Thermal behaviour of xanthinium salts of Zn(II), Cd(II) and Hg(II)

Salts [XanH⁺]₂[MCl ₄ ^2- ] (where XanH⁺=protonated form of xanthine and M=Zn(II), Cd(II) and Hg(II) have been synthesized and studied by IR,¹H-NMR, TG and DSC. The metal is not coordinated to the ligand and forms a salt-like structure. The cationic proton is on N(7). Thermal decomposition of these salts occurs in two steps: (i) dehalogenation and (ii) decomposition. Dehalogenation enthalpies have been calculated from DSC curves.

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Zusammenfassung (XanH⁺)₂(MCl ₄ ^2- )-Salze (worin XanH⁺ die protonisierte Form von Xanthin bedeutet und M=Zn(II), Cd(II) oder Hg(II) ist) wurden synthetisiert und mit IR,¹H-NMR, TG und DSC untersucht. In diesem Fall liegt keine Koordination des Metalls mit dem Liganden vor, und es bildet sich eine salzartige Struktur aus. Das kationische Proton ist an N(7) lokalisiert. Die thermische Zersetzung dieser Salze erfolgt in zwei Schritten: (i) Dehalogenisierung und (ii) Zersetzung. Dehalogenierungsenthalpien wurden aus DSC-Kurven berechnet.

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- -, [XanH⁺]₂[MCl ₄ ^2– ], XanH⁺ — , M — , . , . . : . - .

     

The coordination chemistry of Zn(II), Cd(II) and Hg(II) complexes with 1,2,4-triazole derivatives

This perspective illustrates the coordination features of complexes constructed by 1,2,4-triazole derivatives and transition metal ions which belong to Group IIB, namely Zn(II), Cd(II) and Hg(II), demonstrates their behaviors in thermal stabilities, gas or liquid adsorption, fluorescence and nonlinear optical properties and also discusses the relation between their properties and crystal structures. Various 1,2,4-triazole derivatives containing versatile donor sites for coordination can be obtained through introducing different substituent groups to C3, N4 and C5 positions, thus offering rich coordination modes. The structures of these complexes rely on their triazole ligands, as well as mixed ligands, metal ions, anions and synthetic conditions. Obviously, the diversity in structure induces the controllability of properties, since the properties are influenced by several factors, which is significant for the applications of potential multifunctional materials.     

Protonation and coordination properties towards Zn(II), Cd(II) and Hg(II) of a phenanthroline-containing macrocycle with an ethylamino pendant arm

Protonation and Zn(II), Cd(II) and Hg(II) coordination with the ligand 5-aminoethyl-2,5,8-triaza-[9]-10,23-phenanthrolinophane (L2), which contains an aminoethyl pendant attached to a phenanthroline-containing macrocycle, have been investigated by means of potentiometric, 1H NMR and spectrofluorimetric titrations in aqueous solutions. The coordination properties of L2 are compared with those of the ligand 2,5,8-triaza-[9]-10,23-phenanthrolinophane (L1). Ligand protonation occurs on the aliphatic amine groups and does not involve directly the heteroaromatic nitrogens. The fluorescence emission properties of L2 are controlled by the protonation state of the benzylic nitrogens: when not protonated, their lone pairs are available for an electron transfer process to the excited phenanthroline, quenching the emission. As a consequence, the ligand is emissive only in the highly charged [H3L2]3+ and [H4L2]4+ species, where the benzylic nitrogens are protonated. Considering metal complexation, both [ML1]2+ and [ML2]2+ complexes (M = Zn(II) and Cd(II)) are not emissive, since the benzylic nitrogens are weakly involved in metal coordination, and, once again, they are available for quenching the fluorescence emission. Protonation of the L2 complexes to give [MHL2]3+ species, instead, leads to a recovery of the fluorescence emission. Complex protonation, in fact, occurs on the ethylamino group and gives a marked change of the coordination sphere of the metals, with a stronger involvement in metal coordination of the benzylic nitrogens; consequently, their lone pairs are not available for the process of emission quenching.     

Novel Pb(II), Zn(II), and Cd(II) coordination polymers constructed from ferrocenyl-substituted carboxylate and bipyridine-based ligands

Treatment of two kinds of ferrocenyl-substituted carboxylate ligands (3-ferrocenyl-2-crotonic acid, HOOC-CH=(CH(3))CFc (Fc=(eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) or O-ferrocecarbonyl benzoic acid, o-HOOCC(6)H(4)COFc with Pb(OAc)(2).3H(2)O, Zn(OAc)(2).2H(2)O, or Cd(OAc)(2).2H(2)O) resulted in four novel ferrocene-containing coordination polymers [[Pb(mu(2)-eta(2)-OOCCH=(CH(3))CFc)(2)].MeOH](n) (1), [[Zn(o-OOCC(6)H(4)COFc)(2)(4,4'-bipy)(H(2)O)(2)].2MeOH.2H(2)O](n) (4,4'-bipy = 4,4'-bipyridine) (2), [[Cd(o-OOCC(6)H(4)COFc)(2)(bpe)(MeOH)(2)].2H(2)O](n) (bpe = 1,2-bis(4-pyridyl)ethene) (3), and [Pb(o-OOCC(6)H(4)COFc)(eta(2)-o-OOCC(6)H(4)COFc)(bpe)](n)() (4). Their crystal structures have been characterized by single X-ray determinations. In polymer 1, Pb(II) ions are bridged by tridentate FcC(CH(3))=CHCOO(-) anions, forming an infinite chain [Pb(mu(2)-eta(2)-OOC=CH(CH(3))CFc)(2)](n). In polymers 2-4, there are three kinds of components, metal ions, o-FcCOC(6)H(4)COO(-) units, and organic bridging ligands. The bipyridine-based ligands connect metal ions leading to a one-dimensional chain with o-FcCOC(6)H(4)COO(-) units acting as monodentate or chelate ligands in the side chain. Such coordination polymers containing ferrocenyl-substituted carboxylate and bipyridine-based ligands are very rare. The solution-state differential pulse voltammetries of polymers 1-4 were determined. The results indicate that the half-wave potential of the ferrocenyl moieties is influenced by the Pb(II) ions in polymer 1 and strongly influenced by Zn(II), Cd(II), or Pb(II) ions in polymers 2-4. The thermal properties of the four polymers were also investigated.     

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II)

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.     

Stoichiometrical coordination behaviour of hexaza tripodal ligands towards zinc(II), copper(II), nickel(II) and cobalt(II)

The stability constants of Zn^II, Cu^II, Ni^II and Co^II with different tripodal ligands, 1,3,5-tris(2,5-diazaoctxyl)benzene (L1), 1,3,5-tris(2,5-diazanonxyl)benzene (L2) and 1,3,5-tris[3-(2-pyridyl)-2-azapropyl]benzene (L3) have been studied at 25 °C in 0.1 mol dm^–3 KNO₃ aqueous solution using potentiometric titrations. During the titrations, the ligand concentrations were kept constant at 1 × 10^–3 mol dm^–3, while 1:1 and 1:3 metal:ligand ratios were used for each system. The results indicated that, in the 1:1 metal:ligand ratio, the binding of M^II to the ligand gives rise to several 1:1 complexes differing in their degree of protonation whereas in the 3:1 ratio, polynuclear complexes are formed. Additionally, the ternary complexes of the tripod ligands, with Cu^II-5-substituted-1, 10-phenanthroline have been investigated and the results show that linear free energy relationship exists in such ternary systems.     

Synthesis and spectroscopic characterization of Zn(II), Cd(II), and Hg(II) ciprofloxacin complexes

Ciprofloxacin metal co mplexes with general for mula [M(CPF)₂]X₂·nH₂O [M = Zn(II), Cd(II), and Hg(II)] have been synthesised and characterized using elemental analysis (CHN), spectroscopic (UV-Vis, IR, MS, and ¹H NMR) and ther mogravimetric (TG and DTA) data. Using the Coats-Redfern and Horowitz-Metzeger methods, kinetic analysis of the thermogravimetric data had been performed.     

Foam fractionation of cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III)

An experimental investigation is presented of the batch foam fractionation of the cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III) from 1.0 × 10⁻⁵ M (metal concentration) alkaline aqueous solutions, with the cationic surfactant hexadecyltrimethylammonium chloride. The effects are established of the presence of CN⁻ over the concentration range 2.5 × 10⁻⁵M−1.0 M, of the presence of NO₃⁻ over the concentration range 0.05–0.75 M, and of interferences to metal foam fractionation provided by 0.50 M concentrations of NO₃⁻, Br⁻, CN⁻, Cl⁻ or SO₄²⁻. Results are discussed in terms of the complex cyanide species of each metal that may have been present and in terms of the extent of hydration of the complex cyanide anions and of the potentially-interfering simple anions. The selectivity sequence, Au(CN)₄⁻Hg(CN)₄²⁻Cd(CN)₄²⁻Zn(CN)₄²⁻ is established, both from data for single-metal solutions and for solutions containing equimolar concentrations of all four metals. A partial separation of the metals can be achieved in the presence of high concentrations of NO₃⁻, which can be improved by taking maximum advantage of flotation rate differences.     

Zn(II), Cd(II) and Hg(II) complexes of 6-amino-1-methyl-5-nitrosouracil

The following Zn(II), Cd(II) and Hg(II) complexes of neutral and deprotonated 6-amino-1-methyl-5-nitroso-uracil (HL) were prepared and studied by u.v.-vis, ¹H-NMR and i.r. techniques: ZnL₂·4H₂O,ZnL₂(H₂O)₂·H₂O, CdCl₂(HL)₂·2H₂O and HgL₂·2H₂O. In Zn(II) and Hg(II) complexes, the ligand is coordinated in anionic nitroso-phenolic form, acting as a bidentate ligand through the nitrogen and oxygen atoms of the 5-nitroso and 6-oxide groups, respectively. In the cadmium complex, the ligand seems to be either N,O- or only N-bound to the metal ion, with chlorine bridging. From the data obtained, molecular structures are proposed for each complex.     

Preparation and characterization of vanillin thiosemicarbazone complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)

Complexes of vanillin thiosemicarbazone (3-methoxy-4-hydroxybenzaldehyde thiosemicarbazone), (vtsch) with several divalent metal ions have been isolated. Structures have been assigned to these complexes based on electrical conductivity, magnetic susceptibility and spectroscopic measurements     

A novel class of Cd(II), Hg(II) turn-on and Cu(II), Zn(II) turn-off Schiff base fluorescent probes

N,N'-((5,5'-(quinoxaline-2,3-diyl)bis(1H-pyrrole-5,2-diyl))bis(methanylylidene))bis(4-methoxyaniline) 4 and N,N'-((5,5'-(quinoxaline-2,3-diyl)-bis(1H-pyrrole-5,2-diyl))bis(methanylylidene))dianiline 5 have been prepared and structurally characterized. The X-ray crystal structures of compounds 4 and 4a have been determined. These compounds displayed good sensitivity toward transition metal ions with Cd(II), Zn(II) turn-on and Cu(II), Hg(II) turn-off in fluorescence. It is an elegant example of on/off behavior like a lamp. When Cd(II) or Zn(II) is added into compounds 4 or 5, the lamp will switch on, and then when Cu(II) or Hg(II) is added into the mixture, the lamp will switch off. The binding properties of 4 and 5 for cations were examined by fluorescence spectroscopy. The fluorescence data and crystal structure indicate that a 1:1 stoichiometry complex is formed between compound 4 (or 5) and metal ions, and the binding affinity is very high. The recognition mechanism between compound 4 (or 5) and metal ion was discussed based on the their chemical constructions and the CHEF/CHEQ effect when they interacted with each other.     

Thermal studies and vibrational analyses of m-methylaniline complexes of Zn(II), Cd(II) and Hg(II) bromides

The complexes having the MBr(2)L(2) (M: Zn, Cd and Hg; L: m-methylaniline) formulae have been prepared and characterized by their elemental analyses, thermogravimetric analyses, IR and Raman spectral studies. IR and Raman bands of the complexes have been assigned as compared with the free ligand. Coordination effects on the internal modes of m-methylaniline have been discussed. Vibrational spectra propose that the [ZnBr(2)(mMA)(2)] complex is in a tetrahedral environment around Zn(II) ion with C(2v) symmetry whereas Cd(II) and Hg(II) complexes have 5-coordinate polymeric bromide bridged structures.     

Synthesis, characterization and hypoglycemic activity of Zn(II), Cd(II) and Hg(II) complexes with glibenclamide

A series of group 12 elements for Zn(II), Cd(II), Hg(II) complexes of glibenclamide were synthesized and characterized using various spectroscopic techniques and magnetic moments. The complexes exhibited significant activity against gram-negative and gram-positive bacteria species. Zn(II) complex showed remarkable hypoglycemic activity whereas Cd(II) and Hg(II) complexes exhibited antibacterial activity.     

Spectrophotometric study of Cd(II), Pb(II), Hg(II) and Zn(II) complexes with 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin

The reaction of 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin (TCPP) with Cd(II), Pb(II), Hg(II) and Zn(II) was studied spectrophotometrically and kinetics, equilibrium constants as well as photodecomposition of complexes were determined. It was verified that these metal ions with large radius accelerate the incorporation reaction of zinc into TCPP. On the basis of the mechanism and kinetics of this reaction, a sensitive method for the spectrophotometric determination of trace amounts of Zn(II) has been developed. The molar absorptivity of examined Zn-TCPP complex and Sandell's sensitivity at 423 nm were 3.5×10⁵ M⁻¹ cm⁻¹ and 18.3 ng cm⁻². The detection limit for the recommended procedure was 1.4×10⁻⁹ M (0.9 ng ml⁻¹) and precision in range 20-100 ng ml⁻¹ not exceeds 2.7% RSD. The proposed method applied for zinc determination in natural waters and nutritional supplement was compared with AAS results and declared value.     

Thermal behaviour of Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pd(II) complexes with isatin-β-thiosemicarbazone

The isatin-β-thiosemicarbazone (ITC) complexes of Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pd(II) were prepared and characterized by elemental analysis, as well as molar conductivity, magnetic susceptibility, FTIR, UV-Vis and ¹H NMR spectroscopic methods. The complexes were also studied for its thermal stability. They all behaviour as anhydrous complexes and its thermolysis passes through the stages of deamination (517–547 K) and complete thermal decomposition (619–735 K).