PbII Complexes Research Articles

On the pivotal role of tetrel bonding in the supramolecular architectures of PbII–NCS complexes with chelating thiosemicarbazide derivatives

Detailed analysis of 1D and 2D supramolecular polymeric aggregations in Pb-complexes, driven by Pb⋯NCS and Pb⋯SCN tetrel bonds.

Construction of a PbII coordination polymer from asemi-rigid ditopic 2,2-biimidazole derivative: synthesis, crystal structure and characterization.

<!?tlsb=-0.04pt>A new PbII coordination polymer, poly[0.75(aqua)[μ3-4,4'-(1H,1'H-[2,2'-biimidazole]-1,1'-diyl)dibenzoato-κ5O,O';N;O'',O''']]lead(II)] 1.25-hydrate], {[Pb(C20H12N4O4)(H2O)0.75]·1.25H2O}n or {[Pb(L)(H2O)0.75]·1.25H2O}n (1) [H2L = 4,4'-(1H,1'H-[2,2'-biimidazole]-1,1'-diyl)dibenzoic acid], was synthesized under solvothermal reaction conditions and characterized using microanalysis, IR spectroscopy and thermogravimetric analysis. Single-crystal structure analysis reveals that a two-dimensional corrugated layer structure is formed in 1 and that neighbouring layers are further extended into a three-dimensional structure by hydrogen-bonding interactions. In addition, a fluorescence sensing experiment towards Cu2+ based on the polymeric PbII complex was carried out.

Orthogonal Photoswitching with Norbornadiene.

Orthogonal photoswitching is a convenient but challenging way of controlling multiple functions in a system by selective photoisomerization of one unit before the other in any arbitrarily chosen sequence. Here, we present this concept for the norbornadiene/quadricyclane (NBD/QC) photo/thermo-switch in the presence or absence of a coordinated metal ion. Thus, introducing two pyridyl ligands via ethyne-1,2-diyl bridges provides a system that by chelation of metal ions, such as PdII , has altered optical and switching properties. Mixing the PdII complex with its free ligand furnishes a four-state system where NBD-to-QC photoisomerizations for complexed and uncomplexed species are controlled by the irradiation wavelength and can occur orthogonally, that is, the sequence of photoisomerizations can be swapped. Studies on AgI and PbII complexes, being less stable than the PdII complex, are also presented; these exhibit like the PdII complex significantly red-shifted NBD absorptions.

Mono-N-benzyl cyclen: A highly selective, multi-functional “turn-on” fluorescence sensor for Pb2+, Hg2+ and Zn2+

Metal complexing and fluorescence properties of MB-cyclen (1-phenylmethyl-1,4,7,10-tetraazacyclododecane) and its complexes with metal ions in 50% CH3OH/H2O are described. The crystallographic structures of the complexes [(Zn(MB-cyclen))2OH](ClO4)3(2·13H2O), [Ag(MB-cyclen)(ClO4)], [Pb(MB-cyclen)(ClO4)2], [Hg(MB-cyclen)(ClO4)2], [Cu(MB-cyclen)(ClO4)2], and [Ni(MB-cyclen)(ClO4)2] are reported. The normal fluorescence peak of the benzyl group was observed at 289 nm and only the ZnII ion showed a strong CHEF (chelation enhanced fluorescence) effect for the 289 nm peak, which is in line with its lower position in the well-known order of ability to form fluorescence quenching π contacts: ZnII ≪ CdII < PbII < CuII ~ PdII ~ HgII < AgI. On the other hand, it is proposed that the apparent AIE (aggregation induced emission) nature of the 353 nm peak in the emission spectra of the HgII MB-cyclen complex and the neutral MB-cyclen ligand in 50% CH3OH/H2O arises from exciplex formation in nanoparticulate precipitates. The AIE nature of the 353 nm peak is supported by its appearance being accompanied by intense light scattering peaks in the absorbance spectra at about 200 nm. Finally, it was observed that the PbII complex exhibits an intense emission at 438 nm. The PbII MB-cyclen complex shows no Pb⋯C π contacts in the crystal structure, which is consistent with its lower position in the order of ability to form such contacts. However, time-dependent DFT studies on the PbII complex suggest that a Pb⋯C π contact is stabilized in the excited state, which gives rise to the 6s ← 6p transition of PbII coupled with transitions within the π-system of the benzyl fluorophore. Given that MB-cyclen responds to the bindings of PbII, HgII, and ZnII at very different wavelengths in their emission spectra, it can be used as a highly selective “turn-on’ sensor for the three metal ions.

A Design Strategy for Single-Stranded Helicates using Pyridine-Hydrazone Ligands and PbII.

The reactions of py-hz ligands (L1-L5) with Pb(CF3 SO3 )2 ⋅H2 O resulted in some rare examples of discrete single-stranded helical PbII complexes. L1 and L2 formed non-helical mononuclear complexes [PbL1(CF3 SO3 )2 ]⋅CHCl3 and PbL2(CF3 SO3 )2 ][PbL2CF3 SO3 ]CF3 SO3 ⋅CH3 CN, which reflected the high coordination number and effective saturation of PbII by the ligands. The reaction of L3 with PbII resulted in a dinuclear meso-helicate [Pb2 L3(CF3 SO3 )2 Br]CF3 SO3 ⋅CH3 CN with a stereochemically-active lone pair on PbII . L4 directed single-stranded helicates with PbII , including [Pb2 L4(CF3 SO3 )3 ]CF3 SO3 ⋅CH3 CN and [Pb2 L4CF3 SO3 (CH3 OH)2 ](CF3 SO3 )3 ⋅2 CH3 OH⋅2 H2 O. The acryloyl-modified py-hz ligand L5 formed helical and non-helical complexes with PbII , including a trinuclear PbII complex [Pb3 L5(CF3 SO3 )5 ]CF3 SO3 ⋅3CH3 CN⋅Et2 O. The high denticity of the long-stranded py-hz ligands L4 and L5 was essential to the formation of single-stranded helicates with PbII .

Exciplex Formation and Aggregation Induced Emission in Di‐(N‐benzyl)cyclen and Its Complexes – Selective Fluorescence with Lead(II), and as the Cadmium(II) Complex, with the Chloride Ion

DB‐cyclen [1,7‐bis(phenylmethyl)‐1,4,7,10‐tetraazacyclododecane] was investigated in 50 % CH3OH/H2O (v/v) as a fluorescent sensor for heavy metal ions, and as the CdII complex as a sensor for anions. The PbII complex showed a unique strong emission at 447 nm, possibly a charge‐transfer band involving the 6p←6s2 transition of PbII and the benzyl fluorophore. ZnII uniquely produced a significant emission at 353 nm, suggested to be due to an aggregation induced (AIE) mechanism, possibly involving exciplex formation. The free DB‐cyclen ligand produces a fluorescence band at 354 nm above pH ca. 9, accompanied by the slow formation of an aggregate in suspension as indicated by the presence of light scattering peaks in the absorbance spectra, an AIE effect, due to formation of an intermolecular exciplex in the solid state. The role of M···C π contacts in quenching fluorescence in DB‐cyclen complexes or in AIE effects was investigated in the structures of [Pb(DB‐cyclen)(ClO4)2] (1), [Cu(DB‐cyclen)(ClO4)2] (2), [Ag(DB‐cyclen)(ClO4)] (3), and [Cd(DB‐cyclen)(ClO4)(H2O)]ClO4 (4). In 1 there is an intermolecular π contact between the PbII and a benzyl group from an adjacent complex individual, which is also the case in 3, where very short η2 intermolecular Ag···C π contacts are found. A strong band at 336 nm is shown in the CdII DB‐cyclen complex on titration with Cl– only: Br–, I–, S2O32–, and SCN– produced no AIE/exciplex band in the CdII DB‐cyclen complex: the exciplex forming species may be a Cl– bridged dimer [Cd(DB‐cyclen)Cl]22+.

Indole-based fluorescence sensors for both cations and anions

The fluorescence properties of the ligand idpa (1H-Indole-3-ethanamine, N,N-bis(2-pyridinylmethyl)amine) complexed with metal ions along with their crystal structures were investigated to further understand the role of π contacts in quenching fluorescence. In particular, the π contacting ability of indole fluorophore of idpa and its impact on the fluorescence properties are compared to those of anthracene (in adpa) and coumarin fluorophores (in cdpa) investigated previously by us. Unlike adpa and cdpa, the fluorescence of free idpa increases with rising pH, which is attributed via TD-DFT studies to quenching at lower pH values by a proton transfer in the excited state from the protonated tertiary amine to the pydridyl nitrogen. Structural studies show that the AgI complex of idpa is a dimer held together by very short inter-complex η1 Ag···C π contacts of 2.382 Å, indicating powerful π contacting ability of indole as expected from the electrostatic potential map. However, structural studies of the ZnII, NiII, PbII, and CdII complexes of idpa show no metal-fluorophore π contacts present in the solid state, which was ascribed to a plethora of other π contacts and hydrogen bondings possible only in solid state. All metal ions on complex-formation cause quenching of fluorescence of idpa relative to that of free idpa at pH 7.45, suggesting the existence of π contacts in solution. DFT/TD-DFT studies showed that O-H···C π contacts with the solvent stabilizes the excited state and makes the S1 → S0 emission to be a charge transfer transition, quenching the fluorescence of ZnIIidpa, and possibly CdIIidpa as well. The existence of π contacts in solution was also reflected in the fact that the ZnII and CdII complexes show increased fluorescence intensity when titrated with Cl−, which could be due to the disruption of fluorescence-quenching O-H···C π contacts with solvent molecules. The observed fluorescence responses of ZnII and CdII complexes to Cl− render these complexes to be used as a possible sensor for Cl−.

A quantum chemistry evaluation of the stereochemical activity of the lone pair in PbII complexes with sequestering ligands.

The stereochemical activity of the lone pair on PbII complexes is assessed using several theoretical methods, including structural analyses, computations of Fukui functions, natural bond orbitals, electron localization function, investigation of the electron density and of its laplacian. The attention is focused on four octadentate N-carbamoylmethyl-substituted tetraazamacrocycles of various ring sizes ranging from 8 to 14 atoms associated with the PbII cation. The theoretical study illustrates the geometrical constraints imposed by the ring structure which limits the spatial development of the lone pair but without fully preventing it. For a given coordination number, the lone pair activity is strongly correlated to the geometry of the ligand and in particular to the size of the cage that the ligand forms around the PbII cation. Some limitations of the theoretical tools used are also evidenced, among them the necessity to sample around a critical point instead of just analyzing its nature. In the case of the laplacian of the electron density, a visualization method is introduced to moderate the results based only on the nature of a critical point. These limitations should also be related to the difficulty to extend the lone pair concept for the heaviest atoms of the classification.

Speciation of binary complexes of PbII and CdII with maleic acid in acetonitrile medium

Speciation of binary complexes of PbII and CdII with maleic acid in acetonitrile medium

0D and 1D PbII complexes constructed from pyridyldicarboxamide by varying the ratios of mixed solvent

By varying the ratio of mixed reaction solvent, the reactions of PbAc2 with N,N′-bis(1,3,4-thiobiazolyl)-2,6-pyridyldicarboxamide (H2btapca) afford two different crystal structures: a novel discrete hexanuclear cage of formula [Pb6(btapca)6]·(H2O)2 (1) and a 1-D double-chain polymer [Pb2(btapca)2(H2O)2]n (2). Fluorescence investigations reveal that both complexes display enhanced emissions in contrast to the free ligand H2btapca.

Chemical speciation of ternary complexes of PbII, CdII and HgII with L-phenylalanine and maleic acid in TX100-water mixtures

Chemical speciation of ternary complexes of PbII, CdII and HgII with L-phenylalanine and maleic acid in TX100-water mixtures

PH-metric investigation on binary complexes of PbII, CdII and HgII with maleic acid in SLS-water mixtures

pH-metric investigation on binary complexes of PbII, CdII and HgII with maleic acid in SLS-water mixtures

Chemical speciation of PbII, CdII and HgII binary complexes of L-phenylalanine in CTAB-water mixtures

Chemical speciation of PbII, CdII and HgII binary complexes of L-phenylalanine in CTAB-water mixtures

Lead electrochemical speciation analysis in seawater media by using AGNES and SSCP techniques

Environmental context Metal contamination of seawater can present severe environmental problems owing to the high toxicity of metals and their persistence in the environment. This study explores the possibility of analysing lead in seawater media using two recently developed electrochemical methods. The methods are shown to be very useful tools to monitor the behaviour and fate of lead and other metals in seawater. Abstract The speciation of PbII in synthetic and real seawater is studied by absence of gradients and Nernstian equilibrium stripping (AGNES) and stripping chronopotentiometry at scanned deposition potential (SSCP). The usefulness of the combination of both techniques in the same electrochemical cell for trace metal speciation analysis is assessed at different pH values (2.7, 5.0, 6.0, 7.0 and 8.6). The AGNES (free metal ion concentrations) and SSCP (stability constants) results for synthetic seawater agree reasonably with each other and with the theoretical predictions of the software Visual MINTEQ 3.0. This is also true for real seawater media below pH 7.0. Because of the influence of natural organic matter (2.01mgL–1 total organic carbon) in the real seawater at pH 7.0 and 8.6 the SSCP signal showed that the PbII complexes became less labile and were formed by chemically heterogeneous ligands. At these pH values, free metal concentrations determined by AGNES agreed with concentrations predicted by Visual MINTEQ using a generic fulvic acid concentration.

Structural diversity of 5-methylnicotinate coordination assemblies regulated by metal-ligating tendency and metal-dependent anion effect

Nine 5-methylnicotinate (L–CH3−) coordination complexes, namely, {[Ni(L–CH3)2(H2O)2](H2O)}n (1), [Ni2(L–CH3)4(H2O)]n (2), Ni(HL–CH3)2Cl2 (3), [Cd2(L–CH3)2(SO4)(H2O)6]n (4), [Cd(L–CH3)2(H2O)]n (5), {[Cu(L–CH3)2(H2O)2](H2O)}n (6), {[Co(L–CH3)2(H2O)2](H2O)}n (7), [Mn(L–CH3)2(H2O)2]n (8), and [Pb(L–CH3)2]n (9), were synthesized with different metal salts. For complexes 1–3, the use of different NiII salts (SO42−, OAc−, or Cl−) leads to three distinct coordination motifs, including a 3D lvt framework, a 3D self-interpenetrating (3·4·5)(32·43·53·6·74·82) network, and a mononuclear species, respectively. For CdII, two different 1D chain complexes can be assembled from HL–CH3 with CdSO4 (4) and Cd(OAc)2 or CdCl2 (5). However, such an anion effect has not been observed for the CuII (6), CoII (7), MnII (8), and PbII (9) complexes, which show a 3D lvt network for 6 and 7, a 2D (4,4) layer for 8, and a 3D (3,5)-connected (4·62)(4·67·82) network for 9. These results demonstrate that the diverse coordination motifs for 1–9 (from 0D, 1D, 2D, to 3D) can be effectively adjusted by the metal-ligating tendency and metal-dependent counter-anion effect. Thermal stability and solid-state fluorescence have also been investigated.

Scanned stripping chronopotentiometry at bismuth film rotating disc electrodes: a method for quantitative dynamic metal speciation

Environmental context Electroanalytical methods have found wide application in trace metal speciation analysis in environmental systems. The need to find functional alternatives to mercury electrodes for in situ speciation studies has encouraged the use of bismuth as a solid-state electrode substrate. We demonstrate the utility of bismuth electrodes for quantitative dynamic speciation analysis. Abstract Bismuth film electrodes are employed for dynamic metal speciation analysis of PbII complexes by stripping chronopotentiometry at scanned deposition potential (SSCP). Their performance is found to be comparable to that of mercury-film electrodes. The quantitative SSCP expressions that describe the thermodynamic and kinetic complexation parameters are straightforwardly applicable to this solid electrode.

The Syntheses, Crystal Structure, and Exceptional Chemical Stability of Three Multinuclear PbII Complexes

AbstractThree multinuclear PbII complexes―[Pb2(ptptp)2(H2O)2] (1), [Pb2(p‐PDA)(Hptptp)2] (2), and [Pb4(o‐PDA)2(ptptp)2]·2H2O (3) [H2ptptp = 2‐(5‐{6‐[5‐(pyrazin‐2‐yl)‐1H‐1,2,4‐triazol‐3‐yl]pyridin‐2‐yl}‐1H‐1,2,4‐triazol‐3‐yl)pyrazine, H2PDA = phenylenediacetic acid]―have been synthesized under hydrothermal conditions. Complexes 1, 2, and 3 show di‐, di‐, and tetranuclear structures, respectively. The study of the chemical stability of the three complexes demonstrates their remarkable chemical resistance to boiling water and organic solvents. More importantly, complex 1 shows remarkable acid and alkali resistance, which is outstanding among metal–organic solids. The thermogravimetric analysis curve shows that complex 1 possesses high thermal stability (up to 491 °C). Furthermore, the fluorescence of complexes 1, 2, and 3 has also been investigated.

Construction of one pH-independent 3-D pillar-layer lead-organic framework containing tetrazole-1-acetic acid

Abstract One new 3-D PbII complex, {[Pb2(tza)(μ3-OH)(μ3-Cl)(μ4-Cl)]n (1) (Htza = tetrazole-1-acetic acid), has been synthesized from the reaction of tetrazole-1-acetic acid (Htza) with PbCl2 at pH = 8.5 under hydro-solvent condition and characterized by X-ray single crystal diffraction, elemental analysis, thermogravimetric analysis, and IR spectra. The results show that the coordination chemistry of the multi-dentate ligand Htza on PbII ion has good pH sensitivity. At pH = 5 and 7, two once reported 3-D framework complexes {[Pb(tza)2]n (2) and [Pb(tza)(μ3-Cl)]n (3) are obtained, respectively. And then at pH = 8.5, the resultant three-dimensional complex 1 presents the pillar-layer framework network with a thickness of 8.25 A of layer [Pb2(μ3-OH)(μ2-O)2(μ3-Cl)(μ4-Cl)]n, in which there still exists the μ3-bridging mode of OH− group and the μ2-carboxyl oxygen atom besides the μ3- and μ4-bridging manners of the Cl− ion. Furthermore, the luminescent property of complex 1 has also been investigated, and the result exhibits blue photoluminescence in the solid state at room temperature, which shows that this complex may be a good candidate for photoactive material.

Syntheses, Crystal Structures, and Properties of Lead(II), ­Zinc(II), and Manganese(II) Complexes Constructed from 2, 3, 5, 6‐Tetraiodo‐1, 4‐benzenedicarboxylic Acid

AbstractThree new coordination compounds, [Pb(HBDC‐I4)2(DMF)4](1) and [M(BDC‐I4)(MeOH)2(DMF)2]n (M = ZnII for 2 and MnII for (3) (H2BDC‐I4 = 2, 3, 5, 6‐tetraiodo‐1, 4‐benzenedicarboxylic acid), were synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric (TG) analysis, and X‐ray single crystal structure analysis. Single‐crystal X‐ray diffraction reveals that 1 crystallizes in the monoclinic space group C2/c and has a discrete mononuclear structure, which is further assembled to form a two‐dimensional (2D) layer through intermolecular O–H···O and C–H···O hydrogen bonding interactions. The isostructural compounds 2 and 3 crystallize in the space group P21/c and have similar one‐dimensional (1D) chain structures that are extended into three‐dimensional (3D) supramolecular networks by interchain C–H···π interactions. The PbII and ZnII complexes 1 and 2 display similar emissions at 472 nm in the solid state, which essentially are intraligand transitions.

ZnII and PbII coordination chemistry of 2,6-bis(1,2,3-triazol-4-yl)pyridine (clickate) and the metal ion-dependent emission of ‘clickate’–appended anthracene

The effect of metal coordination of 2-(1-(9-anthryl)methyl-1,2,3-triazol-4-yl)-6-(1-n-octyl-1,2,3-triazol-4-yl)pyridine (2) on the emission of the appended anthryl group was investigated in acetonitrile. The tridentate 2,6-bis(1,2,3-triazol-4-yl)pyridyl ligand included in 2 is referred herein as ‘clickate’. Titrating zinc(II) perchlorate or zinc(II) chloride into the solution of fluorescent ligand 2 results in quenching, which is attributed to the formation of a dark 1:1 ZnII complex of 2. Frontier molecular orbital analysis and cyclic voltammetric data support the occurrence of photoinduced electron transfer from the excited state of the anthryl group to the ZnII-bound clickate moiety, which relaxes the excited fluorophore non-radiatively, i.e. quenches fluorescence. Fluorescence quenching of clickate 2 upon forming the PbII complex was also observed. The ZnII/PbII-coordination chemistry of clickate was characterised via X-ray crystallography, isothermal titration calorimetry, 1H NMR spectroscopy and absorption spectroscopy using the symmetrically substituted clickate 2,6-bis(1-n-octyl-1,2,3-triazol-4 yl)pyridine (1).