Aerial carbon dioxide conversion to carbonate mediated by a lead(ii) complex with tridentate bipyridine containing a hydrazide ligand under electrochemical conditions yielding single-component white-light-emitting phosphors

Abstract

A novel tetranuclear complex [Pb₄L₄(CO₃)₂]·4H₂O (1·4H₂O) is reported, which was obtained through the electrochemical oxidation of a lead anode under an ambient atmosphere in a CH₃CN : MeOH solution of N’-isonicotinoylpicolinohydrazonamide (HL). CO₃²⁻ anions were formed through the conversion of aerial CO₂via the Pb²⁺–L complex system under electrochemical conditions. The ligand L links two Pb²⁺ cations through the carbonyl oxygen atom, while the CO₃²⁻ anion links two Pb²⁺ cations through two monodentate and one bidentate oxygen atoms. The molecular structure of 1 is stabilized by a pair of Pb⋯O tetrel bonds formed with the bidentate oxygen atom of the CO₃²⁻ anion, while molecules of 1 are interlinked through reciprocal π(chelate ring)⋯π(chelate ring), π(chelate ring)⋯π(noncovalent ring) and Pb⋯π(noncovalent ring) interactions, yielding a 1D supramolecular chain. The same reaction but under a nitrogen atmosphere yielded a novel mononuclear complex [PbL₂]·MeOH·2H₂O (2·MeOH·2H₂O). In the structure of 2, each ligand L exhibits a tridentate coordination mode. Molecules of 2 are also interlinked through reciprocal π(chelate ring)⋯π(chelate ring), π(chelate ring)⋯π(noncovalent ring) and Pb⋯π(noncovalent ring) interactions, similar to 1, yielding a 1D supramolecular chain. The energetic features of these assemblies were studied using DFT calculations. Additionally, QTAIM analysis was employed to characterize noncovalent contacts, including intermolecular Pb⋯N tetrel bonds. These tetrel bonds were further analyzed using the ELF and Laplacian of electron density 2D maps, which confirmed their noncovalent nature. The optical properties of the complexes were revealed using UV–vis and diffuse reflectance spectroscopy and spectrofluorometry. Both complexes were found to be emissive in a solution of MeOH. CIE-1931 chromaticity coordinates of (0.38, 0.37) and (0.31, 0.32) for 1·4H₂O and 2·MeOH·2H₂O, respectively, fall within the white gamut of the chromaticity diagram.