Multifunctional Eu(III) and Sm(III) Coordination Polymers Built with Silane-Bridged Dicarboxylate Ligand: Structure, Luminescence and Magnetism

Abstract

Three novel coordination polymers ‒ [LnLNO3(o-Phen)] (Ln: Eu(III) (1), Sm(III) (2)) and [Eu2L3EtOH(H2O)3]·1.5EtOH·H2O (3) ‒ were synthesized by reacting the respective lanthanide nitrates with the organosilane dicarboxylic acid bis(p-carboxyphenyl)diphenylsilane (H2L) with or without o-phenanthroline (o-Phen) as coligand. The o-Phen-assisted route yielded isostructural one-dimensional coordination polymers (CP) 1 and 2, incorporating both ligands and the nitrate anion. These ribbon-like chains assemble into hydrogen-bonded 2D networks that further stack into 3D architectures through non-covalent interactions. In contrast the o-Phen-free conditions produced the 3D CP 3, based solely on H2L, with ethanol and water molecules retained in the lattice. All three architectures are highly dense, with free volumes of only 2.7% (1, 2) and 11.0% (3). Photophysical studies reveal an exceptional quantum yield of 67% for Eu-based complex 1 attributed to complete ligand-to-Eu energy transfer. In contrast, the Sm-based compound 2 achieves a modest 2% quantum yield, while compound 3 reaches 8%. Magnetic measurements confirm typical Van Vleck paramagnetism for Eu³⁺ in 1 and 3, with spin-orbit coupling constants of Λ = 379 and 352 cm⁻¹, respectively. The magnetism of the Sm-based CP 2 is governed by its ground 6H5/2 and first excited 6H7/2 multiplets (Λ = 310 cm⁻¹), and notably displays field-induced slow magnetic relaxation. Remarkably, Eu-based CP 1 affords exfoliation by sonication into nanometric flakes that retain a high quantum yield of 57% upon deposition, opening up exciting opportunities for surface-integrated sensing, photonic, and quantum applications.