that makes these complexes promising near-IR dyes. In the absence of nickel the reaction yields generally the compounds 4,5,6,7-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraalkane-2,9-dithione (2) instead of the expected 1,3-dialkylimidazolidine-2,4,5-trithione. However, with bulky substituents on the nitrogen atoms, well-characterized reaction products have not been obtained until now. Only in the R = Pr(i) case, the new tetrathiocino isomer (4,5,9,10-tetrathiocino[1,2-b:5,6-b']diimidazolyl-1,3,6,8-tetraisopropane-2,7-dithione (3) in trace amounts and the bis(1,3-diisopropyl-2-thioxoimidazolin-4-yl) disulfide (4) were isolated from the reaction with the Lawesson reagent and P(4)S(10), respectively. Reaction of 5 with different amounts of I(2) leads to a variety of products, and among them the following derivatives have been characterized: [Ni(II)(Pr(i)(2)timdt(-))(2)].2I(2) (6) a neutral adduct in which each I(2) molecule interacts with each peripheral thione sulfur atom of 5; [Ni(II)(Pr(i)(2)timdt(-))(2)].2I(2).(1)/(2)I(2) (7), which differs from 6 with the presence of half diiodine as a guest; with a larger diiodine excess (starting from a 1:10 molar ratio) a partial oxidation of 5 is achieved and [Ni(II)(Pr(i)(2)timdt(-))(2)] [Ni(II)(I)(2)(Pr(i)(2)timdt)(2)].5I(2) (8) is formed, a ligand mixed-valence compound in which the square-planar complex 5 and the octahedral complex [Ni(II)(I)(2)(Pr(i)(2)timdt)(2)] (the ligand in neutral form) are bound by diiodine molecules in such a way that a sequence of 12 iodine atoms (S.I(2).I(2).I(-).I(2).I(-).I(2).I(2).S) is formed. Spectroscopic and X-ray diffractometric studies of 3 (monoclinic, space group P2(1)/n, a = 13.104(6) Å, b = 15.091(6) Å, c = 6.067(7) Å, beta = 103.00(2) degrees, Z = 2), 4 (monoclinic, space group C2/c, a = 18.717(5) Å, b = 8.846(5) Å, c = 14.475(5) Å, beta = 97.78(2) degrees, Z = 4), 5 (orthorhombic, space group Pna2(1), a = 18.806(5) Å, b = 5.628(7) Å, c = 23.665(5) Å, Z = 4), 7 (triclinic, space group P&onemacr;, a = 9.126(7) Å, b = 9.153(7) Å, c = 12.924(6) Å, alpha = 82.11(2), beta = 70.14(2), gamma = 72.51(2) degrees, Z = 1), and 8 (monoclinic, space group C2/c, a = 21.971(6) Å, b = 28.081(5) Å, c = 12.207(8) Å, beta = 93.57(2) degrees, Z = 4) are given.

1,2-Bis(3-methyl-imidazolin-2-ylium iodobromoselenanide)ethane: Oxidative Addition of IBr at the Se Atom of a >C=Se Group.

Almost linear I-Se-Br groups with d(Se-Br)>d(Se-I) occur in 1⋅2 IBr, the first "T-shaped" Se adduct with IBr, which was synthesized by the oxidative addition of IBr to 1,2-bis(3-methylimidazoline-2-selonyl)ethane (1) in MeCN. Density functional theory calculations indicate the intramolecular Br⋅⋅⋅H interactions as being responsible for the peculiar structural features of the I-Se-Br groups.

Reactivity of phosphonodithioato-dppt Ni(II) mixed ligand complexes with halogens: first example of a metal-coordinating tribromide anion.

The first example of a metal complex containing a tribromide anion is presented and characterised by X-ray diffraction. Hybrid DFT calculations were used to investigate the nature of the bond in coordinating trihalides and the differences with the corresponding mono-halide complexes.

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-edt(2-)=pyren-1-yl-ethylene-1,2-dithiolato). The intense electrochromic NIR absorption (λ(max)=1432 nm; ε=13000 M(-1) cm(-1) in CH(2)Cl(2)) 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 ß(tot) were calculated (ß(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].

Synthesis and characterization of novel gold(III) complexes of asymmetrically aryl-substituted 1,2-dithiolene ligands featuring potential-controlled spectroscopic properties.

The tetrabutylammonium (TBA(+)) salts of square-planar monoanionic gold complexes of the unsymmetrically substituted Ar,H-edt(2-) 1,2-dithiolene ligands (Ar,H-edt(2-)=arylethylene-1,2-dithiolato; Ar=phenyl (1(-)), 2-naphthyl (2(-)), and 1-pyrenyl (3(-))) were synthesized and characterized by spectroscopic and electrochemical methods and the corresponding neutral species (1, 2, and 3, respectively) were obtained in CH(2)Cl(2) solution at room temperature by diiodine oxidation. The single-crystal X-ray diffraction structural data collected for (TBA(+))(2(-)), supported by DFT theoretical calculations, are consistent with the ene-1,2-dithiolate form of the ligand and the Au(III) oxidation state. All complexes feature intense near-IR absorptions (at about 1.5 microm) in their neutral states and Vis-emitting properties in the 400-550 nm range, the energy of which is controlled by the charge of the complex in the case of the 3(-)/3 couple. The spectroscopic and electrochemical features of 1(x-) and 2(x-) (x=0, 1), both in their cis and trans conformations, were investigated by means of DFT and time-dependent (TD) DFT calculations.

Investigation on the reactivity of dithiophosphonato/dithiophosphato Ni(II) complexes towards 2,4,6-tris-2-pyridyl-1,3,5-triazine: developments and new perspectives.

The reactions between tptz and differently substituted dithiophosphonato [Ni(ROpdt)2] [ROpdt = (RO)(4-MeOC6H4)PS2-; R = Et (2); Pr (3); i-Pr (4); Bu (5)] and dithiophosphato [Ni((EtO)2PS2)2] (6) Ni(II) complexes have been investigated, and the characterisation of the resulting neutral mixed complexes (2.tptz)-(6.tptz) is reported. In all these complexes, tptz forces one of the two dithiophosphonato/dithiophosphato ligands to behave as a monodentate ligand, a coordination mode rarely found in analogous Ni(II) phosphorodithioato complexes. A comparison has been performed between the Ni-S bond distances of the new complexes and those of isologous dithiophosphonato, dithiophosphato and dithiophosphito Ni(II) square-planar complexes, and of their penta- and hexa-coordinated adducts. The results, also supported by DFT calculations, are discussed and explained in terms of the structural trans-effect (STE). The reactivity of 2.tptz towards AgNO3 and CuSO4 to yield the complex [Ni(EtOpdt)(tptz)(H2O)]NO3 (7), and the dimer [(Ni(tptz)(mu-SO4)(H2O)]2.6H2O (8), respectively, is consistent with the proposed bonding models.

Interaction of methimazole with I2: X-ray crystal structure of the charge transfer complex methimazole-I2. implications for the mechanism of action of methimazole-based antithyroid drugs.

The antithyroid drug methimazole (MMI) reacts with molecular iodine to form, in a multistep process, 1-methylimidazole as final product. In this process, the charge transfer complex MMI-I 2 and the ionic disulfide [(C 4H 6N 2S-) 2] (2+) ( 1, dication MMI disulfide) have been isolated and their X-ray crystal structures solved. Dication MMI disulfide perchlorate acts effectively both in reducing I 2 to I (-) ions and in showing antioxidant properties in inactivating the enzyme lactoperoxidase compound I.

The nature of the chemical bond in linear three-body systems: from i3- to mixed chalcogen/halogen and trichalcogen moieties.

The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I(3) (-) and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I(3) (-) anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom.

Investigation into the reactivity of the coordinatively unsaturated phosphonodithioato [Ni(MeOpdt)2] towards 2,4,6-tris(2-pyridyl)-1,3,5-triazine: goals and achievements.

The reaction between the coordinatively unsaturated phosphonodithioato complex [Ni(MeOpdt)2] (1) [MeOpdt = (MeO)(4-MeOC(6)H(4))PS2-] and tptz [2,4,6-tris(2-pyridyl)-1,3,5-triazine] has been investigated. Spectrophotometric and conductometric titrations showed the formation of a neutral and an ionic species, i.e. [Ni(MeOdtp)2(tptz)] (2) and [Ni(tptz)2](MeOdtp)2 (3), in correspondence to 1 : 1 and 2 : 1 tptz : ratios, respectively. XRD studies confirmed the formation of both complexes isolated in the compounds 2.MeOH and 3.4H(2)O. In the neutral complex 2 the central Ni(II) ion features a distorted octahedral coordination, achieved through three N-atoms of tptz and three S-atoms belonging to two MeOpdt anions, one of which unexpectedly acts as a monodentate S-donor. In 3.4H(2)O, the two phosphonodithioato anions are non-coordinating and counterbalance the charge of the [Ni(tptz)2](2+) distorted octahedral complex. From the reaction 2 of with I2 and Br2, crystals of [Ni(tptz)2](I3)2 (5) and [Ni(tptz)Br(micro-Br)]2 (6) have been obtained. The dinuclear complex 6 features a structure showing tubular canals with openings of about 6 x 6 A.

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.

Tuning the selectivity/specificity of fluorescent metal ion sensors based on N2S2 pyridine-containing macrocyclic ligands by changing the fluorogenic subunit: spectrofluorimetric and metal ion binding studies.

Two new fluorescent chemosensors for metal ions have been synthesized and characterized, and their photophysical properties have been explored; they are the macrocycles 5-(2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L5) and 5-(5-chloro-8-hydroxyquinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L6). Both systems have a pyridyl-thioether-containing 12-membered macrocycle as a binding site. The coordination properties of these two ligands toward CuII, ZnII, CdII, HgII, and PbII have been studied in MeCN/H2O (1:1 v/v) and MeCN solutions and in the solid state. The stoichiometry of the species formed at 25 degrees C have been determined from absorption, fluorescence, and potentiometric titrations. The complexes [CuL5](ClO4)(2).1/2MeCN, [ZnL5(H2O)](ClO4)2, [HgL5(MeCN)](ClO4)2, [PbL5(ClO4)2], [Cu3(5-Cl-8-HDQH-1)(L6H-1)2](ClO4)(3).7.5H2O (HDQ=hydroxyquinoline), and [Cu(L6)2](BF4)(2).2MeNO2 have also been characterized by X-ray crystallography. A specific CHEF-type response of L5 and L6 to the presence of ZnII and CdII, respectively, has been observed at about pH 7.0 in MeCN/H2O (1:1 v/v) solutions.