Multifunctional Eu(iii) and Sm(iii) coordination polymers built with silane-bridged dicarboxylate ligand: structure, luminescence and magnetism

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 ⁶H_5/2 and first excited ⁶H_7/2 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.