Bimetallic Coordination Research Articles

PtCl2(phen) disrupts the metal ions binding to amyloid-β peptide

Platinum phenanthroline complexes have been found to inhibit Aβ aggregation and reduce Aβ caused neurotoxicity. Our previous results revealed the synergistic roles of phenanthroline ligand and Pt(ii) coordination in the inhibition of Aβ aggregation. In this work, the reactions of PtCl2(phen) with metal bound Aβ complexes were investigated. HPLC results show that the copper coordination decreases the reaction rate of PtCl2(phen) with Aβ1-16 and influences the distribution of products on HPLC profiles. EPR results reveal that Cu(2+) remains coordinated to the Aβ peptide upon the binding of [Pt(phen)](2+), however, the Cu(2+) coordination sites are changed. The formation of bimetallic coordination complex [Pt(phen)+Aβ1-16+Cu(II)] was confirmed by ESI-MS. Tandem MS analysis shows that, similar to the reaction of apo-Aβ peptide, the His6/His14 chelation is also the preferred binding mode for [Pt(phen)](2+) in the presence of copper ions. EPR spectra suggest that the binding of [Pt(phen)](2+) alters the copper coordination from mode I to mode II in Aβ. Tandem MS analysis indicates that His13 and N-terminal amine could be involved in the Cu(2+) coordination in the bimetallic adduct. Similar results were observed in the reaction of Zn(2+) bound Aβ peptide, although the different zinc binding residues were detected in the bimetallic complex. These results indicate that the binding of platinum complex disturbs the most favorable coordination sphere of Cu(2+)/Zn(2+) and turns these metal ions to the secondary coordination site on Aβ. The release of Cu(2+)/Zn(2+) occurs at low pH. This result suggests that the binding of [Pt(phen)](2+) scaffold could interfere with the binding of Zn(2+) and Cu(2+) to Aβ, thus reducing the metal-induced Aβ aggregation and toxicity.

Nine cyanide-bridged bimetallic magnetic chains derived from octacyanomolybdate(v) and lanthanide(iii) building blocks

The reactions of octacyanometallates [MoV(CN)8]3− and lanthanide ions in the solution of DMF (DMF = N,N-dimethylformamide) have yielded nine bimetallic coordination polymers: [LnIII(DMF)6MoV(CN)8]∞ [Ln = Pr(1), Nd(2), Sm(3), Eu(4), Gd(5), Ho(6), Er(7), Tm(8), Yb(9)]. All the coordination polymers consist of one-dimensional chains, in which [LnIII(DMF)6]3+ and [MoV(CN)8]3− ions link each other in an alternating fashion through the cyano-bridged coordination bonds. The variable-temperature magnetic susceptibility studies reveal the ferromagnetic interactions between LnIII and MoV ions in compounds 3 and 4, while antiferromagnetic interactions are found in compounds 1, 2, and 5–9.

Precise Electrochemical Control of Ferromagnetism in a Cyanide-Bridged Bimetallic Coordination Polymer

Magnetic coordination polymers can exhibit controllable magnetism by introducing responsiveness to external stimuli. This report describes the precise control of magnetism of a cyanide-bridged bimetallic coordination polymer (Prussian blue analogue: PBA) through use of an electrochemical quantitative Li ion titration technique, i.e., the galvanostatic intermittent titration technique (GITT). K(0.2)Ni[Fe(CN)(6)](0.7)·4.7H(2)O (NiFe-PBA) shows Li ion insertion/extraction reversibly accompanied with reversible Fe(3+)/Fe(2+) reduction/oxidation. When Li ion is inserted quantitatively into NiFe-PBA, the ferromagnetic transition temperature T(C) gradually decreases due to reduction of paramagnetic Fe(3+) to diamagnetic Fe(2+), and the ferromagnetic transition is completely suppressed for Li(0.6)(NiFe-PBA). On the other hand, T(C) increases continuously as Li ion is extracted due to oxidation of diamagnetic Fe(2+) to paramagnetic Fe(3+), and the ferromagnetic transition is nearly recovered for Li(0)(NiFe-PBA). Furthermore, the plots of T(C) as a function of the amount of inserted/extracted Li ion x are well consistent with the theoretical values calculated by the molecular-field approximation.

From Coordination Polymers to Doped Rare‐Earth Oxides

AbstractA series of bimetallic coordination polymers were synthesised from lanthanide salts (chlorides or nitrates of Ce, Nd, Gd) and 2,5‐dihydroxy‐1,4‐benzoquinone (DHBQ) under aqueous and anhydrous conditions, to be used as preceramics for mixed oxide synthesis. Syntheses in water or tetrahydrofuran (THF) gave rise to two different types of metal–organic frameworks. A new polymeric species, [Gd(DHBQ)Cl(THF)2]n, was characterised by single‐crystal X‐ray diffraction {[Gd(DHBQ)Cl(THF)2]n, a = 8.643(2) Å, b = 9.917(5) Å, c = 10.422(3) Å, α = 104.611(3)°, β = 109.623(3)°, γ = 96.097(3)°, V = 796.1(5) Å3, triclinic, P$\bar {1}$, Z = 2}. Characterisation by IR and Raman spectroscopy, powder X‐ray diffraction and scanning electron microscopy showed that the mixed‐metal polymers are solid solutions and highlighted the fact that their shape and morphology are strongly influenced by the presence of water in the reaction mixture. Micrometric, well‐defined cylindrical objects were obtained from the aqueous synthesis, while the reaction in anhydrous THF led to nanometric spheres. Calcination at 850 °C of the coordination polymer preceramics easily yielded mixed NdxGd(1–x) and NdxCe(1–x) oxides as solid solutions, in which x varies between 0 and 1. The morphology of the preceramic powders is retained upon calcination. This allows easy control of some of the oxide properties from the coordination compound synthesis step. Indeed, BET measurements pointed out that the choice of anhydrous reaction conditions for the preceramic synthesis leads to enhancement of the specific surface areas of the oxides by one order of magnitude.

Novel bimetallic Cr3Yb3 mixed salt containing a 3d-4f heterometallic Cr2Yb3 cluster

A novel bimetallic Cr3Yb3 coordination compound containing a 3d-4f heterometallic Cr2Yb3 cationic cluster has been synthesized and structurally characterized. The crystal structure was determined by X-ray analysis. Results denote that the complex consists of an original [Cr2IIIYb3III]3+ moiety with a trigonal-bipyramidal topology of the [Cr2Yb3(μ-OOCCH3)6(μ-OH)6(H2O)6]3+ core, an isolated [CrIII(CN)6]3− anion, and four molecular neutral 4,4′-bipyridene (Bipy) ligands, namely, [Cr2Yb3(μ-OOCCH3)6(μ-OH)6(H2O)6][Cr(CN)6] · 4Bipy · 13H2O.

Patterning of Magnetic Bimetallic Coordination Nanoparticles of Prussian Blue Derivatives by the Langmuir–Blodgett Technique

We report a novel method to prepare patterns of nanoparticles over large areas of the substrate. This method is based on the adsorption of the negatively charged nanoparticles dispersed in an aqueous subphase onto a monolayer of the phospholipid dipalmitoyl-l-α-phosphatidylcholine (DPPC) at the air-water interface. It has been used to prepare patterns of nanoparticles of Prussian blue analogues (PBA) of different size (K(0.25)Ni[Fe(CN)(6)](0.75) (NiFe), K(0.25)Ni[Cr(CN)(6)](0.75) (NiCr), K(0.25)Ni[Co(CN)(6)](0.75) (NiCo), Cs(0.4)Co[Cr(CN)(6)](0.8) (CsCoCr), and Cs(0.4)Co[Fe(CN)(6)](0.9) (CsCoFe)). The behavior of DPPC monolayer at the air-water interface in the presence of the subphase of PBA nanoparticles has been studied by the compression isotherms and Brewster angle microscopy (BAM) images. Atomic force microscopy (AFM) of the transferred films on mica substrates shows that patterns of the nanoparticles are observed for a 10(-4) M concentration of the subphase, based on the nanoparticle precursors, at surface pressures between 1 and 6 mN/m and transfer velocities from 10 to 80 mm/min. Vertical, horizontal, or tilted fringes of the nanoparticles with respect to the transfer direction can be obtained depending on the transfer velocity and surface pressure.

Solvethermal synthesis of mono- and bi-metallic flower-like infinite coordination polymer and formation mechanism

Abstract The mono- and bi-metallic flower-like infinite coordination polymer were synthesized by simple coordination-modulation method using sodium acetate as capping agent. The structure was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Based on a series of comparative experimental results, we have deduced that the possible formation mechanism of these Dy-flower-like microspheres via a three-step process.

Bimetallic coordination networks based on Al(acacCN)3: a building block between inertness and lability

The Al(III) complex of 3-cyanopentane-2,4-dionate (acacCN) features peripheric nitrile groups which may coordinate to silver cations. As the Al(acacCN)(3) building block ranges between inertness and lability, its reactivity towards Ag(I) salts depends on the solvent and the weakly or non-coordinating counter anions; an impressive range of different extended structures has been encountered. With AgPF(6), the original building block is retained and hexafluorophosphate remains uncoordinated. A highly symmetric 3D crystalline solid forms in the presence of trichloromethane, and with benzene a tetrasolvate with large solvent-filled voids is obtained. Two different classes of reaction products with silver triflate have been observed. In addition to networks incorporating Al(acacCN)(3), partial solvolysis may lead to a dinuclear methoxide-bridged derivative. The resulting Al(2)(μ-OMe)(2) core may be perceived as a four-connected node in a self-interpenetrating 3D network. Earlier studies reported transmetalation for the reaction of Al(acacCN)(3) with AgNO(3) and we find the same reactivity for silver tetrafluoroborate. Full degradation of the Al(III) building block with formation of [Ag(acacCN)] is observed.

Ordered bimetallic coordination networks featuring rare earth and silver cations

Three lanthanide complexes of the ditopic ligand 3-cyanopentane-2,4-dionate (acacCN) have been synthesized and structurally characterized. Longer intermolecular contacts result in ninefold coordination of the cation in Ce(acacCN)(3)(H(2)O)(2), whereas mononuclear complexes of the same stoichiometry with coordination number eight are obtained for the smaller Eu(III) and Yb(III) cations. Reaction of these labile compounds with AgPF(6) leads to re-organization of the coordination sphere of the rare earth cations: neutral extended structures are formed in which the peripheric -CN moieties of Ln(acacCN)(4) anions coordinate to silver cations. The initially formed heterometallic networks show additional coordination of water or inclusion of solvent molecules; three different structure types, two of them as isomorphous pairs, have been characterized. In the case of Eu(III) and Yb(III), these solids are instable when stored in their mother liquor and undergo a slow aging process, finally resulting in phase pure stable and solvent-free 3D networks Ln(acacCN)(4)Ag.

New Organotin/CuCN/Quinazoline 3D-Supramolecular Coordination Polymers Having Catalytic and Luminescence Activities

The new bimetallic supramolecular coordination polymers (SCP); 3 ∞[Cu(CN)2·Me3Sn·qaz], 1 and 3 ∞[Cu2(CN)4·(Ph3Sn)2·qaz], 2 (qaz = quinazoline), are prepared in water/acetonitrile solvent at room temperature. The structure of 1 consists of the anionic Cu(CN)2 building blocks connected by the Me3Sn cations to form zigzag chains which are bridged by qaz creating 2D-sheets. The interwoven infinite sheets are arranged in parallel A···A···A fashion developing 3D-network structure via H-bonds, π–π stacking, and Cu–C contacts. The network structure of 2 exhibits two different copper sites forming two Cu(CN)2 building blocks which are connected by the Ph3Sn groups constructing elongated corrugated chains. The qaz ligand connects these chains forming 3D-network structure containing the rhombic [Cu2(μ3-CN)2] motif. 1 and 2 are luminescent materials which can be used in applications as molecular sensing systems. Also, the catalytic activity of 1 and 2 was investigated towards the degradation of Metanil Yellow (MY) dye by dilute solution of hydrogen peroxide as oxidant.

High Proton Conduction in a Chiral Ferromagnetic Metal–Organic Quartz-like Framework

A complex-as-ligand strategy to get a multifunctional molecular material led to a metal-organic framework with the formula (NH(4))(4)[MnCr(2)(ox)(6)]·4H(2)O. Single-crystal X-ray diffraction revealed that the anionic bimetallic coordination network adopts a chiral three-dimensional quartz-like architecture. It hosts ammonium cations and water molecules in functionalized channels. In addition to ferromagnetic ordering below T(C) = 3.0 K related to the host network, the material exhibits a very high proton conductivity of 1.1 × 10(-3) S cm(-1) at room temperature due to the guest molecules.

Observation of Long-Range Vicinal Effect in Chiral Cu(II)-Cr(VI) or Cu(II)-W(VI) Bimetallic Coordination Polymers

We have prepared some diastereomers of [CuL2][M2O7] (L is 1,2-diaminocyclohexane and its derivatives; M = Cr and W) bimetallic coordination polymers and confirmed their structural similarity and inner electronic states by means of XRD and XAS, respectively. For the first time, we have successfully observed distant vicinal effect of which the chiral source is only chiral organic ligands of [CuL2]2+ moieties (acting as ligand complex), while probe bands for solid state CD spectra are charge transfer (CT) bands of [M2O7]2− moieties (achiral complex) with the d0 electronic configuration. The new concept (interpretation) of this observation will be important for supramolecular chirality of coordination polymers built by ligand complexes.

Seven Coordinated Metal Complexes derived from (3-Carboxymethoxy-Naphthalen-2-yloxy)-Acetic Acid and Coordination Polymers

A design principle for seven coordinated metal carboxylate complexes and coordination polymers of Mn(II), Cd(II) and Na(I) derived from (3-carboxymethoxy-naphthalen-2-yloxy)-acetic acid (LH2) is presented. The complexes/coordination polymer [Mn(L)(H2O)3]·3H2O (1), [{Cd(L)(H2O)2}·H2O]n (2); [Cd(L)(py)3]·3H2O (3) have metal ions in pentagonal bipyramid environments (py = pyridine). The coordination polymer [{Cd(L)(H2O)2}·H2O]n (2) may be considered to be the self-assembly of hexacoordinated [Cd(L)(H2O)2] units; it reacts with pyridine to form mono-nuclear complex 3. Depending on the reaction conditions, Ni-coordination polymers of L adopt different compositions. From the reaction carried out with NiCl2 and NaOH in quinoline and water, a hetero bimetallic coordination polymer; namely, [[NaL(H2O)]2Ni(H2O)4]n (4) is obtained. A similar reaction in pyridine-water solvent led to [{Ni(L)(py)3}.py]n (5). The coordination polymer 5 has pyridine in its interstices held by C–H···π interactions.

Vapour-adsorption and chromic behaviours of luminescent coordination polymers composed of a Pt(ii)-diimine metalloligand and alkaline-earth metal ions

Four new bimetallic coordination polymers (CPs), {M[Pt(CN)(2)(5,5'-dcbpy)]·4H(2)O}(n) (M = Mg(2+), Ca(2+), Sr(2+), Ba(2+); 5,5'-H(2)dcbpy = 5,5'-dicarboxy-2,2'-bipyridine) were synthesized using four alkaline-earth metal ions and a Pt(II)-diimine metalloligand [Pt(CN)(2)(5,5'-H(2)dcbpy)]. All four CPs are isomorphous with the Zn complex, {Zn[Pt(CN)(2)(5,5'-dcbpy)]·4H(2)O}(n), which exhibits effective metallophilic interactions between Pt(II) ions. These CPs exhibited colourful thermochromic behaviour and solid-state solvatochromic-like behaviours when suspended in various solvents. Thermogravimetric analysis and vapour-adsorption measurements revealed that the CPs can reversibly adsorb water and MeOH vapours. The emission energy of the triplet metal-metal-to-ligand charge-transfer ((3)MMLCT) state varied markedly upon guest adsorption/desorption. The chromic and vapour-adsorption properties of these CPs depend strongly on the cross-linking M(2+) ions.

Spin-crossover in cyanide-based bimetallic coordination polymers—insight from first-principles calculations

Employing density functional theory (DFT) based calculations, we perform a computational investigation to unravel the intricate spin-crossover transitions that have been observed (Niel et al., Angew. Chem., Int. Ed., 2003, 42, 3760) in cyanide-based bimetallic coordination polymers, [Fe(pmd)-(H2O){M(CN)2}2]·H2O (M = Ag or Au and pmd = pyrimidine). Our calculations provide an explanation for the observed temperature-induced low-spin (LS) to high-spin (HS) spin-crossover occurring in both Ag and Au hydrated networks due to Fe–N bond stretching, concomitant with charge re-distribution from Fe to the ligands. For dehydrated compounds, we find that relativistic effects in AuversusAg lead to differences in the degree of covalent bonding, which in turn, gives rise to a differential behavior, viz. the Ag dehydrated network exhibits a LS-HS spin transition whereas the Au hydrated network remains in HS state. As a critical test of our first-principles study we propose to investigate a Cu-based bimetallic coordination polymer, which we predict to be in LS state.

Microporous {[Ni(cyclam)]3[W(CN)8]2}n affording reversible structural and magnetic conversions

Methanol adsorption into the porous 2D bimetallic coordination network {[Ni(cyclam)](3)[W(CN)(8)](2)}(n) (cyclam = 1,4,8,11-tetraazacyclotetradecane) causes significant modification of its structure and magnetic properties. Fully reversible transformations between the three states of the network: anhydrous, hydrated and methanol-modified are observed with the transition to the magnetic ordered state at T(c) equal to 4.9 K, 8.3 K and 11.4 K respectively. All three phases have a metamagnetic character but the methanol-modified one most easily turns to ferromagnetic and shows a hysteresis loop with coercivity field of 250 Oe. The differences in magnetic behaviour of the anhydrous and guest-induced forms of the compound are discussed in terms of changes in the structure: CN-bridge geometry and distance between the layers.

Synthesis, Crystal Structures and Fluorescent Properties of Two Bimetallic Coordination Polymers

Two novel 2D and 3D bimetallic CdIINiII coordination polymers, Cd(2Mpz)(H2O)Ni(CN)4(I) (2Mpz: 2-methylpyrazine) and Cd(2Epz)(H2O)Ni(CN)4(II) (2Epz: 2-ethylpyrazine), have been synthesized and characterized by elemental analysis, powder X-ray diffraction, IR spectra, fluorescent spectra, single crystal X-ray diffraction and thermogravimetric analysis. Based on the analysis of structures, it can be found that the Cd(II) ions in the two complexes have the similar octahedral coordination geometry of CdN5O, which are linked by [Ni(CN)4]2− units at the equatorial plane to form 2D sheet layers [CdNi(CN)4]n. However, it’s noted that the coordination environment of Ni(II) ions and action of ligands are different. All the Ni(II) ions in I are the five-coordinated pentahedron configuration and 2-methylpyrazine acts as a bridging ligand linking the Cd(II) and Ni(II) ions of the adjacent layers, leading to the 3D metal–organic framework. The structure of II indicates all the Ni(II) ions are the four-coordinated square plane and 2-ethylpyrazine is a terminal ligand coordinated to Cd(II) ions, forming the 2D layer structure. Moreover, the two complexes display significant thermal stability and fluorescent properties.

Linear 6,6′-Biazulenyl Framework Featuring Isocyanide Termini: Synthesis, Structure, Redox Behavior, Complexation, and Self-Assembly on Au(111)

The key step in accessing the title species (5), the first nonbenzenoid diisocyanobiaryl, involved an unexpected homocoupling of a 6-bromoazulene derivative. The reversible 2e(-) reduction of 5 was addressed electrochemically and computationally. The shifts in energies of the S(0)→S(1) and S(0)→S(2) transitions for a series of related 6,6'-biazulenyl derivatives correlate with the e(-)-donating/-withdrawing strength of their 2,2'-substituents but follow opposite trends. Species 5 adsorbs end-on (η(1)) to the Au(111) surface via one of its -NC groups to form a 2-nm-thick film. In addition, bimetallic coordination of 5's -NC termini can be readily achieved.

Self‐Assembly of a Two‐Dimensional Bimetallic Coordination Framework and Dynamic Control of Reversible Conversions to Homo‐Metallic Hydrogen‐Bond Arrays

Self‐Assembly of a Two‐Dimensional Bimetallic Coordination Framework and Dynamic Control of Reversible Conversions to Homo‐Metallic Hydrogen‐Bond Arrays

A novel tricyanoruthenium(iii) building block for the construction of bimetallic coordination polymers

Reaction of excess cyanide with a ruthenium(VI) nitrido complex bearing a tridentate Schiff base ligand produces a novel tricyanoruthenium(III) complex in which nucleophilic substitution of an imine hydrogen of the Schiff base by cyanide has occurred, this complex is a useful building block for the construction of 3d-Ru(III) magnetic materials.