Structural Speciation in Binary-Ternary Pb(Ii)-(Di)Carboxylato-(Aromatic Chelator) Aqueous Systems.  Architecture Correlations with Luminescence Properties

Abstract

The attributes of Pb(II) as a metal ion, entering chemical reactivity in catalytic and non-catalytic systems of abiotic and biological nature, draw considerable attention, which directs efforts toward development of well-defined materials of technological interest.  To that end, (di)carboxylic acids of variable chain length (C6-C10) have been employed to pursue the systematic synthetic and structural speciation of binary and ternary systems of Pb(II) in the presence of aromatic N,N’-containing chelators.  Consequently, pH-specific synthetic efforts guided by molecular stoichiometry and reaction conditions (temperature, solvent, pressure) led to the isolation of crystalline coordination polymeric products, which were further characterized by elemental analysis, FT-IR, TGA-DTG, Luminescence, and X-ray diffraction.  The structure and spectroscopic fingerprint of all investigated species attest to their unique Pb(II)-coordination geometry and associated chemistry, revealing ligand-binding modes and spatial characteristics accounting for their lattice architecture, in line with the increasing chain length of the dicarboxylic acid ligands employed.  The arising features were further probed into through Bond Valence Sum and Hirshfeld analysis, thereby unraveling architectural insight into the unique physicochemical properties of all crystalline materials.  The collective experimental data provide a well-defined profile of the chemistry in the ternary systems of Pb(II) with variable carbon chain-bound dicarboxylato ligands, when aromatic chelators enter the reactivity, thereby guiding generation of uniquely configured coordination polymers.  Parameterization of the investigated systems of Pb(II) at the binary-ternary level formulate the luminescent properties displayed by the emerging metal-organic species, with the experimental and theoretical work supporting structural-optical correlations useful to the pursuit of advanced materials.

Keywords: Lead, (di)carboxylic acid, coordination polymers, aqueous structural speciation, structure-luminescence correlation