The first examples of lanthanide selenite-carboxylate compounds: syntheses, crystal structures and properties

Abstract

[Ln₈(SeO₃)₄(2,6-pdc)₈(H₂O)₁₀]·2H₂O (Ln = La (1), Nd (2), Eu (3); 2,6-pdcH₂ = pyridine-2,6-dicarboxylic acid) represent the first examples of luminescent lanthanide selenite–carboxylate compounds. The compounds have been hydrothermally synthesized and structurally characterized. The structures feature two-dimensional (2D) host frameworks composed of Ln₈(SeO₃)₄(2,6-pdc)₈(H₂O)₁₀clusters connected to each other via inter-cluster Ln₂O₂ rhombic units along the b-axis and 12-membered Ln₄O₂(COO)₂ rings along the c-axis. Inter-layer H-bonding interactions between coordinated water molecules and carboxylate groups lead to three-dimensional architectures. Thermogravimetric analysis (TGA) indicated that the 2D networks were thermostable up to ∼450 °C after losing both coordinated and lattice water molecules and underwent reversible process of dehydration and rehydration. Study on photoluminescent properties revealed that compounds 1, 2 and 3 were new rare-earth materials with violet, near-infrared, and red luminescence, respectively.