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