Ditopic bis(oxazolines): Synthesis and structural studies of zinc(II), copper(II) and nickel(II) complexes

The synthesis, crystal structures, magnetic and spectroscopic properties of zinc(II), nickel(II) and copper(II) dinuclear complexes 2-4 of a novel dinucleating polyoxazoline ligand 1 are reported. X-ray analysis revealed that the three complexes are centrosymmetric dinuclear species with an overall S shape, the bisoxazoline moieties pointing toward the aromatic core of the molecule. Magnetic susceptibility measurements suggest that there is a very weak exchange interaction between the copper or nickel ions in complexes 3 and 4.     

Structural and fluorescent study of zinc complexes of dansyl aminoquinoline

We have shown previously that 8-(5′-N,N-dimethylamino-1′-naphthalene)-sulfonamidoquinoline (DANQUIN) demonstrated a remarkable selectivity and sensitivity for the Zn(II) ion. In this work, the crystal structures of DANQUIN, Cu(DANQUIN)₂ and Cu(DANPY)₂ (DANPY, N-2-picolyl-(5′-N,N-dimethylamino-1′-naphthalene)-sulfonamide) are reported and compared with the simulated structure of Zn(DANQUIN)₂, which is important for the understanding of the factors that govern the fluorescence of DANQUIN. Free DANQUIN mainly displays the fluorescence of the dansyl group at 547 nm while the Zn(II)-DANQUIN complex mainly shows the enhanced fluorescence of aminoquinoline at 469 nm, while the emission of the dansyl group shifted to 517 nm with an almost constant intensity. This result demonstrates the advantage of this hybrid fluorescent chemosensor for Zn(II), and also makes it a potential candidate for ratiometric Zn(II) detection.     

Dinuclear nickel(II) and zinc(II) complexes of 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methylphenol

Reaction of the symmetrical proligand H₂L with metal(II) acetate and a counteranion to promote crystallisation has given the homodinuclear complexes [Zn₂L(OAc)₂](BF₄)]·2MeOH and [Ni₂L(OAc)₂](BF₄)]·2MeOH the crystal structures of which are reported. These show the presence of a triply bridging (μ-cresolato)bis(μ-carboxylato) dimetal core.     

Cobalt(II), nickel(II) and zinc(II) do not bind to intra-helical N(7) guanine positions in the B-form crystal structure of d(GGCGCC)

Three novel X-ray crystal structures for the DNA hexamer d(GGCGCC) in the B-form complexed to divalent cobalt, nickel and zinc ions have been determined to a resolution of 2.9–3.0 Å. The structures were isomorphous and had five DNA strands and five metal cations per asymmetric unit. In all three cases, divalent metal cations were coordinated only to the terminal guanine residue at the N(7) position, with no metal ions binding to non-terminal guanine positions. Water molecules bound to the metal cations interacted with neighboring guanine residues 3 to the ones to which the cations were coordinated, affecting the propeller twist. Even though DNA occupied only about 35% of the unit cell volume, it is interesting that the few interactions involving the metal cations were sufficient to stabilize the crystal lattice. As well as lending support to the proposal that these metals do not coordinate to B-DNA in a stable manner, the results presented here also extend the crystallographic evidence for this phenomenon to the GGC and CGC sequences for all three metal cations.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Abbreviations MPD 2-methyl-2,4-pentanediol - TAPS N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonate     

Synthesis and structural diversity of 2-pyridylmethylideneamine complexes of zinc(II) chloride

The addition reactions of zinc(II) chloride to N-substituted pyridine-2-carbaldimines [Py-CHNR, R = Me (1a), Ph (1b), Bz (1c), allyl (1d)] lead to different complexes dependent on the N-bound substituent R. The 1:1 complexes show molecular structures of the type [(Py-CHNR)ZnCl₂] for R = methyl (2a), phenyl (2b), and allyl (2d) with a distorted tetrahedral environment for the zinc atom. The zinc complex with the N-methylated pyridine-2-carbaldimine also forms a dimer of the type [(Py-CHNR)ZnCl₂]₂ (2a)₂ with a square pyramidal coordination sphere of zinc. A 3:2 stoichiometry is observed for R = benzyl and an ion pair of the type [Zn(Py-CHNR)₃]²⁺ [ZnCl₄]²⁻ (2c) is found in the solid state.     

Protective role of zinc in nickel induced hepatotoxicity in rats

This study was planned to determine the protective role of zinc, if any, in attenuating the toxicity induced by nickel sulfate in rat liver. Female Sprague Dawley (SD) rats received either nickel alone in the dose of 800 mg/l in drinking water, zinc alone in the dose of 227 mg/l in drinking water, and nickel plus zinc or drinking water alone for a total duration of eight weeks. The effects of different treatments were studied on various parameters in rat liver which include antioxidant enzymes, levels of nickel and zinc and histoarchitecture at the light microscopic level. Further, the activities of hepatic marker enzymes AST and ALT were also studied in rat serum. Nickel treatment to the normal control animals, resulted in a significant increase in lipid peroxidation and enzyme activities of catalase and glutathione-S-transferase. On the contrary, nickel treatment to normal rats caused a significant inhibition in the levels of reduced glutathione. Superoxide dismutase activity was found to be decreased which however was not significant. Interestingly, when Zn was supplemented to nickel treated rats, the activities of catalase, and glutathione-S-transferase and the levels of GSH and lipid peroxidation came back to within normal limits. Activities of serum AST and ALT were increased significantly following nickel treatment to normal rats. Simultaneous zinc administration to nickel treated rats tended to restore the altered levels of AST and ALT. Normal control and zinc treated animals revealed normal histology of liver. On the other hand, nickel treated animals showed alterations in normal hepatic histoarchitecture which comprise of vacuolization of the hepatocytes and dilatation of sinusoids as well as increase in the number of bi-nucleated cells. Administration of zinc to nickel treated rats resulted in marked improvement in the structure of hepatocytes, thus emphasizing the protective potential of zinc in restoring the altered hepatic histoarchitecture. The nickel administration to normal rats indicated increased concentrations of nickel and decreased concentrations of zinc. However, zinc effectively brought the altered levels of nickel and zinc to within normal range. The study concludes that zinc has the potential in alleviating the toxic effects of nickel in rat liver because of its property to induce metallothionein (S-rich protein) as a free radical scavenger, or its indirect action in reducing the levels of oxygen reactive species.     

Novel halogen-bridged bisphosphine nickel(II) complexes

Reaction of [NiCl₂(dtbpe)] (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) with one equivalent of NaBAr^F₄ (BAr^F₄ = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) gives the dinuclear chloro-bridged nickel complex [Ni₂(μ-Cl)₂(dtbpe)₂](BAr^F₄)₂ (1). [Ni(solv)₆](BF₄)₂ reacts with dtbpe to give, depending on the solvent, the fluoro-bridged complex [Ni₂(μ-F)₂(dtbpe)₂](BF₄)₂ (2) (solv = THF) or the mononuclear chelate complex [Ni(MeCN)₂(dtbpe)](BF₄)₂ (3) (solv = MeCN). In 1-3, nickel cations are coordinated in a square-planar fashion according to X-ray crystallography. No Ni-Ni interaction was observed in dinuclear halogen-bridged complexes 1 and 2.     

Lightinduced sulfur-dealkylation of phosphino-thioether nickel(0) complexes

The observation of homolytic S---CH₃ bond cleavage in (Ph₂P(o-C₆H₄)SCH₃)₂Ni⁰ under photochemical conditions has prompted further investigation of nickel(0) complexes and their stability. Tetradentate P₂S′₂ donor ligands (S′ = thioether type S donor) with aromatic rings incorporated into the P to S links, Ph₂P(o-C₆H₄)S(CH₂)₃S(o-C₆H₄)PPh₂ (arom-PSSP), or the S to S links, Ph₂P(CH₂)₂SCH₂(o-C₆H₄)CH₂S(CH₂)₂PPh₂ (PS-xy-SP), have been used to form four-coordinate, square planar nickel(II) complexes, [(arom-PSSP)Ni](BF₄)₂ (2) and [(PS-xy-SP)Ni](BF₄)₂ (3). The bidentate and tetradentate ligands, Ph₂P(o-C₆H₄)SCH₂CH₃ (arom-PSEt) and Ph₂P(CH₂)₂S(CH₂)₃S(CH₂)₂PPh₂ (PSSP), give similar complexes, [(arom-PSEt)₂Ni](BF₄)₂ (1) and [(PSSP)Ni](BF₄)₂ (4), respectively. Cyclic voltammograms of the Ni¹¹ complexes in CH₃CN show two reversible redox events assigned to and . The one-electron reduction product produced by stoichiometric amounts of Cp₂Co can be characterized by EPR. At 100 K rhombic signals show hyperfine coupling to two phosphorus atoms. Complete bulk chemical reduction of complexes 1, 2, 3 and 4 with Na/Hg amalgam provided the corresponding nickel(0) complexes 1^R, 2^R, 3^R and 4^R which were isolated as red solutions or solids characterized by magnetic resonance properties and reaction products. Photolysis of these nickel(0) complexes leads to S-dealkylation to produce alkyl radicals and dithiolate nickel(II) complexes. Complex 3 crystallized in the monoclinic space group P_2t/c with a=20.740(5), B=9.879(3), C=17.801(4) åA, ß=92.59(2)°, V=3644(2) ų and Z=4; complex 4: P2₁/c with A=13.815(4), B=13.815(4), C=15.457(5) åA, V=3365.4(14) ų and Z=4.     

P Chemical shift anisotropies of dihalobis(trialkylphosphine)nickel(II) complexes

The ³¹P CP-MAS NMR spectra of trans-square-planar complexes of dihalonickel(II) complexes with tribenzyl-, tricyclohexyl- and tricyclohexylmethylphosphines have been examined and the chemical shift tensors determined. The spans, δ₁₁-δ₃₃, of the tensor components decrease with change in the halide, Cl > Br > I, for all the tertiary phosphines due principally to the deshielding of the δ₃₃ component.     

Self-assembled monolayers of bis(salicylaldiminato)nickel(II) Schiff-base complexes: synthesis and structure

The synthesis of two derivatized Ni^II Schiff-base complexes is reported. Self-assembled monolayers (SAMs) have been obtained by reaction of coupling layers, functionalized glass substrates and the derivatized complex precursors. The self-assembled films have been characterized by contact angle measurements, X-ray photoelectron spectroscopy, and UV-Vis absorption spectroscopy. A structure of these SAMs is proposed on the basis of spectroscopic data and molecular metrical parameters.     

Antiplasmodial activity of targeted zinc(II)-dipicolylamine complexes

This study measured the antiplasmodial activity of nine zinc-dipicolylamine (ZnDPA) complexes against three strains of Plasmodium falciparum, the causative parasite of malaria. Growth inhibition assays showed significant activity against all tested strains, with 50% inhibitory concentrations between 5 and 600 nM and almost no toxic effect against host cells including healthy red blood cells. Fluorescence microscopy studies with a green-fluorescent ZnDPA probe showed selective targeting of infected red blood cells. The results suggest that ZnDPA coordination complexes are promising antiplasmodial agents with potential for targeted malaria treatment.     

Ternary nickel(II) complexes as hydrolytic DNA-cleavage agents

A series of small model complexes made from Ni(II) and the ligands ethylenediamine (en), histamine (hist), and histidylleucine (HisLeu) were prepared and studied as potential hydrolytic DNA-cleavage agents. The stability constants and species-distribution curves for these complexes were determined as a function of pH. The 1 : 1 : 1 ternary complexes [Ni(II)(en)(HisLeu)] (1) and [Ni(II)(hist)(HisLeu)] (2) were the only major species present at the physiologically relevant pH of 6-7, as further corroborated by ESI-MS analysis. The complex geometries of 1 and 2 were analyzed by UV/VIS experiments and molecular dynamics (MD) simulations. Both ternary complexes were found to intercalate with DNA, as shown by UV/VIS, thermal-denaturation, and fluorescence-titration studies with ethidium bromide (EB). The intrinsic binding constants (K(b)) for the bound complexes 1DNA and 2DNA were determined as 150 and 290, resp. Gel-electrophoresis experiments revealed that 1 and 2 cleave supercoiled (type-I) to nicked-circular (type-II) DNA at physiological pH, with rate constants of 0.64 and 0.75 h(-1), resp. A tentative mechanism for this hydrolytic cleavage is proposed.     

Structural and spectroscopic comparison of five-coordinate cobalt(II) and nickel(II) thiolato complexes with the related four-coordinate complexes

Five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co and Ni) (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion and HSMeIm = 2-mercapto-1-methylimidazole), were synthesized. These complexes were compared with the corresponding Cu(II) and Zn(II) complexes with the same ligands and were also compared with the related four-coordinate complexes [L1M(SC₆F₅)] (HSC₆F₅ = pentafluorobenzenthiol). All the complexes were characterized by X-ray crystallography and UV-Vis absorption, IR, ¹H NMR, and other spectroscopic techniques. All five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co, Ni, and Cu), form a distorted square pyramidal structure with a high spin state, and only [L1Zn(SMeIm)] takes a four-coordinate structure with a distorted tetrahedral configuration. The N21-M-S bond angles of the obtained five-coordinate complexes were proportional to the corresponding d value, which comes from between the equatorial basal plane with N4S ligand donor sets and metal ion. These observations and M-S bond distances affect on UV-Vis and far-IR spectral behavior.     

Organometallic nickel(II) complexes with dithiophosphate, dithiophosphonate and monothiophosphonate ligands

The hydroxo complex [NBu₄]₂[Ni₂(C₆F₅)₄(μ-OH)₂] reacts with ammonium O,O^′-dialkyldithiophosphates, O-alkyl-p-methoxyphenyldithiophosphonate acids and ammonium O-alkylferrocenyldithiophosphonates in dichloromethane under mild conditions to give, respectively, [NBu₄][Ni(C₆F₅)₂{S(S)P(OR)₂}] (R=Me (1), Et (2), ⁱPr (3)) and [NBu₄][Ni(C₆F₅)₂{S(S)P(OR)Ar}] (Ar=p-MeOC₆H₄, R=Me (4), Et (5), ⁱPr (6); Ar=ferrocenyl; R=Me (7), Et (8), ⁱPr (9)). The monothiophosphonate nickel complexes [NBu₄][Ni(C₆F₅)₂{S(S)P(OR)(ferrocenyl)}] (R=Et (10), ⁱPr (11)) are obtained by reaction of the hydroxo complex with O-alkylferrocenyldithiophosphonate acids. Analytical (C, H, N, S), conductivity, and spectroscopic (IR, ¹H, ¹⁹F and ³¹P NMR, and FAB-MS) data were used for structural assignments. A single-crystal X-ray diffraction study of [NBu₄][Ni(C₆F₅)₂{S(S)P(OMe)(p-MeOC₆H₄)}] (4) and [NBu₄][Ni(C₆F₅)₂{S(O)P(OEt)(ferrocenyl)}] (10) shows that in both cases the coordination around the nickel atom es essentially square planar with NiC₂S₂ and NiC₂SO central cores, respectively.     

Synthesis and characterization of nickel(II) complexes bearing 2-(imidazol-2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/oxazoles and their polymerization of norbornene

Series of 2-R₁-6-(1-R₂-4,5-diphenyl-1H-imidazol-2-yl)pyridine (R₁ = R₂ = H, L1; R₁ = Me, R₂ = H, L2; R₁ = H, R₂ = Me, L3; R₁ = R₂ = Me, L4), 2-(6-R₁-pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (R₁ = H, L5; R₁ = Me, L6) and 2-(pyridin-2-yl)phenanthro[9,10-d]oxazole (L7) were synthesized and used to prepare their corresponding dihalonickel complexes (C1-C9). All organic compounds and nickel complexes were characterized by elemental and spectroscopic analyses. Molecular structures of C1, C4, C5 and C8 were confirmed by the single-crystal X-ray diffraction analysis. The single-crystal X-ray analysis revealed complex C1 as a distorted octahedral geometry, complex C4 as a distorted square pyramidal geometry, complex C5 as a distorted trigonal bipyramidal configuration, and complex C8 as a tetrahedral geometry. Upon activation with methylaluminoxane (MAO), the nickel complexes showed good activity towards norbornene polymerization through main additional and minor ring-opening metathesis. The reaction parameters such as norbornene concentration, reaction temperature and different coordinate environments caused by the ligands affected their catalytic performances.     

Distribution of nickel,zinc, and copper in rat organs after oral administration of nickel(II) chloride

The distribution of Ni administered as NiCl₂ · 6H₂O in the drinking water (300 and 1200 ppm Ni for 90 d) was studied using male Wistar rats. Next, the effect of Ni on the concentration of zinc (Zn) and copper (Cu) in selected organs and serum was measured. The metals were analyzed in the liver, kidney, lung, spleen, brain, and serum by electrothermal (Ni) or flame (Zn, Cu) atomic absorption spectrophotometry. The results indicate that exposed rats drank less nickel solutions than the volume of water drunk by controls, but there was no mortality of animals. In comparison to control animals, a very high increase in Ni levels was found in the kidney and then lung and serum of all exposed rats. In the liver, spleen, and brain, the metal accumulation was lower. A directly proportional relation between the nickel intake and its deposition was observed in the collected organs and in the serum. The metal level did not change significantly in the course of exposure (the first analysis was after 30 d). The administration of 300 ppm Ni did not affect the zinc and copper concentration in studied organs, except the serum, where zinc content was significantly reduced. At a dose of 1200 ppm Ni, these metals were found to be depressed in the liver, kidney, serum (zinc), and copper in the kidney.     

Synthesis and chemical characterization of Cu, Ni and Zn complexes of 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole ligands

The synthesis and structural characterization of Ni^II, Cu^II and Zn^II complexes of two chelating 1,2,4-oxadiazole ligands, namely 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole (bipyOXA) and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole (pyOXA), is here reported. The formed hexacoordinated metal complexes are [M(bipyOXA)₂(H₂O)₂](ClO₄)₂ and [M(pyOXA)₂(ClO₄)₂], respectively (M = Ni, Cu, Zn). X-ray crystallography, ¹H and ¹³C NMR spectroscopy and C, N, H elemental analysis data concord in attributing them an octahedral coordination geometry. The two coordinated pyOXA ligands assume a trans coplanar disposition, while the two bipyOXA ligands are not. The latter result is a possible consequence of the formation of H-bonds between the coordinated water molecules and the nitrogen atom of the pyridine in position 5 of the oxadiazole ring. The expected splitting of the d metal orbitals in an octahedral ligand field explains the observed paramagnetism of the d⁸ and d⁹ electron configuration of the nickel(II) and copper(II) complexes, respectively, as determined by the broadening of their NMR spectra.     

[S2], [S3], and [N3] coordination modes of hydrotris(thioxotriazolyl)borato. Zinc, nickel, cobalt, and bismuth complexes

The ligand hydrotris(1,4-dihydro-3-methyl-4-phenyl-5-thioxo-1,2,4-triazolyl)borato (Tr^Ph,Me) was synthetized as natrium salt and the complexes [Zn(Tr^Ph,Me)₂] · 7.5H₂O · 1.5CH₃CN (2a), [Zn(Tr^Ph,Me)₂] · 8DMF (2b), [Co(Tr^Ph,Me)₂] · 8DMF (3a), [Ni(Tr^Ph,Me)₂] · H₂O · 6DMSO (4a), [Bi(Tr^Ph,Me)₂]NO₃ (5), have been isolated and structurally characterized by X-ray diffraction. In the zinc derivatives the ligand adopts different denticity and coordination modes, η² and [S₂] for 2a and η³ and [N₃] for 2b, depending on the crystallization solvent, giving rise to tetrahedral and octahedral geometry, respectively. In the octahedral cobalt and nickel complexes the ligand is η³ and [N₃] coordinated whereas in the bismuth complex the η³ and [S₃] coordination is exhibited.     

A new tris(2-furyl) substituted pyrazolylborate ligand and its zinc complex chemistry

The new ligand hydrotris(3-(2′-furyl)-5-methylpyrazolyl)borate (Tp^Fu,Me) was prepared by the usual procedure. With zinc salts, it forms the Tp^Fu,MeZn-X complexes (X = Cl, Br, I, NCS, CH₃COO, CF₃COO). With zinc perchlorate, the bis-ligand complex Zn(Tp^Fu,Me)₂ is formed preferrably, but by carefully controlling the reaction conditions, the “enzyme model” Tp^Fu,MeZn-OH could be obtained. The latter models carbonic anhydrase by inserting CO₂ and CS₂ in methanol producing Tp^Fu,MeZn-OCOOMe and Tp^Fu,MeZn-SCSOMe. It models hydrolases by the hydrolytic cleavage of tris(p-nitrophenyl)phosphate and γ-thiobutyrolactone. It does not hydrolyse trifluoroacetamide, but instead deprotonates it, yielding Tp^Fu,MeZn-NHCOCF₃.     

Coordination modes of the novel bifunctional nitrogen ligands 8-(2-pyridyl)quinoline and 8-(6-methyl-2-pyridyl)quinoline towards palladium and platinum. X-ray crystal structures of (8-(2-pyridyl)quinoline)Pd(Me)Cl, (8-(2-pyridyl)quinoline)-Pd(C(O)Me)Cl and (8-(2-pyridyl)quinoline)Pd(PEt3)Cl2

The coordination chemistry of the new bidentate nitrogen ligands 8-(2-pyridyl)quinoline (8-PQ) and 8-(6-methyl-2-pyridyl)quinoline (Me-8-PQ) towards palladium and platinum has been studied. Several (NN)Pd(R)Cl and (NN)Pd(alkene) complexes have been synthesized. The complex (8-PQ)Pd(Me)Cl has been characterised by a single crystal X-ray determination (crystal data triclinic space group

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). A fast CO insertion occurs into the palladium-carbon bond of the complexes (NN)Pd(Me)Cl providing the (NN)Pd(C(O)Me)Cl complexes. For (8-PQ)Pd(C(O)Me)Cl an X-ray structure determination has been carried out (crystal data: monoclinic space group P2₁/c with a=9.084(4), B=10.179(3), C=16.400(3) Å, β=95.59(2)°, V=1509.2(9) ų, R=0.043, Z=4). Unexpected in both molecular structures is the large dihedral angle between the plane of the bidentate nitrogen ligand and the coordination plane of the palladium. Both bidentate coordinating ligands 8-PQ and Me-8-PQ show a relatively large bite angle. A monodentate coordination mode has been observed for the complexes (NN)M(PEt₃)Cl₂ (M=Pd, Pt), as the pyridyl group of the ligand is coordinated to the metal while the quinoline group is dissociated from the metal, which is shown in the X-ray structure determination for the complex (8-PQ)Pd(PEt₃)Cl₂ (crystal data: monoclinic space group P2₁/a with A=15.736(2), B=7.782(1), C=18.255(3) Å, β=102.98(1)°, V=2178.3(6) ų, R=0.062, Z=4).