Studies on the Complexation of Transition Metal Ions with Macrocyclic Compounds in Mixed Solvents by Competitive Potentiometry and Polarography

Complexation of Cu(II), Zn(II), Ni(II), Co(II), Pb(II), Cd(II), Cr(III) and Fe(III) ions with 15-crown-5, benzo-15-crown-5, 18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, dibenzo-24-crown-8, 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene, 1,4,10-trioxa-7,13-diazacyclopentadecane and cyclam has been investigated in 75% (v/v) DMF+water using the silver(I) ion as an auxiliary cation at 0.05?M ionic strength adjusted with tetrabutylammonium perchlorate (TBAP) by competitive potentiometry. Stability constant values obtained for the metal ion–aza macrocyclic complexes are higher than those for the oxa crowns. Shifts in the peak potential and reduction in the peak current in the differential pulse polarography (DPP) method were also used to determine the stability constants of some of the metal ions with aza and tosylated-aza macrocycles using TBAP as supporting electrolyte in 75% (v/v) DMF+water and 90% (v/v) DMSO+water media. Stability constant values determined both by shifts in the potential and by reduction in the peak current were found to be in good agreement with each other.     

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.     

硫杂冠醚的合成

冠醚化合物对金属离子的络合不仅具有较高的稳定性,而且更重要的是具有良好的选择性。当冠醚环中的氧原子部分或全部被氮或硫原子取代后,它们对碱金属、碱土金属的亲和性能降低,而对过渡金属离子的亲和能力相应提高。硫杂冠醚对亲硫的贵金属、重金属离子具有更强的络合能力和更高的选择性。1974     

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.     

Kinetics of the Protonation of Macrocyclic Amines in the Presence of Monovalent Cations in Aqueous Solution

Abstract

For macrocyclic bases such as: 1-aza-15-crown-5 (N15C5),1,4,10-trioxa-7,13-diazacyclopentadecan (21), 1,7,10,16-tetraoxa-4,13-diazacyclooctadecan (22) and 1, 4, 7, 13, 16-pentaoxa-10, 19-diazacycloheneicosane (23), the kinetics of deprotonation and protonation reactions in the presence of monovalent cations was studied using the temperature jump technique. For the sake of comparison, the measurements were also performed for 1,4-diazabicyclo[2,2,2]octane (DABCO) base, which does not form complexes with monovalent cations. The monovalent cations affect the temperature dependence of the kinetic parameters of deprotonation. They also affect the activation parameters, which is shown by a distribution of ΔH≠ and ΔS≠ values, but do not influence the value of ΔG≠.     

Mixed nitrogen/oxygen ligand affinities for bipositive metal ions and dioxygen binding to cobalt(II) complexes

The complex formation of Co(II) and Cd(II) with mixed N/O ligands in dimethylsulfoxide (dmso) at 298 K is investigated by means of potentiometric, UV-Vis, calorimetric, FT-IR, NMR and electrochemical techniques. The linear and cyclic ligands investigated are: 2,2'-oxydiethylamine (NON), N-(2-hydroxyethyl)-ethylenediamine (NNO), 1,4,10-trioxa-7,13-diaza-cyclopentadecane (2,1) and 1,4,7,10-tetraoxa-13-azacyclopentadecane (2,2). The results are discussed by taking into account the donor strength of donor atoms, strain effects in the formation of chelate rings, steric and inductive effects and the size of the cavity when macrocyclic ligands are concerned. DFT studies are also performed to gain an insight into the stabilization of the lower oxidation state of the CoL2(2+/3+) couple in order to understand the different reactivity of the Co(II) complexes towards dioxygen. The kinetics of dioxygen uptake has been studied by UV-Vis measurements and the results reveal an interesting strong solvent effect, which is active in lowering the rate constant for formation of the initial superoxo complex.     

Complexation of Macrocyclic Compounds with Nicotinamide in Dimethylsulphoxideand its Water Mixture

The complexation behavior of nicotinamide with macrocyclic polyethers viz, 15-crown-5, benzo-15-crown-5, 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, dibenzo-24-crown-8, 1,4,7,10,13,16-hexathiacyclooctadecane, monoaza-15-crown-5, 1,4,10-trioxa-7,13-diaza-cyclopentadecane, 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane, 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, 1,4,7-tritosyl-1,4,7-triazacyclononane, 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclododecane and 1,4,8,11-tetraazacyclooctadecane has been studied in dimethylsulphoxide (DMSO) and 90% DMSO + water using differential pulse polarography and complexation constants have been reported. Nicotinamide forms stable complexes with six-membered coronand rings of the crown ethers. The nature of the atoms (oxygen, sulfur and nitrogen) in the coronand ring is observed to affect the stability of the complex. The stoichiometry and stability constants of the complexes were determined by monitoring the shifts in peak potentials of the polarograms of nicotinamide against the ligand concentration. The Gibbs free energy change turns out to be negative at 25°C, which indicates the spontaneity of the binding of nicotinamide with crown ethers. The mole ratio of nicotinamide to the macrocyclic compound was also determined and it was found that the complexes were of 1:1 type with respect to crown ethers. The tendency of nicotinamide to form complexes with macrocycles is found to be greater in DMSO than in DMSO + water.     

Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane

We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.     

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.     

Solvent control: dinuclear versus tetranuclear complexes of a bis-tetradentate pyrimidine-based ligand

A new bis-tetradentate acyclic amine ligand L(Et) has been synthesized from 4,6-bis(aminomethyl)-2-phenylpyrimidine and 2-vinylpyridine. Dinuclear complexes, Mn(II)(2)L(Et)(MeCN)(H(2)O)(3)(ClO(4))(4) (1), Fe(II)(2)L(Et)(H(2)O)(4)(BF(4))(4) (2), Co(II)(2)L(Et)(H(2)O)(3)(MeCN)(2)(BF(4))(4) (3), Ni(II)(2)L(Et)(H(2)O)(4)(BF(4))(4) (4), Ni(II)(2)L(Et)(H(2)O)(4)(ClO(4))(4)·8H(2)O (4'), Cu(II)(2)L(Et)(BF(4))(4)·MeCN (5), Zn(II)(2)L(Et)(BF(4))(2)(BF(4))(2)·?MeCN (6), were obtained from 1 : 2 reactions of L(Et) and the appropriate metal salts in MeCN, whereas in MeOH tetranuclear complexes, Mn(II)(4)(L(Et))(2)(OH)(4)(ClO(4))(4) (7), Fe(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·5/2H(2)O (8), Co(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·3H(2)O (9), Ni(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·4H(2)O (10), Cu(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·3H(2)O (11) and Zn(II)(4)(L(Et))(2)(F)(4)(BF(4))(4) (12), result. Six complexes have been structurally characterized: in all cases each L(Et) is bis-tetradentate and provides a pyrimidine bridge between two metal centres. As originally anticipated, complexes 1, 4' and 6 are dinuclear, while 9, 10 and 12 are revealed to be tetranuclear, with two M(2)(L(Et))(4+) moieties bridged by two pairs of fluoride anions. Weak to moderate antiferromagnetic coupling between the metal centres is a feature of complexes 2, 3, 4, 8, 9 and 10. The dinuclear complexes 1-6 undergo multiple, mostly irreversible, redox processes. However, the pyrimidine-based dicopper(II) complex 5 undergoes a two electron quasi-reversible reduction, Cu(II)(2)→ Cu(I)(2), and this occurs at a more positive potential [E(m) = +0.11 V (E(pc) = -0.03 and E(pa) = +0.26 V) vs. 0.01 M AgNO(3)/Ag] than for either of the dicopper(II) complexes of the analogous pyrazine-based ligands.     

Electrochemical study of oxaferrocene cryptands and their complexation with barium and sodium ions

The electrochemical behaviour and cation recognition properties of two oxaferrocene cryptand ligands, 1,1′-[(1,4,10-trioxa-7,13-diazacyclopentadecane-7,13-diyl)diethoxy]-3,3′,4,4′-tetraphenylferrocene and 1,1′-[(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)diethoxy]-3,3′,4,4′-tetraphenylferrocene, have been characterized in acetonitrile in the presence of Ba²⁺ and Na⁺ by cyclic voltammetry, square wave voltammetry and a rotating disc electrode. The changes in the redox signals for the cryptates at varying concentrations of the target cations are used as a direct measure of the electronic coupling between the two units, leading to the conclusion that the cryptate formation process proceeds in multiple stages and the ligand offers several binding sites in the complex.     

Investigation of group 12 metal complexes with a tridentate SNS ligand by X-ray crystallography and 1H NMR spectroscopy

Two series of zinc triad complexes containing the ligand 2,6-bis(methylthiomethyl)pyridine (L1) were synthesized and characterized by X-ray crystallography and solution-state 1H NMR spectroscopy. The distorted meridional octahedral M(L1)2(ClO4)2 series includes the first structurally characterized Zn(II) and Cd(II) complexes with N2(SR2)4 coordination spheres. Coordination of HgCl2 and ZnCl2 with 1 equiv of ligand afforded mononuclear, five-coordinate species Hg(L1)Cl2 and Zn(L1)Cl2, respectively, with distorted square-pyramidal and trigonal-bipyramidal geometries. With CdCl2, the dimeric [Cd(L1)Cl(mu-Cl)]2 complex was obtained. The distorted octahedral coordination geometry of each Cd(II) center in this complex is formed by one tridentate ligand, two bridging chloride ions, and one terminal chloride ion. NMR spectra indicate that the intermolecular ligand-exchange rate of [M(L1)2](2+) decreased in the order Cd(II) > Zn(II) > Hg(II). Slow intermolecular ligand-exchange conditions on the chemical-shift time scale were found for 1:2 metal-to-ligand complexes of L(1) with Hg(II) and Zn(II) but not Cd(II). Slow intermolecular ligand-exchange conditions in acetonitrile-d(3) solutions permitting detection of (3-5)J(199Hg1H) were found for 1:1 and 1:2 Hg(ClO4)2/L1 complexes, but not for the related Cd(ClO4)2) complexes. The magnitudes of J(199Hg1H) for equivalent protons were smaller in [Hg(L1)2](2+) than in [Hg(L1)(NCCH3)x](2+). The relative intermolecular ligand-exchange rates of the zinc triad complexes investigated here suggest that the toxicity of Hg(II) is accentuated by the relative difficulty of displacing it from the coordination sites encountered.     

Synthesis, crystal structures, photophysical properties, and bioimaging of living cells of bis-β-diketonate phenothiazine ligands and its cyclic dinuclear complexes

Two bis-β-diketones, RCOCH(2)CO-EPTZ-COCH(2)COR (EPTZ = 10-ethylphenothiazine; R = C(6)H(5) for H(2)L(1) and CF(3) for H(2)L(2)) and their cyclic dinuclear Zn(II), Cd(II), Ni(II), Mn(II), Cu(II), Co(II) complexes have been synthesized and fully characterized. Their crystal structures were determined by single crystal X-ray diffraction analysis. Their photophysical properties have been further investigated both experimentally and theoretically. The results revealed that significant enhancement of two-photon absorption cross section values were obtained for the cyclic dinuclear Zn(II) and Cd(II) complexes compared with their free ligands. Additionally, confocal microscopy and two-photon microscopy fluorescent imaging of MCF-7 cells labeled with two ligands and Zn(II) complexes reveal their potential applications as a biological fluorescent probe.     

Cadmium(II) and copper(II) complexes with imidazole-containing tripodal polyamine ligands: pH and anion effects on carbon dioxide fixation and assembling

A new Cd(II) complex [Cd3(L)3(mu3-CO3)](ClO4)4.2CH3CN (1) with two-dimensional (2D) network structure was obtained by reaction of an imidazole-containing tripodal polyamine ligand N1-(2-aminoethyl)-N1-(2-imidazolethyl)-ethane-1,2-diamine (L) with Cd(ClO4)2.6H2O at pH 9.0 in air. The carbonate anions (CO3(2-)) are from the hydration of the atmospheric carbon dioxide, which is the same as in the previously reported Cu(II) complex [Cu3(L)3(mu3-CO3)](ClO4)4.3CH3CN (2). However, the coordination mode of CO3(2-) in 1 is mu3-eta2:eta2:eta2 while the one in 2 is mu3-eta1:eta1:eta1. One-dimensional (1D) chain Cd(II) and Cu(II) complexes [Cd(L)Cl]ClO4.H2O (3) and [Cu(L)(H2O)](ClO4)2 (4) without CO3(2-) were prepared by a similar method as that for 1 and 2 except for the different reaction pH, namely, 3 and 4 were obtained at pH 7 while 1 and 2 were obtained at pH 9. In addition, when Cu(NO3)2 was used to react with L at pH 9, a unique 1D double-stranded helical chain complex [Cu(L)Cl]NO3.1.25H2O (5) was obtained. The results revealed that the reaction pH and the counteranion have great impact on the carbon dioxide absorption and hydration as well as on the assembling and structure of the complexes. The magnetic property of complex 2 was investigated in the temperature range of 1.8-300 K, and weak ferromagnetic coupling among the mu3-eta1:eta1:eta1-CO3(2-) bridged Cu(II) atoms was observed.     

Coordination chemistry of N-aminopropyl pendant arm derivatives of mixed N/S-, and N/S/O-donor macrocycles, and construction of selective fluorimetric chemosensors for heavy metal ions

The coordination chemistry of the N-aminopropyl pendant arm derivatives (L1c-4c) of the mixed donor macrocyclic ligands [12]aneNS2O, [12]aneNS3, [12]aneN2SO, and [15]aneNS2O2(L1a-4a) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) in aqueous solution has been investigated. The protonation and stability constants with the aforementioned metal ions were determined potentiometrically and compared, where possible, with those of the unfunctionalised macrocycles. The measured values show that Hg(II) and Cu(II) in water have the highest affinity for all ligands considered, with the N-aminopropyl pendant arm weakly coordinating the metal centres. Crystals suitable for X-ray diffraction analysis were grown for the perchlorate salt (H2L1c)(ClO4)2.dmf, and for the 1 : 1 complexes [Cd(L3a)(NO3)2](1), [Cu(L4a)dmf](ClO4)2(2), [Zn(L1c)(ClO4)]ClO4(3), [Cd(L1c)(NO3)]NO3(4), and [Hg(L2c)](ClO4)2(5). Their structures show the macrocyclic ligands adopting a folded conformation, which for the 12-membered systems can be either [2424] or [3333] depending on the nature of the metal ion. L1c-4c were also functionalised at the primary amino pendant group with different fluorogenic subunits. In particular the N-dansylamidopropyl (Lnd, n= 1-4), and the N-(9-anthracenylmethyl)aminopropyl (Lne, n= 1, 2, 4, ) pendant arm derivatives of L1a-4a were synthesised and their optical responses to the above mentioned metal ions were investigated in MeCN/H2O (4 : 1 v/v) solutions.     

Coordination chemistry of conformation-flexible 1,2,3,4,5,6-cyclohexanehexacarboxylate: trapping various conformations in metal-organic frameworks

To study the conformations of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid (H(6)L), eleven new coordination polymers have been isolated from hydrothermal reactions of different metal salts with 1e,2a,3e,4a,5e,6a-cyclohexanehexacarboxylic acid (3e+3a, H(6)L(I)) and characterized. They are [Cd(12)(mu(6)-L(II))(mu(10)-L(II))(3)(mu-H(2)O)(6)(H(2)O)(6)]16.5 H(2)O (1), Na(12)[Cd(6)(mu(6)-L(II))(mu(6)-L(III))(3)]27 H(2)O (2), [Cd(3)(mu(13)-L(II))(mu-H(2)O)] (3), [Cd(3)(mu(6)-L(III))(2,2'-bpy)(3)(H(2)O)(3)]2 H(2)O (4), [Cd(4)(mu(4)-L(VI))(2)(4,4'-Hbpy)(4)(4,4'-bpy)(2)(H(2)O)(4)]9.5 H(2)O (5), [Cd(2)(mu(6)-L(II))(4,4'-Hbpy)(2)(H(2)O)(10)]5 H(2)O (6), [Cd(3)(mu(11)-L(VI))(H(2)O)(3)] (7), [M(3)(mu(9)-L(II))(H(2)O)(6)] (M=Mn (8), Fe (9), and Ni (10)), and [Ni(4)(OH)(2)(mu(10)-L(II))(4,4'-bpy)(H(2)O)(4)]6 H(2)O (11). Three new conformations of 1,2,3,4,5,6-cyclohexanehexacarboxylate, 6e (L(II)), 4e+2a (L(III)) and 5e+1a (L(VI)), have been derived from the conformational conversions of L(I) and trapped in these complexes by controlling the conditions of the hydrothermal systems. Complexes 1 and 2 have three-dimensional (3D) coordination frameworks with nanoscale cages and are obtained at relatively low temperatures. A quarter of the L(I) ligands undergo a conformational transformation into L(II) while the others are transformed into L(III) in the presence of NaOH in 2, while all of the L(I) are transformed into L(II) in the absence of NaOH in 1. Complex 3 has a 3D condensed coordination framework, which was obtained under similar reaction conditions as 1, but at a higher temperature. The addition of 2,2'-bipyridine (2,2'-bpy) or 4,4'-bipyridine (4,4'-bpy) to the hydrothermal system as an auxiliary ligand also induces the conformational transformation of H(6)L(I). A new L(VI) conformation has been trapped in complexes 4-7 under different conditions. Complex 4 has a 3D microporous supramolecular network constructed from a 2D L(III)-bridged coordination layer structure by pi-pi interactions between the chelating 2,2'-bpy ligands. Complexes 5-7 have different frameworks with L(II)/L(VI) conformations, which were prepared by using different amounts of 4,4'-bpy under similar synthetic conditions. Both 5 and 7 are 3D coordination frameworks involving the L(VI) ligands, while 6 has a 3D microporous supramolecular network constructed from a 2D L(II)-bridged coordination layer structure by interlayer N(4,4'-Hbpy)--HO(L(II)) hydrogen bonds. 3D coordination frameworks 8-11 have been obtained from the H(6)L(I) ligand and the paramagnetic metal ions Mn(II), Fe(II), and Ni(II), and their magnetic properties have been studied. Of particular interest to us is that two copper coordination polymers of the formulae [{Cu(II) (2)(mu(4)-L(II))(H(2)O)(4)}{Cu(I) (2)(4,4'-bpy)(2)}] (12 alpha) and [Cu(II)(Hbtc)(4,4'-bpy)(H(2)O)]3 H(2)O (H(3)btc=1,3,5-benzenetricarboxylic acid) (12 beta) resulted from the same one-pot hydrothermal reaction of Cu(NO(3))(2), H(6)L(I), 4,4'-bpy, and NaOH. The Hbtc(2-) ligand in 12 beta was formed by the in situ decarboxylation of H(6)L(I). The observed decarboxylation of the H(6)L(I) ligand to H(3)btc may serve as a helpful indicator in studying the conformational transformation mechanism between H(6)L(I) and L(II-VI). Trapping various conformations in metal-organic structures may be helpful for the stabilization and separation of various conformations of the H(6)L ligand.     

pH-specific aqueous synthetic chemistry in the binary cadmium(II)-citrate system. Gaining insight into cadmium(II)-citrate speciation with relevance to cadmium toxicity

The involvement of Cd(II) in toxic manifestations and pathological aberrations in lower and higher organisms entails interactions with low and high molecular mass biological targets. To understand the relevant chemistry in aqueous media, we have launched pH-dependent synthetic efforts targeting Cd(II) with the physiological ligand citric acid. Reactions of Cd(II) with citric acid upon the addition of NaOH at pH 2.5 and pyridine at pH 3 and the addition of ammonia at pH approximately 7 led to the new complexes [Cd3(C6H5O7)2(H2O)5] x H2O (1) and (NH4)[Cd(C6H5O7)(H2O)] x H2O (2), respectively. Complexes 1 and 2 were characterized by elemental analysis, spectroscopy (FT-IR and NMR), and X-ray crystallography. Complex 1 crystallizes in the monoclinic space group P2(1)/n, with a = 18.035(6) A, b = 10.279(4) A, c = 12.565(4) A, beta = 109.02(1) degrees, V = 2202(2) A3, and Z = 4. Complex 2 crystallizes in the monoclinic space group P2(1), with a = 9.686(4) A, b = 8.484(4) A, c = 7.035(3) A, beta = 110.28(1) degrees, V = 542.3(4) A3, and Z = 2. Complex 1 is a trinuclear assembly with the citrate ligand securing a stable metallacyclic ring around one Cd(II), with the terminal carboxylates spanning into the coordination sphere of two nearby Cd(II) ions. Complex 2 contains mononuclear units of Cd(II) bound by citrate in an overall coordination number of 8. In both 1 and 2, the participating citrates exhibit three different modes of coordination, thus projecting a distinct yet variable aqueous structural chemistry of Cd(II) with physiological substrates. The pH-dependent chemistry and its apparent structural diversity validate past solution speciation studies, projecting the existence of mononuclear species such as the one in the anion of 2. The spectroscopic and structural properties of 2 emphasize the significance of the information emerging from synthetic studies that otherwise would not have been revealed through conventional solution studies, while concurrently shedding light onto the linkage of the requisite chemistry with the potential biological toxicity of Cd(II).     

Probing anion-pi interactions in 1-D Co(II), Ni(II), and Cd(II) coordination polymers containing flexible pyrazine ligands

Two flexible thioether-containing heterocyclic ligands bis(2-pyrazylmethyl)sulfide (L1) and 2-benzylsulfanylmethylpyrazine (L2) have arene rings with differing pi-acidities which were used to probe anion-pi binding in five 1-D coordination polymers formed from the metal salts Co(ClO4)2, Ni(NO3)2, and Cd(NO3)2. In {[Co(L1)(MeCN)2](ClO4)2}infinity (1), {[Ni(L1)(NO3)2]}infinity (2), and {[Cd2(L1)(MeCN)(H2O)(NO3)4].H2O}infinity (3.H2O), the symmetrical ligand L1 was bound facially to the metal center and was bridged through a pyrazine donor to an adjacent metal forming a polymer chain. The folding of L1 formed U-shaped pi-pockets in 1 and 3.H2O which encapsulated free and bound anions, respectively. The anions interacted with the pi-acidic centers in a variety of different binding modes including anion-pi-anion and pi-anion-pi sandwiching. A wider pi-pocket was formed in 2 which also contained anion-pi interactions. The polymer chains in 2 were interdigitated through a rare type of complementary T-shaped N(pyrazine)...pi interaction. In {[Co(L2)(H2O)3](ClO4)2.H2O}infinity (4.H2O) and {[Cd(L2)(H2O)(NO3)2]}infinity (5), the unsymmetrical ligand L2 chelated the metal center and bridged through a pyrazine donor to an adjacent metal forming a polymer chain. The ligand arrangement resulted in the anions in both structures being involved in only anion-pi-anion sandwich interactions. In 4.H2O, the noncoordinated ClO4- anions interacted with only one chain while in 5 the coordinated NO3- anions acted as anion-pi supramolecular synthons between chains. Comparison between the polymers formed with ligands L1 and L2 showed that only the more pi-acidic ring was involved in the anion-pi interactions.     

The synthesis of macrocyclic ether-esters,thioether-esters,and ether-thiolesters with the oxalyl moiety

A new series of macrocyclic polyether-diesler compounds ( 3-12 ) have been prepared by treating various oligoethylene glyeols or mercaplans with oxalyl chloride. The compounds prepared were: 1,4,7,10,13-pentaoxacyclopentadecane-2,3-dione ( 3 ), 1,4,7,1 3-tetraoxa-10-thiacyclopenta-decane-2,3-dione ( 4 ), 1,4,10-lrioxa-7,13-dithiacyclopenladecane-2,3-dione ( 5 ), 1,4,7,10,13,16-hexaoxacyclooctadecane-2,3-dione ( 6 ), 1,4,7,10,13, 16-hexaoxacyclooctadecane-2,3,11,12-tetra-one ( 7 ), 1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane-2,3,11,12-tetraone ( 8 ), 7,16-dioxa-1,4, 10,13-letralhiacyclooctadecane-2,3,11,12-tctraone ( 9 ), 1,4,7,10,13,16-hexathiacyclooctadecane-2,3,11,12-tetraone ( 10 ), 1,4,7,10,13,16,19-heptaoxacyclohencicosane-2,3-dione (11), and 1,4,7, 10,13,16,19,22-octaoxacyclolelracosane-2,3,14,15-letraone ( 12 ).     

Synthesis, spectroscopic and redox properties of the copper(II) complexes of N-(di-methylphenyl)-3,5-Bu2t-salicylaldimines

A series of copper(II) complexes (CuL2x) with new N-di-methylphenyl-3,5-Bu2t-salicylaldimines (L(x)H) were prepared and characterized by IR, UV/vis, 1H NMR, ESR, cyclic voltammetry techniques and chemical oxidation. L(x)H ligands have been found selectively bind to a Cu(II), rather than to Ni(II), Co(II), Mn(II), VO(IV), Zn(II) and Cd(II). ESR examinations of the CuL2x complexes demonstrate that they exist in magnetically diluted mononuclear or coupled triplet-state structures in the solid. The temperature dependent (113-283 K) intensity of the powder ESR spectra for some CuL2x is characteristic of ferromagnetic coupling (J > 0). The reduction potentials of CuL2x in DMSO are sensitive to aniline moieties. Chemical oxidation of CuL2x with (NH4)2[Ce(NO3)6] in CHCl3 and MeCN solutions at 300 K affords gradually disappearance of their ESR signals and dramatic changes in the electronic spectra as well as the appearance of new maximum bands at 530-672 (CHCl3) and 670-700 nm (MeCN), suggesting generation of Cu(II)-phenoxyl radical species.