Applications of Pulsed‐Gradient Spin‐Echo (PGSE) Diffusion Measurements in Organometallic Chemistry

Diffusion data from pulsed‐field gradient spin‐echo (PGSE) methods are shown to be qualitatively useful in the investigation of problems involving unknown molecular aggregation and/or the nature of inter‐ionic interactions in metal complexes. For charged species possessing anions such as PF, BF, CF₃SO or BArF⁻, both ¹⁹F‐ and ¹H‐PGSE methods offer a valid alternative and, sometimes, unique view of gross and subtle solution molecular structure and dynamics. Problems associated with solvents, concentration, and reproducibility are discussed.     

A Gas-Phase Model for the Pt+-Catalyzed Coupling of Methane and Ammonia

What exactly are the elementary steps in the Pt-catalyzed coupling of methane and ammonia (Degussa process) shown on the right? Mass spectrometry and ab initio theory have been used to probe the mechanistic details of this technically important synthesis of hydrogen cyanide.     

Structural Studies of a N‐[(N‐Unsubstituted Pyrrole‐3‐carbonyl)oxy]benzamide and its Precursor Spiro[isoxazole‐4,3′‐pyrrole]

The structures of 6‐methyl‐4,8,9‐triphenyl‐2‐oxa‐3,7‐diazaspiro[4.4]nona‐3,6‐dien‐1‐one ( 3 ) and N‐[(2‐Methyl‐4,5‐diphenyl‐1H‐pyrrole‐3‐carbonyl)oxy]benzamide ( 4 ) were established by X‐ray crystal‐structure analysis. A significant improvement in the procedure currently available for the synthesis of these compounds is described. Ab initio and DFT calculations were carried out on the compound 4 and its precursor 3 , and compared with X‐ray results. In particular, to relate structural features to biological properties, the conformational characteristics and rotational barrier of compound 4 were studied.     

Functionalised β-diketonate polynuclear lanthanoid hydroxo clusters: Synthesis,characterisation, and magnetic properties

The controlled hydrolysis of lanthanoid trichloride hexahydrate (Ln = Nd, Eu, Ho) in methanol with the β-diketone ligands dibenzoylmethane and 1,3-bis(4-ethoxyphenyl)propane-1,3-dione yielded tetranuclear and pentanuclear hydroxo clusters for Eu and Ho. In contrast, performing the reaction in the presence of 1,3-bis(4-methoxyphenyl)propane-1,3-dione yielded a mononuclear complex for Nd. The compounds were structurally characterised by means of single crystal X-ray diffraction, showing that the increased bulkiness of the ligand due to the ethoxy functionalities does not affect the capability of the diketonate to stabilize the cluster core. Variable temperature dc susceptibility magnetic measurements were made on the clusters and were indicative of very weak to zero antiferromagnetic, intra-cluster coupling. Variable frequency ac data recorded at low temperatures did not show any evidence for single molecule magnet (SMM) behaviour, unlike the recent reported case of the analogue [Dy₅(OH)₅(Ph₂acac)₁₀], where Ph₂acac⁻ is the dibenzoylmethanide ligand.     

All‐Optical Integrated Logic Operations Based on Chemical Communication between Molecular Switches

Molecular logic gates process physical or chemical “inputs” to generate “outputs” based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine‐type photoacid and a ruthenium polypyridine complex that functions as a pH‐controlled three‐state luminescent switch. The light‐triggered release of protons from the photoacid is used to control the state of the transition‐metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical–chemical–optical) signal‐transduction mechanism, inputs of violet light modulate a luminescence output in the red/far‐red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation.     

Synthesis, multiphase characterization, and helicity control in chiral DACH-linked oligothiophenes

A new class of chiral oligothiophenes is described. Mono-, bi-, ter-, and quarterthiophenes have been linked to enantiopure trans-1,2-cyclohexanediamine (DACH) via diamino or diimino moieties. The stereochemistry of DACH, the type of linker, and oligothiophene size determine the conformational flexibility of these molecules and consequently their molecular and supramolecular helicity in solution and in the solid state. The case of diaminobis(bithiophene), which inverts helicity and shows chiral amplification in the transition from solution to film, is described in detail. Based on the combined use of circular dichroism in solution and in the solid state, single-crystal/thin-film X-ray diffraction, and polarized optical microscopy, a working mechanism has been proposed to explain this unexpected behavior.     

Layered Na(0.71)CoO(2): a powerful candidate for viable and high performance Na-batteries

The present study reports on the synthesis and the electrochemical behavior of Na(0.71)CoO(2), a promising candidate as cathode for Na-based batteries. The material was obtained in two different morphologies by a double-step route, which is cheap and easy to scale up: the hydrothermal synthesis to produce Co(3)O(4) with tailored and nanometric morphology, followed by the solid-state reaction with NaOH, or alternatively with Na(2)CO(3), to promote Na intercalation. Both products are highly crystalline and have the P2-Na(0.71)CoO(2) crystal phase, but differ in the respective morphologies. The material obtained from Na(2)CO(3) have a narrow particle length (edge to edge) distribution and 2D platelet morphology, while those from NaOH exhibit large microcrystals, irregular in shape, with broad particle length distribution and undefined exposed surfaces. Electrochemical analysis shows the good performances of these materials as a positive electrode for Na-ion half cells. In particular, Na(0.71)CoO(2) thin microplatelets exhibit the best behavior with stable discharge specific capacities of 120 and 80 mAh g(-1) at 5 and 40 mA g(-1), respectively, in the range 2.0-3.9 V vs. Na(+)/Na. These outstanding properties make this material a promising candidate to construct viable and high-performance Na-based batteries.     

Status and perspectives in thin films and patterning of spin crossover compounds

Spin crossover compounds are a class of functional materials able to switch their spin state upon external stimuli. They were proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. Here we present a critical overview of the most important approaches for thin film growth and patterning of spin-crossover compounds, giving special attention to Fe(ii) based molecules, which are the most studied materials. We present both conventional approaches to thin film growth (Langmuir-Blodgett, constructive chemical approach, spin coating, drop casting and vacuum sublimation) and patterning (combined top-down/bottom-up method, soft and unconventional lithography). We critically discuss the application of thin film growth and fabrication techniques highlighting the most critical aspects and the perspectives opened by the recent progress.     

Mn(II) and Zn(II) interactions with peptide fragments from Parkinson's disease genes

Two peptide sequences from PARK9 Parkinson's disease gene, ProAspGluLysHisGluLeu, (P(1)D(2)E(3)K(4)H(5)E(6)L(7)) (1) and PheCysGlyAspGlyAlaAsnAspCysGly (F(1)C(2)G(3)D(4)G(5)A(6)N(7)D(8)C(9)G(10)) (2) were tested for Mn(II), Zn(II) and Ca(II) binding. The fragments are located from residues 1165 to 1171 and 1184 to 1193 in the PARK9 encoded protein. This protein can protect cells from poisoning of manganese, which is an environmental risk factor for a Parkinson's disease-like syndrome. Mono- and bi-dimensional NMR spectroscopy has been used to understand the details of metal binding sites at different pH values and at different ligand to metal molar ratios. Mn(II) and Zn(II) coordination with peptide (1) involves imidazole N(ε) or N(δ) of His(5) and carboxyl γ-O of Asp(2), Glu(3) and Glu(6) residues. Six donor atoms participate in Mn(II) binding resulting in a distorted octahedral geometry, possibly involving bidentate interaction of carboxyl groups; four donor atoms participate in Zn(II) binding resulting in a tetracoordinate geometry. Mn(II) and Zn(II) coordination involves the two cysteine residues with peptide (2); Mn(II) accepts additional ligand bonds from the carboxyl γ-O of Asp(4) and Asp(8) to complete the coordination sphere; the unoccupied sites may contain solvent molecules. The failure of Ca(II) ions to bind to either peptide (1) or (2) appears to result, under our conditions, from the absence of chelating properties in the chosen fragments.