A new <i>trans</i>-dioxorhenium(V) complex with 4-aminopyridine: synthesis, structure, electrochemical aspects, DFT, and TD-DFT calculations

<div><p>The reaction of 1 : 4.4 M proportion of <i>cis</i>-[ReO₂I(PPh₃)₂] and 4-aminopyridine (ampy) in acetone–water gives <i>trans</i>-[ReO₂(ampy)₄]I·2H₂O (<b>1a</b>) in 85% yield. <b>1a</b> has been characterized by C, H, and N microanalyses, FT-IR, UV–vis, ¹H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of <b>1a</b> reveals an octahedral <i>trans</i> dioxorhenium(V) complex with a “N₄O₂” coordination for rhenium. <b>1a</b> has an orthorhombic space group <i>C2221</i> with <i>a </i>= 17.576(4), <i>b </i>= 19.370(4), <i>c </i>= 15.730(4) Å, <i>V</i> = 5355(2) ų, and <i>Z</i> = 8. Geometry optimization of the <i>trans</i>-<i>O,O</i> complex, <b>1a</b> and its <i>cis</i>-<i>O,O</i> analog, <b>1b</b> performed at the level of density functional theory reveal that <b>1a</b> is more stable than <b>1b</b> by 25 kcal M^–1 in the gas phase. The electronic spectrum of <b>1a</b> was also analyzed at the level of time-dependent density functional theory. Excitation of <b>1a</b> in methanol at 450 nm leads to a fluorescent emission at 505 nm with a quantum yield (<i>Ф</i>) of 0.04. Electrochemical studies of <b>1a</b> in acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618 V <i>versus</i> Ag/AgCl. This redox potential matches with the calculated redox potential of 0.621 V <i>versus</i> Ag/AgCl.</p></div

A copper(II) complex of benzimidazole-based ligand: synthesis, structure, redox aspects and fluorescence properties

<p>Employing 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1<i>H</i>-benzimidazole (<b>bpb</b>) as a monodentate ligand, a new greenish-blue copper(II) complex, [Cu(<b>bpb</b>)₂(NO₃)₂] (<b>1a</b>), has been synthesized. <b>1a</b> has been characterized analytically and spectroscopically. The X-ray crystal structure of <b>1a</b> reveals that it adopts a <i>cis</i> disposition with respect to the ligands. The solid state structure of <b>1a</b> is stabilized by intramolecular offset face-to-face <i>π</i>–<i>π</i> stacking. Non-covalent supramolecular edge-to-face C–H⋯<i>π</i> interactions with neighboring molecules give 1-D supramolecular chains that further lead to the formation of an assembled 3-D supramolecular metal-organic framework via hydrogen bonding interactions. <b>1a</b> shows blue fluorescence most likely due to intramolecular offset face-to-face <i>π</i>–<i>π</i> stacking. At room temperature, <b>1a</b> is one-electron paramagnetic. It shows a rhombic EPR spectrum with <i>g</i>₁ = 2.12, <i>g</i>₂ = 2.42, and <i>g</i>₃ = 2.52 in the solid state at liquid nitrogen temperature. In cyclic voltammetry, <b>1a</b> displays a one-electron oxidative Cu(II)/Cu(III) couple. Our DFT calculations, corroborate the observed experimental results of <b>1a</b>.</p