Entrapment of [Ru(bpy)3]2+ in the anionic metal-organic framework: novel photoluminescence behavior exhibiting dual emission at room temperature

[Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) ions were entrapped into the cavities of two-dimensional anionic sheet-like coordination polymeric networks of [M(dca)(3)](-) (dca = dicyanamide; M = Mn(II) and Fe(II)). The prepared compounds, {[Ru(bpy)(3)][Mn(dca)(3)](2)}(n) (1) and {[Ru(bpy)(3)][Fe(dca)(3)](2)}(n) (2), were structurally characterized by X-ray single crystal analysis. The spectroscopic properties of the [Ru(bpy)(3)](2+) ion dramatically changed on its entrapment in [M(dca)(3)](-). The [Ru(bpy)(3)](2+) moiety present in 1 and 2 exhibits novel dual photo-emission at room temperature.     

Electrical and magnetic characterization of a molecular material {[Ru(bpy)3][Fe(dca)3]2}n

Electrical and magnetic properties of {[Ru(bpy)₃][Fe(dca)₃]₂}_n (bpy=2,2′-bipyridine, dca=dicyanamide) have been studied. The compound is a non-extrinsic type of semiconductor and paramagnetic in nature. Mössbauer spectroscopy has established the presence of high spin Fe(II) as one major species in this compound, and no high spin-low spin transition of Fe(II) was detected down to 80 K under dark. The photo-response of electrical conductivity with time shows interesting behavior with repeated exposure.     

Structural and Morphological Transformations of Covalent Organic Nanotubes

Covalent organic nanotubes (CONTs) are porous one-dimensional frameworks connected through imine bonds via Schiff base condensation between aldehydes and amines. The presence of two amine groups at the ortho position in the structurally demanding tetraaminotriptycene (TAT) building block leads to multiple reaction pathways between the ditopic aldehyde and the tetratopic amine. We have synthesized five different monomers of CONT-1 by the Schiff base condensation reaction between TAT and o-anisaldehyde. The conversion of imine to imidazole bonding in a monomer is probed using NMR, mass spectrometry, and X-ray diffraction techniques. Solid-state NMR provide insights into the CONTs’ structural connectivity. A theoretical investigation suggests that the π-π stacking could be the driving force for rapid imine to imidazole conversion within the CONT-1. Microscopic imaging sheds further light on the self-assembly process of the CONTs, indicating both head-to-head and side-by-side assembly.     

Ar+ ArH+ Reactive Collisions of Astrophysical Interest: The Case of 36Ar

The reactive collision between ³⁶Ar and the ³⁶ArH⁺ species has been investigated by means of quantum mechanical (QM), quasiclassical trajectories (QCT) and statistical quantum mechanical (SQM) approaches. Reaction probabilities, cross sections as a function of the energy and rate constants in terms of the temperature have been obtained. Cumulative distributions as a function of the collision time and the inspection of selected QCT corresponding to specific dynamical mechanisms have been analysed. Predictions by means of the SQM method are in good agreement with the QM results, thus supporting the complex-forming nature of the process.     

Controlled Construction of Metal–Organic Frameworks: Hydrothermal Synthesis,X‐ray Structure,and Heterogeneous Catalytic Study

The role of pH in the formation of metal–organic frameworks (MOFs) has been studied for a series of magnesium‐based carboxylate framework systems. Our investigations have revealed the formation of five different zero‐dimensional (0D) to three‐dimensional (3D) ordered frameworks from the same reaction mixture, merely by varying the pH of the medium. The compounds were synthesized by the hydrothermal method and characterized by single‐crystal X‐ray diffraction. Increase of the pH of the medium led to abstraction of the imine hydrogen from the ligand and a concomitant increase in the OH^? ion concentration in the solution, facilitating the construction of higher dimensional framework compounds. A stepwise increase in pH resulted in a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a 3D porous solid. A gas adsorption study of the 3D framework compound confirmed its microporosity with a BET surface area of approximately 450 m² g^?1. Notably, the 3D framework compound catalyzes aldol condensation reactions of various aromatic aldehydes with acetone under heterogeneous conditions.     

Investigation of polar and stereoelectronic effects on pure excited-state hydrogen atom abstractions from phenols and alkylbenzenes

The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.