Interdimer exchange in linear chain copper acetate-pyrazine

Oligopyrrolic Cu(II)-based tetragonal cage: synthesis, structure, and spectral and magnetic properties

The first oligopyrrolic Cu(II)-based metallocage featuring two antiferromagnetically coupled dimeric cupric tetracarboxylate units linked by a single molecule of water was assembled successfully using a nonlinear pyridine-pyrrolate ligand. Broken symmetry density functional theory (BS-DFT) calculations show that the exchange couplings between Cu(II) ions in the Cu₂ unit and over the water bridge are -298 and -0.13 cm^-1, respectively.

A Deeper Insight in Metal Binding to the hCtr1 N-terminus Fragment: Affinity, Speciation and Binding Mode of Binuclear Cu2+ and Mononuclear Ag+ Complex Species

Ctr1 regulates copper uptake and its intracellular distribution. The first 14 amino acid sequence of the Ctr1 ectodomain Ctr1_(1-14) encompasses the characteristic Amino Terminal Cu²⁺ and Ni²⁺ binding motif (ATCUN) as well as the bis-His binding motif (His5 and His6). We report a combined thermodynamic and spectroscopic (UV-vis, CD, EPR) study dealing with the formation of Cu²⁺ homobinuclear complexes with Ctr1_(1-14), the percentage of which is not negligible even in the presence of a small Cu²⁺ excess and clearly prevails at a M/L ratio of 1.9. Ascorbate fails to reduce Cu²⁺ when bound to the ATCUN motif, while it reduces Cu²⁺ when bound to the His5-His6 motif involved in the formation of binuclear species. The histidine diade characterizes the second binding site and is thought to be responsible for ascorbate oxidation. Binding constants and speciation of Ag⁺ complexes with Ctr1_(1-14), which are assumed to mimic Cu⁺ interaction with N-terminus of Ctr1_(1-14), were also determined. A preliminary immunoblot assay evidences that the anti-Ctr1 extracellular antibody recognizes Ctr1_(1-14) in a different way from the longer Ctr1_(1-25) that encompasses a second His and Met rich domain.

Exchange couplings and quantum phases in two dissimilar arrays of similar copper dinuclear units

X-ray structure and EPR spectra of two dinuclear copper compounds allow us to study spin entanglement and quantum phase transitions. Their different 3D arrays and interdinuclear exchange paths produce important effects.

Quasi-1D chains of dinickel lantern complexes and their magnetic properties

Four new quasi-1D Ni₂lantern chain complexes of the form [Ni₂(SOCR)₄(L)]_∞were prepared withN,N′-donor bridging ligands pyrazine and DABCO.

One-dimensional coordination polymers of [Co3(dpa)4](2+) and [MF6](2-) (M = Re(IV), Zr(IV) and Sn(IV))

One-dimensional coordination polymers of alternating metal-metal bonded trinuclear [Co3(dpa)4](2+) (dpa = the anion of 2,2'-dipyridylamine) building blocks and [ReF6](2-) (1), [ZrF6](2-) (2) or [SnF6](2-) (3) linkers have been self-assembled and crystallographically characterized. Magnetic measurements reveal a significant ferromagnetic coupling (J/k(B) = +9.9 K) between S = 1/2 {Co3(6+)} and S = 3/2 Re(IV) magnetic sites through a single, unsupported fluoride bridge in 1.

Magneto-structural versatility of copper(ii)-3-phenylpropionate coordination polymers with N-donor coligands

Magneto-structural correlations are exploited in five copper(ii)-3-phenylpropionate coordination polymers with flexible N-donor coligands.

Guest-Induced Emergent Properties in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are crystalline nanoporous materials comprised of organic electron donors linked to metal ions by strong coordination bonds. Applications such as gas storage and separations are currently receiving considerable attention, but if the unique properties of MOFs could be extended to electronics, magnetics, and photonics, the impact on material science would greatly increase. Recently, we obtained "emergent properties," such as electronic conductivity and energy transfer, by infiltrating MOF pores with "guest" molecules that interact with the framework electronic structure. In this Perspective, we define a path to emergent properties based on the Guest@MOF concept, using zinc-carboxylate and copper-paddlewheel MOFs for illustration. Energy transfer and light harvesting are discussed for zinc carboxylate frameworks infiltrated with triplet-scavenging organometallic compounds and thiophene- and fullerene-infiltrated MOF-177. In addition, we discuss the mechanism of charge transport in TCNQ-infiltrated HKUST-1, the first MOF with electrical conductivity approaching conducting organic polymers. These examples show that guest molecules in MOF pores should be considered not merely as impurities or analytes to be sensed but also as an important aspect of rational design.

Strong antiferromagnetic interaction in a 3D copper–organic framework and spin-glass-like behaviour in a 1D nickel compound

Novel 3D frameworks containing D_4h paddle-wheel copper units and 1D zigzag nickel chain have been successfully synthesized and characterized magnetically.

Syntheses, Structures and Magnetic Properties of two New Supramolecular Complexes

Two new complexes, namely [Cu(L1)(NO3)(bipy)] (1) and [Cu2(L2)4(H2O)2] (2) (HL1= 2-ethoxynicotinic acid, HL2= 2-methoxynicotinic acid and bipy=4,4′-bipyridine) have been synthesised and structurally characterised by single-crystal diffraction analysis. The structure of complex 1 is a ladder-like chain, which is connected by stronger hydroge n bond interactions to result in a 2D network. While complex 2 is composed of molecular dimmer based on a paddle-wheel unit with two coppers, four syn–syn carboxylates, and two water molecules coordinated to copper in the axial positions which could also be linked into a 2D supramolecular architecture via hydrogen bond interactions. Magnetic studies reveal the overall antiferromagnetic interactions between neighbouring Cu(II) ions in compounds 1 and 2.

From molecules to materials: molecular paddle-wheel synthons of macromolecules, cage compounds and metal-organic frameworks

Metal-organic frameworks (MOF) are becoming a more and more important class of functional materials. Yet, very often, the synthesis of MOFs is not easy to control and requires a profound knowledge and experience in solid state chemistry. One of the most frequently used metal connectors is the so-called 'paddle-wheel' (PW) unit, which is a well-known molecular compound type in inorganic coordination chemistry. Depending on the ligands, the geometry of PWs strictly directs the assembly of ordered networks. This review focuses on the question, to what extent ordered network structures can be accessed by typical molecular syntheses in solution, starting from molecular PW complexes to ordered macromolecules, finite cage compounds and finally, three-dimensional superstructures.

Alkyl exchange reactions of organocobalt porphyrins. A bimolecular homolytic substitution reaction

Reaction of organocobalt(III) porphyrins with a cobalt(II) complex of a distinguishable porphyrin or tetrapyrrole resulted in the reversible exchange of the organic axial ligand. The exchange reaction was facile in such solvents as benzene, toluene, dichloromethane, chloroform, and pyridine; was unaffected by total exclusion of light; was faster than would be expected for a homolytic process given known Co-C bond dissociation energies; and was of broad scope with respect to the organic ligand. Methyl, benzyl, primary alkyl, secondary alkyl, and acyl groups exchanged, but phenyl groups did not. The position of the exchange equilibrium was independent of the direction of approach and was nonstatistical. The relaxation to equilibrium appeared to be consistent with that of a second-order process. The rate of the reaction varied with the identity of the R group in the order Bzl > or = Me > Et approximately n-Pr > i-Pr > i-Bu > acetyl approximately neopentyl approximately 2-adamantyl. However, the total variation in reaction rates was remarkably small. Attempts to find evidence of free-radical intermediates by trapping with TEMPO or CO or by alkyl group interchange with an excess of an alkyl halide of a distinct alkyl group were unsuccessful over a time scale comparable to multiple half-lives of the exchange reaction. In addition, no rearrangement products were detected in exchange reactions of the 5-hexenyl group. Use of cobalt porphyrin reactants that were sterically encumbered on both faces with groups large enough to prevent formation of a bridged, Co-C-Co structure resulted in a 5 or more order of magnitude decrease in the rate of methyl exchange, if not its outright cessation, when run with total exclusion of light. The decrease in the rate of the thermal exchange process revealed the existence a slow photochemical exchange process that was driven by room lights. All evidence was consistent with a bimolecular S(H)2 mechanism for the thermal exchange mechanism.

Dinuclear Paddle-Wheel Copper(II) Carboxylates in the Catalytic Oxidation of Carboxylic Acids. Unusual Polymeric Chains Found in the Single-Crystal X-ray Structures of [Tetrakis(&mgr;-1-phenylcyclopropane-1-carboxylato-O,O')bis(ethanol-O)dicopper(II)] and catena-Poly[[bis(&mgr;-diphenylacetato-O:O')dicopper](&mgr;(3)-diphenylacetato-1-O:2-O':1'-O')(&mgr;(3)-diphenylacetato-1-O:2-O':2'-O')]

The X-ray structures and spectroscopic and magnetic properties of [tetrakis(&mgr;-1-phenylcyclopropane-1-carboxylato-O,O')bis(ethanol-O)dicopper(II)], 1, and catena-poly[[bis(&mgr;-diphenylacetato-O:O')dicopper](&mgr;(3)-diphenylacetato-1-O:2-O':1'-O')(&mgr;(3)-diphenylacetato-1-O:2-O':2'-O')], 2, two extended-chain copper(II) carboxylates with dinuclear paddle-wheel subunits, are reported. 1 crystallizes in the triclinic space group P&onemacr;, with a = 6.8873(3) Å, b = 11.7367(6) Å, c = 13.7899(7) Å, alpha = 107.076(4) degrees, beta = 93.545(4) degrees, gamma = 103.967(4) degrees, Z = 1. The Cu.Cu distance is 2.6009(4) Å, and the Cu.carboxylate O distances are in the range 1.937(2)-1.962(2) Å. The ethanol at the apex forms an unsymmetrical bifurcated H bond to two carboxylate oxygens of another dinuclear unit with O.O distances 2.980(3) and 3.108(3) Å, thereby extending the structure along the a-axis. The magnetic structure consists of isolated antiferromagnetically coupled dinuclear copper units, with a -2J value of 242 cm(-)(1), in concurrence with the EPR parameters, viz., g(x)() = 2.03(1), g(y)() = 2.07(1), g(z)() = 2.35(1), A( parallel) = 0.064(2) cm(-)(1), D = 0.316(15) cm(-)(1), E = 0.005(1) cm(-)(1). The -2J value is the smallest value measured for dinuclear copper carboxylates with oxygen-donor ligands at the axial position and no electron-withdrawing carboxylate R groups. 2 crystallizes in the monoclinic space group P2(1)/c, with a = 15.953(2) Å, b = 5.385(6) Å, c = 28.322(10) Å, beta = 120.22(3) degrees, Z = 2. The compound contains tetrakis(diphenylacetato)dicopper(II) units, forming a polymeric structure along the b-axis by axial coordination of a carboxylate oxygen to copper of a subsequent dinuclear unit, at 2.323(11) Å. The intradimer Cu.Cu distance is 2.594(4) Å; the interdimer Cu.Cu distance is 3.425(5) Å. The -2J value of 321 cm(-)(1) was interpreted as originated from isolated antiferromagnetically coupled dinuclear copper units. The EPR parameters are g(x)() = 2.07(1), g(y)() = 2.02(1), g(z)() = 2.33(1), D = 0.347(10) cm(-)(1), E = 0.0034(5) cm(-)(1). The dinuclear subunits are likely candidates for the catalytically active Cu species in copper(II)-catalyzed oxidation of carboxylic acids.