Elucidation of the DNA-interacting properties and anticancer activity of a Ni(II)-coordinated mithramycin dimer complex

Mithramycin (Mith) forms a drug-metal complex with a 2:1 stoichiometry by chelation with a Ni(II) ion, which was determined using circular dichroism spectroscopy. Mith exhibits an increased affinity (~55 fold) for Ni(II) in the presence of DNA compared to the absence of DNA, suggesting that DNA acts as an effective template to facilitate chelation. Also, we characterized the DNA-acting properties of a Ni(II) derivative of Mith. Kinetic analysis using surface plasmon resonance and UV melting studies revealed that Ni^II(Mith)₂ binds to duplex DNA with a higher affinity compared to Mg^II(Mith)₂. The thermodynamic parameters revealed a higher free energy of formation for duplex DNA in the presence of Ni^II(Mith)₂ compared to duplex DNA in the presence of Mg^II(Mith)₂. The results of a DNA-break assay indicated that Ni^II(Mith)₂ is capable of promoting one-strand cleavage of plasmid DNA in the presence of hydrogen peroxide; the DNA cleavage rate of Ni^II(Mith)₂ was calculated to be 4.1 × 10^?4 s^?1. In cell-based experiments, Ni^II(Mith)₂ exhibited a more efficient reduction of c-myc and increased cytotoxicity compared to Mith alone because of its increased DNA-binding and cleavage activity. The evidence obtained in this study suggests that the biological effects of Ni^II(Mith)₂ require further investigation in the future.     

Nonphysiological binding of ethylene by plants

Ethylene binding to seedling tissue of Vicia faba, Phaseolus vulgaris, Glycine max, and Triticum aestivum was demonstrated by determining transit time required for ethylene to move through a glass tube filled with seedling tissue. Transit time for ethylene was greater than that for methane indicating that these tissues had an affinity for ethylene. However, the following observations suggest that the binding was not physiological. Inhibitors of ethylene action such as Ag⁺ ions and CO₂ did not decrease binding. Mushrooms which have no known sites of ethylene action also demonstrated ethylene binding. The binding of acetylene, propylene, ethylene, propane, and ethane more closely followed their solubility in water than any known physiological activity.     

Hydroxylation of a methyl group: synthesis of [Cu2(btmmO)2I] and of [Cu2(btmmO)2] containing the novel ligand {bis(trimethylmethoxy)guanidino}propane (btmmO) by copper-assisted oxygen activation

The reaction of the bisguanidine copper(I) compounds [Cu(btmgp)I] and [Cu₂(btmgp)₂][PF₆]₂ with molecular oxygen afforded at low temperatures complexes containing the bis-μ-oxo dicopper(III) core, which is capable to hydroxylate one of the N-CH₃-groups of the {bis(tetramethyl)guanidino}propane ligands. The formation of the novel ligand {bis(trimethylmethoxy)guanidino}propane (btmmO) is reported as it represents the first hydroxylation of a N-methyl group. The products of this reaction are novel alkoxo-bridged binuclear copper complexes, namely [Cu₂(btmmO)₂I]⁺ containing an iodide ion in a novel bridging situation, as well as [Cu₂(btmmO)₂]²⁺ which have been identified in their complex salts and [Cu₂(btmmO)₂][PF₆]₂ · 2MeCN, respectively. Concomitantly, the hydroxo-bridged binuclear copper compounds [Cu₂(btmgp)₂(μ-OH)₂]I₂ and [Cu₂(btmgp)₂(μ-OH)₂][PF₆]₂ are formed as couple products. The formation of the bis-μ-oxodicopper(III) complexes was monitored by UV/Vis-spectroscopy, and the reaction products were characterised by X-ray diffraction, vibrational spectroscopy and elemental analysis.     

Stimulation of rice coleoptile growth by ethylene

Summary The growth rate of rice coleoptiles is increased by low concentrations of ethylene, especially in oxygen concentrations lower than air; carbon dioxide enhanced this response. C₂H₄ is produced by rice seedlings, and this production is also enhanced by carbon dioxide. Ethane and propane were produced in trace amounts but were inactive in growth stimulation as were also methane, propylene, and butane.This investigation was supported in part by research grants (FD-00071 and GM-12885) from the U. S. Public Health Service.     

Conformational flexibility of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L) in [(L)Co(H2O)3]Cl2 and [(L)Ni(H2O)2Cl]Cl·H2O. Molecular structures and non-covalent interactions

Using a non-planar tridentate ligand 2,6-bis(pyrazol-1-ylmethyl)pyridine (L⁵) two new coordination complexes [(L⁵)Co^II(H₂O)₃]Cl₂ (1) and [(L⁵)Ni^II(H₂O)₂Cl]Cl·H₂O (2) have been synthesized and structurally characterized. Complex 1 has N₃O₃ distorted octahedral environment around Co^II with coordination by L⁵ (two pyrazole and a pyridine nitrogen in a facial mode) and three water molecules. Complex 2 has N₃O₂Cl distorted octahedral geometry around Ni^II with meridional L⁵ coordination, two water molecules, and a Cl⁻ ion. Analysis of the crystal packing diagram reveals the involvement of solvent (water as metal-coordinated and as solvent of crystallization) and counteranion (Cl⁻) to play significant roles in generating 1D chains, involving O-H···Cl, and O-H···O interactions.     

Separation of hexahistidine fusion proteins with immobilized metal ion affinity chromatographic (IMAC) sorbents derived from MN+‐tacn and its derivatives

The capabilities of a new class of immobilized (im) metal ion chelate complexes (IMCCs), derived from 1,4,7‐triazacyclononane (tacn), bis(1,4,7‐triazacyclononyl) ethane (dtne) and bis(1,4,7‐triazacyclononyl)propane (dtnp) complexed with the borderline metal ions Cu²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Co²⁺, and Cr³⁺, for the purification of proteins have been investigated. In particular, the binding behavior of a model protein, the C‐terminal hexahistidine tagged recombinant fusion protein Schistosoma japonicum glutathione S‐transferase‐Saccharomyces cerevisiae mitochondrial ATP synthase δ‐subunit (GST‐δATPase‐His₆), with these new immobilized metal ion affinity chromatographic (IMAC) sorbents was compared to the properties of a conventional sorbent, derived from immobilized Ni(II)‐nitrilotriacetic acid (im‐Ni²⁺‐NTA). Investigations using the recombinant GST‐δATPase‐His₆ and recombinant S. japonicum glutathione S‐transferase (GST) lacking a hexahistidine tag have confirmed that the C‐terminal tag hexahistidine residues were required for the binding process to occur with these IMAC systems. The results also confirm that recombinant fusion proteins such as GST‐δATPase‐His₆ can be isolated in high purity with these IMAC systems. Moreover, these new macrocyclic systems manifest different selectivity features as a function of pH or ionic strength when compared to the conventional, unconstrained iminodiacetic acid (IDA) or NTA chelating ligands, complexed with borderline metal ions such as Cu²⁺ or Ni²⁺, as IMAC systems. Biotechnol. Bioeng. 2009;103: 747–756. © 2009 Wiley Periodicals, Inc.     

Interaction of Ni(II) with 2,3-dihydroxybenzoic acid

The reaction of NiCl₂·6H₂O with 2,3-dihydroxybenzoic acid=L in n-PrOH:H₂O=1:1 solution, produced the complex {[Ni₅L₅(OH)₇]K₄·13H₂O}_n. Its structure was investigated using elemental analysis, IR, UV–Vis, NMR and ES MS spectroscopy. The complex is unstable in aqueous solution and its decomposition scheme was proposed on the basis of NMR and ES MS spectra. This may contribute to the understanding of oxidative degradation of catecholic derivatives by Ni(II), as well as to other similar ones.     

Simultaneous butyrate oxidation by Syntrophomonas wolfei and catalytic olefin reduction in absence of interspecies hydrogen transfer

Methanogenesis by a Syntrophomonas wolfei/ Methanospirillum hungatei coculture was inhibited in presence of ethylene and the hydrogenation catalyst Pd-BaSO₄. However, butyrate oxidation by S. wolfei continued and ethylene was reduced to ethane. Per mol of butyrate oxidized, 2.4 mol acetate was produced and 0.8 mol ethylene was reduced. Acetylene, propylene and butene were less effective as H₂ acceptors than ethylene, and addition of bromoethanesulfonic acid was necessary to inhibit methanogenesis in the presence of the two longer-chain olefins. Other hydrogenation catalysts were less effective in the order Pd-charcoal < PE-asbestos < Pd-PEI beads < Pt-Al₂O₃, Pd-CaCO₃. Optimal ethylene hydrogenation was achieved with still incubation in presence of 7.2 mg Pd-BaSO₄ and 0.7 g sand per ml medium. The higher catabolic rate of S. wolfei in presence of the methanogen indicated that the biological H₂ removal mechanism was more efficient than the catalytic olefin reduction.Abbreviations BES bromoethane sulfonic acid - VFA volatile fatty acid     

XPS evidence for the formation of Ni(II) complexes on treated activated carbon

X-ray photoelectron spectroscopy (XPS) was applied to a solid-state investigation on adsorbed systems obtained by contacting different samples of an activated carbon (Chemviron Filtrasorb 400) with solutions containing (a) 1,10-phenanthroline (phen); (b) NiCl₂·6H₂O. (c) Ni²⁺ ions and phen in a 1:3 molar ratio.XPS results on these systems are discussed with particular regard to the chemical state of the ligand (interaction of functional groups with the substrate) and of the metal ions on carbon (assessment of Ni oxidation state; detection of Ni complexes on carbon and information on their stoichiometries and structures). Various effects of successive chemical treatments on the above reported carbon species were also revealed by XPS, such as:(i) the formation of a ‘carbon–ligand’ system (activated carbon with ligand firmly present on it) after acid elution of the activated carbon treated with Ni–phen complexes in solution, and (ii) the adsorption of Ni²⁺ ions on this ‘carbon–ligand’ system, with fomation of Ni–phen complexes on carbon.     

3D hydrogen bonded metal-organic frameworks constructed from [M(H2O)6][M′(dipicolinate)2] · mH2O (M/M′ = Zn/Ni or Ni/Ni). Identification of intercalated acyclic (H2O)6/(H2O)10 clusters

New heterodinuclear Zn^II/Ni^II (1) and homodinuclear Ni^II/Ni^II (2) water-soluble and air stable compounds of general formula [M(H₂O)₆][M′(dipic)₂] · mH₂O have been easily prepared by self-assembly of the corresponding metal(II) nitrates with dipicolinic acid (H₂dipic) in water solution at room temperature.  The compounds have been characterized by IR, UV/Vis and atomic absorption spectroscopies, elemental and X-ray single crystal diffraction (for 1 · 4H₂O and 2 · 5H₂O) analyses.  3D infinite polymeric networks are formed via extensive hydrogen bonding interactions involving all coordinated and crystallization water molecules, and all dipicolinate oxygens, thus contributing to additional stabilization of dimeric units, metal-organic chains and 2D layers.  In 1 · 4H₂O, the latter represent a rectangular-grid 2D framework with multiple channels if viewed along the c crystallographic axis, while in 2 · 5H₂O intercalated crystallization water molecules are associated to form acyclic nonplanar hexameric water clusters and water dimers which occupy voids in the host metal-organic matrix, with a structure stabilizing effect via host-guest interactions.  The hexameric cluster extends to the larger (H₂O)₁₀ one with an unusual geometry (acyclic helical octamer with two pendent water molecules) by taking into account the hydrogen bonds to water ligands in [Ni(H₂O)₆]²⁺.  The obtained Zn/Ni compound 1 relates to the recently reported family of heterodimetallic complexes [M(H₂O)₅M′(dipic)₂] · mH₂O (M/M′ = Cu/Co, Cu/Ni, Cu/Zn, Zn/Co, Ni/Co, m = 2, 3), what now allows to establish the orders of the metal affinity towards the formation of chelates with dipicolinic acid (Co^II > Ni^II > Zn^II > Cu^II) or aqua species (Co^II < Ni^II < Zn^II < Cu^II).     

Effects of Ni(2+), Co(2+), and Mn(2+) on desensitized butyrylcholinesterase prepared from human serum

Human serum butyrylcholinesterase (BChE) has been converted into a stable but less active desensitized form when heated at 45°C for 24 h. The desensitized BChE follows Michaelis-Menten kinetics, whereas native enzyme exhibits slightly negative cooperativity with respect to butyrylthiocholine binding. In this study, we investigated the effects of Ni²⁺, Co²⁺, and Mn²⁺ on the desensitized BChE. It is found that all three ions were noncompetitive inhibitors of the desensitized BChE, and K _i values have been determined as 7.816±1.060 mM, 48.722±4.635 mM, and 84.795±5.249 mM for Ni²⁺, Co²⁺, and Mn²⁺, respectively. In our previous study, these ions were linear mixed-type inhibitors of the native BChE. This finding confirms that desensitized BChE changes to a different conformation than native BChE. From the comparison of K _i values of the trace elements, it can be said that Ni²⁺ is a more effective inhibitor of the desensitized BChE than Co²⁺ and Mn²⁺.     

Synthesis, crystal structure, hydrogen bonding and spectroscopy of Co, Mn and Ni oxalate complexes with the ligand (N,N′-bis(2-pyridylmethyl)-1,3-propanediamine)

Three new compounds are reported with the tetradentate ligand (N,N′-bis(2-Pyridylmethyl)-1,3-propanediamine) (abbreviated as pypn), two mononuclear compounds i.e. [Co(pypn)(C₂O₄)](ClO₄) (1), [Mn(pypn)(C₂O₄)](ClO₄) (2) and one dinuclear compound [Ni₂(pypn)₂(C₂O₄)](ClO₄)₂(C₂H₆O)_1/4(H₂O) (3). In the Co(III) and Mn(II) complexes the oxalate behaves as bidentate ligand, chelating the metal in the O,O′ mode, whereas in the Ni(II) compound the oxalate behaves as tetradentate ligand binding each Ni(II) ion by two oxygen atoms and bridging the two metallic centers.The synthesis, X-ray crystal structure of all three compounds and their spectroscopic properties are presented in detail. The geometry around the Co³⁺, Mn³⁺, Ni²⁺ ions is essentially octahedrally based, while the stabilization of the crystal lattice in all cases is maintained by interesting hydrogen bond systems.     

Biomass‐Derived 3D Carbon Aerogel with Carbon Shell‐Confined Binary Metallic Nanoparticles in CNTs as an Efficient Electrocatalyst for Microfluidic Direct Ethylene Glycol Fuel Cells

Flexible and 3D carbon aerogels (CAs) composed of carbon nanotubes (CNTs) with carbon shell‐confined binary palladium–nickel (Pd_x–Ni_y) nanocatalysts on carbon fibers (Pd_x–Ni_y/NSCNT/CA) have been developed through a facile chemical vapor deposition method. The 3D porous carbon network and the synergistic effect of carbon shell‐confined bimetal nanoparticles of rationally constructed aerogels facilitate enhanced electrocatalytic and antipoisoning activities toward ethylene glycol (EG) oxidation reaction compared to the commercial Pt/C catalyst. With the 3D morphological features and direct growth of Pd–Ni bimetallic nanoparticles encapsulated CNTs on carbon fibers, the Pd₅₂–Ni₄₈/NSCNT/CA delivers a maximum microfluidic direct ethylene glycol fuel cell (µDEGFC) power density and durability of, respectively, 62.8 mW cm^?2 and 60 h. The superior performance observed, with Pd₅₂–Ni₄₈/NSCNT/CA amongst the catalysts reported in the literature, opens an exciting research avenue towards powering next‐generation, portable electronics.     

Ferromagnetic and antiferromagnetic spin coupling in Ni4O4 cubane-type clusters with 4-amino-3,5-bis(hydroxymethyl)-1,2,4-triazole as a ligand. The x-ray structure of a new dumbbell-like double cubane cluster

The synthesis, spectroscopic and magnetic properties of two nickel clusters are described, Ni₈(NCS)₈(Hahmt)₆(H₂ahmt)₄(ahmt)(H₂O)₁₂ (A) and Ni₄(Hahmt)₄(H₂ahmt)₂(NCS)₄(H₂O)₄ (B) (H₂ahmt = 4-amino-3,5-bis(hydroxymethyl)-1,2,4-triazole). The X-ray structure of A has been determined. The compound crystallizes in the space group C2/c, a = 25.458(2), b = 15.466(2), c = 26.959(3) Å, β = 90.648(5)°. The structure was refined to R = 0.108 for 4169 observed reflections. The structure consists of two Ni₄O₄ cubane-type clusters, each consisting of four nickel atoms, three singly deprotonated and one doubly deprotonated ligands. Hahmt coordinates as a bidentate chelating ligand through its triazole-N₁ and its 3-oxymethyl-part. The doubly deprotonated ligand chelates in a bis-bidentate manner to two Ni₄ clusters. In this way dumbbell-like pairs of ligand bridged cubanes are formed. Along two opposite diagonals of the Ni₄O₄ cubanes a neutral ligands, coordinating through its triazole-N₁,N₂ atoms, forms a bridge between two nickel ions. The NiN₃O₃ chromophore is completed by a monodentate N-coordinating thiocyanate anion. Compound B, for which only partial structure determination was possible, has the same Ni₄O₄ cubane-type cluster, however, without the bridging ligand between the cubanes. The two types of NiNi bridges result in two unequivalent superexchange pathways. In the compounds both ferromagnetic and antiferromagnetic interaction pathways are present, resulting in an overall antiferromagnetic behaviour. The nature of the interaction for the different pathways is related to the observed NiONi angles. The intercluster exchange is much larger through the triazole bridge in A than it is in B, where only hydrogen bridges keep the clusters together.     

Enneanuclear Ni(II) complexes from the use of the flexible ligand 2-pyridinealdoxime: The nature of the inorganic anion does not affect the chemical and structural identity of the cationic cluster

The use of 2-pyridinealdoximate(−1) [(py)CHNO⁻] in nickel(II) chemistry has been further investigated. The synthetic investigation has led to two new salts of the very recently reported (in the form of its tetraperchlorate salt, 1) enneanuclear cation [Ni₉(μ₃-OH)₂(μ₂-OH)₂{μ₃-(py)CHNO}₄{μ₂-(py)CHNO}₆(μ₂-OH₂)₂(H₂O)₆]⁴⁺. The two new cationic clusters [Ni₉(OH)₄{(py)CHNO}₁₀(H₂O)₈](SCN)₂(OH)₂ · 9.91H₂O (2 · 9.91H₂O) and [Ni₉(OH)₄{(py)CHNO}₁₀(H₂O)₈]{N(CN)₂}₃(ClO₄) · 11.11H₂O (3 · 11.11H₂O) have been structurally characterized by single-crystal X-ray crystallography at 100 K. The nature of the inorganic anions (Cl⁻/SCN⁻,) present in the reaction mixtures does not affect the chemical and structural identity of the enneanuclear cation. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the complexes. The variable-temperature magnetic susceptibility data of 1, which had also been obtained by our group, were simulated by means of a 3-J model, which is compared with the 2-J model reported for this cluster by Chaudhuri and co-workers [S. Khanra, T. Weyhermüller, E. Rentschler, P. Chaudhuri, Inorg. Chem. 44 (2005) 8176]. The ground-state total spin of the cluster is S_T = 1.     

An inspection into the class of bis(alkyne)-undecacarbonyl-quadro-tetraruthenium complexes. Crystal structure and dynamic behaviour of Ru4(CO)11 (μ4, η2-MeC2Ph)2

The reactions of the butterfly complex Ru₄(CO)₁₂(MeC₂Ph) with several alkynes give the quasiplanar derivatives Ru₄(CO)₁₁(MeC₂Ph)(Alkyne) in almost quantitative yields.The structure of Ru₄(CO)₁₁(MeC₂Ph)₂ has been determined by X-ray methods. Crystals are monoclinic, space group C2/c, with Z = 4 in a unit cell of dimensions a 22.383(16), b 9.048(8), c 18.268(12) Å, β = 127.25(4)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.034 for 1420 observed reflections. The complex, having an imposed C₂ symmetry, presents a tetranuclear metal cluster in which the Ru atoms are in a tetrahedrally-distorted square arrangement. Ten carbonyls are terminal and one symmetrically bridges an edge of the cluster. Each of the two alkyne ligands is σ-bonded to two Ru atoms on the opposite vertices of the cluster and π-bonded to the other two. The organometallic cluster has a Ru₄C₄ core in which the metal and carbon atoms occupy the vertices of a triangulated dodecahedron.     

Microbially-enhanced chemisorption of Ni2+ ions into biologically-synthesised hydrogen uranyl phosphate (HUP) and selective recovery of concentrated Ni2+ using citrate or chloride ion

Hydrogen uranyl phosphate (HUP) deposited enzymatically on Citrobacter N14 immobilized in polyacrylamide gel removed nickel ions from solution via intercalative ion-exchange into the HUP lattice. Using flow-through columns containing 100 mg dry weight of biomass and 200–250 mg loaded uranium column saturation and breakthrough of Ni²⁺ occurred after ca. 600 ml, with a total of 30 mg Ni²⁺ loaded per column, corresponding to a molar ratio of U:Ni of 2:1, in accordance with the identity of the material as Ni(UO₂PO₄)₂, identified previously. Ni²⁺ was selectively desorbed using 100 mM sodium citrate-citric acid buffer over 140 ml or a short pulse (5 ml) of 500 mM citrate buffer followed by a water wash, giving a total recovery volume of 80 ml, with a total citrate concentration of 30 mM in the wash solution of the latter. As an alternative eluant which gives no residual BOD NaCl (0.6 M) or seawater gave comparable recovery of Ni²⁺ to the 0.5 M citrate pulse, but with a Ni²⁺ recovery volume of 40–50 ml. The concentration ratio of Ni²⁺-deposition:desorption (vol:vol) was 3–4 fold better with chloride ion than with 100 mM citrate.     

Strain in organometallics II: controlling the properties of tetra-coordinated iridium complexes using diastereomers of a bis(tropp) ligand system

The tetra-chelating ligands 1,2-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-ethane, bis(tropp^Ph)ethane, and 1,3-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-propane, bis(tropp^Ph)propane, were synthesised. For the binding of transition metals, these ligands offer two olefin moieties and two phosphorus centres and form mixtures of diastereomers with a R,S-configuration at the phosphorus centres (meso), or a R,R(S,S)-configuration (rac), respectively. meso/rac-bis(tropp^Ph)ethane was separated by fractional crystallisation and reacted with [Ir(cod)₂]OTf (cod=cylcooctadiene, OTf⁻=CF₃SO₃ ⁻) to give the penta-coordinated complex-cations meso/rac-[Ir(bis(tropp^Ph)ethane)(cod)]⁺, where the bis(tropp^Ph)ethane serves as tridentate ligand merely. One olefin unit remains non-bonded, however, a slow intra-molecular exchange between this olefin and the coordinated olefin unit was established (meso-[Ir(bis(tropp^Ph)ethane)(cod)]⁺: k<0.5 s⁻¹; rac-[Ir(bis(tropp^Ph)ethane)(cod)]⁺: k≈35 s⁻¹). The ligand meso/rac-bis(tropp^Ph)propane reacts with [Ir(cod)₂]OTf to give the corresponding complexes containing the tetra-coordinated 16-electron complex-cations meso/rac-[Ir(bis(tropp^Ph)propane)]⁺. The diastereomers were separated by fractional crystallisation. The complex rac-[Ir(bis(tropp^Ph)propane)]⁺ is reduced at relatively low potentials (E¹_1/2=−0.95 V, E²_1/2=−1.33 V versus Ag/AgCl) to give the neutral 17-electron complex [Ir(bis(tropp^Ph)propane)]⁰ and the 18-electron anionic iridate [Ir(bis(tropp^Ph)propane)]⁻, respectively. With acetonitrile, [Ir(bis(tropp^Ph)propane)]⁺ reacts to give the penta-coordinated complex rac-[Ir(MeCN)(bis(tropp^Ph)propane)]⁺ (K=45 M⁻¹, k_f=6×10³ M⁻¹ s⁻¹, k_d=1×10² s⁻¹) and with chloride to yield the relatively stable complex rac-[Ir(Cl)(bis(tropp^Ph)propane)] (k_d<0.5 s⁻¹). Compared to the rac-isomer, the meso-[Ir(bis(tropp^Ph)propane)]⁺ shows significantly cathodically shifted reduction potentials (E¹_1/2=−1.25 V, E²_1/2=−1.64 V versus Ag/AgCl), an acetonitrile complex could not be detected, and the chloro-complex, meso-[Ir(Cl)(bis(tropp^Ph)propane)], is much more labile (k_d≈20′000 s⁻¹). meso-[Ir(bis(tropp^Ph)propane)]⁺ reacts with one equivalent H₂ to give the trans-dihydride complex-cation, meso-[Ir(H)₂(bis(tropp^Ph)propane)]⁺, while the rac-isomer, rac-[Ir(bis(tropp^Ph)propane)]+, reacts with two equivalents H₂ to give rac-{Ir(H)₂(OTf)[(tropp^Ph)(H₂tropp^Ph)propane]}, a cis-dihydride complex containing a hydrogenated 10,11-dihydro-5H-dibenzo[a,d]cycloheptene unit, H₂tropp^Ph. The triflate anion in this complex is rather firmly bound and dissociates only slowly (k=29 s⁻¹). All differences between the different stereoisomers are attributed to the fact that the ligand backbone in the meso-isomer, meso-[Ir(bis(tropp^Ph)propane)]⁺, enforces a planar coordination sphere at the metal. On the contrary, already in the tetra-coordinated rac-[Ir(bis(tropp^Ph)propane)]⁺, the metal has a tetrahedrally distorted coordination sphere which does not impede the reduction to the d⁹-Ir(0) and d¹⁰-Ir(−1) complexes and allows more easily a distortion towards a trigonal bipyramidal (tbp) or octahedral structure for penta- or hexa-coordinated complexes, respectively. A comparison of the NMR data for iridium bonded olefins in equatorial or axial positions in tbp structures shows that the latter experience only modest metal-to-ligand back-donation, while the olefins in the equatorial positions have a high degree of metallacyclopropane character.     

Coordination chemistry of 1,2-bis{di-(4-methoxyphenyl)phosphino}ethane (L-L) to nickel, palladium and platinum: Single crystal structures of [MCl2(L-L)] (M = Ni, Pd)

Square planar Ni(II), Pd(II) and Pt(II) complexes of the para-methoxy derivatised analogue of dppe, 1,2-bis{di-(4-methoxyphenyl)phosphino}ethane (L-L), [MCl₂(L-L)] and [M(L-L)₂]Cl₂ (M = Ni, Pd, Pt) are readily prepared, and have been characterised by elemental analysis, IR and NMR spectroscopies. The structures of [NiCl₂(L-L)] and [PdCl₂(L-L)] have been determined by single-crystal X-ray diffraction.     

Ultrathin and Porous Ni3S2/CoNi2S4 3D‐Network Structure for Superhigh Energy Density Asymmetric Supercapacitors

3D‐networked, ultrathin, and porous Ni₃S₂/CoNi₂S₄ on Ni foam (NF) is successfully designed and synthesized by a simple sulfidation process from 3D Ni–Co precursors. Interestingly, the edge site‐enriched Ni₃S₂/CoNi₂S₄/NF 3D‐network is realized by the etching‐like effect of S^2? ions, which made the surfaces of Ni₃S₂/CoNi₂S₄/NF with a ridge‐like feature. The intriguing structural/compositional/componental advantages endow 3D‐networked‐free‐standing Ni₃S₂/CoNi₂S₄/NF electrodes better electrochemical performance with specific capacitance of 2435 F g^?1 at a current density of 2 A g^?1 and an excellent rate capability of 80% at 20 A g^?1. The corresponding asymmetric supercapacitor achieves a high energy density of 40.0 W h kg^?1 at an superhigh power density of 17.3 kW kg^?1, excellent specific capacitance (175 F g^?1 at 1A g^?1), and electrochemical cycling stability (92.8% retention after 6000 cycles) with Ni₃S₂/CoNi₂S₄/NF as the positive electrode and activated carbon/NF as the negative electrode. Moreover, the temperature dependences of cyclic voltammetry curve polarization and specific capacitances are carefully investigated, and become more obvious and higher, respectively, with the increase of test temperature. These can be attributed to the components' synergetic effect assuring rich redox reactions, high conductivity as well as highly porous but robust architectures. This work provides a general, low‐cost route to produce high performance electrode materials for portable supercapacitor applications on a large scale.