Structural and theoretical investigations of a novel hexanuclear Lanthanum (III) cluster self-assembled through a functionalized β-diketone ligand via atmospheric CO2 fixation

Abstract

Trapping atmospheric carbon-di-oxide (CO2) by lanthanide oxo-hydroxo clusters continuously receives a great deal of attention from the viewpoint of environmental concerns. Functionalized β-diketone ligands plays an important role in assembling lanthanide oxo-hydroxo clusters. Reaction between LaCl3 6H2O and phenolic β-diketone ligand 1-(2‑hydroxyl phenyl)-3-phenyl-1,3propanedione (HO-DBM) in methanol solvent in presence of triethylamine base yielded a novel hexanuclear cluster [La6(O-DBM)6 (HO-DBM)4 (μ3OH) (μ2OH2) (HCO3) (OH2)2 (MeOH)2] (1). The compound has been structurally characterized by single crystal X-ray diffraction analysis, it reveals that 1 consist of a La6 assembly template by (µ4HCO3)− anion. It was anticipated that the bicarbonate anion that bridge lanthanum units is introduced via spontaneous fixation of atmospheric carbon dioxide in the basic medium. Interestingly the bicarbonate anion exhibits a new bridging mode µ4-η1: η1: η1: η1. We applied the fundamental concept of bond valance sum (BVS) method in establishing the level of protonation of the various oxygen atoms in this cluster including water, hydroxide, bicarbonate, methanol and ligand. The values obtained for the title compound totally validate the crystal structure. Further the stability of the structure has been investigated by theoretical studies, the geometrical parameters (bond length and bond angles) are in line with the experimental observation.